Patent Application
20090170199
The present invention relates to a method for the separation of biological objects in a solution which have different viscoelastic properties, wherein said method comprises a filtration step allowing the higher viscoelastic biological objects to pass through the membrane while retaining the lower viscoelastic biological objects above the membrane, and a recovery step wherein the separated lower viscoelastic biological objects are recovered above or onto the membrane and/or the separated higher viscoelastic biological objects are recovered in the filtrate. Advantageously, the biological objects are cells. More advantageously, the recovered cells are viable cells. In one preferred embodiment, the cells are tumor cells. In another preferred embodiment, the cells are fetal cells and the method finds an application in prenatal diagnosis.
It is often desirable to examine biological samples, and specimens for signs of abnormality and disease.
As an example, the cells in a sample of blood or spinal fluid might need to be examined for indications of cancer. Because these types of samples might well contain millions of cells, it is very advantageous to separate the majority cells and fluids that are not of interest, thus concentrating the cells of interest.
In blood and spinal fluids it is desirable to remove plasma, erythrocytes red blood cells, and leukocytes (white blood cells), thus concentrating the small number of cells that are not normally present and that might exhibit signs of abnormality such as cancer. As leukocytes are often very similar to the cells of interest it is difficult to remove these cells without losses. The resulting concentrated cells of interest are then used for further analysis.
The methods currently available for separating cell types comprise separation by size, separation by centrifugation (density/specific gravity), and separation relative to the chemical or biochemical properties.
Separation by centrifugation works well when the two types of cells are very different as in the example of the separation of white and red blood cells. But centrifugation fails when the two types of cells have similar density and size, such as white blood cells and cancer cells. A further limitation of centrifugation-based cell separation is that the density of the cells are not constant, as even dead cells react to the conditions of their surrounding and environment.
Separation by (bio)chemical properties utilizing immuno-based chemistry by antibody binding of the cell to a surface antigen (which can possibly be attached to magnetic beads) is expensive, labor-intensive, and time-consuming. Many of the steps can have cell losses thus reducing the separation efficiency of this type of method. Also, cells will be lost if they don't have the matching antigen, and/or if the antigen is obscured by other blood components. Blood plasma proteins may coat the cells in circulation (a possible method of cancer cells evading the immune system) thus preventing their recognition by the antibody. The cells separated by this method are often in a form that is difficult for a visual examination of the results.
Separation by size is usually done by filtering through a filter, or an array of one or more hollow tubes with a specific hole size. Cells that are larger than the hole stay on one side of the filter while smaller cells go through the filter and are collected on the other side of the filter. In this separation method, a fixative agent is used for stabilizing the membrane of the cells, such as formaldehyde. However, cells are no more viable after the action of fixative agents, and cannot be cultured. Moreover, if the two types of cells have an overlapping size distribution (a certain portion of the cells of one type are larger while another portion are smaller than the other type of cell), then the filter does not separate the two types effectively, resulting in a loss of some of the cells of interest thus reducing separation efficiency.
Consequently, separation by the above methods can damage the cells both bio-chemically, and mechanically, thus changing the cell morphology, and inhibiting subsequent processing and analysis.
There is thus a need for a method which allows the separation of different biological objects which may have the same size or an overlapping size distribution and which, advantageously, does not denature said biological objects such that, in the case of cells, the separated cells are viable and can be further cultured.
The Inventors have elaborated a new method of separation which meets the need in the art. According to this method, the biological objects are separated relative to their different biological properties, even if their size is the same or overlaps. Moreover, this method allows advantageously the recovered biological objects to be further used for culture applications.
Accordingly the present invention relates to a method to separate the objects by object type where the different object types can not be fully differentiated by size, shape, and density (leukocytes and certain cancer cells are two important examples). This method also provides a high separation efficiency, which allows the use of smaller sample sizes with less risk of missing objects of interest. Moreover, without any damage to the objects of interest, both biochemically, and morphologically, this method does not interfere with subsequent processing and analysis, and the correct morphology of the resulting objects is maintained. No chemical/biochemical preparation of the objects of interest is used (all such known per se preparations modifying biochemical, and/or biophysical and/or morphological properties of such objects). The separated objects can then be easily presented on a slide in a way that is preferred by a pathologist, or be read by automated vision system, or remain in a liquid solution for subsequent processing.
