Radiation attenuated sporozoite (RAS), a whole parasite vaccine approach provides sterile protection against malaria. However, RAS immunization does not confer protection for long, and that has been correlated with the waning parasite-induced memory CD8+ T cell responses. Interestingly, an intermittent infectious (wild-type) sporozoite challenge to the RAS vaccinated mice lengthened the protection period from 6 to 18 months. Herein, we have studied the changes that infectious sporozoite brought in RAS-induced memory CD8+ T cells for conferring lengthened protection. We observed that the infectious sporozoite challenge has boosted the frequency of foreign antigen-experienced memory CD8+ T cells. In those CD8+ T cells, it has reduced the Annexin-V reactivity, raised Bcl-2 expression, and also more cells undergone homeostatic proliferation (Ki-67+). It has also scaled down the frequency of Nur77 and CX3CR1 high expressing cells in those memory CD8+ T cell populations which we further correlated with better survival signals.

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