LYMPHOCYTE STIMULATING FACTOR FROM TRYPANOSOMA

Abstract: The present invention relates to a lymphocyte stimulating factor comprising a protein component having the ability to stimulate, in a living animal body, CD8+ T-cells resulting in the release of interferon- gamma (IFN- gamma ) to elicit immunosuppression or immunostimulation in said body, wherein said protein component is selected from amino acid sequences within the sequence of amino acids numbered 1 to about 150 in Fig. 1B, which are in possession of said ability. The invention also relates to the nucleotide sequence of the lymphocyte triggering factor according to the invention as well as to a monoclonal antibody directed against said factor. Additionally, the invention relates to the use of the lymphocyte stimulating factor for medical purposes as well as to a method of treating or vaccinating a mammal in respect of African sleeping sickness.

Description: LYMPHOCYTE STIMULATING FACTOR FROM TRYPANOSOMA INTRODUCTION The present invention relates to a lymphocyte trig ¬ gering factor, which has the ability to stimulate CD8+ T cells in a living body. The invention also relates to a nucleotide sequense coding for said lymphocyte triggering factor as well as a monoclonal antibody directed against said factor. BACKGROND African Trypanosomiasis is a disease widespread in the tropical Africa. It exists in (i) humans as Sleeping Sickness, caused by Trypanosoma brucei gambiense (T. b . gambiense) or T. b. rhodesiense, (ii) in cattle as Nagana caused by T. congolense and T. vivax and (iii) in camels as Surra and caused by T. evansi . Mortality is caused either by massive parasitosis or secondary infections due to immunosuppression, which is an important trait of the disease (Werry et al., 1982, Askonas,B.A. "Interference in general immune function by parasite infections; Afri- can trypanosomiasis as a model system", Parasitology 1984; 88:633-638). Existing therapies are either cumbersome or toxic and there is no available vaccine. Furthermore, methods for diagnosing the disease are poorly developed. A new principle for how a microorganism may subvert the host defense has been detected using an experimental model for African tryptanosomiasis where rodents have been infected with T. b. brucei . The studies focused on CD8 + T cells and interferon gamma (IFN-γ) as putative i - portant host derived elements in the interactions with the parasite during infection. IFN-γ production in the spleen increased markedly early after infection (Bakhiet.M., Olsson, T., Van der Meide, P., and Kristens- son, K. , "Depletion of CD8 + T cells suppresses growth of T. brucei brucei and IFN-γ production in infected rats", Clin Exp Immunol 1990; 81: 195-199). Both in vivo monoc- lonal antibody CD8 + T cell depleted rats, as well as geno- mically CD8 deleted mice, showed absence of IFN-γ induction, dramatically decreased parasitaemia and prolonged survival (Bakhiet et al., 1990, supra, Olsson, T., Bakhi- et, M., Hδjeberg, B. , Ljungdahl, A., Edlund, C, Anders- son, G., Ekre, H-P, Fung Leung, W-P, Mak, T., Wigzell, H., Fiszer, U., Kristensson, K., "CD8 is critically involved in lymphocyte activation by a Trypanosoma brucei brucei released molecule", Cell 1993; 72:715-727). Also, intraperitoneal injeciton of anti IFN-γ antibody suppressed parasite growth and increased survival of the animals (Olsson et al., 1993, supra) . In vi tro studies showed that the trypanosome released a lymphocyte triggering factor (TLTF) , which through binding to CD8 on lymphoid cells, triggers these cells to IFN-γ, which in turn constitutes a growth stimulus for the parasite (Olsson, T., Bakhiet, M., Edlund, C, Hδjeberg, B., Van der Meide, P., and Kristensson, K. , "Bidirectional activating signals between Trypanosoma brucei and CD8 + T cells: A trypanoso- me-released factor triggers interferon gamma production that stimulate parasite growth", Eur. J. Immunol. 1991; 21:2447-2454; Olsson et al, 1993, supra) . A mouse monoclonal antibody (MOl) was raised and used to purify TLTF with affinity chromatography. In addition, passive immu- notherapy in vivo with MOl strongly reduced parasite levels and prolonged survival of the animals (Bakhiet, M., Olsson, T., Edlund, C, Hδjeberg, B. , Holmberg, K., Lo- rentzon, J., and Kristensson, K., "A trypanosoma brucei brucei derived factor that triggers CD8 + lymphocytes to interferon gamma secretion: Purification, characterization and protective effects in vivo by treatment with a monoclonal antibody against the factor", Scand. J. Immunol. 