Thus, the subject-matter of the present invention is a method of separating multiple natural biological objects in a solution, wherein the biological objects are composed of at least a natural lower viscoelastic biological object type and a natural higher viscoelastic biological object type, and the natural lower viscoelastic biological objects have lower viscoelastic properties than the natural higher viscoelastic biological objects, wherein the natural lower viscoelastic biological objects are at least one of the group consisting of circulating fetal cells and tumoral or cancer cells, the method comprising:
It must be understand throughout the whole application that the term “natural” is used to qualify an object or a property that is not chemically/biochemically modified between the sampling and the recovery step of the method according to the invention.
The biological objects may be of any type, such as cells, bacteria, viruses, and yeasts, such list being not limiting. The biological objects in solution may be obtained from any biological sample. The biological sample may be bodily fluids, such as blood, spinal fluids, urine, any tissue and tumor biopsies. The method is not limited to a liquid biological sample. As an example a solid tissue biopsy can be preprocessed to break the tissue down into individual cells. The cells can then be suspended in a preservative fluid. It may also be water and soil samples, plant tissues and fluids, etc. . . .
Advantageously, the multiple biological objects are at least two cell types.
The cells to be separated may be of any type. These can be cells naturally present in the blood such as megakaryocytes, monocytes, macrophages, dendritic cells, neutrophil granulocytes, eosinophil granulocytes, basophil granulocytes, mast cells, helper T cell, suppressor T cell, cytotoxic T cells, B cells, natural killer cells, reticulocytes, stem cells and committed progenitors for the blood and immune system. Cells to be separated can also belong to other origins. They can be epithelial cells (keratinizing epithelial cells, wet stratified barrier epithelial cells, exocrine secretory epithelial cells), cells from the gut, exocrine glands and urogenital tract, endothelial cells, metabolism and storage cells (hepatocyte, white fat cell, brown fat cell, liver lipocyte), barrier function cells (lung, gut, exocrine glands and urogenital tract), epithelial cells lining closed internal body cavities, extracellular matrix secretion cells, contractile cells, sensory transducer cells, autonomic neuron cells, sense organ and peripheral neuron supporting cells, central nervous system neurons and glial cells, lens cells, pigment cells, germ cells, nurse cells.
The cells to be separated could also be diseased cells such as mutant, virally infected cells or tumor cells and belong to any of the above cell types.
In a preferred embodiment, the cell types which are recovered are destined to be analyzed by biological, genetic, immunohistochemical and biochemical methods after further division and expansion in culture. Accordingly, the cells recovered are advantageously viable cells and the solutions used for the filtration step do not contain any reagent that kills the isolated cells.
In another embodiment, the cell types which are recovered are processed for further analysis by biological, genetic and biochemical, or immunohistochemical, methods without further expansion in culture.
In another embodiment, after recovery of the target cells onto the membrane, their nucleic acid material is extracted for further analysis. The acid nucleic (DNA, RNA) may allow the identification of genetic defects or genes specifically expressed in the target cells.
The cytoskeleton is a three-dimensional polymer scaffold which spans the cytoplasm of eukaryotic cells. This network is mainly composed of actin filaments, microtubules, intermediate filaments, and accessory proteins. It provides the cell structure and affects cell motility as well as viscoelastic properties. The viscoelastic properties of cells determine the degree of cell deformation as a result of mechanical forces and, consequently, affect cellular structure and function. The determination of the viscoelastic properties of living cells requires the quantification of force versus strain relationship of cells under physiological conditions. Several papers describe the techniques which can be used to determine the viscoelastic properties, and are well known by the man skilled in the art.
Numerous systems have been described in order to measure the rheological/viscoelastic properties of cells, including micropipette aspiration (Evans E. and Yeung A., Biophys. J. (1989), 56, 151-160.), passage through the micro holes of a membrane (Frank R. S., Tsai M. A. J Biomech Eng. (1990); 112, 277-82), optical tweezers (Ashkin A. and Dziedzic J. M., Proc. Natl. Acad. Sci. USA (1989), 86, 7914-7918), Atomic Force Microscopy [Benoit M. et al., Nature Cell Biol. (2000), 2, 313-317). These techniques can be coupled to an adequate Theological model.
