the starting point of the process are synthetic antigens in accordance with the foregoing definition in the preamble , which contain in their known chemical structure at least one defined epitope of a pathogenic microorganism which can be recognized by the immune system . hereby the epitope can be a b - cell epitope , a t h - cell epitope , a t c - epitope or an arbitrary mixture of these epitopes . the so - called multiple antigen peptides ( map ), alone or in combination with a t c - epitope , preferably constitute the starting point of the process . the origin of the epitopes includes bacteria , viruses , protozoa and tumor cells . in accordance with the invention , the synthetic antigen is embedded into biodegradable microparticles . it is essential for the invention that biopolymers with specific physico - chemical properties are selected for producing the biodegradable microparticles . important properties are wettability , insolubility , swelling and biodegradability of the biopolymers and the spherical microparticles produced therefrom in aqueous media an physiological liquids . the extent of swelling of the biodegradation and their biodegrading time greatly determine the release kinetics of the antigens from the microcapsules . it has now been surprisingly found that these release kinetics also affect the time course of the immune response . examples of such biopolymers of varying wettability , swelling and biodegradation time are poly ( lactic acid ), poly ( lactic - co - glycolic acid ), poly ( hydroxybutyric acid ), poly ( hydroxybutyoric - co - valeric acid ), poly ( caprolactone ). embedding of the synthetic antigen into the biopolymer is performed by means of various known methods such as spray - drying , solvent evaporation or coacervation . antigen - loaded , spherical microparticles of a size of 1 to 200 μm result from this . in the second step , the antigen - loaded microparticles in accordance with the invention are placed into a dispersion medium which is suitable for the parenteral administration of the microparticles . in this connection it is essential for the invention that the dispersion medium be biocompatible and biodegradable and in addition have advantageous properties for potentiating the immune response . such advantageous dispersion media are , for example , aqueous or oily solutions of lecithin or aqueous - oily emulsions with lecithin at a concentration range of 0 . 1 to 20 %, preferably 2 to 10 %. further suitable dispersion media are so - called microemulsions comprising a water , oil , tenside and co - tenside component . biocompatible and biodegradable substances , such as natural or synthetic mono -, di - and triglycerides , lecithin , poloxamers and polysorbates are used for this . the dispersion media mentioned are charaterized by surprisingly good wetting and suspension properties for the biodegradable microparticles . these wetting and suspension properties are for example considerably better than those of the usually employed dispersion media , such as carboxymethyl cellulose or solutions . the dispersion of the microparticles in the dispersion medium can be performed simply by shaking , by means of in which an injectable preparation is created . the antigen - loaded microparticles suspended in the suspension medium are administered parenterally , whereby this administration can take place once or several times at defined intervals . the latter form of administration is known under the term “ booster ”. the first and second booster dose can be administered 1 to 4 weeks and 3 to 6 months after the initial injection , for example . a potentiated immune response lasting for several months is triggered following the single or multiple administration of the formulations in accordance with the invention . the potentiation of the immune response is generally measured in balb / c mice after a single , in exceptional cases also after a triple parenteral administration of the microparticles loaded with synthetic antigens in accordance with the invention . a map , produced from a universal t h - epitope of the tetanus toxin ( sequence 947 to 967 ) and a b - cell epitope of the repetitive region of the circumsporozoite protein of plasmodium berghei , as well as a t c - epitope of the circumsporozoite protein of plasmodium berghei ( sequence 252 to 260 ) are used as synthetic model antigens ( s . demotz et al ., j . of immunology 142 , 394 - 402 ( 1989 ); p . romero et al ., nature 341 , 323 ( 1989 ); j . l . weber et al . ; exp . parasitology 63 , 295 ( 1987 )). the intensity and length of the immune potentiation is measured by means of the specific antibody titers , the t - lymphocyte proliferation and the specific cytotoxic t - lymphocyte activity . these three parameters are determined in accordance with known immunological methods . [ 0025 ] fig1 illustrates schematically the relevant parameters of the immune potentiation achieved by means of the process in accordance with the invention . according to the present invention