Priming at the site of natural infection typically elicits a protective T cell response against subsequent pathogen encounter. Here, we report the identification of a novel fungal antigen that we harnessed for mucosal vaccination and tetramer generation to test whether we can elicit protective, antigen-specific tissue resident memory (Trm) CD4 + T cells in the lung parenchyma. In contrast to expectations, CD69 + , CXCR3 + , CD103 − Trm cells failed to protect against a lethal pulmonary fungal infection. Surprisingly, systemic vaccination induced a population of tetramer + CD4 + T cells enriched within the pulmonary vasculature, and expressing CXCR3 and CX3CR1, that migrated to the lung tissue upon challenge and efficiently protected mice against infection. Mucosal vaccine priming of Trm may not reliably protect against mucosal pathogens.

The development of vaccines against fungi and other intracellular microbes is impeded in part by a lack of suitable adjuvants. While most current vaccines against infectious diseases preferentially induce production of antibodies, cellular immunity is essential for the resolution of fungal infections. Microbes such as fungi and Mycobacterium tuberculosis require Th17 and Th1 cells for resistance, and engage the C-type lectin receptors including Dectin-2. Herein, we discovered a novel Dectin-2 ligand, the glycoprotein Blastomyces Eng2 (Bl-Eng2). Bl-Eng2 triggers robust signaling in Dectin-2 reporter cells and induces IL-6 in human PBMC and BMDC from wild type but not Dectin-2-/- and Card9-/- mice. The addition of Bl-Eng2 to a pan-fungal subunit vaccine primed large numbers of Ag-specific Th17 and Th1 cells, augmented activation and killing of fungi by myeloid effector cells, and protected mice from lethal fungal challenge, revealing Bl-Eng2’s potency as a vaccine adjuvant. Thus, ligation of Dectin-2 by Bl-Eng-2 could be harnessed as a novel adjuvant strategy to protect against infectious diseases requiring cellular immunity.

Memory homeostasis of Th1/Tc1 cells is well characterized, whereas memory Th17-cell homeostasis, persistence and plasticity are debated. We have shown that IL-17A-producing CD8+ T-cells (Tc17) are necessary for vaccine-induced fungal immunity in CD4+ T-cell compromised hosts. Here, we systematically evaluated persistence, fidelity, plasticity and functional role in immunity of anti-fungal Tc17 cells using IL-17A fate-mapping reporter mice. We show that Tc17 cells stably maintained as functional bona fide IL-17A producing memory cells, with little plasticity towards IFNγ, even in the absence of vaccine antigen. Memory Tc17 cells stably and progressively improved in their production of multiple Tc1 cytokines but not IFNγ, and contributed for IL-17A-dependent vaccine resistance. Memory Tc17 cells were canonical CD8+ T cells portraying a set of phenotypic attributes that were distinct from Tc1 cells while remaining Ror(γ)hi, T-betlo and EOMESlo. Interestingly, in contrast to Tc1, memory Tc17 cells expressed lower levels of anti-apoptotic factors Bcl-1, Bcl-xL and MCL-1. However, basal homeostatic proliferation of memory Tc17 cells was significantly higher than Tc1 cells. Finally, we unraveled a dichotomous role of HIF-1α for effector vs memory Tc1 and Tc17 cells, where HIF-1α was essential for expression of IL-17A in memory cells while it was required for expression of IFNγ in effector cells.