Browsing by Author "Taylor, D.W."
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Item Analysis of human T cell clones specific for conserved peptide sequences within malaria proteins: Paucity of clones responsive to intact parasites(Journal of Immunology, 1994) Quakyi, I.A.; Currier, J.; Fell, A.; Taylor, D.W.; Roberts, T.; Houghten, R.A.; Good, M.F.T cells are thought to be of central importance in malaria immunity. Peptides copying malaria protein sequences often stimulate human CD4+ T cells and it was thought that they represented T cell epitopes present in the parasite and may thus have particular relevance to malaria vaccine development. To verify whether synthetic peptides representing highly conserved regions of parasite Ags may contribute to a malaria vaccine, we searched the data bank for conserved regions of Plasmodium falciparum malaria proteins that were not homologous to known self (human) proteins. We synthesized 24 such peptides representing 11 of the cloned and sequenced malaria asexual stage Ags, which were predicted by algorithms to represent T cell epitopes, and 6 peptides not predicted to be T cell epitopes and used these to generate T cell clones from individuals with an extensive previous history of malaria exposure. The T cell clones responded vigorously to many peptides but only a single clone, specific for a peptide within merozoite surface protein-1, 20-39, VTHESYQELVKKLEALEDAV, and not previously defined to be a T cell epitope responded to malaria parasites by proliferation and secretion of IFN-γ. This epitope was not revealed by studying parasite- induced T cell lines and is thus subdominant. The clone was able to significantly inhibit parasite growth in vitro. The final step in the inhibition of parasite growth appears to be nonspecific because other activated clones (not specific for malaria sequences) can inhibit parasite growth. Our data suggest that few conserved peptides within malaria parasites can be processed from the intact parasite. However, such peptides that can be processed from malaria parasites may be expected to stimulate parasite- specific T cells that could inhibit parasite growth and as such may be lead candidates for a vaccine aimed at inducing cellular immunity to malaria.Item The antibody response of pregnant Cameroonian women to VAR2CSA ID1-ID2a, a small recombinant protein containing the CSA-binding site(PLoS ONE, 2014) Babakhanyan, A.; Leke, R.G.F.; Salanti, A.; Bobbili, N.; Gwanmesia, P.; Leke, R.J.I.; Quakyi, I.A.; Chen, J.J.; Taylor, D.W.In pregnant women, Plasmodium falciparum-infected erythrocytes expressing the VAR2CSA antigen bind to chondroitin sulfate A in the placenta causing placental malaria. The binding site of VAR2CSA is present in the ID1-ID2a region. This study sought to determine if pregnant Cameroonian women naturally acquire antibodies to ID1-ID2a and if antibodies to ID1-ID2a correlate with absence of placental malaria at delivery. Antibody levels to full-length VAR2CSA and ID1-ID2a were measured in plasma samples from 745 pregnant Cameroonian women, 144 Cameroonian men, and 66 US subjects. IgM levels and IgG avidity to ID1-ID2a were also determined. As expected, antibodies to ID1-ID2a were absent in US controls. Although pregnant Cameroonian women developed increasing levels of antibodies to full-length VAR2CSA during pregnancy, no increase in either IgM or IgG to ID1-ID2a was observed. Surprisingly, no differences in antibody levels to ID1-ID2a were detected between Cameroonian men and pregnant women. For example, in rural settings only 8-9% of males had antibodies to full-length VAR2CSA, but 90-96% had antibodies to ID1-ID2a. In addition, no significant difference in the avidity of IgG to ID1-ID2a was found between pregnant women and Cameroonian men, and no correlation between antibody levels at delivery and absence of placental malaria was found. Thus, the response to ID1-ID2a was not pregnancy specific, but predominantly against cross-reactivity epitopes, which may have been induced by other PfEMP1 antigens, malarial antigens, or microbes. Currently, ID1-ID2a is a leading vaccine candidate, since it binds to the CSA with the same affinity as the full-length molecule