1993; 37:165-178). Hitherto, it has not been possible to clone TLTF for the production of recombinant material or peptide parts of the molecule, which could be tested in future vaccination attempts. Had this been possible, the molecule might furthermore be used in the targeting of CD8 + cells both in vivo and in vi tro. GENERAL DESCRIPTION OF THE INVENTION The present inventors have succeeded in the cloning of TLTF. Thus, this invention relates to a lymphocyte stimulating factor comprising a protein component having the ability to stimulate, in a living animal body, CD8+ T-cells resulting in the release of interferon-γ (IFN-γ) to elicit immunosuppression or immunostimulation in said body. In addition, the invention relates to a nucleotide sequence coding for said lymphocyte stimulating factor as well as a monoclonal antibody directed against it. LEGENDS TO THE FIGURES For a better understanding therof, the present invention will be disclosed under reference to figures. While a more detailed disclosure thereof will be found below, a summary of the figures is as follows: Figure IA depicts SEQ ID NO 1, which is the complete cDNA sequence for TLTF. Figure IB depicts SEQ ID NO 2, which is the amino acid translation of the cloned cDNA. Figure 1C depicts SEQ ID NO 3, which is the protein according to Figure IB. Figure ID depicts SEQ ID NO 4, which is the complete predicted amino acid sequence of TLTF. Figure 1E-H depicts SEQ ID NO 5-8, which are the predicted amino acid sequences of four truncations of TLTF according to the invention. Figure 2 shows the number of IFN-γ secreting cells determined in an immunospot assay by a graph, wherein the number of IFN-γ spots/10 6 rat MNC are plotted for TLTF, rTLTF and 0V7. Figure 3 shows monoclonal anti-TLTF antibodies effect on rTLTF triggering of human peripheral blood (PBL) . Figure 4 shows the effects of TLTF and rTLTF on MNC from mice with genomic deletion of CD8 + or CD4 + T cells. Figure 5 shows the anti-rTLTF immune sera inhibitory effect on native TLTF-induced IFN-γ as measured by the immunospot assay. DETAILED DESCRIPTION OF THE INVENTION The object of the present invention is more specifically a lymphocyte stimulating factor comprising a prote- in component having the ability to stimulate, in a living animal body, CD8+ T-cells resulting in the release of in- terferon-γ (IFN-γ) to elicit immunosuppression or immunostimulation in said body, wherein said protein component is selected from amino acid sequences within the sequence of amino acids numbered 1 to about 150 in Fig. IB, which are in possession of said ability. The amino acid sequence showed no ho ologies to previously described proteins, and since it represents a non-variable protein it is a potential candidate for immune therapy. One object of the invention is a lymphocyte stimulating factor, which comprises a protein component consisting of at least about 70 amino acid residues according to Figure IB. Another object of the invention is a lymphocyte sti- mulating factor, which comprises a protein component consisting of at least about 100 amino acid residues according to Figure IB. Yet another object of the invention is a lymphocyte stimulating factor, which comprises a protein component consisting of at least about 120 amino acid residues according to Figure IB. Further, another object of the present invention is a lymphocyte stimulating factor as defined above, comprising a protein component having the ability to stimula- te, in a living animal body, CD8+ T-cells resulting in the release of interferon-γ (IFN-γ) to elicit immunosuppression or immunostimulation in said body, wherein SUBSTITUTE SHEET (Rill F 26) said protein component is selected from amino acid sequences within the sequence of amino acids numbered 1 to about 300 in Fig. IB. A further object of the present invention is a ly - phocyte stimulating factor as defined above for use as a vaccine against African sleeping sickness. Another object of the present invention is such a lymphocyte stimulating as is defined above for use in the preparation of an antiserum useful for combatting African sleeping sickness. Yet another object of the present invention is a nucleotide sequence coding for any of the lymphocyte stimulating factors according to the invention. Another object of the invention is such a nucleotide sequence, as is shown in Fig. IA. Another object of the invention is a monoclonal antibody directed against any one of the lymphocyte stimulating factors according to the invention. One further object of the present invention is a method of treating African sleeping sickness, comprising the administration to a mammal, including man, in need of such treatment of an effective amount of an antibody against any of the lymphocyte stimulating factors according to the invention, said antibody interacting with said factor released by the parasite causing said sickness. A further object of the invention is a method of vaccinating a mammal, including man, against African sleeping sickness, comprising the administration to the mammal of an immunologically active amount of any one of the described lymphocyte stimulating factors. EXPERIMENTAL MATERIAL AND METHODS Parasites The following trypanosome preparations were used in the present work: (a) T. b . brucei An Tat 1/1, which was used to generate the native TLTF. The parasites were obtained from Dr. Nestor Van Meirvenne, Laboratory of Sero- logy, Institute of Tropical Medicine, Prins Leopold, Antwerp, Belgium. The parasite were passaged once in rats and purified from infected blood (according to Lanham, S.M., Godfrey, D.G., "Isolation of salivarian trypanoso- mes from man and other animals using DEAE-cellulose", Exp. Parasitol. 