Malaria vaccine development based on merozoite surface proteins of Plasmodium falciparum.

Malaria is a global health problem and the need for a vaccine that could prevent millions of deaths annually cannot be further justified. A number of strategies have been adopted in the pursuit of making a successful malaria vaccine including the use of blood stage antigens which would primarily target the merozoite and prevent its replication through the asexual blood cycle of the parasite. In this regard, merozoite surface proteins have gained a lot of attention by the malaria vaccine fraternity for development as subunit vaccines. In spite of concentrated efforts spanning a long number of years, we are not close on producing a successful blood stage vaccine, especially one based on merozoite surface proteins (MSP). However, a recent systematic review with meta-analysis of 33 different studies has reported that antibodies against MSP proteins (MSP-1(19) and MSP-3) exhibit the strongest association with lower incidence of malaria and protection. Also the efficacy of an MSP based vaccine, Combination B, in significantly reducing parasite density among infected children in Papua New Guinea supports the development of MSP based malaria vaccines. In light of these developments, in this commentary, we address different aspects and concerns about MSP based vaccines-the need to develop MSP based blood stage malaria vaccines, our successes and failures from the current and past MSP vaccine trails, the lessons learnt from these studies, the future directions and challenges that still face us.