and elicits binding-inhibitory antibodies in animals. Further studies are needed to determine if the presence of naturally acquired cross-reactive antibodies in women living in malaria endemic countries will alter the response to ID1-ID2a following vaccination with ID1-ID2a. © 2014 Babakhanyan et al.Item The antibody response of pregnant Cameroonian women to VAR2CSA ID1-ID2a, a small recombinant protein containing the CSA-binding site(Public Library of Science, 2014) Babakhanyan, A.; Leke, R.G.F.; Salanti, A.; Bobbili, N.; Gwanmesia, P.; Leke, R.J.I.; Quakyi, I.A.; Chen, J.J.; Taylor, D.W.In pregnant women, Plasmodium falciparum-infected erythrocytes expressing the VAR2CSA antigen bind to chondroitin sulfate A in the placenta causing placental malaria. The binding site of VAR2CSA is present in the ID1-ID2a region. This study sought to determine if pregnant Cameroonian women naturally acquire antibodies to ID1-ID2a and if antibodies to ID1-ID2a correlate with absence of placental malaria at delivery. Antibody levels to full-length VAR2CSA and ID1-ID2a were measured in plasma samples from 745 pregnant Cameroonian women, 144 Cameroonian men, and 66 US subjects. IgM levels and IgG avidity to ID1-ID2a were also determined. As expected, antibodies to ID1-ID2a were absent in US controls. Although pregnant Cameroonian women developed increasing levels of antibodies to full-length VAR2CSA during pregnancy, no increase in either IgM or IgG to ID1-ID2a was observed. Surprisingly, no differences in antibody levels to ID1-ID2a were detected between Cameroonian men and pregnant women. For example, in rural settings only 8-9% of males had antibodies to full-length VAR2CSA, but 90-96% had antibodies to ID1-ID2a. In addition, no significant difference in the avidity of IgG to ID1-ID2a was found between pregnant women and Cameroonian men, and no correlation between antibody levels at delivery and absence of placental malaria was found. Thus, the response to ID1-ID2a was not pregnancy specific, but predominantly against cross-reactivity epitopes, which may have been induced by other PfEMP1 antigens, malarial antigens, or microbes. Currently, ID1-ID2a is a leading vaccine candidate, since it binds to the CSA with the same affinity as the full-length molecule and elicits binding-inhibitory antibodies in animals. Further studies are needed to determine if the presence of naturally acquired cross-reactive antibodies in women living in malaria endemic countries will alter the response to ID1-ID2a following vaccination with ID1-ID2a.Item Characterization of conserved T- and B-cell epitopes in plasmodium falciparum major merozoite surface protein 1(Infection and Immunity, 2000) Parra, M.; Hui, G.; Johnson, A.H.; Berzofsky, J.A.; Roberts, T.; Quakyi, I.A.; Taylor, D.W.Vaccines for P. falciparum will need to contain both T, and B-cell epitopes. Conserved epitopes are the most desirable, but they are often poorly immunogenic. The major merozoite surface protein 1 (MSP-1) is currently a leading vaccine candidate antigen. In this study, six peptides from conserved or partly conserved regions of MSP-1 were evaluated for immunogenicity in B10 congenic mice. Following immunization with the peptides, murine T cells were tested for the ability to proliferate in vitro and antibody responses to MSP-1 were evaluated in vivo. The results showed that one highly conserved sequence (MSP-11, VTHESYQELVKKLEALEDAV; located at amino acid positions 20 to 39) and one partly conserved sequence (MSP-123, GLFHKEKMIL NEEEITTKGA; located at positions 44 to 63) contained both T- and B-cell epitopes. Immunization of mice with these peptides resulted in T-cell proliferation and enhanced production of antibody to MSP-1 upon exposure to merozoites. MSP-11 stimulated T-cell responses in three of the six strains of mice evaluated, whereas MSP-123 was immunogenic in only one strain. Immunization with the other four peptides resulted in T-cell responses to the peptides, but none of the resulting peptide-specific T cells recognized native MSP-1. These results demonstrate that two sequences located in the N terminus of MSP-1 can induce T- and B-cell responses following immunization in a murine model. Clearly, these sequences merit further consideration for inclusion in a vaccine for malaria.Item Detection of antigens and antibodies in the urine of humans with plasmodium falciparum malaria.