1970; 28:521-534) and then disrupted by freezing and thawing before experimentation, (b) T. b . rhodesiense clone MVAT4 Rx (Alarcon, CM., Son, H.J., Hall, T., and Donelson, J.E., "A monocistronic transcript for a trypanosoma variant surface glycoprotein", Mol. Cell Biol. 1994;14:5579-5591), from which total RNA was isolated to construct the cDNA library. Animals Rats and mice were used in this study. Sprague- Dawley rats were purchased from Alab (Stockholm, Sweden) . DBA/2 MHC H-2d/d mice were locally bred at the Department of Immunology, Karolinska Institute, Stockholm. Mutant mice (CDδ ' )with disrupted lyt 2 gene lacking CD8 expression (Fung-Leung, -P, Schillham, M. ., Rahemtulla, A., Kundig, T.M., Vollenweider, M., J., van Ewijk, W., and Mak, T.W. "CD8 is needed for the development of cytotoxic T cells but not helper T cells", Cell 1991; 443-449), and mutant mouse strain lacking CD4 expression (Rahemtulla A., Fung-Leung W.P., Schillman M.W., Kundig T.M., Sambara S.R., Narendran A., Arabian, A., Wakeham., A., Paige., C.J., Zinkernagel, R.M., Miller, R.G., and Mak, T. ., "Normal development and function of CD8+ cells but markedly decreased helper cell activity in mice lacking CD4", Nature 1991; 353:180-184) originally from Depart- ent of Medical Biophysics and Immunology, University of Toronto, Canada, were bred and kept at the Department of Immunology, Karolinska Institute, Stockholm, Sweden) . Antibodies In in vi tro antibody TLTF modulation experiments (see below) the following Mabs were used: (a) IB-4; a Mab directed against TNP (anti-trinitrophenylphosphate) was used as an isotype matched control antibody (mouse IgG2b) . The hybridoma producing IB-4 was obtained from Dr. Birgitta Hey an (Uppsala, Sweden), and antibodies prepared from culture supernatants (b) 0X8; an anti-rat CD8 antibody (mouse IgGl) . The hybridoma producing 0X8 was originally obtained from Dr. Alan Williams (Oxford, UK) . In some experiments Fab fragments of 0X8 was used. The fragments were prepared by papain digestion followed by removal of Fc fragments and any undigested 0X8 on protein A (c) MOl, M02 and M03; mouse Mabs directed against TLTF. MOl was prepared as described previously (Bakhiet et al 1993, supra) , while M02 and M03 were produced recently. Two male DBA/2 mice were immunized in the foot pads with a gel fraction of T. b. brucei that showed a high ability to induce MNC to IFN-γ production (Olsson et al 1991, supra; Bakhiet et al 1993, supra) . The immunogen and Freund ' s complete adjuvant (Sigma, St. Louis) was mixed 1:1 and 50μl of this mixture was injected into each hind foot pad. Eleven days later regional lymph nodes were removed. Suspended lymphocytes from these nodes were hybridized with mouse Sp 2/0 cells as previously descri- bed (Holmdahl, R., Olsson, T. , Moran, T., Klareskog, L., " In vi vo treatment of rats with monoclonal anti-T-cell antibodies. Immunohistochemical and functional analysis in normal rats and experimental allergic neuritis", Scand. J. Immunol. 1985; 22:157-169). Subcloning was done once and hybridomas, whose supernatants inhibited or stimulated TLTF induced IFN-γ production by rat mononuclear cells cultures were selected. Ten hybridomas supernatants significantly inhibited TLTF induced IFN-γ production, while 7 hybridomas exhibited stimulatory effects. One of the inhibitory hybridomas (M02) and one of the stimulatory hybridomas (M03) were further propagated and characte- rized. Both of these hybridomas produced antibodies of the IgG 2b subclass, and were purified on Protein A Sep- harose according to standard techniques. The affinity purified TLTF (Bakhiet et al., 1993, supra) was also used to immunize rabbits to generate im- mune sera according to standard protocols. The anti-TLTF polyclonal antibody (NR4) from rabbit number 300 was used for immunoblotting and for screening of the trypanosome cDNA library. Preparation of ononuclear cell suspensions Mononuclear cells were prepared from rats and mice spleens, and from human peripheral blood. To prepare spleen MNC, animals were sacrificed, the spleens dissected and crushed through a stainless steel meshwork. The cells were washed once in tissue culture medium. The medium consisted of Isocove ' s modified Dulbecco's medium (Flow lab. Irvine, UK) supplemented with 5% foetal calf serum (GIBCO, Baisley, UK) , 1% minimal essential medium (Flow Lab), 2 ml*, glutamine (Flow Lab), 50μg/ml penicil- lm, and 60μl,/ml streptomycin. Erythrocytes in the cell pellets were haemolysed by adding 2 ml cold sterile water for 30 sec followed by addition of 1 ml 2.7% saline. The cells were then washed in medium twice and rediluted to obtain a cell concentration of 5 x lOVml. The cells were then washed twice in medium and rediluted to obtain appropriate cell concentrations (see below) . Human peripheral blood cells from healthy donors were obtained by density gradient centrifugation . In some experiments human CD8 and CD4 enriched populations were used. They were isolated by negative selection using Mab coated magnetic beads as described previously (Olsson et al 1993, supra) . Single cell assay for IFN-γ secretion. The method described by Czerkinsky et al 1988 as adapted to rat IFN-γ (Mustafa, M.I., Diener, P., Hδje ¬ berg, B., Van der Meide, P., and Olsson, T., "T cell im- munity and interferon-γ secretion during experimental al ¬ lergic encephalo yelitis in Lewis rats", J. Neuroimmunol . 