Individuals who are immunocompromised, including AIDS patients with few CD4+ T cells, are at increased risk for opportunistic fungal infections. The incidence of such infections is increasing worldwide, meaning that the need for antifungal vaccines is increasing. Although CD4+ T cells play a dominant role in resistance to many pathogenic fungal infections, we have previously shown that vaccination can induce protective antifungal CD8+ T cell immunity in the absence of CD4+ T cells. However, it has not been determined whether vaccine-induced antifungal CD8+ T cell memory can be maintained in the absence of CD4+ T cell help. Here, we have shown in a mouse model of vaccination against blastomycosis that antifungal memory CD8+ T cells are maintained in the absence of CD4+ T cells without loss of numbers or function for at least 6 months and that the cells protect against infection. Using a system that enabled us to induce and track antigen-specific, antifungal CD8+ T cells, we found that such cells were maintained for at least 5 months upon transfer into naive mice lacking both CD4+ T cells and persistent fungal antigen. Additionally, fungal vaccination induced a profile of transcription factors functionally linked with persistent memory in CD8+ T cells. Thus, unlike bacteria and viruses, fungi elicit long-term CD8+ T cell memory that is maintained without CD4+ T cell help or persistent antigen. This has implications for the development of novel antifungal vaccine strategies effective in immunocompromised patients.
Som G. Nanjappa, Erika Heninger, Marcel Wüthrich, Thomas Sullivan, Bruce Klein