Peripheral blood CD4⁺ and CD8⁺ T cell responses to Cryptococcus candidate vaccine antigens in human subjects with and...

Immunological studies of persons with cryptococcal disease without known immunocompromise could inform vaccine development and identify novel requirements for antifungal immunity. We tested recall responses to heat-killed (HK) Cryptococcus and recombinant cryptococcal candidate vaccine antigens in peripheral blood T cells from subjects with a history of cryptococcosis and no recognized predisposing condition at the time of study enrollment, alongside healthy controls. In response to stimulation with HK Cryptococcus, CD4⁺ and CD8⁺ T cells from the cryptococcosis subjects had greater activation compared to healthy controls. Responses to recombinant antigens, while less robust, were also more frequent in patient samples compared to healthy controls. Fungal strains stimulated much higher interferon gamma (IFNγ) secretion compared with interleukin (IL)-17A and IL-4. A mouse model of vaccination and cryptococcal infection was established to determine the degree to which antigen-specific IFNγ responses in the periphery reflect responses in the tissue. Peripherally, the mouse model mimicked the human studies with the additional finding that responses were greatest in mice following both vaccination and infection. Moreover, responses in splenocytes and lung cells exceeded those in PBMCs suggesting PBMC responses underestimate those at sites of infection. In summary, in otherwise immunocompetent patients with cryptococcosis, antigen-stimulated CD4⁺ and CD8⁺ T cell activation, as measured by cytokine, was intact and biased towards a T-helper 1 (Th1) response. The mouse data support vaccination as a strategy to boost immune responses to prevent clinical Cryptococcus infection.