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Unbiased functional identification and therapeutic targeting of T cell neoantigens in a spontaneous murine squamous cell carcinoma [Single cell]

ABSTRACT: The comparative resistance of some cancers including head and neck squamous cell carcinoma to checkpoint blockade is speculated to derive from the low frequency of expressed somatic mutations targeted by T cells as neoantigens. SCCVII, a spontaneously arising murine squamous carcinoma resembling human HNSCC in several key features, is likewise poorly immunogenic as irradiated tumor cells alone fail to induce protective immunity within syngeneic hosts. Justifying use of this model to identify NeoAgs, we confirm activated CD4+ and CD8+ T cells are detectable and essential for vaccine efficacy of SCC VII and polyI:C co-administration. Whole-exome sequencing tumor versus normal genome identified 39 nonsynonymous missense mutations that were synthesized into 81 representative 20-mers. NeoAg-specific CD4+ T cell IFN-γ responses were found against mutations of Pik3ca, Ctnnd1, and Otud5 while both CD4+ and CD8+ T cells produced IFN-γ when stimulated by a single Cltc mutation during in vitro recall assays. Prophylactic immunization with a mixture of all stimulatory peptides or the Cltc NeoAg alone protected hosts from subsequent tumor challenge. Further, the Cltc NeoAg, eliciting both CD4+ and CD8+ T cell responses, was also therapeutically beneficial in vivo. Anti-PD-1 combinatorial blockade resulted in synergistic tumor rejection via boosting Cltc-specific responses and increasing response diversification via epitope spreading. These data show that a functional NeoAg identification platform can be used to select immunotherapeutically relevant targets and filtration of neoepitopes that co-prime both CD4+ and CD8+ T cell responses is superior for practical intervention of poorly immunogenic tumors.

ORGANISM(S): Mus musculus

PROVIDER: GSE125077 | GEO | 2021/01/15

REPOSITORIES: GEO

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Project description:Accumulating data support the concept that ionizing radiation therapy (RT) has the potential to convert the tumor into an in situ, individualized vaccine; however this potential is rarely realized by RT alone. Transforming growth factor β (TGFβ) is an immunosuppressive cytokine that is activated by RT and inhibits the antigen-presenting function of dendritic cells and the differentiation of effector CD8+ T cells. Here we tested the hypothesis that TGFβ hinders the ability of RT to promote anti-tumor immunity. Development of tumor-specific immunity was examined in a pre-clinical model of metastatic breast cancer. Mice bearing established 4T1 mouse mammary carcinoma treated with pan-isoform specific TGFβ neutralizing antibody, 1D11, showed significantly improved control of the irradiated tumor and non-irradiated metastases, but no effect in the absence of RT. Notably, whole tumor transcriptional analysis demonstrated the selective upregulation of genes associated with immune-mediated rejection only in tumors of mice treated with RT+TGFβ blockade. Mice treated with RT+TGFβ blockade exhibited cross-priming of CD8+ T cells producing IFNγ in response to three tumor-specific antigens in tumor-draining lymph nodes, which was not evident for single modality treatment. Analysis of the immune infiltrate in mouse tumors showed a significant increase in CD4+ and CD8+ T cells only in mice treated with the combination of RT+TGFβ blockade. Depletion of CD4+ or CD8+ T cells abrogated the therapeutic benefit of RT+TGFβ blockade. These data identify TGFβ as a master inhibitor of the ability of RT to generate an in situ tumor vaccine, which supports testing inhibition of TGFβ during radiotherapy to promote therapeutically effective anti-tumor immunity. We used genome-wide microarray to depict main biological processes responsibles for the therapeutic benefit of the combination ofTGF-beta blockade and local radiotherapy. To gain a more comprehensice protrait of the effects of RT and TGFbeta blockade on gene expressionin tumors, we collected 4T1 tumors 4 days after completion of RT. Three tumors from each group were then subjected to RNA extraction and hybridization on affymetrix array.

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Unbiased functional identification and therapeutic targeting of T cell neoantigens in a spontaneous murine squamous cell carcinoma [Single cell]

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