Method of using cytokine receptors on microorganism

Abstract

Cytokine receptors for tumor necrosis factor e which are found on microorganisms may, if bound with exogenous TNF.alpha., enhance the response of natural killer cells activated by the microorganisms, or increase TNF.alpha. production by peripheral blood lymphocytes treated with the microorganisms. Microorganisms with receptor-bound exogenous TNF.alpha. have enhanced cellular invasion ability which may change the immune response thereto. Clinical and pharmaceutical applications of these discoveries are provided.

Description

BACKGROUND OF THE INVENTION

The invention relates generally to the discovery of cytokine receptors on microorganisms, and more specifically to new methods and products in medical treatment and research related to the discovery. Cytokines produced by monocytes/macrophages are called monokines, and those produced by lymphocytes are called lymphokines. Stimuli for their production include endotoxin and Gram-negative bacteria. One cytokine of particular interest is tumor necrosis factor .alpha. (TNF.alpha.).

TNF.alpha. is an inflammatory cytokine which has numerous biological activities and is believed to play important roles, not only in host defense but also in some of the pathological sequelae associated with bacterial infections. Receptor(s) for TNF.alpha. are found on most somatic cells, and they have recently been characterized and cloned. Biological effects of TNF.alpha. and other cytokines binding to eukaryotic cells are well known.

For example, it is now well established that cytokines play important roles in regulating aspects of the immune response. Cytokines have been shown to be essential for host defense against viruses, tumors and bacterial infections. There is, however, a delicate balance between when a cytokine is advantageous to a host and when it contributes to the pathology of a disease. Thus, knowledge of how to make the choice between administering a cytokine and blocking its action in a disease process could be a valuable tool in clinical medicine. The need for such knowledge is rapidly increasing as cytokines and cytokine blockers become more readily available.

Many cytokines have now been cloned and new cytokines are constantly being discovered and cloned. Recombinant cytokines are now also being used in clinical trials all over the world. Recently, much attention has been focused on identifying and cloning cytokine receptors on eukaryotic cells previously identified as being targets for the many cytokines produced by the immune system. But similar work on pathogenic cells such as bacteria has not been published; there are no reports of TNF.alpha. or any other cytokine binding to bacteria until quite recently (1A).

SUMMARY OF THE INVENTION

The present invention concerns findings that microorganisms, including bacteria and imperfect fungi, have cytokine receptors. A microorganism receptor for TNF.alpha. is of particular interest. With receptor-bound TNF.alpha. microorganisms more effectively enhance natural killer (NK) cell activity and induce the production of TNF.alpha. by human peripheral blood lymphocytes (PBL's). Further, bacteria with receptor-bound TNF.alpha. are taken up by macrophages and epithelial cells to a much greater extent than bacteria without receptor-bound TNF.alpha.. Although it is known that many cytokines are produced as a consequence of bacterial interaction with monocytes/macrophages or lymphocytes, there are few reports of bacteria and none of imperfect fungi having receptors for cytokines. None previously have reported microorganisms becoming more immunogenic as a result of bound cytokine effects. In this regard, it was found that coating S. typhimurium with TNF.alpha. resulted in a complex which induced higher levels of antibody in vivo to this bacterium as compared to animals given uncoated bacteria.

One form of the invention is a composition comprising microorganisms having receptors for TNF.alpha. or other cytokines, with exogenous cytokines such as TNF.alpha. bound thereto. These are novel compositions of matter which those skilled in the art will recognize as having many uses. Specific applications include those where the source of exogenous cytokines such as TNF.alpha. is living eukaryotic cells, as well as those where the source is a recombinant microorganism or process based thereon.

Among the microorganisms to which the invention may be applied are Gram-positive or Gram-negative bacteria, as well as imperfect fungi. Specific examples of microorganisms to which the invention may be applied include Candida albicans, Salmonella typhimurium, Shigella flexneri, and Escherichia coli. Those skilled in the art will recognize that any microorganism with receptors for cytokines, including TNF.alpha., can be used in applications of the invention.

The compositions or methods of the invention may be used for activating human NK cells by treating them with microorganisms having receptors for TNF.alpha. or other cytokines to which exogenous TNF.alpha. or other cytokines have been bound. Analogously, human PBL's may be treated with microorganisms having receptor-bound exogenous TNF.alpha. or other cytokines to stimulate the production of additional cytokines such as TNF.alpha. by the PBL's. Other cells may be substituted for the human NK and PBL cells in these applications.