Micropipette aspiration technique is a frequently used method to measure viscoelastic properties of cells. This technique has the advantage to measure viscoelastic properties in solution and in the physiological environment of the cells. As an example, viscoelastic of both hepatocytes and hepatocellular carcinoma (HCC) cells were measured by means of a micropipette aspiration technique (Wu ZZ and al., Biorheology, 2000, 37, 279-290).
According to the present invention, during the first step of the process, cells are sorted according to their natural viscoelastic properties by a filtering step across a membrane containing holes with an appropriate size. Preferably, a controlled force is applied during the filtration step, which is kept lower than the predetermined force needed to force the natural lower viscoelastic biological object to pass through the membrane, and which is higher than or equal to the predetermined force needed to force the natural higher viscoelastic biological object to pass through the holes.
The expression “controlled force”, according to the invention, is used to designate the force applied during the filtration step to force the natural higher viscoelastic biological objects to pass through the membrane, containing holes with an appropriate size, while retaining the natural lower viscoelastic biological objects, and preserving the integrity of the cells to be isolated.
This applied force results from a differential pressure created between the both side of the filtrating membrane, with force=(differential pressure)×(biological object surface). On another embodiment according to the invention, this applied force results from the acceleration applied by centrifugation, for example, on the biological objects, with force=acceleration×(biological object mass)
In the present invention, isolation of circulating cells of interest, starting from a peripheral blood sample, is based on the difference in viscoelastic properties between leukocytes cells and the circulating cells of interest. In a particular embodiment, the natural lower viscoelastic cells are tumor or cancer cells or fetal cells.
The membranes used in the present invention display hydrophobic properties and are mostly inert and strong, resulting in a constant pore size even when under pressure. The membranes used in the present invention are, for example, polycarbonate membranes. Polycarbonate membranes have the properties described above and a highly efficient cell transfer rate of isolated cells from the membrane to the glass slide used for its biological characterization.
In a particular embodiment, the natural lower viscoelastic cells are tumor or cancer cells. In a second particular embodiment, the natural lower viscoelastic cells are fetal cells. Preferably, the fetal cells are fetal cells circulating in maternal blood. Preferably, the controlled force which is applied during the filtration step corresponds to a force resulting from a differential pressure between 20 kPascals and 190 kPascals, advantageously between 40 kPascals and 60 kPascals, and more advantageously between 45 kpascals and 55 kPascals, and the average diameter of the pores is comprised between 3 μm and 15 μm, advantageously between 6 and 10 μm, and more advantageously between 8 and 10 μm, thus allowing to recover the tumor cells or the fetal cells on or above the membrane. A good adequacy between the pore size and the controlled force applied is desirable. In alternative, the filtration step is realized under a temperature comprised between 20° C. and 40° C.
Indeed, normal, fetal and cancerous circulating cells display different viscoelastic properties. Scientific literatures indicate that the most of leukocyte cell types have folded membranes. The unfolding of the membrane gives leukocytes viscoelastic properties that allow the cell when under pressure to elongate and to pass through a micropipet tip without damage even when the tip is less than ¼ the diameter of the leukocyte (E Evans and A Yeung, (1989). Biophysical Journal 56: 151-160). Neutrophils, whose diameter size is comprised between 10 and 12 μm, can be made to pass through 3 μm holes. In details, the different types of leukocytes are::
Other types of cells lack this folded membrane and therefore have difficulty passing through a hole of less than the diameter of the cell. The smaller the membrane pore size in relation to the leukocyte size the greater the differential pressure is needed to force the leukocyte through the hole. For example, as the morphology of cell progresses from normal to cancer cell, the membrane changes in some cases getting thicker and in other cases getting thinner (Gang Zhang et al., 2002, World J Gastroenterol; 8(2), 243-246). When the cell membrane gets thinner it is more susceptible to damage and lyses. The damage threshold for the cells of interest puts an upper limit on the pressure differential which can be applied across the membrane without damaging the cells of interest. It thus seems that malignant transformation induces a decrease in viscoelastic properties.
