Patent Grant
10919944
The present invention relates to vaccines for the prevention and/or treatment of filarial nematode infections, and to methods of prevention and/or treatment using such vaccines. The invention also relates to novel proteins, suitable for use in the prevention and/or treatment of filarial nematode infections. The invention further relates to pharmaceutical compositions comprising proteins of the invention, or nucleic acids encoding such proteins. The various aspects of the present invention are applicable to the prevention and/or treatment of filarial nematode infections in canine subjects, and also in human subjects.
Nematodes are frequent infectious agents of both human and veterinary animal subjects. Filarial nematodes (belonging to the superfamily Filarioidea) are responsible for a global health burden of approximately 6.3 million disability-adjusted life-years, which represents the greatest single component of morbidity attributable to helminths affecting humans. No vaccine exists for the major filarial diseases, lymphatic filariasis and onchocerciasis; in part because research on protective immunity against filariae has been hampered by the inability of the human-parasitic species to complete their lifecycles in laboratory mice. However, the rodent filaria Litomosoides sigmodontis has become a popular experimental model over the past two decades, as BALB/c mice are fully permissive for its development and reproduction.
Lymphatic filariasis (LF) or “elephantiasis”, which is distributed across Africa, South Asia, the Pacific, Latin America and the Caribbean, accounts for 92% of this toll; while the remainder is caused by onchocerciasis or “river blindness”, primarily in sub-Saharan Africa. The major human filarial pathogens are Wuchereria bancrofti (which is responsible for 90% of LF cases), Brugia malayi and Brugia timori (geographically restricted causes of LF), and Onchocerca volvulus (the sole agent of human onchocerciasis). In addition, Loa loa affects ˜13 million people in West and Central Africa, generally causing a relatively mild disease, although infection has been associated with severe and sometimes fatal adverse events following chemotherapy. Filarial parasites are primarily drivers of chronic morbidity, which manifests as disabling swelling of the legs, genitals and breasts in LF; or visual impairment and severe dermatitis in onchocerciasis. Furthermore, filarial parasites are also a major problem in small animal veterinary medicine, with ˜0.5 million dogs in the USA alone infected with Dirofilaria immitis, the cause of potentially fatal heartworm disease.
Currently, control of human filarial diseases is almost entirely dependent on three anthelminthic drugs (ivermectin, diethylcarbamazine and albendazole), while prevention of heartworm also relies on prophylactic treatment of dogs and cats with ivermectin or other macrocyclic lactones. Reports of potential ivermectin resistance in O. volvulus and D. immitis have highlighted the importance of maintaining research efforts in vaccine development against filarial nematodes. However, rational vaccine design has been constrained for several decades by the intrinsic complexity of these metazoan parasites and their multistage lifecycle, which involves uptake of the first-stage larvae (microfilariae, Mf) by an haematophagous arthropod, two moults in the vector, transmission of third-stage larvae (L3) to a new vertebrate host, and two further moults before the worms mature as dioecious adults in a species-specific, parenteral predilection site. Moreover, the presence of obligate bacterial endosymbionts (Wolbachia) in many species of filarial nematodes adds another level of immunogenic stimuli to these pathogens, the impact of which remains incompletely defined. Following the publication of annotated genome sequences for B. malayi, D. immitis and L. loa, our understanding of the protein repertoire in filarial nematodes has been extended considerably by proteomic analyses of both whole body extracts (WBE) and excretory-secretory products (ESP), although only two studies (both of B. malayi) have examined stage-specific filarial secretomes to date. In the context of vaccine design, the identification of ESP proteins and determination of their expression in each major lifecycle stage can facilitate the prioritisation of candidates for efficacy screening in animal models.
One of the most popular rodent models for filarial research, which was first used during the 1940s in its natural host (the cotton rat, Sigmodon hispidus), is Litomosoides sigmodontis which was previously designated as L. carinii, though this nomenclature is taxonomically incorrect. The utility of this model for both basic immunological studies and vaccine screening changed radically with the discovery that unlike B. malayi and indeed all other filarial species, L. sigmodontis can complete its lifecycle in immunocompetent laboratory mice. Consequently, over the past two decades this model has drawn on the full power of murine immunology, including defined knockout strains, to address questions regarding the fundamental immunomodulatory mechanisms employed by filarial parasites, their susceptibility to different modes of vaccination, and most recently, their ability to mitigate proinflammatory pathology and autoimmune disease. In particular, the L. sigmodontis model has been central in defining the role of T-regulatory cells in filarial immune evasion, and has enabled the assessment of the impact of various vaccine strategies not only on adult worm burden, but on fecundity as determined by the density of Mf circulating in the bloodstream.
In a first aspect, the invention provides a polypeptide comprising a ShK domain of a filarial nematode protein, or a variant thereof, for use as a vaccine for the prevention and/or treatment of a filarial nematode infection.
In a second aspect, the invention provides an artificial polypeptide comprising a plurality of ShK domains of a filarial nematode protein, or variants of such domains, and an artificial spacer separating the ShK domains or variants.
In a third aspect, the invention provides a nucleic acid encoding a polypeptide according to the second aspect of the invention.
In a fourth aspect, the invention provides a nucleic acid encoding a polypeptide comprising a ShK domain of a filarial nematode protein, or a variant thereof, for use as a vaccine for the prevention and/or treatment of a filarial nematode infection.
In a fifth aspect, the invention provides a pharmaceutical composition comprising a polypeptide that comprises a ShK domain of a filarial nematode protein, or a variant thereof.
In a sixth aspect, the invention provides pharmaceutical composition comprising a nucleic acid encoding a polypeptide that comprises a ShK domain of a filarial nematode protein, or a variant thereof.
In a seventh aspect, the invention provides a method of preventing and/or treating a filarial nematode infection, the method comprising providing to a subject in need of such prevention and/or treatment a therapeutically effective amount of a polypeptide comprising a ShK domain of a filarial nematode protein, or a variant thereof.
These various aspects of the present invention arise from the inventors' finding that polypeptides containing ShK domains from filarial nematodes, or nucleic acids encoding such polypeptides, are able to confer protective immunity in respect of filarial nematodes associated with the development of diseases.
As discussed below, the various aspects of the invention have utility in the prevention and/or treatment of filarial nematode infections in human subjects, or in veterinary subjects such as dogs.
For the avoidance of doubt, definitions will now be provided in respect of certain terms used in the description of the present invention.
“ShK Domain of a Filarial Nematode Protein”
Filarial nematodes (those that belong to the superfamily Filarioidea) are those most commonly responsible for diseases in humans, and to a lesser extent, other animal hosts. A good deal of information is available regarding the proteome of filarial nematodes.
ShK domains, which are so called due to their similarity to the Stichodactyla toxin produced by the sea anemone Stichodactyla helianthus, contain six cysteine residues with a characteristic spacing. ShK domains present in an amino acid sequence are readily identified using a bioinformatics approach. For example, they are defined in the Pfam database by the identifier “PF01549” and in the InterPro database by the identifier “IPR003582”.
The inventors have found that proteins from filarial nematode species that vary quite significantly in terms of their sequence across the protein as a whole share notably higher levels of similarity in their ShK domains. This opens the possibility of using polypeptides comprising ShK domains (or variants thereof) derived from a first filarial nematode pathogen in the prevention and/or treatment of diseases caused by infection with a second, different, filarial nematode pathogen.
ShK domains in filarial nematode proteins are illustrated in the sequence information and comparison section of this specification. Here the characteristic arrangement of six cysteines within the ShK domains can be seen, as can the increased degree of sequence identity within ShK domains of different nematodes (as compared to sequence identity shared by the proteins as a whole).
As discussed elsewhere in the specification, the L. sigmodontis ShK domain protein nLs_04059 represents an example of a filarial nematode protein; a ShK domain of which may be employed in the various aspects of the invention. ShK domains from this protein or orthologues of this protein, or variants thereof, may be employed in the various aspects of the invention.
nLs_04059 orthologues including suitable ShK domains, or variants thereof, are shown in
All Gene ID sequences identified in the preceding paragraph are from WormBase ParaSite database version 1 (September 2014).
For the sake of brevity, the specification will use the terms “ShK domain of a filarial nematode protein” and “Shk domain” interchangeably.
“Variants” of Domains
For the purposes of the present disclosure, a variant of a ShK domain of a filarial nematode protein should be considered to encompass sequences sharing at least 70% identity with a ShK domain of a filarial nematode protein. Optionally, variants may share at least 75% identity, at least 80% identity, at least 85% identity, or at least 90% identity with a ShK protein. In suitable embodiments, variants may share at least 91% identity, at least 92% identity, at least 93% identity, at least 94% identity, at least 95% identity, at least 96% identity, at least 97% identity, at least 98% identity, at least 99% identity with a Shk domain of a filarial nematode protein.
