CD8+ T cell responses following replication-defective adenovirus serotype 5 immunization are dependent on CD11c+ dendritic cells but show redundancy in their requirement of TLR and nucleotide-binding oligomerization domain-like receptor signaling.

Replication-defective adenovirus serotype 5 (rAd5) is the most potent recombinant vector for eliciting CD8 T cell responses in humans. In this study, the innate mechanisms that influence T cell responses following rAd5 immunization were assessed in mice. Using rAd5 expressing enhanced GFP (eGFP-rAd5), we show that rAd5 transfects CD11c(+) dendritic cells (DCs) in draining lymph nodes in vivo following s.c. or i.m. immunization. Among distinct DC subsets, eGFP expression was highest in CD11c(+)CD8(-)B220(-) with a lower frequency detected in CD11c(+)CD8(+)B220(-) and CD11c(+)B220(+) plasmacytoid DCs. CD11c(+) DCs but not CD11c(-) cells from mice immunized with rAd5 encoding the SIINFEKL peptide induced proliferation of naive OT-I CD8 T cells. Furthermore, CD11c(+)CD8(+)B220(-) was the most potent DC subset for eliciting naive OT-I CD8 T cell proliferation. Of note, mice with pre-existing immunity to rAd5 had a substantial decrease in eGFP expression in DCs, which was associated with approximately 2-fold decrease in Th1 and complete inhibition of CD8 responses. Thus, pre-existing rAd5 immunity has a greater influence on CD8 compared with CD4 T cell responses. In terms of how innate cytokines and signaling pathways influenced T cell immunity following rAd5 immunization, we show that the magnitude and quality of CD8 T cell responses are partially dependent on MyD88 but independent of IL-12, type I IFN, apoptosis-associated speck-like protein, nucleotide-binding oligomerization domain-like receptor protein 3, and IL-1. Taken together, these data demonstrate a critical role for CD11c(+) DCs for CD8 responses but striking redundancy for innate cytokines and signaling by TLR and nucleotide-binding oligomerization domain-like receptor pathways.

Identification of naturally processed CD8 T cell epitopes from prostein, a prostate tissue-specific vaccine candidate.

Prostein is a prostate tissue-specific protein that is uniquely and abundantly expressed in normal and cancerous prostate tissues. Due to this expression profile, we examined the immunogenicity of prostein as a potential vaccine candidate for prostate cancer. To determine the presence of CD8 T cells specific for naturally processed prostein-derived epitopes in healthy individuals, we developed and applied an in vitro stimulation protocol. Using this protocol, we identified CD8 T cells specific for prostein in the peripheral blood of a male and a female donor. Prostein-specific CD8 T cell clones specifically recognized prostein-expressing targets, including prostate tumor cell lines expressing the relevant HLA alleles. CD8 T cell clones isolated from the male donor were significantly less effective in recognizing target cells compared to cells isolated from the female donor and appeared to recognize subdominant epitopes. The identification of a prostein-specific CD8 T cell repertoire supports the development of prostein in vaccination strategies against prostate cancer. Furthermore, the naturally processed peptide epitopes identified provide tools for the development of peptide-based vaccination strategies against prostate cancer and for monitoring of prostein-specific responses in vaccinated patients.