Browsing by Author "Peters, B."
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Item Comparative analysis of the ex vivo IFNgamma responses to CD8+ T cell epitopes within allelic forms of PfAMA1 in subjects with natural exposure to malaria(PLOS ONE, 2021) Nlinwe, O.N.; Ofori, E.A.; Akyea-Mensah, K.; Kyei-Baafour, E.; Ganeshan, H.; Belmonte, M.; Peters, B.; Villasante, E.; Sedegah, M.; Asamoah Kusi, K.Antigen polymorphisms in essential malarial antigens are a key challenge to the design and development of broadly effective malaria vaccines. The effect of polymorphisms on antibody responses is fairly well studied while much fewer studies have assessed this for T cell responses. This study investigated the effect of allelic polymorphisms in the malarial antigen apical membrane antigen 1 (AMA1) on ex vivo T cell-specific IFN-γ responses in subjects with lifelong exposure to malaria. Human leukocyte antigen (HLA) class I-restricted peptides from the 3D7 clone AMA1 were bioinformatically predicted and those with variant amino acid positions used to select corresponding allelic sequences from the 7G8, FVO, FC27 and tm284 parasite strains. A total of 91 AMA1 9-10mer peptides from the five parasite strains were identified, synthesized, grouped into 42 allele sets and used to stimulate PBMCs from seven HLA class 1-typed subjects in IFN-γ ELISpot assays. PBMCs from four of the seven subjects (57%) made positive responses to 18 peptides within 12 allele sets. Fifty percent of the 18 positive peptides were from the 3D7 parasite variant. Amino acid substitutions that were associated with IFN-γ response abrogation were more frequently found at positions 1 and 6 of the tested peptides, but substitutions did not show a clear pattern of association with response abrogation. Thus, while we show some evidence of polymorphisms affecting T cell response induction, other factors including TCR recognition of HLA-peptide complexes may also be at play.Item Comparison of the impact of allelic polymorphisms in PfAMA1 on the induction of T Cell responses in high and low malaria endemic communities in Ghana(Malaria Journal, 2021) Ofori, E.A.; Tetteh, J.K.A.; Frimpong, A.; Geneshan, H.; Belmonte, M.; Peters, B.; Villasante, E.; Sedegah, M.; Ofori, M.F.; Kusi, K.A.Background: Malaria eradication requires a combined efort involving all available control tools, and these eforts would be complemented by an efective vaccine. The antigen targets of immune responses may show polymor phisms that can undermine their recognition by immune efectors and hence render vaccines based on antigens from a single parasite variant inefective against other variants. This study compared the infuence of allelic polymor phisms in Plasmodium falciparum apical membrane antigen 1 (PfAMA1) peptide sequences from three strains of P. fal ciparum (3D7, 7G8 and FVO) on their function as immunodominant targets of T cell responses in high and low malaria transmission communities in Ghana. Methods: Peripheral blood mononuclear cells (PBMCs) from 10 subjects from a high transmission area (Obom) and 10 subjects from a low transmission area (Legon) were tested against 15 predicted CD8+T cell minimal epitopes within the PfAMA1 antigen of multiple parasite strains using IFN-γ ELISpot assay. The peptides were also tested in simi lar assays against CD8+enriched PBMC fractions from the same subjects in an efort to characterize the responding T cell subsets. Results: In assays using unfractionated PBMCs, two subjects from the high transmission area, Obom, responded pos itively to four (26.7%) of the 15 tested peptides. None of the Legon subject PBMCs yielded positive peptide responses using unfractionated PBMCs. In assays with CD8+enriched PBMCs, three subjects from Obom made positive recall responses to six (40%) of the 15 tested peptides, while only one subject from Legon made a positive recall response to a single peptide. Overall, 5 of the 20 study subjects who had positive peptide-specifc IFN-γ recall responses were from the high transmission area, Obom. Furthermore, while subjects from Obom responded to peptides in PfAMA1 from multiple parasite strains, one subject from Legon responded to a peptide from 3D7 strain only. Conclusions: The current data demonstrate the possibility of a real efect of PfAMA1 polymorphisms on the induc tion of T cell responses in malaria exposed subjects, and this efect may be more pronounced in communities with higher parasite exposure.Item Comparison of the impact of allelic polymorphisms in PfAMA1 on the induction of T Cell responses in high and low malaria endemic communities in Ghana(Springer Nature, 2021) Ofori, E.A.; Tetteh, J.K.A.; Frimpong, A.; Ganeshan, H.; Belmonte, M.; Peters, B.; Villasante, E.; Sedegah, M.; Ofori, M.F.; . Kusi, K.A.Background: Malaria eradication requires a combined effort involving all available control tools, and these efforts would be complemented by an effective vaccine. The antigen targets of immune responses may show polymorphisms that can undermine their recognition by immune effectors and hence render vaccines based on antigens from a single parasite variant ineffective against other variants. This study compared the influence of allelic polymorphisms in Plasmodium falciparum apical membrane antigen 1 (PfAMA1) peptide sequences from three strains of P. falciparum (3D7, 7G8 and FVO) on their function as immunodominant targets of T cell responses in high and low malaria transmission communities in Ghana. Methods: Peripheral blood mononuclear cells (PBMCs) from 10 subjects from a high transmission area (Obom) and 10 subjects from a low transmission area (Legon) were tested against 15 predicted CD8 + T cell