It should be borne in mind that the overall level of identity between L. sigmodontis ShK domain protein nLs_04059 (SEQ ID NO: 1) and its orthologues in filarial pathogens ranges from 31% (in W. bancrofti) to 51% (in O. volvulus). However, the level of identity between individual ShK domains between species always exceeds 70% and preferably exceeds 85%,
It will be appreciated that, in order to function as a useful vaccine, a polypeptide of the invention should exhibit the ability to induce a protective immune response. Suitably a variant may retain at least 70% of the immunogenic capacity of the ShK domain from which it is derived. Indeed, a variant may retain at least 80%, at least 90%, or even at least 95% of the immunogenic capacity of the ShK domain from which it is derived. Suitably a variant may have a greater immunogenic capacity than the ShK domain from which it is derived.
“Prevention and/or Treatment”
The medical uses, methods of treatment, and pharmaceutical compositions of the invention may be used to establish protective immunity that prevents the establishment of a filarial nematode infection in a subject. This prophylactic use exemplifies the “prevention” of a filarial nematode infection as this term is used in the present disclosure.
The advantages of these various aspects of the invention may also be applicable to subjects that have previously undergone infection with a filarial nematode parasite. For the purposes of the present disclosure, such applications of the invention, in which a disease associated with an existing infection is alleviated, may be considered to represent “treatment” of the filarial nematode infection.
Prevention and/or treatment of a filarial nematode infection brings about a corresponding prevention and/or treatment of the disease associated with the filarial nematode infection.
“Polypeptides of the Invention”
In the context of the present disclosure, references to “a polypeptide of the invention” or to “polypeptides of the invention” should be taken as encompassing not only the artificial polypeptides of the second aspect of the invention, but also the polypeptides for medical use (as vaccines for the prevention and/or treatment of a filarial nematode infection) defined by the first aspect of the invention.
As discussed further below, the medical uses of the first aspect of the invention may employ naturally occurring polypeptides, or may make use of artificial polypeptides such as those of the second aspect of the invention.
For the sake of brevity, the majority of the following embodiments of the invention will be discussed primarily in the context of polypeptides of the invention, whether the polypeptides for medical use of the first aspect of the invention, or the artificial polypeptides of the second aspect of the invention. However, it should be appreciated that the considerations set out herein in respect of polypeptides of the invention will also, except for where the context requires otherwise, be applicable to the other aspects of the invention, such as nucleic acids (where the considerations may be applicable to the polypeptides encoded by such nucleic acids sequences), pharmaceutical compositions, and methods of treatment.
As referred to above, the polypeptide or nucleic acids of the invention are suitable for use as vaccines, where the vaccine is for the prevention and/or treatment of a filarial nematode infection.
In a suitable embodiment, a polypeptide of the invention may comprise an ShK domain from L. sigmodontis. As the results set out herein illustrate, the inventors have believe that polypeptides comprising ShK domains from L. sigmodontis (and specifically nucleic acids encoding such polypeptides) are surprisingly able to act as vaccines conferring protective immunity in respect of infections by filarial nematodes other than L. sigmodontis.
Without detracting from the above, in a suitable embodiment a polypeptide in accordance with the invention comprises an ShK domain from a filarial nematode infection which is to be prevented and/or treated (or a variant of such an ShK domain).
Suitably, a polypeptide for of the invention may be for use in the prevention and/or treatment of canine heartworm. In such an embodiment, the polypeptide may comprise a ShK domain from D. immitis, or a variant thereof.
A polypeptide of the invention may be for use in the prevention and/or treatment of a disease in a human subject, the disease being selected from the group consisting of: lymphatic filariasis (also referred to as “elephantiasis”); onchocerciasis (also referred to as “river blindness”); and loiasis.
Suitably a polypeptide of the invention for use in the prevention and/or treatment of lymphatic filariasis will comprise a ShK domain from a filarial nematode selected from the group consisting of: Wuchereria bancrofti; Brugia malayi; and Brugia timori, or a variant thereof. Of these three filarial nematodes, W. bancrofti is responsible for approximately 90% of lymphatic filariasis cases, and so polypeptides comprising an ShK domain from W. bancrofti may be preferred for use in the prevention and/or treatment of lymphatic filariasis.
In an embodiment in which a polypeptide of the invention is for use in the prevention and/or treatment of onchocerciasis, it may comprise a ShK domain from Onchocerca volvulus, or a variant thereof.
A suitable polypeptide for use in the prevention and/or treatment of loiasis, may comprise a ShK domain from Loa loa, or a variant thereof.
In a suitable embodiment, a polypeptide of the invention comprises a plurality of ShK domains, or variants thereof. Thus, by way of non-limiting example, a polypeptide of the invention may comprise at least two, at least three, at least four, at least five, or at least six ShK domains or variants thereof. In suitable embodiments, a polypeptide of the invention may comprise two, three, four, five or six ShK domains or variants thereof.
In the event that a polypeptide according to the invention comprises a plurality of ShK domains (or variants thereof), it may comprise a plurality of the same ShK domain (or variants of the same ShK domain). In an embodiment utilising variants of the same ShK domain these variant may be the same variant, or may comprise a plurality of different variants.
Alternatively, a polypeptide of the invention comprising a plurality of ShK domains (or variants thereof), it may comprise a plurality of the different ShK domains (or variants of these different domains). Suitably each one of the plurality of ShK domains may be different, or alternatively the polypeptide may comprise more than one copy of a single ShK domain among a plurality of different domains.
Merely by way of example, in the case of D. immitis the naturally occurring ShK domain protein contains six ShK domains, each of which has its own characteristic sequence. A polypeptide of the invention may comprise each of these six ShK domains. Alternatively, a polypeptide of the invention may comprise six ShK domains made up of six copies of the same ShK sequence, such as the sixth of the sequences found in the native protein.
The sixth ShK sequence found in the native ShK domain protein of D. immitis may represent a preferred ShK domain to be included (either directly, or in variant form) in a polypeptide of the invention. Thus, in a suitable embodiment a polypeptide of the invention may comprise one or more ShK domains (or variants thereof) selected from ShK domains one to five of the native protein, in addition to the sixth ShK domain (or a variant thereof).
In the event that a polypeptide of the invention comprises only a single ShK domain derived from D. immitis, the single ShK domain may be the sixth ShK domain from the ShK domain protein of D. immitis (or a variant based upon this domain).
It will be appreciated that the considerations set out in the preceding paragraphs also apply to polypeptides of the invention comprising variants of the ShK domains found in D. immitis.
A polypeptide of the invention may be a branched protein. In a suitable embodiment, each branch of the protein may carry an antigenic sequence. Some, and potentially all, of these antigenic sequences may comprise ShK domains, or their variants.
In a suitable embodiment, a polypeptide of the invention may further comprise an additional antigen that is able to confer protective immunity on a subject to whom the additional antigen is provided. Suitably such a polypeptide may comprise an additional antigen that does not comprise an ShK domain.
In a suitable embodiment, the additional antigen incorporated in such a polypeptide may be a further nematode antigen. Suitably the additional antigen capable of conferring protective immunity is derived from the same filarial nematode as the ShK domain incorporated in the polypeptide.
Some of the embodiments referred to above may be provided by naturally occurring polypeptides comprising an ShK domain. In a suitable embodiment a polypeptide to be employed in accordance with the various aspects or embodiments of the invention may be a naturally occurring polypeptide.
Certain of the embodiments referred to above may only be provided by artificial polypeptides comprising an ShK domain. As set out above, the second aspect of the invention provides an artificial polypeptide comprising a plurality of ShK domains of a filarial nematode protein, or variants thereof, and an artificial spacer separating the ShK domains or variants.
A suitable artificial spacer serves to expose the ShK domains to cells of the immune system, thereby allowing the development of protective immunity. The spacer itself need not contribute to the development of the protective immunity and may itself be immunologically inert.
The artificial spacer may be any spacer, other than naturally occurring sequence found between ShK domains in a natural protein, that serves to separate the ShK domains, or variants, within the artificial protein. In a suitable embodiment an artificial spacer suitable for use in the artificial polypeptides of the invention may comprise a sequence of amino acid residues that separates the ShK domains or variant. In a suitable embodiment the spacer may comprise poly-L-lysine.
Artificial polypeptides of the invention may comprise a plurality of artificial spacers, as necessitated by the number of ShK domains (or variants thereof) incorporated in the artificial polypeptide.
In a suitable embodiment a polypeptide to be employed in accordance with the various aspects or embodiments of the invention may be an artificial polypeptide, such as an artificial polypeptide of the 2nd aspect of the invention.
Suitably an artificial polypeptide of the invention may be a chimeric polypeptide. Artificial polypeptides of the invention may comprise a ShK domain, or variant thereof, and an additional antigen that is not found in the polypeptide from which the ShK domain is derived. Merely by way of example, an artificial protein of the invention may comprise an ShK domain (or variant thereof) and an additional antigen from a nematode that the ShK domain is derived from, or an additional antigen from a nematode other than that which the ShK is derived from, or an additional antigen that is derived from a source other than a nematode. Chimeric polypeptides of the invention comprising an ShK domain or variant thereof, and an additional antigen from a source other than the filarial nematode from which the ShK domain was derived are able to induce protective immunity against more than one pathogen.
