From the circumsporozoite protein to the RTS, S/AS candidate vaccine

The RTS,S/AS01(E) malaria vaccine candidate has recently entered Phase 3 testing. Reaching this important milestone is the culmination of more than 20 years of research and development by GlaxoSmithKline and partners and collaborators. The vaccine has been developed to protect young children and infants living in Sub-Saharan Africa against clinical and severe disease caused by Plasmodium falciparum infection. Over the past 9 years, RTS,S/AS has been evaluated in multiple Phase 2 studies. The vaccine was shown to have a favorable safety profile and to be well tolerated in all age groups in which it was tested, including the intended target population of infants and young children in Sub-Saharan Africa. Data obtained so far suggest that RTS,S/AS can be co-administered with other vaccines included in the routine Expanded Program of Immunization (EPI). In Phase 2 testing, the vaccine candidate was shown to confer significant protection against P. falciparum infection and clinical disease, including severe malaria. Furthermore, a trend towards an indirect beneficial effect of the vaccine on non-malarial morbidities has been observed in several trials. In this paper, we will describe the genesis of the RTS,S/AS concept, including the rationale for selecting the circumsporozoite protein (CSP) as the target antigen. Early development history of the vaccine will be briefly described. We will present the most salient results from recent Phase 2 studies conducted in the target pediatric population, which have led to the decision to progress RTS,S/AS to Phase 3 testing. If the Phase 3 results confirm the observations made during Phase 2 testing, the RTS,S/AS vaccine, when broadly implemented and judiciously integrated with other malaria-prevention measures, would have a major public-health impact in Sub-Saharan Africa.