The method of this patent is an effective method to separate cell types and relies on the difference in viscoelastic properties between different cells.
As an example, in the case of separation of circulating cells according to their viscoelastic properties within a blood sample, a polycarbonate membrane with conservative 8 μm pore size applying a differential pressure of 40 to 60 kPascals (In Custom cut from sheets 8 μm Whatman polycarbonate Nuclopore membranes) can be used under a temperature between 20° C. and 40° C. Because of their viscoelasticity, this will suffice to pass the majority of leukocytes although the size of 75% of those cells is larger than 8 μm. On the other hand other cells, i.e. not leukocytes, larger than 8 μm in diameter will be blocked.
For separating leukocytes from other types of cells that are smaller than 8 μm in diameter, a membrane as small as 4 μm can be used with the corresponding need for higher pressures only being limited by the damage threshold for the cell or by forcing the cell types of interest through the membrane. Polycarbonate membranes are used because they are hydrophilic, mostly inert, and strong with low elasticity resulting in the pore size remaining constant even when under pressure. Also polycarbonate membranes have a highly efficient cell transfer rate from the membrane to a glass slide.
Preferably, the solution containing the cell types is a mononuclear cell fraction which results from a centrifugation step of a blood sample. In a particular embodiment, the lower viscoelastic cells are circulating tumor cells.
In another embodiment, the at least one of the cell types is a fetal cell type. Preferably, the fetal cells are fetal cells circulating in maternal blood.
Fetal cells are present in the maternal circulation. Successful isolation of fetal cells from maternal blood will open new routes to replace invasive prenatal diagnosis methods (chorionic villus sampling or amniocentesis) with their inherent risks to the mother and fetus by non-invasive methods followed by genetic analysis on fetal cells (FISH, PCR, sequencing). Three different fetal cells are known to circulate in maternal blood: trophoblasts, fetal leukocytes and fetal erythrocytes (for review see Bianchi, British Journal of Haematology, 1999).
Fetal trophoblast cells, located outside the villus (extravillous) migrate during the first trimester into the maternal tissue of the placental bed. This process of invasion is unique to trophoblast cells and induces vascular adaptation of the maternal spinal arteries. As a consequence, a specific subset of trophoblast cells appears in the maternal blood as a normal feature (for review see Oudejans et al. 2003, Prenatal Diagnosis). The first wave peaks around the middle of the first trimester, the second wave peaks at the end of the first trimester.
A second aspect of the invention is an in vitro prenatal diagnosis comprising the method according to present invention wherein the at least one of the two cell types is a fetal cell type, as described above.
If we considered that in one milliliter of blood, there are 7 millions leukocytes, the number and size of the different type of leukocytes is described as follow:
We will see that the method according to the invention is very adapted for separation of the fetal cells circulating in the maternal blood through annexed examples.
While the above description contains many specificities, these should not be construed as limitations on the scope of the invention, but as exemplifications of the presently preferred embodiments thereof. Many other ramifications and variations are possible within the teachings of the invention.
a, 1b, 1c, 1d: Closely related conceptual drawings of a cell being forced through a smaller hole by a pressure differential or a centrifugation force.
a is a schematic representation of two cell populations with overlapping size distribution. Cell population A has a larger mean size than cell population B. On the other hand, cell population A has higher viscoelastic properties than cell population B.
In the case of
In the case of
Cells of type A even when they are larger then the hole (pore) size of the membrane will pass through because of their higher viscoelastic properties as compared to type B cells. Type B cells will not get through the holes membrane unless the cell size is less than or close to the pore size of the membrane.
c represents the distribution of cells remaining above or onto the membrane using the principle of the present invention.