Artificial polypeptides of the invention may comprise a plurality of the same ShK domain, or variants thereof. Alternatively, artificial polypeptides of the invention may comprise a plurality of different ShK domains, or variants thereof.
In a suitable embodiment an artificial polypeptide of the invention further comprises an additional vaccine antigen. Suitably the additional vaccine antigen may be derived from an antigen that does not comprise a ShK domain.
An artificial polypeptide of the invention may comprise an additional vaccine antigen derived from the same filarial nematode (or filarial nematodes) as the ShK domains incorporated in the polypeptide.
Examples of suitable additional vaccine antigens that may be incorporated in artificial polypeptides of the invention include cysteine proteinase inhibitor (CPI) and/or abundant larval transcript (ALT). As discussed elsewhere in the specification, these proteins represent secreted immunomodulators secreted by female filarial nematodes, and targeting of these immunomodulators by vaccination leads to greatly reduced microfilaremial. Accordingly, introduction of these additional vaccine antigens into artificial polypeptides of the invention will be expected to confer therapeutic advantages that go beyond the surprising benefits provided by the polypeptides of the invention. Therapeutic vaccination of Onchocerca volvulus-infected hosts with vaccines comprising CPI and/or ALT in combination with the ShK domain-containing polypeptides of the invention may provide further suppression of microfilarial production, prevent the progression of disease, reduce morbidity and block transmission, even if adult worm burden remains unaffected.
Furthermore, it will be appreciated that in a suitable embodiment a polypeptide, medical use, or method of treatment of the invention utilising as a vaccine a polypeptide comprising a ShK domain of a filarial nematode protein, or a variant thereof, may be used in conjunction with a vaccine comprising CPI and/or ALT. Suitably the polypeptide of the invention may be provided in the same vaccine as the CPI and/or ALT. Alternatively the polypeptide of the invention and the CPI and/or ALT may be provided in separate vaccines.
The invention provides a nucleic acid encoding a polypeptide of the invention. The nucleic acid may encode an artificial polypeptide in accordance with the second aspect of the invention.
The invention also provides a vector comprising a nucleic acid of the invention, and such a vector may be adapted for expression in bacteria, such as E. coli.
Pharmaceutical compositions of the invention may comprise a polypeptide of the invention and/or a nucleic acid of the invention. The nucleic acid may be provided in the form of a vector.
Suitable pharmaceutical compositions of the invention may be formulated for use as a vaccine, and may be formulated for any appropriate route of administration, including (but not limited to) injection.
That said, suitable routes of administration include, but are not limited to, oral (e.g, by ingestion); buccal; sublingual; transdermal (including, e.g., by a patch, plaster, etc.); transmucosal (including, e.g., by a patch, plaster, etc.); intranasal (e.g., by nasal spray); ocular (e.g., by eyedrops); pulmonary (e.g., by inhalation or insufflation therapy using, e.g., via an aerosol, e.g., through the mouth or nose); rectal (e.g., by suppository or enema); vaginal (e.g., by pessary); parenteral, for example, by injection, including subcutaneous, intradermal, intramuscular, intravenous, intraarterial, intracardiac, intrathecal, intraspinal, intracapsular, subcapsular, intraorbital, intraperitoneal, intratracheal, subcuticular, intraarticular, subarachnoid, and intrasternal; by implant of a depot or reservoir, for example, subcutaneously or intramuscularly.
Pharmaceutical compositions in accordance with the invention may be formulated such that the polypeptide or nucleic acid of the invention is delivered in alum adjuvant, or in virus-like particles.
As referred to above, the seventh aspect of the invention provides a method of preventing and/or treating a filarial nematode infection, the method comprising providing to a subject in need of such prevention and/or treatment a therapeutically effective amount of a polypeptide comprising a ShK domain of a filarial nematode protein, or a variant thereof. For brevity, such methods may be referred to in the present disclosure as “methods of treatment”, but, unless the context requires otherwise, it should be considered that such methods of treatment also encompass prophylactic use to prevent filarial nematode infections.
It will be appreciated that the various polypeptides of the invention described herein represent suitable polypeptide to be used in such methods of treatment, and the various considerations set out in connection with the nature of such polypeptides will also be applicable to polypeptides for use in such methods of treatment.
The methods of treatment of the invention are applicable to veterinary subjects. In a suitable embodiment of a method of the invention the subject is a dog, and the filarial nematode infection to be prevented and/or treated is heartworm. In a method in which it is desired to prevent and/or treat heartworm, the polypeptide provided in the method suitably comprises a ShK domain from D. immitis, or a variant thereof.
The methods of treatment of the invention are also applicable to human subjects. Suitably, when the subject is a human, the filarial nematode infection to be prevented and/or treated is one that causes a disease selected from the group consisting of: lymphatic filariasis; onchocerciasis; and loiasis.
In an embodiment of the invention in which the disease to be prevented and/or treated is lymphatic filariasis, the polypeptide suitably comprises a ShK domain from Wuchereria bancrofti; Brugia malayi; and Brugia timori, or a variant thereof.
W. bancrofti is responsible for approximately 90% of lymphatic filariasis cases, and so it may be preferred that methods for the prevention and/or treatment of lymphatic filariasis make use of polypeptides comprising an ShK domain from W. bancrofti.
Suitably a method of the invention in which it is wished to prevent and/or treat onchocerciasis may make use of a polypeptide comprising a ShK domain from Onchocerca volvulus, or a variant thereof.
Methods of the invention in which it is desired to prevent and/or treat loiasis may make use of a polypeptide that comprises a ShK domain from Loa loa, or a variant of such a domain.
The skilled reader will appreciate that in suitable embodiments of methods of treatment in accordance with the invention, the therapeutically effective amount of the polypeptide is provided by administration of the polypeptide. The therapeutically effective amount may be provided through single or multiple incidences of administration, as required. Suitably such embodiments of the invention may utilise pharmaceutical compositions of the invention for the provision of the required amount of the polypeptide.
The invention also encompasses methods of treatment in which the therapeutically effective amount of the polypeptide is provided by administration of a nucleic acid encoding the polypeptide, for example by provision of the nucleic acid in a suitable vector. In such embodiments expression of the nucleic acid by the cells of the recipient subject leads to the production of the therapeutically effective amount of the protein, thus leading to the development of protective immunity. These embodiments of the methods of treatment may utilise pharmaceutical compositions comprising nucleic acids, which are also aspects of the present invention.
Factors that may be considered in the determination of a therapeutically effective amount of a polypeptide, variant, or nucleic acid of the invention may include: the nature of the agent in question (i.e. whether the agent in question is a polypeptide, a variant thereof, or a nucleic acid); the activity of the agent in question; the severity of the infection to be prevented and/or treated; the size of the subject requiring prevention and/or treatment; and the route by which the agent is to be administered.
Merely by way of example, a therapeutically effective amount of a polypeptide comprising a ShK domain, or a variant thereof, or a nucleic acid encoding such a polypeptide or variant, may be between 1.5 g and 1 μg. A suitable therapeutically effective amount may be between 1500 mg and 1 mg; for example between 1000 mg and 50 mg; such as between 500 mg and 100 mg. Alternatively a suitable therapeutically effective amount may be between 100 mg and 1 mg; for example between 50 mg and 5 mg; such as between 25 mg and 10 mg. In a further suitable embodiment, a suitable therapeutically effective amount may be between 500 μg and 1 μg; for example between 400 μg and 5 μg; such as between 250 μg and 10 μg. Merely by way of example, a suitable therapeutically effective amount may be between 200 μg and 15 μg, such as between 150 μg and 20 μg, between 100 μg and 25 μg, or between 50 μg and 30 μg. Suitably a therapeutically effective amount may be approximately 40 μg.
Within a course of treatment to prevent and/or treat a filarial nematode infection a polypeptide comprising a ShK domain, or a variant thereof, or a nucleic acid encoding such a polypeptide or variant, may be provided in one or more administrations. Incidences of administration may be provided once per 24 hours, once a week, once, a month, or as otherwise required.
The invention will now be further described with reference to the following Experimental Results and Figures in which:
Study 1
The ability of polypeptides comprising ShK domains of filarial nematode proteins to as vaccines conferring protective immunity in respect of filarial nematode infection, and the suitability of nucleic acids encoding such polypeptides to serve as vaccines, was demonstrated by the following study. The L. sigmodontis ShK domain containing protein used as an exemplary vaccine was designated LsShK for the purposes of this study.
Immunisations and infections were performed with female BALB/c mice, starting at ages of 6-7 weeks, with five animals per experimental group. Mice were housed in individually ventilated cages and infected subcutaneously with 30 or 40 L. sigmodontis infective larvae (iL3). Naïve, uninfected animals were maintained and sampled in parallel as controls for the immunological readouts.