1991; 31: 165-177) was used to detect IFN-γ production by single secretory cells. In principle, nitro-cellulose- bottomed, 96 well icrotitre plates (Millipore, Bedford, MA) were coated overnight with 15 μg/ml (100 μl aliquots) of the mouse monoclonal antirat IFN-γ antibody DB1, which crossreacts with mouse IFN-γ (Van Der Meide, P.H., Dub- beld, M., Vijverberg, K. , Kos, T., Schellekens, H, "The purification and characterization of rat gamma interferon by use of two monoclonal antibodies", J. Gen. Virol. 1986; 67: 1059-1071). DB1 was a generous gift from Dr. Peter Van der Meide, TNO Center, Netherlands. After repeated washings with PBS, 2% bovine serum albumin was applied for 2-4 h, the plates were washed in PBS and aliquots of 5X10 5 MNC (200 μl) were applied in triplicate. Ten μl aliquots of native TLTF, recombinant material (see below) or Con A as a control were added to different cultures. In some experiments other reagents were added (see below) . This was followed by incubation overnight at 37°C in humidified atmosphere of 7% C0 2 . Cells were then removed by flicking the plate, followed by repeated washings in PBS. Polyclonal rabbit anti-rat IFN-γ (Van der Meide et al 1986, supra) , diluted 1/1000, was applied for 4 h. After washing, biotinylated goat anti-rabbit IgG (Vector Lab, Burlingame, CA) was applied for 4 h followed by avi- dine-biotin-peroxidase complex (ABC Vectastain Elite Kit, Vector Lab) . Peroxidase staining with 3-amino-9 ethylcar- bazole and H 2 0 2 was performed (Kaplow, L.S: "Substitute of benzidine in myeloperoxidase stains", Am. J. Clin. Pat- hoi. 1974; 63:451). Spots corresponding to cells that had secreted IFN-γ were counted in a dissection microscope. Lymphocyte proliferation assay Aliquots of 5X10 5 MNC (200 μl) were added in triplicate to 96-round-bottomed well microtitre plates (Nunc, Copenhagen, Denmark) . The cells were incubated 72 h after addition of 10 μl aliquots of native TLTF, recombinant material (see below) or Con A as a control. Ten h before harvest 10 μl aliquots containing 1 μCi of. [ 3 H]- methylthymidine (specific activity 42 Ci/mmol) (Amersham, Little Chalfont, UK) in saline were added to each well. Cells were harvested onto glass fibre filters with a multiple channel semiautomated harvesting device (Titertek, Skatron AS, Lierbyen, Norway) and thymidine incorporation was measured as counts per minute (CPM) in a liquid beta- scintillation counter (Mark II, Searle, Analytic, Des Plaines, IL, USA) . Cell ELISA for TLTF-CD8 interaction Hundred μl aliquots of 10 5 cells in suspension were added and allowed to dry into wells of polystyrene micro- titre plates (Nunc, Copenhagen, Denmark) . The plates were washed with PBS, pH 7.4, and wells subjected to 0.5% bovine serum albumin (BSA, Sigma) for 24 h at room temperature. After washing with PBS, 100 μl aliquot of different dilution or no TLTF were added for 2 h. After washing with PBS, biotinylated M03 was added, followed by ABC al P. Enzyme substrate solution was added and absorvence measured at 405 n in a multiscan photometer (Labsystem, Helsinki, Finland). Antibody modulation experiments Tel μl aliquots of the IB-4, 0X8, MOl, M02 and M03 Mabs to obtain final concentration in medium of 5 μg/ml were added to microtitre plate wells immediately after plating the MNC. Ten μl aliquots of native TLTF, recombi- nant material or as control similar volumes of Con A (5 μg/ml as final concentration in medium; Pharmacia, Uppsala, Sweden) were added. After 24 h of culture the effects on IFN-γ secretion and after 72 h the effect on cell proliferation were determined. Procedure used for cloning the gene encoding TLTF The gene was cloned from a λZAPII (Strategene) cDNA library constructed with total RNA isolated from blood stream forms of Trypanosoma brucei rhodesiense clone MVAT4 Rx. Host strain cells (bacterial strain) for the Lambda ZAP II Vector (phage) used here was XLl-Blue MRF ' . Predigested λZap II/EcoR I/CIAP cloning kit (Stratagene) was used to construct and amplify the Lambda Zap II library according to the instruction manual. Preparation of plating bacteria for phage lambda: Using sterile technique, bacterial host from a single colony was inoculated into NCZYM medium, pH 7.5 (50 ml in 250 ml flask). Maltose in final