The cellular invasion ability of microorganisms may be enhanced by application of the invention by binding exogenous TNF.alpha. or other cytokines to microorganism receptors. Because alteration of the cellular invasion ability of a microorganism changes the cellular response to such microorganisms, the immune response will also change. Those skilled in the art will appreciate that vaccines comprised of components with enhanced invasion ability may have improved efficacy.

Applications of the invention include the use of bacterial-derived receptors for TNF.alpha. or other cytokines for isolating an purifying particular cytokines. Additionally, a more effective clinical treatment of diseases involving the modulation of the immune system by inhibiting or enhancing the effects of TNF.alpha. or other cytokines is feasible. Pharmaceutical applications of the invention may include the use of bacteria with receptor-bound TNF.alpha. or another cytokine to make the bacteria better antigens and thereby improve the efficacy of vaccines by enhancing host immune response. The latter application may include preparation of vaccines for human and animal use. Those skilled in the art will recognize that other cytokines may substitute for TNF.alpha., depending on the application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Saturation binding curve of .sup.125 I-TNF.alpha. after 40 min at 37.degree. C. with Shigella flexneri.

FIG. 2. Time course of .sup.125 I-TNF.alpha. binding by Shigella flexneri at 37.degree. C. showing binding is saturable, with optimal binding occurring at 40 minutes at 37.degree. C.

FIG. 3. Competition of TNF.alpha. (open circles) and TNF.beta. (solid circles) with .sup.125 I-TNF.alpha. for binding to Shigella flexneri. Unlabeled TNF.beta. is ineffective at competing with .sup.125 I-TNF.alpha.. FIG. 3A shows Scatchard analysis indicating a Kd of 2.5 nM, with 276 binding sites for TNF.alpha. per bacterium.

FIG. 4. HeLa cell invasion by (virulent) S. flexneri (SA100) is increased up to 20-fold in bacteria pretreated with TNF.alpha., compared with invasion by untreated bacteria.

FIG. 5. HeLa cell invasion by (avirulent) S. flexneri (SA100NI) is essentially unchanged in bacteria pretreated with TNF.alpha., compared with invasion by untreated bacteria.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relies in part on the fact that receptors for cytokines such as TNF.alpha. are found on microorganisms such as Gram-negative bacteria, Gram-positive bacteria, and the yeast form of Candida albicans. Other aspects of the invention derive from the fact that bacteria with receptor-bound TNF.alpha. enhance NK cell activity (Table 1) and induce TNF.alpha. production from human PBL's (Table 2) to a much greater extent than bacteria without receptor-bound TNF.alpha.. Such bacteria are also taken up by macrophages and epithelial cells more avidly than bacteria without TNF.alpha. on their surface, viz., a virulence property is altered by the presence of TNF.alpha.. Coating bacteria with TNF.alpha. resulted in a more immunogenic antigen which resulted in higher levels of antibody being produced in mice (Table 4). These observed TNF.alpha.-related effects support the claimed clinical and laboratory applications in the present invention. Those skilled in the art will recognize that both other cytokines and other microorganisms than those exemplified herein may be quite analogously utilized.

TABLE 1______________________________________NK cell activation by TNF.alpha. coated bacteria NK cell activity ##STR1##Culture conditions 3:1 12:1 50:1______________________________________Human PBL plus:Medium 3 10 32IL2 15 40 60S. flexneri 6 14 38S. flexneri coated 10 25 49with TNF.alpha.S. typhimurium 8 12 30S. typhimurium coated 13 29 52with TNF.alpha.______________________________________ Human PBL are incubated 18 hr with one of the following: 1) IL2 500 u/ml, 2) 10.sup.5 CFU of S. flexneri either untreated or coated with TNF.alpha. or 3) 10.sup.5 CFU of S. typhimurium either untreated or coated with TNF.alpha.. NK cell activity is assessed using a 4 hr .sup.51 Cr release assay with K562 tumor cells. TABLE 2______________________________________TNF production by human PBL stimulated withTNF.alpha.-coated S. flexneriCulture conditions TNF u/ml______________________________________Human PBL plus:Medium 12S. flexneri 13S. flexneri coated with 109TNF.alpha.______________________________________ Human PBL are incubated 18 hr with 1) medium, 2) S. flexneri, or 3) S. flexneri coated with TNF.alpha.. Supernatants from these cultures are assessed for TNF bioactivity using the L929 assay.