All cloning was carried out following the recommendations of the pcDNA 3.1 Directional TOPO Expression Kit (Invitrogen). LsShK (gene ID nLs.2.1.2.t04059-RA) was amplified from a cDNA preparation of adult L. sigmodontis using specific primers. Fusion constructs containing single-chain anti-DEC205 antibody (DEC) upstream of the LsShK sequence were produced from ready-made constructs kindly provided by Dr. Ralph Steinman. Briefly, PCR products of genes of interest were digested with NotI and XbaI (Neb laboratory, UK), then ligated into an NotI and XbaI-digested anti-mouse dec-205 single chain antibody-ovalbumin construct (DEC-OVA) or antibody control Ig-OVA to replace the fragment of OVA gene, respectively. All plasmids were sequenced to confirm identity.
Plasmids were injected in the tibialis anterior muscle of the left leg with a 27 G needle, immediately followed by electroporation with an ECM 830 generator+Tweezertrodes (BTX Harvard Apparatus) using as settings 8 pulses, 200 V/cm, 40 ms duration, 460 ms interval. Each mouse was immunised twice separated by 2 weeks interval with 40 μg of DNA total made up by equal quantities of each plasmid species, delivered in 50 μl PBS. As a consequence, the quantity of each individual plasmid was reduced as the number of different plasmids incorporated into the inoculums increased. However, the quantity of each one remained in excess of the minimal efficient dose.
Parasite survival was determined at experiment endpoint. Adult filariae were isolated from the pleural cavity lavage fluid in 10 ml cold PBS, fixed in hot 70% ethanol and counted. Protection was calculated as:
(mean burden in primary infected animals−mean burden of vaccinated animals)/mean burden in primary infected animals.
Microfilariae were counted in 30 μl of blood after fixation in 570 μl of BD FACS lysing solution (BD Biosciences) under an inverted microscope.
Generalised linear models were used to compare the effects of different vaccine formulations on parasitological parameters as they allow more flexibility in specifying the distribution of response variables and better model fitting through Maximum Likelihood estimation.
The results of this study are illustrated in
The inventors found that at day 60 post-infection, the LsShK vaccine had a modest effect on adult worm burden (˜40% reduction), though this was of borderline statistical significance (p=0.07). However, the vaccinated group had no microfilariae detected in the blood, whereas the primary infection group (which received empty plasmid vector only) exhibited a median microfilaraemia of ˜830 parasites per ml (p=0.005). This suggests that the medical use of ShK domains as vaccines achieves its therapeutic use through sterilising the adult female worms, or by killing migrating microfilariae before they can reach the bloodstream.
Study 2
The invention may further be understood by the skilled person on consideration of the following details of a study undertaking quantitative secretome analysis of a model filarial nematode (Litomosoides sigmodontis) across the parasite life cycle.
2.1 Summary
Filarial nematodes (superfamily Filarioidea) are responsible for an annual global health burden of approximately 6.3 million disability-adjusted life-years, which represents the greatest single component of morbidity attributable to helminths affecting humans. No vaccine exists for the major filarial diseases, lymphatic filariasis and onchocerciasis; in part because research on protective immunity against filariae has been constrained because the human-parasitic species cannot complete their lifecycles in laboratory mice. However, the rodent filaria Litomosoides sigmodontis has become a popular experimental model, as BALB/c mice are fully permissive for its development and reproduction. Here, we provide a comprehensive analysis of excretory-secretory products from L. sigmodontis across five lifecycle stages. Applying intensity-based quantification, we determined the abundance of 302 unique excretory-secretory proteins, of which 64.6% were present in quantifiable amounts only from gravid adult female nematodes. This lifecycle stage, together with immature first-stage larvae (microfilariae), released four proteins that have not previously been evaluated as vaccine candidates: a predicted 28.5 kDa filaria-specific protein, a zonadhesin and SCO-spondin-like protein, a vitellogenin, and a protein containing six metridin-like ShK toxin domains. Female nematodes also released two proteins derived from the obligate Wolbachia symbiont. Notably, excretory-secretory products from all parasite stages contained several uncharacterised members of the transthyretin-like protein family. Furthermore, biotin labelling revealed that redox proteins and enzymes involved in purinergic signalling were enriched on the adult nematode cuticle. Comparison of the L. sigmodontis adult secretome with that of the human-infective filarial nematode Brugia malayi (reported previously in three independent published studies) identified differences that suggest a considerable underlying diversity of potential immunomodulators. The molecules identified in L. sigmodontis excretory-secretory products show promise not only for vaccination against filarial infections, but for the amelioration of allergy and autoimmune diseases.
2.2 Introduction
Filarial nematodes are the most important helminth parasites of humans in terms of overall impact on public health, with an annual global burden of ˜6.3 million disability-adjusted life-years (1). Lymphatic filariasis (LF) or “elephantiasis”, which affects populations across Africa, South Asia, the Pacific, Latin America and the Caribbean, accounts for 92% of this toll. The remainder is caused by onchocerciasis or “river blindness”, primarily in sub-Saharan Africa. The major human filarial pathogens are Wuchereria bancrofti (responsible for 90% of LF cases), Brugia malayi and Brugia timori (geographically restricted causes of LF), and Onchocerca volvulus (the sole agent of human onchocerciasis). In addition, Loa loa affects ˜13 million people in West and Central Africa. This parasite usually induces a relatively mild disease, but has been associated with severe and sometimes fatal adverse events following anthelmintic chemotherapy (2). Filarial parasites are primarily drivers of chronic morbidity, which manifests as disabling swelling of the legs, genitals and breasts in LF; or visual impairment and severe dermatitis in onchocerciasis. The filariae are also a major problem in small animal veterinary medicine, with ˜0.5 million dogs in the USA alone infected with Dirofilaria immitis (3), the cause of potentially fatal heartworm disease. However, in domesticated ungulates, filarial infections are generally quite benign (4).
Currently, control of human filarial diseases is almost entirely dependent on three drugs (ivermectin, diethylcarbamazine and albendazole). Prevention of heartworm also relies on prophylactic treatment of dogs and cats with ivermectin or other macrocyclic lactones. Reports of possible ivermectin resistance in O. volvulus (5) and D. immitis (6) have highlighted the importance of maintaining research efforts in vaccine development against filarial nematodes. However, rational vaccine design has been constrained for several decades (7) by the intrinsic complexity of these metazoan parasites and their multistage lifecycle. Moreover, many filarial species carry obligate bacterial endosymbionts (Wolbachia), which may also stimulate the immune response during infection (8). As part of global efforts to improve prevention and treatment of these diseases, large-scale projects have been undertaken, including sequencing of the nematodes (9-11) and their Wolbachia (10, 12, 13), and proteomic analyses of both whole organisms and excretory-secretory products (ESP) (14, 15). Additionally, two studies (both on B. malayi) have examined lifecycle stage-specific secretomes (16, 17). In the context of vaccine design, the identification of ESP proteins and determination of their expression in each major lifecycle stage can facilitate the prioritisation of candidates for efficacy screening in animal models.
One barrier to the progression of research in the filarial field is our inability to maintain the full lifecycle of the human parasites in genetically tractable, inbred hosts. The filarial lifecycle involves uptake of the first-stage larvae (microfilariae, Mf) by a haematophagous arthropod, two moults in this vector, followed by transmission of third-stage larvae (L3) to a new vertebrate host. Two further moults occur in the definitive host before the nematodes mature as dioecious adults in a species-specific, parenteral predilection site. However, the complete lifecycle of the New World filaria Litomosoides sigmodontis can be maintained in laboratory rodents, including inbred mice (18). This species was first studied in its natural host (the cotton rat, Sigmodon hispidus) (19) [the previous designation of these isolates as L. carinii is taxonomically incorrect (20)]. Drawing on the full power of murine immunology, including defined knockout strains, this model has been address questions regarding the fundamental immunomodulatory mechanisms employed by filarial parasites (21), their susceptibility to different modes of vaccination, their ability to mitigate proinflammatory pathology and autoimmune disease (22), and the impact of various vaccine strategies on adult nematode burden and fecundity (23) (24). The L. sigmodontis model has also been central in defining the role of T-regulatory cells in filarial immune evasion (25).
Using the resource of a newly-determined genome sequence, coupled with a derivative of intensity-based absolute quantification (iBAQ) proteomics, we have examined the stage-specific secretome of L. sigmodontis in vector-derived L3 (vL3), adult males (AM), pre-gravid adult females (PAF), gravid adult females (GAF), and immature Mf (iMf). In addition to identifying dynamic changes in the ESP profile through the lifecycle, we show important differences in the adult secretomes of L. sigmodontis and B. malayi, especially in the abundance of two novel proteins released by female L. sigmodontis that lack orthologues in B. malayi. As has been observed in other parasitic nematodes, we find transthyretin-like family (TTL) proteins to be particularly dominant in the ESP. Leakage of uterine fluid may account for the remarkable diversity of proteins that we detect in GAF ESP, and we highlight several novel proteins that warrant evaluation in vaccine trials and as anti-inflammatory mediators.