concentration of 0.2% (0.5 ml of 20% stock ) was added to induce malt operon, which contains the gene lamb for the lambda receptor. The bacteria were allowed to grow overnight with shaking at 30°C. This lower temperature ensures that the cells will not overgrow. After incubation, the cell suspension was poured into centrifuge tubes and spinned in bench Sorvsall for 10 minutes at about 3500 rpm. The superna- tant was discarded and the pellet was re-suspended in 20 ml 10 mM MgS0 4 . Optical density was measured at 600 nm against a blank of 10 mM MgS0 4 and adjusted to 2 by adding more MgS0 4 or re-pelleting cells and re-suspending them in a smaller volume. The cells were stored in aliquots at 4°C until use. Plating phage: LB Broth medium supplemented with 1% agar that has been autcclaved was poured into plates placed on flat surface. The surface of the poured plate was flamed to remove any air bubbles. When agar had set, plates were put to dry in 37°C oven overnight in inverted position. Next day, 80 μl of plating bacteria was mixed by inver ¬ sion with 180 μl phage suspension from different dilu ¬ tions and incubated at 37°C for 15-20 minutes. Meanwhile, top agar was melted and dispensed in 8 ml volumes into sterile Falcon tubes, which are then placed in a water bath at 46°C to equilibrate. Following phage/bacterial incubation, molten top agar was removed from water bath and mixed gently with the diluted phage and host strain using vortex at minimum speed to prevent introducing bubbles. The mixer poured quickly into center of plate in smooth motion and plate was rocked to create an even layer. Plates were left to set for 15 minutes and then incubated overnight at 37°C in inverted position. After incubation, the number of plaques was counted and the plaque forming units (pfu) was determined per ml concentration of the library based on the dilution. Immunoscreening: After titration of the bacteriophage, 2,7xl0 4 pfu were incubated with XL-1 Blue cells to obtain plaques. The plaques were then lifted in doublicate on nitrocellulose filters (Schleicher & Schuell) impregnated with 0.01M IPTG. Filters were blocked in 5%- milk * at 4°C over ¬ night to decrease non-specific binding. Immunoscreening was done using as primary antibody the rabbit polyclonal sera, from rabbit number 300, (NR4) directed against the MOl affinity purified TLTF. The primary antibody was diluted 1:2000, pre-absorbed with E. coli lysate (Bio-Rad) and incubated with the filters for 2 hours at room tempe- rature. Horseradish peroxidase-linked anti-rabbit donkey IgG (Amersham) diluted 1:5000 was applied for 2 hours at room temperature. Positive plaques were detected using ECL che iluminescent system (Amersham) where 6 potential phages were picked. The phage titer for the six selected phage was amplified and a secondary immunoscreening was done as described above using 100 μl of 10 "3 dilution of each phage elute. After detection by ECL system, phage 1 and 2 were positive; phage 3 was negative and phage 4,5 and 6 were borderline. Three phages from each group were picked and eluted in SM buffer and phage titer from each pick was amplified. Rescue of phagemids and expression of the protein: The inserts in each phage were rescued into SOLR cells using the ExAssist™ helper phage (M13) obtained from Stratagene. One clone from each rescue was analyzed further by Western blot. Only one clone (#2.3) had reactive protein, therefore, decided to sequence as TLTF. The nucleotide sequence of #2.3 was determined by using the dedeoxy sequencing method (sequence 2.0 kit, USB). Synthetic oligo primers were used to obtain overlapping sequence. Re-cloning of the gene and different truncated forms was done the ThioFusion Expression system. Proteins were then purified and examined for TLTF biological activity. STATISTICS Mann-Whitney s test was used for statistical significance. RESULTS: cDNA sequence of the recombinant TLTF: The complete cDNA sequence of the recombinant TLTF, clone #2, is shown in Fig. IA. From 3 reading frames, the 2nd, which is shown, is the longest one and it is open until near the polyA at the 3 'end. Supposing that the first MET in this reading frame is a start MET, the deduced protein has 467 ammo acids. A geneBank search did not reveal any significant homologies. Using PCR-based approach, 3 truncated forms of the molecule were obtained and over-expressed. Truncated forms of the recombinant protein, disclosed in Figure 1A-H, are examined to define the minimum length of the TLTF with retained bioactivity. A 145 ammo acids long part of the molecule (#4, which is the shortest part; amino acid 1-145) is still biologically active (Fig 4B) . The translation of the TLTF clone #2 is shown in fig IB. The C terminus of this deduced protein is very hydrophobic, suggesting that the protein is either in a membrane or is secreted. In Western blot ana ¬ lysis of the recombinant E. col i extract, using NR4 (TLTF polyvalent antisera), the corresponding fusion protein