RTS,S/AS01E Malaria Vaccine Induces Memory and Polyfunctional T Cell Responses in a Pediatric African Phase III Trial

Comprehensive assessment of cellular responses to the RTS, S/AS01E vaccine is needed to understand potential correlates and ultimately mechanisms of protection against malaria disease. Cellular responses recognizing the RTS, S/AS01E-containing circumsporozoite protein (CSP) and Hepatitis B surface antigen (HBsAg) were assessed before and 1 month after primary vaccination by intracellular cytokine staining and 16-color flow cytometry in 105 RTS, S/AS01-vaccinated and 74 rabies-vaccinated participants (controls) in a pediatric phase III trial in Africa. RTS, S/AS01E-vaccinated children had significantly higher frequencies of CSP- and HBsAg-specific CD4(+) T cells producing IL-2, TNF-alpha, and CD40L and HBsAg-specific CD4(+) T producing IFN-alpha and IL-17 than baseline and the control group. Vaccine-induced responses were identified in both central and effector memory (EM) compartments. EM CD4(+) T cells expressing IL-4 and IL-21 were detected recognizing both vaccine antigens. Consistently higher response rates to both antigens in RTS, S/AS01E-vaccinated than comparator-vaccinated children were observed. RTS, S/AS01E induced polyfunctional CSP-and HBsAg-specific CD4(+) T cells, with a greater degree of polyfunctionality in HBsAg responses. In conclusion, RTS, S/AS01E vaccine induces T cells of higher functional heterogeneity and polyfunctionality than previously characterized. Responses detected in memory CD4(+) T cell compartments may provide correlates of RTS, S/AS01-induced immunity and duration of protection in future correlates of immunity studies.