2.3 Experimental Procedures
Ethical Considerations
All experimental procedures on the animals required for vL3 production at the Muséum National d'Histoire Naturelle were approved by the ethical committee “Cuvier” (no 68-002) and carried out in strict accordance with EU Directive 2010/63/UE and the relevant national legislation (French Décret no 2013-118, 1 Feb. 2013). All other parasite stages were harvested from animals maintained at the University of Edinburgh in compliance with a UK Home Office Animals (Scientific Procedures Act) 1986 project license and the recommendations of the local ethical review committee.
Parasites and Protein Preparations
The life cycle of L. sigmodontis was maintained in jirds (Meriones unguiculatus) infected with vL3 harvested from the mite vector Ornithonyssus bacoti. After 70-90 days, GAF and AM were recovered from the pleural cavity by lavage with serum-free RPMI 1640 medium (Life Technologies), whereas PAF were recovered 32 days post-challenge. To harvest iMf liberated in vitro, GAF culture medium was removed after 24 h and centrifuged at 1,900 g for 20 minutes (4° C.). Blood-derived microfilariae (bMf) were obtained by overlay of blood (from cardiac puncture of jirds >75 days post-infection) onto a 25% Percoll suspension, centrifugation at 1,900 g for 20 minutes (4° C.), and passage of the bMf fraction through a PD-10 desalting column (GE Healthcare) prior to culture. The vL3 larvae were dissected directly from the mite vector and washed three times in RPMI 1640 before transfer to culture vessels.
To determine the relative abundance of proteins in the secretome of each parasite stage, ESP and whole body extracts (WBE) were extracted and analysed separately. All parasite stages were incubated in serum-free RPMI 1640 supplemented with 100 U/ml penicillin, 100 μg/ml streptomycin and 1% glucose at 37° C. (5% CO2) in ultra-low attachment flasks (Corning), and were confirmed to be viable during incubation by microscopic examination. The medium was replaced every 24 h, and spent media recovered at 24 h and 48 h were centrifuged at 1,900 g for 20 minutes (4° C.) in low protein-binding Oak Ridge tubes (polypropylene copolymer; Thermo Scientific Nalgene) to remove debris. To purify proteins from the supernatant, hydroxylated silica slurry (StrataClean Resin, Agilent Technologies) was added at 30 μl/ml and vortex-mixed at high speed for 2 min. Resin used for each 24 h incubation sample was reused for the respective 48 h sample to concentrate ESP prior to storage at −80° C. Initial experiments using soluble WBE (used as a proxy for ESP, as limited amounts of the latter were available) displayed no visible differences in protein profiles by SDS-PAGE using resin-bound protein compared to equivalent unbound material (data not shown). Analyses were performed with separate ESP batches in quadruplicate for GAF, triplicate for AM, and duplicate for PAF, iMf and vL3.
Soluble WBE was prepared by homogenisation in 25 mM ammonium bicarbonate, 1% RapiGest SF surfactant (Waters) and cOmplete Protease Inhibitor Cocktail (Roche) using a mini-pestle in a microcentrifuge tube. This was followed by 10 cycles of sonication on ice using a Vibra-Cell VCX130PB sonicator (Sonics & Materials, Inc.) with microprobe (10 sec sonication alternating with 30 sec incubation on ice). Homogenised samples were centrifuged at 13,000 g for 20 minutes (4° C.) and the supernatant retained. The WBE preparations were obtained from single pools of parasites for all stages except GAF and AM, where two biological replicates were available. Protein concentrations were determined using the Pierce Coomassie Plus (Bradford) Protein Assay (Thermo Scientific).
Surface Biotinylation of Live Worms
Samples of 10 adult male and five female nematodes were washed three times with pre-chilled PBS buffer and incubated for 30 min with 1 mM EZ-link Sulfo-NHS-SS-Biotin (Thermo scientific), or PBS only (negative control), at 4° C. with gentle agitation. The biotinylating solution was removed, and the reaction quenched with 100 mM glycine in PBS before washing the nematodes three times in PBS-glycine. Labelled nematodes were stored at −80° C. Surface proteins were extracted by sequential incubations in PBS buffer alone, 1.5% octyl β-D-glucopyranoside (Sigma), 0.5% SDS and then 4 M urea (all in PBS) for 1 h each (room temperature). Proteins released at each step were incubated with 30 μl of high-capacity streptavidin-agarose beads (Thermo Scientific) for 2 h at room temperature with rotary mixing. To recover bound biotinylated proteins, the supernatant was removed and the beads were washed three times in PBS and three times in 25 mM ammonium bicarbonate prior to incubation in 50 mM DTT (Sigma), 25 mM ammonium bicarbonate at 50° C. for 30 min. The supernatant was removed and the DTT diluted tenfold before digestion with 0.2 μg proteomic-grade trypsin (Sigma) overnight at 37° C. The resultant peptides were concentrated using C18 reverse-phase spin filters (Thermo Scientific) according to the manufacturer's instructions prior to MS analysis.
To confirm efficient and specific labelling of the parasite surface, AM and GAF were fixed in 70% hot ethanol after subjection to biotin and control labelling as above. Paraffin-embedded sections (4 μm) were deparaffinised, rehydrated and blocked in 1% BSA and 0.3% Triton X-100 in PBS (blocking buffer) for 1 h (room temperature), followed by two 5-min washes in PBS with gentle agitation. The sections were incubated with streptavidin-FITC (Sigma) at a 1/1,000 dilution in blocking buffer for 1 hr (room temperature), washed three times, and mounted with ProLong Gold anti-fade reagent (Life Technologies). Images were obtained on an Axio Imager.M2 fluorescence microscope (Zeiss) using Zen 2012 software (Zeiss), combining the FITC channel with brightfield illumination.
Sample Preparation for Proteomics
StrataClean Resin containing bound ESP was washed twice with 25 mM ammonium bicarbonate before suspension in 0.1% RapiGest SF, 25 mM ammonium bicarbonate. The resin samples were heated at 80° C. for 10 min, reduced with 3 mM DTT at 60° C. for 10 min, cooled, then alkylated with 9 mM iodoacetamide (Sigma) for 30 min (room temperature) protected from light. All steps were performed with intermittent vortex-mixing. The samples were then digested using 0.2 μg proteomic-grade trypsin at 37° C. overnight with rotation, centrifuged at 13,000 g for 5 min, and the supernatant removed. The resin was washed twice with 0.1% RapiGest SF, 25 mM ammonium bicarbonate and the supernatants pooled. To remove RapiGest SF, the samples were precipitated using TFA (final concentration, 1%) at 37° C. for 2 h and centrifuged at 12,000 g for 1 hr (4° C.). The peptide supernatant was concentrated using C18 reverse-phase spin filters according to the manufacturer's instructions. The WBE samples were reduced and alkylated as above, digested with trypsin at a protein:trypsin ratio of 50:1 at 37° C. overnight, and precipitated to remove RapiGest SF as for the ESP preparations.
NanoLC MS ESI MS/MS Analysis
Peptide solutions (2 μl) were analysed by on-line nanoflow LC using the nanoACQUITY-nLC system (Waters) coupled to an LTQ-Orbitrap Velos (Thermo Scientific) MS as previously described (13, 26). Thermo RAW files were imported into Progenesis LC-MS (version 4.1, Nonlinear Dynamics) and spectral data were transformed to MGF files prior to export for peptide identification using the Mascot (version 2.3.02, Matrix Science) search engine as detailed previously (26). Tandem MS data were searched against the protein predictions from the L. sigmodontis genome and its Wolbachia symbiont, wLs [obtained from the online nematode genome of L. sigmodontis, release nLs 2.1.2, 10,246 protein sequences (M. Blaxter, S. Kumar, G. Koutsovoulos; unpublished); and release wLs 2.0, 1,042 protein sequences (27)], together with predicted proteomes for the rodent host (Mus musculus, Uniprot release 2012_08, 16,626 protein sequences; and Meriones unguiculatus, Uniprot release 2012_08, 223 protein sequences) and a general contaminant database (GPMDB, cRAP version 2012.01.01, 115 protein sequences). Search parameters, allowable modifications and the false discovery rate were defined as reported previously (13, 26). Mascot search results were imported into Progenesis LC-MS as XML files and analysed according to the following criteria: at least two unique peptides were required for reporting protein identifications, and an individual protein had to be present in ≥2 biological replicates to be included in the ESP dataset. Protein abundance was calculated by the iBAQ method; i.e., the sum of all peak intensities from the Progenesis output was divided by the number of theoretically observable tryptic peptides (28). For ESP and WBE, protein abundance was normalised by dividing the protein iBAQ value by the summed iBAQ values for the corresponding sample, and the reported abundance is the mean of the biological replicates. Normalised peptide intensities rather than iBAQ values were used to calculate fold-changes between control and biotinylated worm surface preparations. Mass spectrometric data have been deposited in the ProteomeXchange Consortium database (http://proteomecentral.proteomexchange.org) via the PRIDE partner repository (29) with the dataset identifier XXXXXXXXX.