has the same sized bands as the native TLTF and T. b . rhodesiense lysate (not shown) . IFN-γ production by rat splenocytes in response to rTLTF and MOl blocking effect In the present work we have evaluated IFN-γ production in form of number of cells secreting the cytokine, detected in an antibody capture immunospot assay (Fig. 2). Lymphoid rat MNC cultures were exposed to antibody affinity purified TLTF diluted 10 "3 , 1 μg/ml rTLTF and 1 μg/ml of an irrelevant oncoserca protein (0V7) that has been cloned and expressed in a similar way to rTLTF. Ot- her cultures were left non-stimulated. Native TLTF and rTLTF induced significant number of cells to produce IFN- γ compared t non-stimulated cells while OV7 did show a significant effect on IFN-γ produced by rat -MNC. The monoclonal mouse anti-TLTF (MOl) was incubated at a con- centration of 5 μg/ml with MNC in a set of experiments. This was followed by addition of the 3 proteins to sti u- late the cells. MOl significantly inhibited native TLTF and rTLTF induced IFN-γ production by MNC. Thus, in Figure 2, the number of IFN-γ secreting cells determined in the immunospot assay are shown. Normal rat splenocytes suspension was plated at a concentration of 10 6 MNC per well and cultured for 24 h. Triplicate cultures were exposed to optimal dilutions of native TLTF, rTLTF at a concentration of 1 μg-per ml or OV7 (oncosera protein that has been cloned and expressed in a similar way to rTLTF) at a concentration of 1 μg per ml. Control cultures received no stimulation. Similar data were obtained on three different occasions. Note the inhibitory effect by anti-TLTF mouse monoclonal antibody (MOl) at a concentration of 5 μg/ml on both native TLTF and rTLTF when incubated with MNC prior to stimulation. As shown previously (Bakhiet et al., 1993, supra) , MOl did not show any effect when incubated with Con A or with non-stimulated MNC. Bars denote S.D. Effect of anti-TLTF antibodies on rTLTF-induced IFN-γ production by human peripheral blood lymphocytes (PBL) The immunospot assay was also used here to evaluate the action of the recombinant TLTF on human PBL and to study the effects of anti-TLTF monoclonal antibodies in the rTLTF triggering activity. Thus, native TLTF at 10 ~3 dilution, lμg and 0.1 μg rTLTF per ml all induced PBL to produce IFN-γ. Both MOl and M02 are monoclonal antibodies that showed inhibitory effect on native TLTF-induced IFN- γ production. The 2 monoclonals herein significantly inhibited the triggering effect of rTLTF at a concentration of 0.1 μg/ml on PBL. Conversely, M03, a third monoclonal antibody against native TLTF with stimulatory effect, has also exhibited here an enhanced effect on rTLTF-induced IFN-γ production (Fig 3). Thus, figure 3 shows the monoclonal anti-TLTF anti- bodies effects on rTLTF triggering of human peripheral blood (PBL) . After 24 h of culture the number of IFN-γ secreting cells was measured by the immunospot assay. Immediately before addition of rTLTF, different cultures received mouse monoclonal antibodies (MOl, M02 or M03) to reach a final concentration in the medium of 5 μg/ml. Other cultures received no antibodies. Note that rTLTF induced IFN-γ production by human (PBL) was inhibited by MOl and M02, while M03 enhanced the effect of the rTLTF. Irrelevant antibodies (0X19, W3/13, W3/25, " Hy2-15) were previously shown to have no effects (Olsson et al, 1993, supra) . Each staple represent data from triplicate or quadruplicate cultures. Bars denote S.D. The experiment was repeated twice with similar results. Studies on cells of mice with CD8-, CD4-genotype and nor- ai DBA/2 MNC from mutant mice lacking CD8 or CD4 and normal DBA/2 used to study (a) IFN-γ production (b) T cell proliferation and (c) TLTF-CD8 binding. In vi tro stimulation of spleen MNC obtained from the 3 mouse strains showed no increased IFN-γ production using native or recombinant TLTF in CD8 " mice, while Con-A induced high production of IFN-γ studied in these mice (Fig 4A) . Similar effect was recorded when proliferation assay was used. Thus, native and recombinant TLTF did not trigger MNC from CD8 " mice, while Con A showed a high proliferative response in all groups. 0V7 was used as a control in this assay and did not exhibit any effect (Fig 4B) . The direct binding of TLTF to CD8 was studied by applying native or rTLTF to mouse CD8 T CD4 " or CD4 + CD8 " mononuclear cell suspensions using cell ELISA. TLTF was allowed to interact with thy- mocytes from mice with genomic deletions of CD4 or CD8. Thus, binding of TLTF (native and recombinant) was recorded in microtitre plate wells that had been coated with thymocytes containing CD8 + cells from the genomically CD4 detected mice, but not in wells that had been coated with thymocytes containing CD4 + cells from genomically CD8 deleted mice. A signal above background was obtained with dilution of TLTF down to 10 ~3 during exposure to the CD8 + containing wells (Fig 4). Thus, in Figure 4, the effects of TLTF and