A histidin alanine rich recombinant antigen protects Aotus monkeys from P. falciparum infection

We have isolated a cDNA clone coding for 165 amino acids of a histidine alanine rich protein. An extended repeat region of this clone codes for the tripeptide Ala-His-His, which is extremely conserved, and for the tripeptide Ala-Ala-Asp, which shows only slight variability among the repeat units. This antigen exhibits high homology to the HRPII antigen described by Wellems and Howard (1986). The coding region was expressed in E. coli as a MS2-polymerase fusion protein, which was purified and used for immunization of Aotus monkeys. The animals immunized with this fusion protein showed only low parasitemias (less than 2%) after infection with P. falciparum, while animals from the control group or animals immunized with a MS2-fusion protein carrying other malaria specific sequences were not protected. The result suggests that this antigen is a good candidate for a malaria vaccine.