High-throughput sequence typing of T-cell epitope polymorphisms in Plasmodium falciparum circumsporozoite protein.

We report a method for typing polymorphisms at the T-cell epitopes within the Th2R and Th3R regions of the Plasmodium falciparum circumsporozoite protein (CSP). This method combines the use of PCR and sequence specific oligonucleotide probes (PCR-SSOP), and allows the identification of single nucleotide polymorphisms in these epitope regions. PCR-SSOP is a robust and a high-throughput sequence typing technique which has the same specificity and fidelity as direct sequencing. This method has been developed specifically for the assessment of the protective efficacy of RTS,S/SBAS2 vaccine against the 3D7 strain of P. falciparum (RTS,S/SBAS2 vaccine contains a part of the 3D7 CSP protein) in a phase IIb trial in Gambia which has been completed recently. PCR-SSOP could be used to determine the allelic frequencies of other parasite antigens and their geographical distribution.