Androgens inhibit protective CD8+ T cell responses against pre-erythrocytic malaria parasites

Attenuated whole organism vaccines targeting the malaria liver stage reliably confer sterile immunity. These vaccines can completely protect female mice from infection, but protection in male mice remains unproven. We discovered that male BALB/cJ mice vaccinated with prime-and-trap, a whole organism-based vaccine strategy, exhibit poorer protection against Plasmodium yoelii sporozoite challenge than females. We investigated this sex difference, and identified vaccinated males have fewer hepatic memory CD8+ T cells than females when scaling for differences in liver biomass, and reduced acute inflammatory responses post-vaccination. Surgical hormone manipulation clarified that the presence of testicular hormones, not the absence of ovarian hormones, hindered protection in male mice. The presence of androgens did not affect memory CD8+ T cells quantity nor quality of, but inhibited protective cellular responses during sporozoite challenge. Thus, both males and females form functional memory responses following prime-and-trap vaccination, but androgens during sporozoite challenge impair protection in male mice.