(Journal of Clinical Microbiology, 1991) Rodriguez-del Valle, M.; Quakyi, I.A.; Amuesi, J.; Quaye, J.T.; Nkrumah, F.K.; Taylor, D.W.Humans infected with Plasmodium falciparum frequently have elevated levels of proteins in their urine, but it is unclear if any of these proteins are parasite antigens or antimalarial antibodies. To resolve this question, urine samples from malaria patients and controls living in Thailand and Ghana were evaluated. Urine samples from 85% of the patients had elevated protein levels and contained proteins with M(r)s ranging from <29,000 to >224,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Antisera were produced against urine from infected and control subjects. Antisera raised against infected, but not control, urine were positive by indirect immunofluorescence on P. falciparum parasites and immunoprecipitated approximately 12 unique bands from extracts of parasites metabolically labeled with 35S-methionine. These data suggest that a variety of P. falciparum antigens are released into urine during acute infection. It is also likely that anti-P. falciparum antibodies are present in the urine of malaria patients because samples from these patients, but not controls, were positive in indirect immunofluorescence assays and immunoprecipitated at least 19 P. falciparum antigens from extracts of metabolically labeled parasites. The detection of malarial antigens and antibodies in urine may lead to a new approach for the diagnosis of malaria.Item Development of a malaria T-cell vaccine for blood stage immunity.(Scandinavian Journal of Immunology, 1992) Quakyi, I.A.; Taylor, D.W.; Johnson, A.H.; Allotey, J.B.; Berzofsky, J.A.; Miller, L.H.; Good, M.F.We have defined a strategy for the development of a T-cell vaccine for blood stage immunity, taking into consideration the central role of T cells and MHC restriction in malaria immune responses. We have used the AMPHI computer algorithm lo identify putative T-cell epitopes from conserved regions of 11 Plasmodium falciparum asexual stage proteins. Ten of the eleven proteins arc currently candidates for vaccine development. Using this algorithm we selected 22 putative T-cell epitope peptides und 8 control peptides. These peptides were used to test the T-cell responses of three defined populations of Caucasians who have (1) recovered from P. falciparum malaria. (2) been exposed, but never clinically infected, (3) never been exposed or infected. Preliminary analysis of our data shows population differences in T-tell responses to putative T-cell epitope peptides. Ultimately, these studies will help to identify those T epitopes that can be incorporated into a T-cell vaccine for protective immunity.Item The epidemiology of plasmodium falciparum malaria in two cameroonian villages: Simbok and etoa.(American Journal of Tropical Medicine and Hygiene, 2000) Quakyi, I.A.; Leke, R.G.F.; Befidi-Mengue, R.; Tsafack, M.; Bomba-Nkolo, M.; Manga, L.; Taylor, D.W.In support of ongoing immunologic studies on immunity to Plasmodium falciparum, demographic, entomologic, parasitologic, and clinical studies were conducted in two Cameroonian villages located 3 km apart. Simbok (population = 907) has pools of water present year round that provide breeding sites for Anopheles gambiae, whereas Etoa (population = 485) has swampy areas that dry up annually in which A. funestus breed. Results showed that individuals in Simbok receive an estimated 1.9 and 1.2 infectious bites per night in the wet and dry season, respectively, whereas individuals in Etoa receive 2.4 and 0.4 infectious bites per night, respectively. Although transmission patterns differ, the rate of acquisition of immunity to malaria appears to be similar in both villages. A prevalence of 50-75% was found in children < 10 years old, variable levels in children 11-15 years old, and 31% in adults. Thus, as reported in other parts of Africa, individuals exposed to continuous transmission of P. falciparum slowly acquired significant, but not complete, immunity.