minimal epitopes within the PfAMA1 antigen of multiple parasite strains using IFN-γ ELISpot assay. The peptides were also tested in similar assays against CD8 + enriched PBMC fractions from the same subjects in an effort to characterize the responding T cell subsets. Results: In assays using unfractionated PBMCs, two subjects from the high transmission area, Obom, responded positively to four (26.7%) of the 15 tested peptides. None of the Legon subject PBMCs yielded positive peptide responses using unfractionated PBMCs. In assays with CD8 + enriched PBMCs, three subjects from Obom made positive recall responses to six (40%) of the 15 tested peptides, while only one subject from Legon made a positive recall response to a single peptide. Overall, 5 of the 20 study subjects who had positive peptide-specific IFN-γ recall responses were from the high transmission area, Obom. Furthermore, while subjects from Obom responded to peptides in PfAMA1 from multiple parasite strains, one subject from Legon responded to a peptide from 3D7 strain only. Conclusions: The current data demonstrate the possibility of a real effect of PfAMA1 polymorphisms on the induction of T cell responses in malaria exposed subjects, and this effect may be more pronounced in communities with higher parasite exposure.Item Identification of Plasmodium falciparum circumsporozoite protein-specific CD8+ T cell epitopes in a malaria exposed population(Plos One, 2020-02-10) Kusi, K.A.; Aggor, F.E.; Amoah, L.E.; Anum, D.; Nartey, Y.; Amoako-Sakyi, D.; Obiri-Yeboah, D.; Hollingdale, M.; Ganeshan, H.; Belmonte, M.; Peters, B.; Kim, Y.; Tetteh, J.; Kyei-Baafour, E.; Dodoo, D.; Villasante, E.; Sedegah, M.Background Sterile protection against malaria, most likely mediated by parasite-specific CD8+ T cells, has been achieved by attenuated sporozoite vaccination of animals as well as malarianaïve and malaria-exposed subjects. The circumsporozoite protein (CSP)-based vaccine, RTS,S, shows low efficacy partly due to limited CD8+ T cell induction, and inclusion of such epitopes could improve RTS,S. This study assessed 8-10mer CSP peptide epitopes, present in predicted or previously positive P. falciparum 3D7 CSP 15mer overlapping peptide pools, for their ability to induce CD8+ T cell IFN-γ responses in natural malaria-exposed subjects. Methods Cryopreserved PBMCs from nine HLA-typed subjects were stimulated with 23 8-10mer CSP peptides from the 3D7 parasite in IFN-γ ELISpot assays. The CD8+ T cell specificity of IFN-γ responses was confirmed in ELISpot assays using CD8+ T cell-enriched PBMC fractions after CD4+ cell depletion. Results Ten of 23 peptide epitopes elicited responses in whole PBMCs from five of the nine subjects. Four peptides tested positive in CD8+ T cell-enriched PBMCs from two previously positive responders and one new subject. All four immunodominant peptides are restricted by globally common HLA supertypes (A02, A03, B07) and mapped to regions of the CSP antigen with limited or no reported polymorphism. Association of these peptide-specific responses with anti-malarial protection remains to be confirmed. Conclusions The relatively conserved nature of the four identified epitopes and their binding to globally common HLA supertypes makes them good candidates for inclusion in potential multi-epitope malaria vaccinesItem Immunodominant T cell peptides from four candidate malarial antigens as biomarkers of protective immunity against malaria(Vaccine, 2023) Belmonte, M.; Ganeshan, H.; Huang, J.; Belmonte, A.; Inoue, S.; Velasco a, R.; Acheampong, N.; Ofori, E.A.; Akyea-Mensah, K.; Frimpong, A.; Ennuson, N.A.; Frempong, A.F.; Kyei-Baafour, E.; Amoah, L.E.; Edgel, K.; Peters, B.; Villasante, E.; Kusi, K.A.; Sedegah, N.A malaria vaccine with high efficacy and capable of inducing sterile immunity against malaria within genetically diverse populations is urgently needed to complement ongoing disease control and elimination efforts. Parasite-specific IFN-c and granzyme B-secreting CD8 + T cells have been identified as key mediators of protection and the rapid identification of malaria antigen targets that elicit these responses will fast-track the development of simpler, cost-effective interventions. This study extends our previous work which used peripheral blood mononuclear cells (PBMCs) from adults with life-long exposure to malaria parasites to identify immunodominant antigen-specific peptide pools composed of overlapping 15mer sequences spanning full length proteins of four malarial antigens. Our current study aimed to identify CD8 + T cell epitopes within these previously identified positive peptide pools. Cryopreserved PBMCs from 109 HLA-typed subjects were stimulated with predicted 9-11mer CD8 + T cell epitopes from P. falciparum circumsporozoite protein (CSP), apical membrane antigen 1 (AMA1), thrombospondin related anonymous protein (TRAP) and cell traversal for ookinetes and sporozoites (CelTOS) in FluoroSpot assays. A total of 135 epitopes out of 297 tested peptides from the four antigens were experimentally identified as positive for IFN-c and/or granzyme B production in 65 of the 109 subjects. Forty three of 135 epitopes (32 %) were promiscuous for HLA binding, with 31 of these promiscuous epitopes (72 %) being presented by HLA alleles that fall within at least two different HLA supertypes. Furthermore, about 52 % of identified epitopes were conserved when the respective sequences were aligned with those from 16 highly diverse P. falciparum parasite strains. In summary, we have identified a number of conserved epitopes, immune responses to which could be effective against multiple P. falciparum parasite strains in genetically diverse populations.