patent an immune potentiation means that the intensity during the time course of the immunological response as a result of an administered synthetic antigen has been potentiated with respect to an aqueous antigen solution and has been potentiated in a comparable or increased amount in respect to an ifa formulation on the levels of the antibody titer , the t - cell proliferation and the t c - stimulation . the possibility arises from this by means of mixing biopolymers of different wettability , swelling and biodegradation time to potentiate the humoral antibody response as well as the cellular t - lymphocyte response to an extent which is comparable or even greater than the potentiation achieved by means of incomplete freund &# 39 ; s adjuvant . in addition , the immune responses in accordance with this process can be time - controlled and are prolonged over several weeks in contrast to ifa and aqueous solutions . because of the custom - made properties of the biodegradable microparticles used , the process here described makes possible a specific potentiation of the humoral and cellular immune responses to synthetic antigens , in particular to the so - called maps , which can be controlled in its progression over course time . moreover , the process has the extraordinary advantage that it is possible to stimulate cytotoxic t - lymphocytes in addition to the specific and potentiated stimulation of b - and t h - lymphocytes , because of which it is also possible to successfully provide immunization against viruses , protozoa and tumor cells in particular . it was surprisingly possible to demonstrate this cytotoxic stimulation of t - lymphocytes here for the first time . in contrast to the immune potentiation described in ps ep - a2 - 333 , 523 and pct wo 92 / 19263 , the present one is primarily systemic , i . e . not mucosal , and can be controlled in intensity as well as duration or progression over time . furthermore , a narrow , exactly defined particle size distribution is not required for the immune potentiation , which entails technological advantages . the process here described is used for the immunization of humans and animals against diseases caused by bacteria , viruses , protozoa and tumor cells . in particular the immunization against viruses , protozoa and tumor cells , which can be achieved only in an unsatisfactory way with conventional vaccines , i . e . insufficiently and by accepting undesired side effects , represents a main application of this method . the stimulation of the cytotoxic t - cells by means of the process in accordance with the invention as well as the immune response lasting over an extended period of time constitute the basis for this application . example 1 describes the potentiation of the antibody response to the branched multiple antigen peptide identified as p30b2 , which is constructed from a universal t h - cell epitope of the tetanus toxin ( sequence 947 to 967 ) and a b - cell epitope of plasmodium berghei : 0 . 02 g p30b2 were dissolved in 2 . 00 g water and this solution was subsequently dispersed with the aid of an ultrasonic generator in a solution of 2 . 0 g poly ( d , 1 - lactic acid co - glycolic acid ) 50 : 50 ( resomer 502 , boehringer ingelheim ) in 40 . 0 g dichloromethane . spherical microparticles ( rg502 ) were produced from this dispersion by means of spray drying . microparticles loaded with antigen were subsequently suspended in a 5 % sterile solution of egg lecithin ( ovothin 170 , lukas meyer , d - hamburg ) by shaking . this suspension was subcutaneously injected into a group of 8 balb / c mice in respective amounts of 0 . 5 ml . the amount of antigen injected into each mouse was 30 μg . a second group of 8 balb / c mice was immunized with the same amount of antigen in incomplete freund &# 39 ; s adjuvant ( ifa ) as a control . the antibody titers were determined by means of elisa . [ 0030 ] fig2 shows the time course of the immune potentiation by rg502 in comparison to ifa , associated with example 1 . the antibody titers obtained from rg502 and ifa are comparable to each other during the first 15 weeks following immunization . after that the titers induced by ifa drop off , while the titers induced by the microcapsules regain constant over at least 28 weeks . antibody titers of 1 to 2 · 10 3 were obtained already two weeks after administration of a hydrophilic , strongly swelling , fast - releasing and fast degradable biopolymer such as plga 50 : 50 , and remain constant over a period of at least 28 . weeks . in contrast thereto , the titers measured following a single administration of an ifa preparation drop off already after 15 weeks and after 28 weeks are only level at 2 · 10 2 after 28 weeks . example 2 describes the potentiation of the antibody response to the branched multiple antigen peptide of the designation p30b2 ( in accordance with example 1 ), constructed from a universal t h - cell epitope of the tetanus toxin ( sequence 947 to 967 ) and a b - cell epitope of the repetitive region of the circumsporozoite protein of plasmodium berghei : 0 . 