Note the high efficiency of separation in
a, 1b, 1c, 1d are conceptual drawings of a cell being forced through a smaller hole by the pressure differential of the centrifugation force.
a) Cell is attracted to empty hole by fluid flow through the hole. (higher pressure on the top or centrifugation force)
b) Pressure differential or centrifugation force starts to deform and fold cell pushing it into the hole.
c) Cell is pushed through the hole by pressure differential or centrifugation force
d) Cell is expelled away from the hole by fluid flow through the hole
The force (pressure differential or centrifugation) needed to push the cell through the smaller hole is dependent on size and the viscoelastic properties of the cell. Viscoelastic properties of an object are the properties that allow the object to elastically fold, and to bend, and to distort their shape, and to flow through holes and passageways that are smaller than the object. Literature indicates that the white blood cells (leukocytes) have relatively high viscoelastic properties; this allows them to flow through small diameter passageways and reach tissues via the body's microscopic blood vessels.
Tumor or cancer cells and fetal cells from the maternal blood can be of a similar size to that of white blood cells. But tumor or cancer cells and fetal cells are found to have considerably natural lower viscoelastic properties. Hence a tumor or cancer cell or a fetal cell needs considerably more force to push it through a small diameter hole as compared to a white blood cell of a similar size. The tumor or fetal cells will be stopped by the small hole size and will not go past the point in
The protocols outlined below describe the method to isolate cancer cells from human blood samples. The samples are either taken from cancer patients, with the objective of isolating endogenous patient circulating tumor cells. Alternatively, as an experimental model for the validation of the present invention, cultured tumor cells are seeded into blood samples from healthy volunteers. In this latter setting the objective is to assess the yield and sensitivity of the isolation procedure.
A similar protocol can be used for the purification of fetal cells from maternal blood.
1. Equipment & Reagents
The following items need frequent washing (for large processing runs it is recommended that more are purchased). Includes 2 each of:
Manufacturer Kimble—Kontes
953701-0000 Glass Funnel top, 25 mm, 15 mL
953702-0001 Fritted Glass Support Base (it is anticipated that in future versions of device the glassware will be replaced by disposable)
2. Seeding Method
Cultured cancer cells (preferably a cell line that is not overly prone to clumping) are harvested according to usual cell biology procedures, e.g. cell containers are washed, detached by trypsinization for a suitable length of time, and then collected by centrifugation.
The collected cells are resuspended and washed in a 90% culture medium/10% serum solution (solution A), then centrifuged again for collection.
The cell density (cells/volume) is determined for the stock using a hemocytometer, taking a known volume from the well-dispersed stock.
A 4-mL whole blood sample is collected from the peripheral circulation of a healthy volunteer. The blood is collected in a commercial Vacutainer® with EDTA as the anticoagulant.
Cultured cancer cells are then added to the blood sample at a known nominal value by serial dilution of the dispersed stock. Solution A is used as the diluant throughout the series.
At every step in the series, and in the final seeded blood sample, the tube is gently mixed for cell dispersal.
The nominal value represents the approximate number of cells seeded into the sample; the exact desired number of cells cannot be achieved using the serial dilution method because of heterogeneity of the cell mixture. For exact seeding values (especially at low cell numbers), methods such as micromanipulation or flow cytometry are recommended.
3. Enrichment Method
4. Alternative Enrichment Method
The following procedure describes the enrichment method for culturing and expansion of recovered cells. In this alternative enrichment method, the 40% ethanol solution is replaced by a isotonic buffered solution.
Seeding of Blood Cells with Exogenous Tumor Cells
In this experiment, blinded samples were seeded with 4 to 120 cells. Analysis by immunohistochemial detection showed that over 80% of seeded cells in each sample were recovered. See
5. Appendices
1. Attach a 10 cm and 12 cm silicon tubes to two 5 mL syringes.
2. The blood is transferred from the collection tube to a suitable centrifuge tube.
3. The blood collection tube may be washed with a small amount of phosphate-buffered saline (PBS)<1 mL, and added to the centrifugation tube.
4. Fill the syringe with 3.0 mL of Ficoll-Paque gradient centrifugation media at room temperature. Place tip of 12 cm silicon tube at the bottom of centrifugation tube. Slowly inject the 3.0 mL of Ficoll-Pague into the bottom of the tube.
5. The blood samples are centrifuged at a speed of 400 g for 30 minutes, using a partial or no brake at the end of the run (the centrifuge has horizontal swing-out buckets). Batch size should be determined by the total batch processing time of 30 minutes excluding centrifugation time. It is estimated the maximum size of a batch depending on the speed of the operator should be from 4 to 6 samples every 30 minutes.
