PRECURSOR FREQUENCY-ANALYSIS OF CYTOTOXIC T-LYMPHOCYTES TO PRE-ERYRTHROCYTIC ANTIGENS OF PLASMODIUM-FALCIPARUM IN WEST-AFRICA

Some individuals living in malaria-endemic areas have CTL to Plasmodiu m falciparum liver stage Ags. We have quantified these CTL responses u sing limiting dilution analysis studies on the peripheral blood cells of naturally exposed Gambian donors. CTL precursor frequencies were de termined to a wide range of epitopes derived from different liver stag e Ags (liver stage protein 1, circumsporozoite protein, thrombospondin -related anonymous protein, and sporozoite threonine/asparagine-rich p rotein) restricted through common HLA alleles present in this populati on (HLA-A2.1, -A2.2, -B7, -B8, -B35, and B53). Precursor frequencies w ere between 17 and 98/million PBMC and correlated with the levels of s pecific lysis in parallel bulk cultures. The quantitative nature of li miting dilution assay analysis revealed varying degrees of immunodomin ance in the CTL responses to different epitopes within single proteins (thrombospondin related anonymous protein: tr42, tr43, tr26, tr29, an d tr39; circumsporozoite protein: cp6, cp26, and cp29) and within indi vidual donors. The temporal stability of some of these CTL responses w as determined over a 4-yr period. This is the first quantitative study of CTL specific for any plasmodial species or nonviral pathogen in hu mans and provides a basis for a multiepitope approach to malaria vacci nation.