The following examples are presented to describe preferred embodiments and utilities of the present invention and are not meant to limit the present invention unless otherwise specified in the claims appended hereto. Taken together, the examples illustrate the best mode of implementing the invention as it is currently understood.

EXAMPLE 1

TNF.alpha. binding to Shigella flexneri

TNF.alpha. binding to a Shigella flexneri is investigated using .sup.125 I-labeled human recombinant TNF.alpha. and bacterium-.sup.125 I-TNF.alpha. complexes quantitated by filtration. .sup.125 I-labeled recombinant human TNF.alpha. (200-800 Ci/mMol) is obtainable from Amersham Corp., Arlington Heights, Ill., or may be produced using the iodogen method with rhTNF.alpha. obtained from UBI Inc., Lake Placid, N.Y. Unlabeled recombinant human TNF.alpha. (2.times.10.sup.7 units/mg) and TNF.alpha. (3.times.10.sup.7 units/mg) are available from Genzyme, Boston, Mass. Bacteria from overnight cultures of S. flexneri serotype 2a, strain SA100 are grown to mid-logarithmic phase, then incubated 10 min at 37.degree. C. with 0.01% azide in RPMI medium. Four Shigella flexneri strains of this serotype are available from the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Md. 20852-1776. Treated-bacteria (2.times.10.sup.9 cfu) are then washed and incubated in 250 .mu.l of PBS containing 1% heat inactivated FCS or 1% BSA plus varying concentrations of labeled or unlabeled TNF.alpha. or TNF.beta.. After appropriate incubation at 37.degree. C. with mixing every 10 min, bacteria-TNF mixtures are transferred to a syringe (10 ml) equipped with a 0.45 .mu.m nitrocellulose filter. Tubes (BSA-coated microfuge) which contained bacteria-TNF mixtures are washed with 250 .mu.l of RPMI, and this volume added to the syringe-filter. Bacteria are then isolated by filtration and filters containing bacteria washed with 1 ml of RPMI. Filters are then assessed for the amount of bound .sup.125 I-TNF.alpha.. Filters used in these experiments are pretreated with FCS. .sup.125 I-TNF.alpha. binding to filters in the absence of bacteria is .ltoreq.6% of the total cpm added to the binding mixture. This value is always subtracted from cpm obtained from .sup.125 I-TNF-bacteria complexes isolated by filtration. Non-specific binding to bacteria is assessed using .gtoreq.100-fold excess of unlabeled TNF.alpha.. Non-specific binding is usually about 10% of total bound cpm. Scatchard analysis is performed as described by Stuart.

.sup.125 I-TNF.alpha. binding to S flexneri varies among different commercial lots of .sup.125 I-TNF.alpha.. This appears to correlate with the level of biological activity retained by the .sup.125 I-labeled TNF.alpha.. Little binding is detected when .sup.125 I-TNF.alpha. has <20% of its biological activity as measured by the L-929 bioassay. In this regard, over one-half of the commercially obtained lots of .sup.125 I-TNF.alpha. have lost 80-90% of their biological activity and give low levels of binding to S. flexneri.

.sup.125 I-TNF.alpha. binding to azide-treated versus untreated bacteria is identical during the first 20 min of incubation. However, untreated bacteria have a doubling time of around 30-40 min and consistently bind more TNF.alpha. than azide-treated bacteria at time periods longer than 20 min. Data presented above and in Table 1 are obtained using azide-treated bacteria when binding is assessed at 37.degree. C. Non-azide-treated bacteria are used when binding is assessed at 4.degree. C., which is optimal at 4 hr incubation. Scatchard analysis of data obtained from binding experiments done at 4.degree. C. gives a Kd of 3.0 nM with 215 binding sites for TNF.alpha. per bacterium.

