Analysis of Pre-Erythrocytic Immunity During Plasmodium Vivax Infection Reveals a Diversity of Responses That is Partially Due to Blood Stage Cross-Reactivity

Abstract BackgroundPlasmodium vivax (Pv) represents the most geographically widespread human malaria parasite. Targeting the pre-erythrocytic (PE) stage of the parasite life cycle is especially appealing for Pv vaccines as it would prevent disease and transmission. Here, we explore naturally acquired immunity to a panel of Pv PE antigens as a first step to enable vaccine development and to better understand naturally-acquired PE immunity.MethodsHumoral and cellular immunity were evaluated by ELISA and ELISpot, using samples from Pv infected individuals from a low endemic malaria region in the Peruvian Amazon Basin. In addition, we utilized experimental infection of Aotus non-human primates with Pv or P. falciparum (Pf) in order to evaluate the contribution of blood stage infection to the humoral response observed in human samples.ResultsIn our clinical samples, twelve PE antigens showed positive antibody reactivity with variable prevalence of 58–99%. The magnitude of the IgG antibody response against PE antigens was lower compared with blood stage antigens MSP1 and DBP-II although titers persisted better for PE antigens, six months later after infection (average decrease of 6% for PE antigens and 43% for MSP1) in general. A significant correlation between IgG antibodies and number of previous malaria episodes was observed only for blood stage antigens. High IgG responders across PE and blood stage antigens showed a significantly lower parasitemia compared to low responders (median 1873 vs 4663 par/µl). We observed a positive T cell response in 35% vs 9–35% of total volunteers against blood stage antigen MSP1 and PE antigens, respectively, and saw no correlation with IgG responses. Aotus monkeys infected with Pv blood stage showed positive reactivity against the seven PE antigens tested. In contrast, only 2 of 10 monkeys infected with Pf showed low positive IgG cross-reactivity against Pv MSP1 and none of which cross-reacted to Pv CSP.ConclusionsOur results demonstrate clear humoral and T cell responses against Pv PE antigens in individuals naturally infected with P. vivax. In addition, these results are largely replicated in a novel Aotus nancymaae Pv blood stage challenge model which suggest a contribution from blood stages to PE cross-reactivity. Together, these data clearly identify novel attractive PE antigens suitable for use in the development of new malaria vaccine candidates.