Immediate dysfunction of vaccine-elicited CD8+ T cells primed in the absence of CD4+ T cells

CD4+ T cell help is critical for optimal CD8+ T cell expansion after priming in many experimental systems. However, a role for CD4+ T cells in regulating the initial steps of CD8+ T cell effector differentiation is not well established. Here we demonstrate that absence of CD4+ T cells at the time of replication-incompetent adenovirus vector immunization of C57BL/6 mice led to immediate CD8+ T cell dysfunction characteristic of exhaustion at the first detectable timepoints as well as impaired expansion of antigen-specific CD8+ T cells. The absence of CD4+ T cell help resulted in antigen-specific CD8+ T cells that had reduced ex vivo cytotoxicity and decreased capacity to produce IFN-γ and TNF-α. CD8+ T cells primed in the absence of CD4+ T cells expressed elevated levels of the inhibitory receptors PD-1, LAG-3, and Tim-3, and these cells exhibited transcriptomic exhaustion profiles by gene set enrichment analysis. This dysfunctional state was imprinted within 3 days of immunization and could not be reversed by provision of CD4+ T cell help after priming. Partial rescue of unhelped CD8+ T cell expansion and effector differentiation could be achieved by PD-1 pathway blockade or recombinant IL-2 administration. This study identifies a novel, previously undescribed role of CD4+ T cells to prevent immediate dysfunction and features of exhaustion in CD8+ T cells following antigen priming. Splenic AL11-specific CD8 T cells from mice immunized with Ad5HVR48(1-7)-SIV Gag and treated with anti-CD4 antibody or not were purified by FACS on day 14 post-immunization