6. Place a new membrane into the apparatus. (see
Prime membrane to remove air from under membrane:
i. Filling top with 10 mL of 40% ethanol
ii. Aspirate (F) approximately 5 mL
iii. Backflush (BK)
iv. Aspirate (F) approximately 2 mL
vi. Aspirate (F) approximately 1 mL
vii. Top up to the 10 mL mark with 40% ethanol
There should be no indication of air leaking into the system.
Note: (F) and (BK) refer to instrument controls.
7. The mononuclear cell fraction (or buffy coat) is aspirated from the centrifuge tube by immersing the tip of a 5-mL syringe fitted with the 10 cm silicon-tubing tip attachment below the level of the buffy coat, and aspirating in a steady manner until a very small amount of serum is aspirated. The tip should be lowered slightly and aspiration should continue until once again a small amount of serum is aspirated. An alternative to holding the tube by hand would be to place it in a stand.
The aspirated buffy coat is added directly onto the membrane with 10 mL 40% ethanol. Flush the syringe out by aspirating some of the fluid back into and back out of the syringe.
8. Filter (F) the contents down to approximately 3 mL remaining in the top chamber. Wash the sample by addition of 10 mL of 40% ethanol and back flushing (BK) the membrane. Repeat as necessary until filtration is complete (the filtrate is clear and the flow rate is constant). With some samples the flow rate through the membrane may become very slow necessitating a back flush before the contents have reached the 3 mL mark.
9. Filter down to about the 1 mL mark and then slowly filter (S) the contents until the liquid is just removed from above the membrane; do not allow the membrane to dry out.
10. After enrichment of the disseminated cancer cells, the cells are deposited on a slide by removing the membrane from the apparatus. A microscope slide is pressed on the sponge such that the membrane is ‘sandwiched’ between glass microscope slide and sponge resulting in a pressure-transfer of the cells from the membrane to the slide. Remove the clamp, and remove the top of the filtration apparatus by lifting straight up. Remove the membrane using a fine pair of tweezers, being careful not to touch the area at the center that contains the cells.
In some cases the membrane will stick to the top of the membrane apparatus, in which case use the tweezers to gently pull the membrane down and away from the top. Extra care is required not to pull the membrane across the top as the cell layer could be smeared by contact with the top piece.
Place the membrane cell side up on a sponge dampened with 60% ethanol and pre-loaded into the provided jig.
Align the membrane so that the membrane is between the 4 posts and butting up to the 2 short posts. The long axis of the membrane will be across the slide.
Place a slide over the membrane as shown in the picture, the label side should face down.
Gently press down on the microscope slide over the center of the sponge for about 5-8 seconds. Release the pressure (see
Lift the slide off the sponge (the membrane will adhere to the slide). Turn the slide label side up. Carefully peel back the membrane so as not to disturb the transferred cell button on the microscope slide.
11. The slide is immersed in fixative for later immunostaining analysis with an antibody of interest (Using 95% ethanol as the fixative is suggested).
12. Press the (F) control for a few seconds to remove any residue filtrate from the bottom of the membrane support.
The waste bottle vacuum pump should be turned on a few minutes before the instrument is needed to give time to purge the air from the waste bottle.
Then the pump is turned off before cleaning to allow the waste bottle to reach atmospheric pressure.
The instrument has a button (F) for momentary switch, to be pushed to aspirate filtrate.
The instrument further has a button (BK) for momentary switch, to be pushed to back flush. To prevent air getting into the system this switch should only be pulsed briefly for less than a second. Only back flush when there is liquid above the membrane and after the (F)-button has been used for several seconds.
The instrument further has a button (S) for momentary switch, used to slowly remove filtrate from the system.
The human extravillous trophoblast-derived cell line SGUPL-4 is derived by transfection of primary human first trimester extravillous trophoblasts with the early region of SV40. SGHPL-4 cells retain many features of normal extravillous trophoblast, such as expression of cytokeratin-7, BC-1, HLA-G, CD9, hPL and HCG (Choy and Manyonda, 1998; Cartwright et al., 1999, Prefumo et al., 2004b) and behave in the same manner as primary cells (Ganaphthy et al. Hum. Reprod. 21 (5): 1295).