In Silico Analyses of Proteins
The domain content of proteins identified in the ESP assessed using Pfam (v. 27.0) with the gathering threshold as a cut-off. A hypergeometric test for enrichment of Pfam domains in ESP proteins compared with the complete predicted proteome of L. sigmodontis was performed using the phyper toolkit within the R programming environment (30). The Benjamini & Hochberg step-up FDR-controlling procedure was applied to the calculated, adjusted P-values (31). Structural homologues of abundant uncharacterised proteins were identified through comparison to the National Center for Biotechnology Information non-redundant protein database (DELTA-BLAST search; E-value cut-off 1−03) and to the UniProt database (PSI-BLAST search) via the Phyre2 protein fold recognition server (32). The conserved domain structure of selected, abundant ESP proteins was also interrogated in InterProScan 4 (33). Venn diagrams were created using
ShK domains were identified in the complete predicted proteomes of the filariae B. malayi (9), D. immitis (10), L. sigmodontis, Onchocerca ochengi, Acanthocheilonema viteae (draft unpublished genomes available at http://www.nematodes.org/genomes/; Blaxter et al., unpublished), W. bancrofti and L. loa (11), plus the ascaridid nematode Ascaris suum (40) (which is an outgroup for the filarial species), using the Pfam hidden Markov model for the domain and hmmer (version 3.1b.1). Each domain was excised and a total of 531 distinct domains identified, which were aligned using ClustalOmega (41). Inspection of the alignment revealed that a subset of domains were misaligned (and therefore did not have the six cysteine residues in register with the others); these were corrected manually. The alignment was analysed for phylogenetic signal using MrBayes (version 3.2) (42) and two runs of four chains each were run for two million generations. The first million generations were discarded as burn-in after inspection in Tracer (version 1.5; A. Rambaut, unpublished: http://tree.bio.ed.ac.uk/software/tracer/) and a consensus tree was inferred from the remaining 10,000 samples taken every 100 generations. Sequence logos were generated for all 531 ShK domains, all domains from nLs_04059 and orthologues, and each of the six distinct sets of orthologous domains, using the WebLogo server (http://weblogo.berkeley.edu/) (43).
2.4 Results
Distribution of Proteins in ESP Across Parasite Lifecycle Stages
We searched ˜120,000 MS spectra per lifecycle stage against protein sequences predicted from the L. sigmodontis and wLs genome assemblies. A total of 302 quantifiable filarial proteins (i.e., represented by ≥2 unique peptides in ≥2 biological replicates) were detected in ESP across the five lifecycle stages. A majority of these (195 proteins, 64.6%) were uniquely identified in GAF (
We explored functional distinctness of ESP from different lifecycle stages by determining protein domain overrepresentation relative to the complete predicted proteome of L. sigmodontis. The greatest fold-enrichment scores were observed in the AM ESP, which contained three proteins with a major sperm protein (MSP) fibre protein 2b (MFP2b) domain and 10 proteins with a TTL family domain (
Abundant Proteins Released by Adult Parasites
The GAF ESP displayed the most complex composition, and the majority of the abundant proteins secreted by this stage were uncharacterised or contained conserved domains associated with very limited functional information (
Functionally defined components of the ESP included a small cysteine protease inhibitor [CPI (48)], the omega-class glutathione S-transferases [GST (49)], the MSPs (50), and the microfilarial sheath protein (51) (
There was extensive overlap in the identities of the most abundant proteins in the ESP of PAF, AM and iMf compared with that of the particularly diverse GAF. These less complex ESP mixtures nevertheless contained dominant components overrepresented in individual stages. In PAF, abundant proteins included several glycolytic enzymes and two heat-shock proteins, as well as a galectin (β-galactoside-binding protein 1) and a highly unusual protein, nLs_03350, containing both C-type lectin and acetylcholine receptor domains (
Abundant Proteins Released by Larval Parasites
Characterisation of ESP from the bMf stage posed special challenges. Despite the two-stage purification process and prolonged culture in vitro, 92.4% (61 of 66) of proteins robustly quantified in bMf ESP were derived from the rodent host. The dominant serum components identified were fibronectin, complement C3, serum albumin, hemopexin, plasminogen and ceruloplasmin; while lower amounts of IgM were also detected (Table 6). Of the five quantifiable parasite-derived molecules, three were TTL proteins. To obtain characterise Mf-derived ESP in more depth, we harvested iMf from GAF cultures in vitro, separated them from the female nematodes, and proceeded with in vitro incubation. This procedure increased the detection of proteins of nematode origin to 36 (
Although ESP from the vL3 stage was the least diverse dataset in our study, it showed a distinctive repertoire of highly abundant proteins. Thus, vL3 ESP was composed of previously characterised filarial proteins that are known to be uniquely expressed or enriched in this stage [such as ASP-1 (71), ALT-1 (72), and cathepsin-L-like protease (73)], and other antigens that were well represented in ESP from other stages (RAL-2, CPI-2, Ov16 and β-galactoside-binding proteins) (
Phylogenetics of Novel, Filaria-Specific ESP Proteins
The most abundant protein in GAF ESP, nLs_03577, is an enigmatic, uncharacterised molecule with a predicted MW of 28.5 kDa and a lack of conserved domains, with the exception of a classical N-terminal signal peptide. Downstream of the signal peptide, moderate to high levels of sequence conservation were apparent across the Filarioidea in the N-terminal portion (
The ShK domain protein nLs_04059 was a particularly distinctive molecule identified in all ESP preparations except vL3. One other L. sigmodontis ShK domain protein, the astacin protease nLs_03368, was a rare component of GAF ESP only (Table 3). The ShK domain (or metridin-like toxin domain, also known as the SXC or six-cysteine domain) was first identified in cnidarian venoms, but is particularly abundant in nematode proteomes (74), where it is associated with secreted proteins. The prototypic ShK peptide (from the cnidarian Stichodactyla helianthus) is a type 1 toxin that blocks voltage-gated potassium channels, and synthetic analogues are currently under development as a therapy for autoimmune diseases, in which Kv1.3 channels expressed by effector memory T-lymphocytes are specifically targeted (75). Although nLs_04059 was not especially abundant in any ESP preparation, its presence in the secretomes of all mammalian-derived stages and its unusual domain structure (
The nLs_04059 protein has the largest number of ShK domains (six) of any protein in L. sigmodontis. We identified orthologous genes in all the other filarial nematode genomes, each containing six ShK domains (
Proteins Associated with the Adult Nematode Surface
The nematode cuticle is the critical interface between the parasite and the immune system of its host (78). Surface-associated proteins may simply mirror ESP, perhaps by passive adsorption of released material, or comprise a distinct component of the exoproteome. Live AM and GAF nematodes were surface-labelled incubated with Sulfo-NHS-SS-Biotin and fractionated. Immunofluorescent imaging of fixed nematode sections confirmed that biotin labelling was largely confined to the cuticular layers (
A striking feature of the surface-associated proteins was the presence of two ectoenzymes involved in purinergic signalling. These were an adenylate kinase predominant in AM extracts and a purine nucleoside phosphorylase found exclusively found in GAF extracts (79) (Table 2, Table 7). A homologue of complement component 1, q subcomponent-binding protein was identified in GAF surface-labelled extracts. Like the human homologue, the L. sigmodontis protein contained an N-terminal mitochondrial import signal sequence, although the former is expressed in a number of extramitochondrial locations, including on the surface of lymphocytes, endothelial cells, dendritic cells and platelets (80). These proteins may play a role in immunomodulation, as purinergic signalling is known to regulate lymphocyte trafficking (79), while the complement component 1q receptor is involved in vasodilation via the generation of bradykinin (80).
Surface extracts from AM contained a homologue of the actin-binding protein, calponin, which has been localised to both striated muscle and the cuticle in adult O. volvulus (81). The GAF surface extracts contained two proteins, protein disulphide isomerase and a leucine-rich repeat family protein, both of which have previously been associated with cuticle synthesis in filariae and C. elegans (82, 83). Stress response-related proteins were also well represented on GAF (including thioredoxin peroxidase (84), aldehyde dehydrogenase, a thioredoxin-like protein and heat-shock proteins), as were several enzymes of pyruvate metabolism (Table 2 and Table 7). Notably, the endosymbiont-derived Wolbachia surface protein was found to be accessible to surface biotinylation in GAF.