rTLTF on MNC from mice with genomic deletion of CD8" or CD4 + T cells are shown. IFN-γ production (number of IFN-γ secreting cells) was measured after 24 h of culture (A), while proliferation as assessed by 3 H-thymidine uptake was mea- sured after 72 h. MNC were either stimulated with the whole rTLTF or the shortest truncated form #4 (B) . Each staple represent data from triplicate or quadruplicate cultures. Bars denote S.D. The experiment was repeated several times with similar results. (C) Absorbance rea ¬ dings in a cell ELISA to study the TLTF-CD8 binding. Mou ¬ se thymocytes from genomically CD4 " mice (containing CD8 + cells) or CD8 " mice (containing CD4 + cells) were dried on ¬ to plastic of microtitre plate wells. TLTF, rTLTF or 0V7 were applied and binding detected by a biotinylated mouse monoclonal anti-TLTF (M03) . Values denote readings from 6-12 wells after subtraction of the background. Bars de- note S.D. Note selective binding of TLTF and rTLTF, but not 0V7, to wells containing CD8 + cells. rTLTF immune sera blocking studies on native TLTF-induced IFN-γ production Immune sera from 2 immunised mice with the rTLTF and their preimmune sera were used in blocking experiments to inhibit native TLTF-induced IFN-γ production. The preimmune sera from the 2 mice did not show any effect, while the 2 immune sera significantly inhibited the induction cf IFN-γ by TLTF (Fig 5). Thus, figure 5 depicts anti-rTLTF immune sera inhibitory effect on native TLTF-induced IFN-γ as measured by the immuneospot assay. Preimmune sera gave no effect. Each staple denote reading from 8 cultures. Bars denote S.D. DISCUSSION Native TLTF is a glycoprotein that was characterized for its main biological activities, which is determined by the ability to bind CD8 molecule and stimulate CD8 + cells to produce IFN-γ and to proliferate. Evidence for such a role was previously obtained by studying T. b . brucei infection in rats or mice. In the former, CD8 + T cells had been depleted in vivo by anti-CD8 antibodies (Bakhiet et al., 1990, supra) or in vi tro (Olsson et al., 1991, supra) . While in the later, CD8 was genomically deleted (Olsson et al., 1993, supra) . Herein, the functio- nal assays used to demonstrate that the cloned material has similar biological activities as the native TLTF are consequently (a) immunospot method for detection of IFN-γ secreting cells by MNC from rats, humans and mice with genomically deleted CD8 or CD4, (b) T cell proliferation technique and (c) CD8 binding assay. T. b . brucei triggers a high number of lymphoid MNC to IFN-γ secretion in vi tro, while lymphoid cell proliferation as measured by 3 H-thymidine uptake is relatively minor (Olsson et al., 1991, supra) . However, CD8 + CD4 " MNC showed a more potent proliferative response after triggering with TLTF than normal rat or mouse MNC (data not shown) . It is tempting to suggest that this simply is due to a higher proportion of CD8 + TLTF responder cells. All above methods showed that rTLTF selectively acts on CD8. CD8 is a heterodimer with 52% amino acid sequence homology between rat and human (Johnson, P., Gagnon, J., Barclay, A.N., and Williams, A.F. (1985), "Purification, chain separation and esquence of the MRC OX-8 antigen, a marker of rat cyto- toxic T lymphocytes", EMBO J., 4, 2539-2545). It was suggested that native TLTF may act on interspecies conserved parts of CD8 since it has triggered rat, mouse and human CD8 + T cells (Olsson et al., 1993, supra) .- As native TLTF, rTLTF exhibited same effects on CD8 * cells from all those species. This activity is nevertheless either blocked by the anti-TLTF monoclonal antibodies MOl and M02 or enhanced by M03. Also, immune sera against recombinant TLTF inhibited the native TLTF activity. Previously, we estmi- ated that roughly one out of 10-20 CD8 + T cells were triggered by native TLTF (Olsson et al., 1993, supra) . Furthermore, native TLTF is active at very low dilution where no measurable protein could be detected. However, rTLTF was active to a dilution of 0.1 μg per ml. This difference in the concentration of the protein required for biological activity may be related to the absence of carbohydrate molecules in the recombinant protein since it is expressed in E.coii. Carbohydrate was shown to be of importance for dynamic biological activity (Bakhiet et al., 1993, supra) . Moreover, the recombinant material is insoluble in water, which might also be related to the absence of the carbohydrate. Thereby, methods for purifi- cation by elution from gel may affect its activity. In order to overcome this problem expression in other systems, such as mammalian cells, should be tried. One key approach for protection from African trypanosomiasis is to target invariable molecules that are in- teracting with the host defens system. Recently, Ziegel- bauer K and Overath P., "Identification of invariant surface flycoproteins in the bloodstream stage of Trypanosoma brucei, J. Biol. Chem. 1992; 267:10791-10796) described