SGHPL4 cell line is therefore the best cellular model for the demonstration of the unique capacity of our technology to isolate circulating fetal cells from a blood sample. Here we show that starting for a blood sample containing five SGHPL-4 cells per ml of blood, the recovery of fetal cells is more than 80%. The purity of the isolated fetal cells is 5% as compared to 0.00005% before the process.
The following procedure describes the isolation method for fetal cells from a blood sample using the apparatus described in Appendix A and B.
At this point, the identification cells of interest, i.e. fetal cells, can be performed by immunofluorescence, FISH or any other methodology used for genetic diagnosis.
Whole blood sample is collected from the peripheral circulation. The blood is collected in a 15 ml polypropylene tube containing an anticoagulant (heparin, EDTA).
3. Spiking Experiment with SGHPL-4 Cells
SGHPL4 cells, which are considered as fetal cells (vide supra), are harvested according to usual cell biology procedures, e.g. cell containers are washed, detached by trypsinization for a suitable length of time, then collected by centrifugation. The collected cells are suspended in a volume of medium without serum and counting cells is performed using a counting chamber with a cover on the top.
A 5-mL whole blood sample is collected from the peripheral circulation of a healthy volunteer. The blood is collected in a 15 ml polypropylene tube containing an anticoagulant.
SGHPL-4 cells are then added to the blood sample at a known nominal value by serial dilution of the dispersed stock. At every step in the series, and in the final seeded blood sample, the tube is gently mixed for cell dispersal.
In this experiment, blinded samples were seeded with 5 to 50 SGHPL4 cells per ml of blood. The membranes were treated for immune fluorescence cell detection using a specific antibody directed against an antigen expressed by SGHPL-4 cells and not expressed in leukocyte. In the described example, a mouse anti-SV40 Large T, small t Antigen monoclonal antibody was used. At the end of the protocol, analysis by immunofluorescent detection showed that over 80% of seeded cells in each sample were recovered.
The following table shows the number of the different cells type isolated on the membrane. The cells were counted by observation on fluorescent microscope using appropriate filters. The number of all nucleated cells was counted with filter for DAPI staining, and SGHPL-4 cells were counted with filter for CY3 staining.
The enrichment of the fetal cells like isolation was calculated. The total number of leukocytes per mL of circulating blood is comprised between 4 to 10 millions. The enrichment of the fetal cells like by the process of the invention is superior to 105, as this can be seen in the following table
For this analysis, blood samples are collected from peripheral circulation of women healthy volunteer. Blinded samples were seeded with 100 SGHPL4 cells per ml. The SGIPL4 cells are XY, the leukocytes from women healthy volunteer are XX.
The blood sample prepared as described in point 3 is processed following instructions for fetal cells isolation described in the Protocol for fetal cells isolation. At the end of fetal cells isolation process, membranes are removed from the apparatus and treated by 1 mL Paraformaldehyde 4% for 10 minutes and then washed four times with 1 mL of PBS1X.
FISH experiments are performed by following the instruction manual for the kit “2 Color X & Y Probe Panel”, OnCellSystem, Catalog #ASXY.
Analysis of the red and green signals with appropriate filter of a fluorescent microscope allows to clearly discriminate XY cells from XX cells. These results demonstrate that multi FISH experiments can be performed on isolated cells on membrane.
The isolation of circulating rare cells relies on the viscoelastic properties of leukocytes that allow them to pass through membrane pores size smaller than their diameter. This property is dependant to the differential pressure applied between the two compartments but also to the temperature.
Fetal cells isolated on membrane could be identified by specific antibody directed against a marker expressed by fetal cells and not expressed in leukocyte. Commercial antibodies can be used to identify trophoblast cells are listed in the following table:
Alternatively, other antibodies are described in the literature to specifically labeled trophoblast cells as following (PMID: PubMed IDentifier):
| Number | Date | Country | |
|---|---|---|---|
| 60643972 | Jan 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11334303 | Jan 2006 | US |
| Child | 12142696 | US |