Comparison with the Secretome of Adult B. malayi
The ESP from several lifecycle stages of B. malayi have been described previously (14, 16, 17). In these three studies, the only common stage was adult [with both sexes cultured together in (14)]. Of 297 proteins identified in adult L. sigmodontis ESP, 92.6% had an orthologue in B. malayi. However, the majority (61.6%) of these B. malayi orthologues were not observed in the B. malayi secretome (
2.5 Discussion
Quantifying the Secretomes of a Model Filarial Nematode
Filarial nematodes exact a significant burden of morbidity in human populations and are important pathogens of companion animals. While efficacious anti-filarial drugs exist, the spectre of the evolution of genetic resistance to these is ever-present (5, 6), and alternative routes to treatment are required. It would be preferable to be able to prevent infection as well as treat patent disease, and thus an anti-filarial vaccine would be an extremely valuable addition to medical and veterinary treatment options (85). The ESP released by parasites into their hosts have been the target of vaccine development for decades, but the understanding of these molecules in filarial nematodes is limited. Whereas previous studies have catalogued the proteins inferred to be present in filarial ESP, quantitative assessments of their abundance have not been explored previously using an intensity-based approach. Using the model rodent filarial nematode L. sigmodontis, it is possible to prepare material from across the nematode lifecycle, and thus examine the different vertebrate-parasitic stages in detail. Applying semi-quantitative MS analysis of ESP, we identified secreted proteins and determined their abundance, limiting our analysis to 302 proteins that could be robustly quantified using ≥2 unique peptides.
The Secretome of Adult Nematodes
In L. sigmodontis, GAF was responsible for the majority of ESP proteomic diversity. The other four lifecycle stages examined contributed only 11 proteins (3.6% of the total) that were not present in GAF ESP. This finding contrasts with a qualitative analysis of B. malayi secretomes comparing adults, Mf and L3, and incorporating data obtained from single-peptide hits, which found that Mf contributed the greatest proportion of unique proteins (17). However, an earlier assessment of the B. malayi GAF, AM and Mf secretomes concluded that GAF produced the greatest number of unique hits (16), suggesting that methodological differences may underlie these contrasting results. The diversity of GAF ESP is consistent with the material containing not only somatic adult ESP, but also proteins released from the reproductive tract that derive from the processes of oogenesis, fertilisation and embryonic development in utero (all filarial pathogens are ovoviviparous).
Nematode sperm are acutely sensitive to aerobic damage (86). The AM ESP contained proteins suggestive of roles in protection of sperm against oxidants and other stressors, including superoxide dismutase, a serine protease inhibitor and a glutaredoxin-like protein. Glutaredoxins are thiol-containing antioxidant proteins, and C. elegans GLRX-21 plays a key role in mitigating selenium toxicity (87). Mammalian seminal fluid accumulates selenium, which if in excess, can impede sperm motility (88). A homologue of the serine protease inhibitor is secreted by A. suum during the acquisition of motility and contributes to sperm competition by inhibiting the activation of surrounding spermatids (89). Lysis of sperm during aerobic culture may account for the high levels of MSPs observed in AM ESP and in ESP obtained from PAF, GAF and iMf. Female nematodes are fertilised some weeks before the first Mf are produced (90), and the dominance of MSPs in PAF ESP indicates that leakage of sperm from the female reproductive tract occurs before parturition.
Several unique antioxidant proteins (nucleoredoxin-like protein-2, glutathione reductase and translationally-controlled tumour protein) were found in PAF ESP, suggesting an enhanced requirement for protection during this stage. In B. malayi, homologues of the nucleoredoxin-like proteins, which resemble large thioredoxins (91), are present in ESP but do not exhibit stage-specific expression (92). Two unique cuticle biosynthesis related proteins were also released by PAF, suggesting that cuticular remodelling occurs during their final stages of growth. This may result in increased susceptibility to immune-driven oxidative stress or damage during copulation (93). Heat-shock proteins, which were overrepresented in PAF ESP, were detected previously in B. malayi adult nematode ESP (94).
The Mature Microfilarial Secretome is Dominated by Host Proteins
In many filarial nematodes, microfilariae are enclosed in a proteinaceous sheath comprising an inner layer that originates from the eggshell and an outer layer that is produced by secretions in the distal portion of the uterus. Five major structural proteins have been identified in the L. sigmodontis sheath, some of which are synthesised in the developing embryo and others in the uterine epithelium (51), but none of these were found in iMf ESP, indicating that they are stable components. Many host serum proteins were released from bMf in culture. These are likely to derive from specific interactions with the parasite surface, perhaps reflecting a tension between the nematode exploiting the host and the host immune system recognising the parasite. The finding of host at the Mf surface is not new, as five serum components were only proteins released by SDS extraction of L. sigmodontis Mf sheaths (95), and human serum albumin has been detected on the sheath surface of W. bancrofti Mf (96), but is generally not found on Brugia spp. Mf (97). The L. sigmodontis sheath is permeable to molecules of up to 70 kDa (98), and therefore might retain some host proteins after transfer to culture. However, several abundant serum proteins that we detected in bMf ESP are considerably larger than this (for example, ceruloplasmin and fibronectin) and thus must be either adsorbed onto the sheath surface or proteolytically processed prior to uptake. Hemopexin and ceruloplasmin have roles in heme and copper transport (99), respectively; hence, they may be exploited as a source of essential cofactors by the parasite.
Several parasite-derived products were identified as secreted by iMf, including Ls110 [a protein localised in the uterine lumen and variably present on iMf, but absent from bMf (67)] and two possible proteoglycan core proteins. Accordingly, large glycoproteins (˜200 kDa) have been described from B. malayi ESP (100). The closest C. elegans homologue of the perlecan-like proteoglycan, UNC-52, is a major component of the basement membrane of contractile tissues, including the pharynx and anus in developing embryos and subsequent stages (68). The L. sigmodontis iMf-derived CPG-like protein is predicted to have chitin-binding domains and may function in eggshell and sheath development. In C. elegans, CPGs form an inner layer that binds to the central chitinous layer of the eggshell, maintaining the perivitelline space around the embryo (101) forming a barrier to prevent polyspermy (102). In L. sigmodontis, chitin has been detected in the oocytes and zygotes, although it is absent from the iMf sheath (103). The degradation of chitin during Mf sheath development in utero may release the underlying CPG, which is highly soluble (101), into the surrounding milieu. The origin and roles two of the other novel proteins that were enriched in iMf ESP is less clear. The closest homologue in C. elegans of the PAN domain protein is SRAP-1, which is expressed in the hypodermis, central nervous system and vulva of developing larvae and is secreted onto the cuticle surface during moulting (104). In C. elegans, peroxidasin PXN-2 is located in the extracellular matrix and is required for late embryonic elongation, muscle attachment, and motoneuron axon guidance choice (105).
The Abundant Uncharacterised Proteins Released by Gravid Adult Female Nematodes
We identified four abundantly secreted or excreted proteins, found predominantly in GAF and iMf ESP, that had not been reported previously. Two have only marginal similarity to other proteins: nLs_03577, which displayed a significant match to a P-type ATPase (but lacked an ATPase domain), and nLs_08836, which showed some similarity to zonadhesin, a VWD protein located in the head of mammalian sperm (106). However, we note that nLs_08836 is not an orthologue of the C. elegans zonadhesin-domain protein, DEX-1 (107). The third novel protein, nLs_07321, is a vitellogenin. In C. elegans, vitellogenins are expressed exclusively in the intestine, where they bind cholesterol and transport it via the body cavity to the gonad (108). Subsequently, oocytes internalise the protein and its lipid cargo by receptor-mediated endocytosis and store it in yolk granules (108). Several vitellogenins have also been identified in ESP derived from adults of the oviparous gastrointestinal nematode, Heligmosomoides polygyrus (109). The fourth protein, the ShK domain protein nLs_04059, was distinct from other proteins containing this motif in nematodes, both in the number of domains and their specific sequence. Its relative abundance, distinctiveness and presence in all the filarial species surveyed suggest that it may be a viable vaccine candidate for both human filarial diseases and canine heartworm. Its role in vivo may be to interfere with the development of acquired immunity by inhibiting the Kv1 channels of memory T-cells in a manner analogous to the activity of cnidarian ShK toxins (75).
The enigmatic TTL family has emerged as one of the most typical and widespread findings in ESP from both zoo- and phytoparasitic nematodes (110). In C. elegans, there are 63 transthyretin genes, many of which are secreted and apparently upregulated in response to infectious challenge, but only TTR-52 has been ascribed a physiological function [phagocytosis of apoptotic cells (111)]. In the phytoparasite Radopholus similis, Rs-ttl-2, which is closely similar to one of the most abundant L. sigmodontis TTL proteins (nLs_07576; found in ESP from all stages except vL3 in our study), was localised to the ventral nerve cord (112). A second R. similis TTL family member, Rs-ttl-1, was expressed only in the vulval region (112), and a homologue of this molecule (nLs_07332) was detected in iMf WBE only. Furthermore, in the ruminant parasite Ostertagia ostertagi, a TTL family (Oo-TTL-1) was a major component of ESP and could be immunolocalised to the pseudocoelomic fluid of adult worms (113). In our study, a L. sigmodontis homologue of Oo-TTL-1 (nLs_09750) was abundant in all ESP preparations except those of vL3.
