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Abstract

The human malaria parasite Plasmodium falciparum (Pf) is a unicellular organism that infects hepatocytes before reaching the symptom-causing blood stage. The development of a T cell vaccine that could target the liver stage and prevent disease onset remains a challenge. Circumsporozoite protein (CSP) is expressed in infected hepatocytes and elicits a protective antibody response, making it a promising vaccine target. While several CSP T cell epitopes have been described, information of T cell receptor (TCR) gene sequence features, HLA restriction and effects of vaccination on the TCR repertoire are largely unknown. Here, I assessed the human CD8 and CD4 T cell response to CSP after repeated vaccination with recombinant full-length protein compared to pre-vaccination time points at single-cell level. By TR gene repertoire sequencing and the generation of large numbers of transgenic T cell lines expressing representative TCRs, I tracked the clonal dynamics of the CD4 and CD8 T cells over time and assessed the target epitopes of CSP-reactive TCRs and their HLA-linkage. I demonstrate that the activated CD8 T cell pool shows limited clonal diversity at baseline. Prior to vaccination, individual clones comprised up to 10% of the sequenced repertoire and exhibit similarity to genes encoding for TCRs with known virus-reactivity. Upon CSP vaccination, activated cells with shared sequence features were recruited into the immune response. However, among these, I identified only a single CSP-reactive TCR with unique functional properties. In contrast, I identified a potent CSP-specific CD4 response against the same vaccine and find numerous TCRs targeting both novel and known CSP epitopes and defined their HLA linkage. My results demonstrate the differential immunogenicity of CSP among CD4 and CD8 T cells. Through in vitro stimulation combined with repertoire analysis, I address limitations in quantification of a functional and antigen-specific T cell response. The deep assessment of the TCR properties of CSP-reactive T cells is crucial for the evaluation of potent T cell responses by future vaccine approaches.