a class of invariable surface molecules, two of them were isolated and the corresponding genes cloned (Ziegelbauer K, Multhaup G and Overath P., "Molecular characterization of the two invariant surface glycopro- teins specific for the bloodstream stage of Trypanosoma brucei., J. Biol. Chem. 1992; 267:10797-10803). They are inserted in the membrane between the VSG molecules and covered by them. Therefore, they are not accessible to antibodies. In passive immunotherapy, injection of the anti-TLTF monoclonal antibody (MOl) into T. b . brucei infected animals resulted in lower parasitemia and pro- longed survival. This was of strong indication for cloning the TLTF to be used in an active immunotherapy. This work gives evidence for a correct clone for the native TLTF. The recombinant TLTF will hence be used for vaccination attempts and also will be explored in a broader sense in Biomedicine such as in CD8 targeted immune interventions . CONCLUSION Trypanosome-derived lymphocyte triggering factor (TLTF) is a glycoprotein component secreted by Trypanosoma brucei (T.b.) and binds to CD8 molecule. TLTF-CD8 binding activates CD8' T cells to produce IFN-γ and to proli- ferate. IFN-γ in turn stimulates parasite growth. In this study, the gene coding for the TLTF has been isolated. The nucleotide sequence indicates no relationship to other genes. The deduced protein has 467 amino acids with a very hydrophobic T-terminus, suggesting that the protein is either in a membrane or is secreted. Shorter truncated forms of the recombinant protein (rTLTF) were obtained and examined for biological activities that are characteristic for native TLTF. Thus, rTLTF and its truncated forms were evaluated for their ability to trigger MNC from rats, humans and mice - with genomically deleted CD8 or CD4 - to produce IFN-γ and to proliferate. CD8 binding studies revealed that rTLTF selectively binds to the CD8 + cells and trigger these cells to IFN-γ production and proliferation. The data presented here strongly indicate that the cloned gene is coding for the native TLTF and thereby can be used in further immunobiological studies and in CD8 targeted immune interventions.

Claims: CLAIMS 1. A lymphocyte stimulating factor comprising a pro ¬ tein component having the ability to stimulate, in a liv- ing animal body, CD8+ T-cells resulting in the release of interferon-γ (IFN-γ) to elicit immunosuppression or immu ¬ nostimulation in said body, wherein said protein component is selected from amino acid sequences within the sequence of amino acids numbered 1 to about 150 in Fig. IB, which are in possession of said ability. 2. A lymphocyte stimulating factor according to claim 1, wherein said protein component consists of at least about 70 amino acid residues. 3. A lymphocyte stimulating factor according to claim 1 or 2, wherein said protein component consists of at least about 100 amino acid residues. 4. A lymphocyte stimulating factor according to claim 1, 2 or 3, wherein said protein component consists of at least about 120 amino acid residues. 5. A lymphocyte stimulating factor according to claim 1, wherein said protein component having the ability to stimulate, in a living animal body, CD8+ T-cells resulting in the release of interferon-γ (IFN-γ) to elicit immunosuppression or immunostimulation in said body, whe- rein said protein component is selected from amino acid sequences within the sequence of amino acids numbered 1 to about 300 in Fig. IB. 6. A lymphocyte stimulating factor according to any one of the preceding claims for use as a vaccine against African sleeping sickness. 7. A lymphocyte stimulating factor according to any one of claims 1 to 5 for use in the preparation of an an- tiserum useful for combatting African sleeping sickness. 8. Nucleotide sequence coding for the lymphocyte stimulating factor according to any one of the preceding claims . 9. Nucleotide sequence according to claim 8 as shown in Fig . IA . 10. A monoclonal antibody directed against the lym ¬ phocyte stimulating factor according to any one of claims 1 to 5. 11. A method of treating African sleeping sickness, comprising administering to a mammal including man in need of such treatment an effective amount of an antibody against the lymphocyte stimulating factor of any one of claims 1 to 5, said antibody interacting with said factor released by the parasite causing said sickness. 12. A method of vaccinating a mammal including man against African sleeping sickness, comprising administering to the mammal an immunologically active amount of the lymphocyte stimulating factor of any one of claims 1 to 5.

Inventors: BAKHIET ABDEL-MOIZ, DONELSON JOHN E, KRISTENSSON KRISTER, OLSSON TOMAS, VAIDYA TUSHAR, BAKHIET, ABDEL-MOIZ, DONELSON, JOHN, E., KRISTENSSON, KRISTER, OLSSON, TOMAS, VAIDYA, TUSHAR
Applicants: SBL VACCIN AB, UNIV IOWA RES FOUND, UNIVERSITY OF IOWA RESEARCH FOUNDATION INC.
Application year: 1997
Main classification: C07K14
IPC codes: A61K39, C07K14, C07K16