Uterine Fluid as a Source of Nematode and Endosymbiont Products
Proteins excreted or secreted from filarial nematodes could be derived from a number of routes. In addition to oral secretions from the oesophageal glands and release of faecal material from the anus, nematodes also secrete material from the anterior sensory glands (amphids) (114) and the secretory pore, and may also void material from the genital openings during copulation and release of Mf. Proteins can also be released from the hypodermis through transcuticular secretion (115), especially during moulting, and exosome release may also be important (116). From our data, we suggest that vulval excretion is the main source of ESP proteins in GAF and PAF, and that the iMf are coated with proteins secreted by the uterine epithelium. This interpretation is supported not only by the abundance of MSPs and vitellogenin in GAF and PAF ESP, but by the presence of omega-class secreted GST isoforms exclusively in GAF ESP, which in O. volvulus are only produced by embryos at the morula stage (49). Similarly, ESP proteins in the male nematode probably originate primarily from seminal fluid. Immune sera from rodents infected with A. viteae react most strongly with male and female gonad tissues, including the fluid channels between developing embryos and on sperm in both the spermatheca and seminal vesicle (117).
The role of the Wolbachia endosymbionts of filariae remains unclear: are they nutritional commensals, supporting the nematode through provision of energy or cofactors, or part of the immunological avoidance mechanisms of the parasite, or both (13)? It has been proposed that Wolbachia may be present in uterine fluid (118), inside degenerating embryos (119), or exit via the secretory pore (120). Additionally, they may secrete proteins into structures that lack bacterial cells, such as the cuticle (121). Wolbachia-derived proteins were present in very low amounts in B. malayi secreted products (17). We identified Wolbachia GroELS components in ESP of PAF and GAF, but not in other lifecycle stages. GroEL is the most abundant protein in Wolbachia (13, 15), and its detection in ESP may be through release of whole bacterial cells, for example in the female uterus from degenerating oocytes or embryos, or through secretion. GroEL, as a chaperonin, would be expected to be confined to the cytosol, although GroEL homologues have been reported to “moonlight” on the surface of some bacterial species (122). We also detected Wolbachia surface protein by surface labelling of adult L. sigmodontis, as has been reported in B. malayi (121). This protein is a putative ligand of Toll-like receptors 2 and 4 (119), and these findings support the hypothesis that Wolbachia modifies and perhaps misdirects the immune response to filariae (123). Whether Wolbachia GroEL also stimulates proinflammatory Toll-like receptors has not been evaluated, but a precedent exists in other bacteria (124), and antibodies against this protein are associated with pathology in LF (125).
The L. sigmodontis Secretome and Vaccine Development for Filariases
For several decades, vaccine development for human and veterinary filariases has focused on the L3 stage because irradiated L3 are highly efficacious at inducing protective immunity (23, 126) and strong anti-L3 immunity may block parasite establishment. Litomosoides is an excellent model for L3 vaccine research, as the L3 expresses a very similar repertoire of genes to the human and veterinary pathogens (127). Analyses of ESP from L3 of L. sigmodontis aid in defining a stereotypical secretomic profile for this stage. However, no defined parasite antigens (whether alone or in combination) have reproducibly attained an equivalent level of protection to irradiated L3 in any filarial system (7). Furthermore, since a single pair of adult nematodes can generate a patent infection, vaccines directed solely against L3 face a potentially insurmountable challenge.
Targeting of Mf has the potential to block transmission, and in the case of onchocerciasis, to reduce disease pathology. Moreover, the Mf stage has been shown to be more vulnerable to protective immune responses than L3 in several vaccination trials (128-130). Vaccination with a combination of ALT-1 and CPI-2 delivered as a DNA vaccine reduced circulating Mf levels by up to 90% in L. sigmodontis. Importantly, this protection was only achieved if immunomodulatory domains of the antigens were ablated (by mutation or deletion of the coding sequence) and was maintained even when the adult nematode burden was not significantly reduced. This phenomenon was probably to be due to the immunomodulatory effects of the native (active) proteins, as transplantation of a single adult female worm is sufficient to prevent clearance of injected Mf in naïve hosts (131). We suggest that it is likely that many of the other abundant molecules secreted by GAF may similarly have roles in facilitating Mf survival and could be targeted in an “anti-fecundity” vaccination strategy. Furthermore, the proteins identified by surface labelling of the GAF cuticle may also participate in generating a permissive environment (79, 80); thus, vaccination against these molecules, if sufficiently divergent from host homologues, might impede parasite establishment.
2.6 Conclusions
We have shown that L. sigmodontis, especially the GAF stage, releases a remarkable diversity of proteins into the external milieu and the majority of these molecules are uncharacterised. Although many of these proteins may be involved in fundamental aspects of embryogenesis, a subset are likely to be active immunomodulatory agents that protect the nematodes (and especially the circulating Mf) from the host immune response. The abundant ESP protein, CPI, may represent an archetype for this dual functionality, as it plays fundamental roles in oogenesis and fertilisation not only in parasitic nematodes but also in C. elegans (132). This suggests that its immunomodulatory properties are an example of secondary adaptation to a radically different environment. Thus, the pharmacopeia released by GAF may provide the ideal set of molecule(s) to target for immunoprophylaxis and chemotherapy of filariases; moreover, it could provide new compounds to tackle proinflammatory and autoimmune diseases (22)
aData for excretory-secretory products unique to gravid adult females are not shown due to the large number of proteins (195) in this category (see Table 3).
2−174
californica] XP_005091919.1
aFilters were applied only where the top hit was to taxa othe than Caenorhabditis spp.
bOnly annotated hits are shown for non-filarial proteins.
cThe only hits were to hypothetical proteins containing ShK domains.
sigmodontis)
Wolbachia surface protein
Sequence Information and Comparisons
MSPFILLALLINAPANCRPDNGISRSRDASSA
SVDTSISSSSSNATLRVMSPSV
GEKSSYGSVI
Above is domain organisation of the ShK domain-containing protein nLs_04059 from Litomosoides sigmodontis. Linear representation of the amino-acid sequence (SEQ ID NO: 1), showing the signal peptide (in italics), six ShK toxin-like domains (open rectangles) containing six cysteine residues each (highlighted), and a predicted propeptide cleavage site (underlined). Domain six at the C-terminus is unique in containing two lysyltyrosine dyads (bold).
Above is a sequence alignment comparison between ShK domain-containing proteins nLs.2.1.2.t04059-RA (from Litomosoides sigmodontis) of SEQ ID NO: 1 and nDi.2.2.2.t03402-RA (from Dirofilaria immitis) of SEQ ID NO: 2.
While overall identity between the two sequences is only 52.8%, it can be seen that the identity shared between the ShK domains (highlighted) of these two filarial nematode proteins is considerably higher.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1402352.7 | Feb 2014 | GB | national |
This application is a continuation of U.S. application Ser. No. 15/118,043, now issued as U.S. Pat. No. 9,994,624, filed Aug. 10, 2016, which is a U.S. National Phase filing of PCT/GB2015/050380, filed Feb. 11, 2015, which claims the benefit of British Application No. GB 1402352.7, filed Feb. 11, 2014, the entire disclosures of all of which are hereby expressly incorporated by reference herein.
| Number | Name | Date | Kind |
|---|---|---|---|
| 6265198 | Tripp et al. | Jul 2001 | B1 |
| 8962259 | Noordin et al. | Feb 2015 | B2 |
| 20130236490 | Kalyanasundaram | Sep 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| WO 2010068084 | Jun 2010 | WO |
| WO 2015121646 | Aug 2015 | WO |
| Entry |
|---|
| Written Opinion of the International Searching Authority in PCT/GB2015/050380, dated Aug. 20, 2015, 10 pages. |
| International Search Report in PCT/GB2015/050380, dated Aug. 20, 2015, 6 pages. |
| James P. Hewitson et al., “Secretion of Protective Antigens by Tissue-Stage Nematode Larvae Revealed by Proteomic Analysis and Vaccination-Induced Sterile Immunity,” dated Aug. 15, 2016, available at http://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1003492, 15 pages. |
| Blaxter, M., “Caenorhabdities elegans is a nematode,” Science, vol. 282, dated Dec. 11, 1998, http://www.cell.com/biophysj/fulltext/S0006-3495(13)05332-0, 1 page (abstract only). |
| Hai M. Nguyen et al., “Ky1.3-Blocking Peptides from Parasitic Worms Exhibit Immunomodulatory Function,” Biophysical Journal, vol. 106, Issue 2, Supplement 1, dated Jan. 28, 2014, http://www.cell.com/biophysj/fulltext/S00006-3495(13)05332-0, 1 page. |
| Ghedin et al. “BMA-NAS-14, isoform b [Brugia malayi],” dated Sep. 21, 2007, http://www.ncbi.nlm.nih.gov/protein/cdp92843, 1 pages. |
| Nutman et al., “Hypothetical protein LOAG_17826,” http://www.ncbi.nlm.nih.gov/protein/ejd74931.1, dated Apr. 11, 2012, 1 page. |
| Number | Date | Country | |
|---|---|---|---|
| 20180355002 A1 | Dec 2018 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15118043 | US | |
| Child | 15974290 | US |