As illustrated in FIGS. 1-3, S. flexneri binds significant levels of .sup.125 I-TNF.alpha.. This binding is saturable with optimal binding occurring at 40 min when binding is performed at 37.degree. C. (FIGS. 1 & 2). FIG. 2 shows the time course of .sup.125 I-TNF.alpha. binding using 0.1 nM .sup.125 I-TNF.alpha. (3-4.times.10.sup.4 cpm). When binding is measured at 4.degree. C., optimal binding occurs at 4 hr. FIG. 3 shows the competition of TNF.alpha. and TNF.beta. with .sup.125 I-TNF.alpha. for binding to S. flexneri. FIG. 3A shows Scatchard analysis indicating a Kd of 2.5 nM, with 276 binding sites for TNF.alpha. per bacterium. The binding of .sup.125 I-TNF.alpha. to S. flexneri is inhibited by various concentrations of unlabeled TNF.alpha., but unlabeled TNF.beta. is ineffective at competing with .sup.125 I-TNF.alpha.. In contrast, TNF.alpha. receptors on eukaryotic cells can be occupied by both TNF.alpha. and TNF.beta.. Thus, the bacterial receptors for TNF.alpha. appear to differ from TNF.alpha. receptors on eukaryotic cells with regard to binding specificity for TNF.alpha. versus TNF.beta..

EXAMPLE 2

TNF.alpha. binding to bacteria

The ability to bind TNF.alpha. is not exclusive to Shigella flexneri. An avirulent Escherichia coli and a virulent Salmonella typhimurium both bind significant levels of .sup.125 I-TNF.alpha. (Table 3). Further, both a virulent (SA100) and an isogeneic non-pathogenic S. flexneri strain (SA100NI) appear to bind comparable levels of .sup.125 I-TNF.alpha. (Table 3). These data indicate that bacteria-TNF.alpha. binding may be common property of both virulent and avirulent gram-negative bacteria.

No difference is found between the levels of TNF.alpha. bound by rough versus smooth strains of Salmonella. However, heating, (52.degree. C./3 min), formalin fixation or trypsin treatment of bacteria results in complete to partial reduction of TNF.alpha. binding (Table 3), indicating that bacteria-encoded protein forms at least a part of the TNF.alpha. receptor.

TABLE 3______________________________________TNF.alpha. binding to bacteria TNF.alpha. Specific binding (cpm) at:Bacterium 4.degree. C. 37.degree. C.______________________________________Exp. 1 S. flexneri (SA100NI) 6591 .+-. 124 5994 .+-. 404 E. coli 5801 .+-. 58 6150 .+-. 150 S. typhimurium 4951 .+-. 160 5850 .+-. 300Exp. 2 S. flexneri (SA100) untreated 7065 .+-. 48 5226 .+-. 73 formalin-fixed 5818 .+-. 33 4176 .+-. 66 heat-treated 3199 .+-. 91 3056 .+-. 8Exp. 3 S. flexneri (SA100) untreated 3588 .+-. 99 trypsin-treated 327 .+-. 97Exp. 4 C. albicans 6053 .+-. 120 5410 .+-. 91______________________________________ .sup.125 I-TNF.alpha. binding to different bacteria was assessed. Bacteri (2 .times. 10.sup.9) are incubated with 0.1 nM .sup.125 ITNF.alpha. (3- 4 .times. 10.sup.4 cpm) for 40 min at 37.degree. C. or for 4 hr at 4.degree C. A laboratory strain of E. coli (DH5.alpha.) and a rough strain of S. typhimurium (TML) are grown and treated as described in FIG. 1 for S. flexneri. Candida albicans were grown to midlogarithmic phase and washed twice. .sup.125 IINF.alpha. binding to Candida albicans was assessed using 5 .times. 10.sup.7 organisms and using assay conditions exactly as described for .sup.125 ITNF.alpha. binding to bacteria. S. flexneri are also assessed for TNF.alpha. binding following heat treatment (52.degree. C. for 3 min), fixation by 1% formaldehyde, or by trypsin treatment. Trypsin treatment of bacteria is achieved by incubating 4 .times. 10.sup. S. flexneri (SA100) in 10 ml of PBS with trypsin (100 .mu.g/ml, Sigma, St. Louis, MO) for 30 min at 37.degree. C. Soybean trypsin inhibitor (100 .mu.g/ml, Sigma) is then added and after 15 min at 37.degree. C. the bacteria are pelleted and washed. Trypsin treated or control treated bacteria are then assessed for their ability to bind .sup.125 ITNF.alpha. as described in FIG. 1. Data presented are the mean (SD) of duplicated determinations.

