Limited Model Antigen Expression by Transgenic Fungi Induces Disparate Fates during Differentiation of Adoptively Transferred

CD4 T cells are the key players of vaccine resistance to fungi. The generation of effective T cell-based vaccines requires an un-derstanding of how to induce andmaintain CD4 T cells andmemory. The kinetics of fungal antigen (Ag)-specific CD4 T cell memory development has not been studied due to the lack of any known protective epitopes and clonally restricted T cell subsets with complementary T cell receptors (TCRs). Here, we investigated the expansion and function of CD4 T cell memory after vaccination with transgenic (Tg) Blastomyces dermatitidis yeasts that display a model Ag, E-mCherry (E-mCh). We report that Tg yeast led to E display on Ag-presenting cells and induced robust activation, proliferation, and expansion of adoptively transferred TEa cells in an Ag-specific manner. Despite robust priming by E-mCh yeast, antifungal TEa cells recruited and pro-duced cytokines weakly during a recall response to the lung. The addition of exogenous E-red fluorescent protein (RFP) to the E-mCh yeast boosted the number of cytokine-producing TEa cells that migrated to the lung. Thus, model epitope expression on yeast enables the interrogation of Ag presentation to CD4 T cells and primes Ag-specific T cell activation, proliferation, and expansion. However, the limited availability of model Ag expressed by Tg fungi during T cell priming blunts the downstream generation of effector andmemory T cells. Diseases due to fungi represent a growing public health prob-lem that demand new treatments and methods of vaccine prevention (8). The rational design of vaccines against fungi re-quires an understanding of the elements of antifungal immunity