02 g p30b2 were dissolved in 2 . 00 g water and this solution was subsequently dispersed with the aid of an ultrasonic generator in a solution of 2 . 0 g poly ( d , 1 - lactic acid ) ( resomer 206 , boehringer ingelheim ) in 40 . 0 g dichloromethane . spherical microparticles ( r206 ) were produced from this dispersion by means of coacervation , induced by the addition of silicon oil . microparticles loaded with antigen were subsequently suspended in a 5 % sterile solution of egg lecithin ( ovothin 170 , lukas meyer , d - hamburg ) by shaking . this suspension was subcutaneously injected into a group of 8 balb / c mice in respective amounts of 0 . 5 ml . the amount of antigen injected into each mouse was 30 μg . a second group of 8 balb / c mice was immunized with the same amount of antigen in incomplete freund &# 39 ; s adjuvant ( ifa ) as a reference . the antibody titers were determined by means of elisa . [ 0032 ] fig3 shows the time course of the immune potentiation by r206 in comparison to ifa , associated with example 2 . the antibody titers obtained from the hydrophobic , weakly swelling , slow - release and slowly biodegradable r206 continuously rise during the first 12 weeks and then reach the level which had been achieved with ifa already 2 weeks after immunization . while the ifa titers drop again steadily after approximately 15 weeks , the r206 titers remain constant over a period of at least 28 weeks . example 3 describes the potentiation of the antibody response to the branched multiple antigen peptide of the designation p30b2 ( in accordance with example 1 ), constructed from a universal t h - cell epitope of the tetanus toxin ( sequence 947 to 967 ) and a b - cell epitope of the repetitive region of the circumsporozoite protein of plasmodium berghei : analogously to example 1 , p30b2 was incorporated into poly ( d , 1 - lactic acid - co glycolic acid ) 75 : 25 ( resomer rg752 , boehringer ingelheim ) and processed into spherical microparticles ( rg752 ). microparticles of rg752 , rg502 ( from example 1 ) and r206 ( from example 2 ) containing identical amounts of p30b2 were suspended in a 5 % sterile solution of egg lecithin ( ovothin 170 , lukas meyer , d - hamburg ) by shaking . this suspension was subcutaneously injected into a group of 8 balb / c mice in respective amounts of 0 . 5 ml . the amount of antigen injected into each mouse was 30 μg . a second group of 8 balb / c mice was immunized with the same amount of antigen in incomplete freund &# 39 ; s adjuvant ( ifa ) as a control . the antibody titers were determined by means of elisa . [ 0034 ] fig4 shows the time course of the immune potentiation obtained with a mixture of rg506 , rg752 and r206 in comparison to ifa , associated with example 3 . the antibody titers obtained from this microcapsule mixture of fast ,- amid slow - release biopolymers rises quickly and reaches after two weeks a level higher by a factor of 2 . 5 than the antibody titers achieved with ifa . while the ifa titers drop again steadily after approximately 15 weeks , the titers achieved with the microcapsule mixture remain relatively constant over a period of at least 28 weeks . example 4 describes the potentiation of the antibody response to the branched multiple antigen peptide of the designation p30b2 ( in accordance with example 1 ), constructed from a universal t h - cell epitope of the tetanus toxin ( sequence 947 to 967 ) and a b - cell epitope of the repetitive region of the circumsporozoite protein of plasmodium berghei : analogously to example 1 , p30b2 was incorporated into poly ( d , 1 - lactic acid - co glycolic acid ) 50 : 50 ( resomer rg502 , boehringer ingelheim ) and processed into spherical microparticles ( rg502 ). the microparticles loaded with antigen were suspended in a 5 % sterile solution of egg lecithin ( ovothin 170 , lukas meyer , d - hamburg ) by shaking . this suspension was subcutaneously injected into a group of 8 balb / c mice in respective amounts of 0 . 5 ml . the amount of antigen injected into each mouse was 3 × 10 μg . the injection was repeated after 16 days ( first booster ) and 113 days ( second booster ). a second group of 8 balb / c mice was immunized with he same amount of antigen in incomplete freund &# 39 ; s adjuvant ( ifa ), used as reference , and according to the same vaccination schedule . the antibody titers were determined by means of elisa . [ 0036 ] fig5 shows the time course of the immune potentiation after booster injections with rg502 in comparison to ifa , associated with example 4 . the antibody titers obtained from rg502 and ifa rise comparatively . accordingly , the process in accordance with the invention is also suitable for the immune potentiation achieved by boosters . example 5 describes the potentiation of the t h - lymphocyte proliferations to the multiple antigen peptide of the designation p30b2 in accordance with examples 1 to 4 . p30b2 was incorporated into rg502 , rg752 and r206 analogously to the examples 1 , 2 and 3 and processed into spherical microparticles of different degrees of swelling . identical amounts of microparticles containing p30b2 were suspended in a 5 % sterile solution of egg lecithin ( ovothin 170 , lukas meyer , d - hamburg ) by shaking . this suspension was subcutaneously injected into a group of 8 balb / c mice in respective amounts of 0 . 