EXAMPLE 3

Biological consequences of TNF.alpha. binding to Shigella flexneri

Important virulence factors of S. flexneri are its ability to penetrate and replicate within epithelial cells of the intestinal mucosa, resulting in subsequent tissue damage. These factors are investigated in HeLa cells by pretreatment of S. flexneri SA100 with TNF.alpha.. S. flexneri (SA100 or SA100NI) are incubated in 1 ml of RPMI-1640 with or without varying concentrations of TNF.alpha.. After 4 hr at 4.degree. C., bacteria (10.sup.3 cfu/ml) are pelleted by centrifugation (1500 xg) and washed once with 4 ml of RPMI. Bacteria (pretreated with media vs TNF.alpha.) are then assessed for their ability to invade HeLa cells. HeLa cell invasion is assessed by using an agarose-agar overlaying procedure as previously described.

Data presented are from triplicate determinations and from one representative experiment of 10 experiments. The results show a dramatic enhancement of HeLa cell invasion (FIG. 4). S. flexneri SA100 (10.sup.3 cfu) pretreated with 5000 U of TNF.alpha. for 4 hr at 4.degree. C. and then washed twice has a 20-fold enhancement in cellular invasion.

It is apparent that enhancement of cellular invasion is dependent upon bacterial virulence factor(s) because non-invasive S. flexneri can not be converted to an invasive form by .sup.125 I-TNF.alpha. binding. A non-invasive isogeneic variant of S. flexneri, SA100NI, which binds equivalent levels of .sup.125 I-TNF.alpha. (Table 3) does not invade HeLa cells after TNF.alpha. pretreatment (FIG. 5). The mechanism(s) involved in the enhanced cellular invasion by TNF.alpha.-Shigella complexes is unknown, but could possibly result from enhanced interaction with the cell surface.

EXAMPLE 4

Enhanced Immunogenic Potential of .sup.125 I-TNF.alpha.-coated S. typhimurium

Coating a pathogen with a cytokine was found to result in a more immunogenic antigen. Salmonella typhimurium (10.sup.8) were incubated with rTNF.alpha. (10,000 U) in a volume of 250 ml. After 4 hours at 4.degree. C. the bacteria-TNF.alpha. complexes were formalin-fixed, washed twice and injected (ip) into C57B1/6 mice. As a control, Salmonella were treated in an identical fashion in medium with no TNF. Mice were bled at 6 days post challenge. Results of a representative experiment are illustrated in Table 4.

TABLE 4______________________________________Enhanced Antibody Production in vivo byTNF-Coated S. Typhimurium Antibody to TMLMice Immunized With ELISA Assay (OD Units)______________________________________S. typhimurlium (TML) .6523 .+-. .15S. typhimurlium (TML) 1.075 .+-. .31coated with TNF.alpha.______________________________________ C57B1/6 mice (5) were challenged (ip) with 10.sup.8 formalinfixed TML which had been pretreated with 10.sup.4 of rTNF.alpha.. Serum from individual mice were obtained at 6 days and assessed for antibody to TML by ELISA assay. Data is mean .+-. SD OD units from 5 mice per group.

Coating Salmonella with TNF.alpha. resulted in an enhanced antibody response to Salmonella. These data indicate that coating a pathogen with TNF.alpha. can enhance the immune response to that pathogen. These results could be applied for the preparation of vaccines for both human and animal use. Improved vaccines could result from coating any pathogen with cytokines such as interleukin-1 (IL1), interleukin-2 (IL2) or interferon (IFN). The coating could be easily performed as described above or by cross-linking the cytokine onto the pathogen. Additionally, deactivated microorganisms or antigenic microorganism surface components retaining bound cytokines could be used as administered material in the usual course of human or domestic animal vaccination. Oral administration of cytokine-containing avirulent microorganism strains is a preferred mode of immunization, of course when the elicited immunity precludes adverse effects of analogous virulent microorganisms.

REFERENCES

The following references are incorporated in pertinent part in the specification for the reasons therein.

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Changes may be made in the construction, operation and arrangement of the various microorganisms, cytokines, steps and procedures described herein without departing from the concept and scope of the invention as defined in the following claims.

Claims

1. A method for inducing immunity to a Gram-negative bacterial or imperfect fungal microorganism comprising identifying a Gram-negative bacterial or imperfect fungal microorganism having a tumor necrosis factor binding site and administering to an animal a composition including said Gram-negative bacterial or imperfect fungal microorganism or avirulent strain thereof bound to an exogenous tumor necrosis factor at a tumor necrosis factor binding site.

2. The method of claim 1 wherein said Gram-negative bacterial microorganism is Salmonella typhimurium, Shigella flexneri, or Escherichia coli.

3. The method of claim 1 wherein said imperfect fungal microorganism is Candida albicans.