Transcription status of vaccine candidate genes of Plasmodium falciparum during the hepatic phase of its life cycle.

The CSP, EMP2/MESA, MSP2, MSP3, MSP5, RAP1, RAP2, RESA1, SERA1 and SSP2/TRAP genes of Plasmodium falciparum are vaccine candidates. The hepatic phase of the infection is of major interest due to the protection induced by immunization with radiation-attenuated sporozoites. We therefore performed RT-PCR experiments to determine whether these genes are transcribed during this phase. Whereas transcripts of the CSP gene were detectable only in sporozoites, transcripts of the MSP2, MSP5, RAP1, RAP2, SERA1 and SSP2/TRAP genes were present in both sporozoites and infected hepatocytes. Transcripts of the EMP2/MESA gene were detectable only in infected hepatocytes. Transcripts of the MSP3 and RESA1 genes were not detectable in sporozoites or in infected hepatocytes. Genes presently identified as being transcribed during the hepatic phase may be of interest with respect to the design of preventative vaccination strategies.