5 ml . the amount of antigen injected into each mouse was 30 μg . a second group of 8 balb / c mice was immunized with the same amount of antigen in incomplete freund &# 39 ; s adjuvant ( ifa ) as a reference . the t - cell proliferation in the lymph nodes was determined in a known manner . [ 0038 ] fig6 shows the t - lymphocyte proliferation described in example 5 14 days after the administration of various microcapsule formulations as well as of an ifa preparation . it can be seen from this that all microcapsule formulations , i . e . rg502 with fast antigen release , rg752 with an antigen release of medium rate and r206 with a low antigen release rate , as well as the mixture of all three microcapsule types , all potentiate the t - lymphocyte proliferation in an at least comparable , sometimes even greater extent than an ifa preparation . example 6 describes the triggering of a cytotoxic t - lymphocyte reaction to a t c cell epitope of the circumsporozoite protein of plasmodium berghei ( ctl 359a , sequence 252 to 260 ): 0 . 008 g of ctl 359a were dissolved in 1 . 0 g of water and this solution was subsequently dispersed by means of an ultrasonic generator in a solution of 4 . 0 g poly ( d , 1 - lactic acid - co glycolic acid ) ( resomer 502 , boehringer ingelheim ) in 60 . 0 g dichloromethane . spherical microparticles were produced by means of spray drying . the microparticles loaded with ctl 359a were mixed with microparticles loaded with p30b2 in accordance with example 1 in a ratio of ctl 359a 4p30b2 of 1 : 10 to increase the immune response to ctl359a . the mixture of the microcapsules was subsequently suspended in a 5 % sterile solution of egg lecithin ( ovothin 170 , lukas meyer , d - hamburg ) by shaking . this suspension was subcutaneously injected into a group of 2 balb / c mice in respective amounts of 0 . 5 ml . the amount of antigen injected into each mouse was 4 μg of ctl 359a and 40 μg of p30b2 . the t c - cell response was determined after 10 and 20 days by means of a cell lysis test . [ 0040 ] fig7 shows the t c - lymphocyte response associated with example 6 , which was determined 10 and 20 days after immunization , or administration of the formulations . the percentile cell lysis activity is represented as a function of the effect / target cell ratio e / t . in a surprising manner , the simultaneous administration of microencapsulated t c epitope and t h epitope ( p30b2 + ctl359a in rg502 ) induces a significant t c - lymphocyte stimulation which can be observed 20 days after administration . the time course of the t c response which , in contrast to the t h and antibody responses , requires a considerably longer time , appears to be of particular interest . it is essential for the invention that biodegradable spherical microparticles are proposed which potentiate the immune response to synthetic antigens . by determining the physico - chemical properties of the biopolymers used it is possible to control the extent and time course of this immune potentiation . the process furthermore makes it possible to stimulate also the cytotoxic t - lymphocytes in addition to the antibody and t h - lymphocyte potentiation . the extent of immune potentiation is at least comparable to the potentiation achieved by means of ifa preparations and its time course is clearly prolonged . a process is therefore available which can be employed in the immunization of humans and animals against diseases caused by viruses , bacteria , protozoa or tumor cells .
an immunological response potentiation process is disclosed for synthetic or genetically engineered antigens having low immunogenicity . the antigen is embedded into biodegradable microparticles , these antigen - loaded microparticles are dispersed in a biodegradable medium which triggers when it is parenterally administered a potentiated antibody , t h - lymphocyte and t c - lymphocyte response , as compared to an aqueous antigen solution . the extent of immunological potentiation is at least comparable with that attained by ifa compositions . linear b - t h - cell epitopes , linear t c - cell epitopes , dimers and multimers of said epitopes , as well as their mixtures , are used as low immunogenicity antigens . the microparticles are based on biodegradable biopolymers such as polyester , polyanhydride , polyorthoester . by mixing microparticles with different wettabilities , swellabilities , release and biodegradation times , the most intense and longest immunological potentiation is achieved . this process is useful for immunising human beings and animals against diseases caused by viruses , bacteria , protozoa or tumour cells .