Current success of immunotherapy in cancer has drawn attention to the subsets of TH cells in the tumor which are critical for activation of anti-tumor response either directly by themselves or by stimulating cytotoxic T cell activity. However, presence of immunosuppressive pro-tumorigenic TH subsets in the tumor milieu further contributes to the complexity of regulation of TH cell-mediated immune response. In this review, we present an overview of the multifaceted positive and negative effects of TH cells, with an emphasis on regulation of different TH cell subtypes by various immune cells, and how a delicate balance of contradictory signals can influence overall success of cancer immunotherapy. We focus on the regulatory network that encompasses dendritic cell-induced activation of CD4+ TH1 cells and subsequent priming of CD8+ cytotoxic T cells, along with intersecting anti-inflammatory and pro-tumorigenic TH2 cell activity. We further discuss how other tumor infiltrating immune cells such as immunostimulatory TH9 and Tfh cells, immunosuppressive Treg cells, and the duality of TH17 function contribute to tip the balance of anti- vs pro-tumorigenic TH responses in the tumor. We highlight the developing knowledge of CD4+ TH1 immune response against neoantigens/oncodrivers, impact of current immunotherapy strategies on CD4+ TH1 immunity, and how opposing action of TH cell subtypes can be explored further to amplify immunotherapy success in patients. Understanding the nuances of CD4+ TH cells regulation and the molecular framework undergirding the balancing act between anti- vs pro-tumorigenic TH subtypes is critical for rational designing of immunotherapies that can bypass therapeutic escape to maximize the potential of immunotherapy.

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The HER3/ERBB3 receptor is an oncogenic receptor tyrosine kinase that forms heterodimers with EGFR family members and is overexpressed in numerous cancers. HER3 overexpression associates with reduced survival and acquired resistance to targeted therapies, making it a potential therapeutic target in multiple cancer types. Here, we report on immunogenic, promiscuous MHC class II–binding HER3 peptides, which can generate HER3-specific CD4+ Th1 antitumor immune responses. Using an overlapping peptide screening methodology, we identified nine MHC class II–binding HER3 epitopes that elicited specific Th1 immune response in both healthy donors and breast cancer patients. Most of these peptides were not identified by current binding algorithms. Homology assessment of amino acid sequence BLAST showed >90% sequence similarity between human and murine HER3/ERBB3 peptide sequences. HER3 peptide–pulsed dendritic cell vaccination resulted in anti-HER3 CD4+ Th1 responses that prevented tumor development, significantly delayed tumor growth in prevention models, and caused regression in multiple therapeutic models of HER3-expressing murine tumors, including mammary carcinoma and melanoma. Tumors were robustly infiltrated with CD4+ T cells, suggesting their key role in tumor rejection. Our data demonstrate that class II HER3 promiscuous peptides are effective at inducing HER3-specific CD4+ Th1 responses and suggest their applicability in immunotherapies for human HER3-overexpressing tumors.

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Despite significant improvements in cancer immunotherapies, enhancing immunogenicity of non-responsive tumors warrants further investigation. A prior drug screen of ~3,000 compounds identified NU7441, a DNA PK inhibitor, as an effective compound that promotes immunogenicity of various melanoma lines in vitro. In this study, we hypothesized that in vivo combination therapy NU7441, STING-L, and CD40 agonist will enhance tumor immunogenicity resulting in both expansion and increased cytotoxic activity of CD8+TCRβ tumor-reactive TILs in B16 melanoma models. Results obtained by flow cytometry demonstrated that combination treatment 1) significantly increased the ratio of CD8/CD4 TILs, 2) expanded several tumor-reactive TCRβ clones, 3) increased granzyme B production and expression of 4-1BB and PD-1, 4) increased ratio of DC/MDSC infiltration, and 5) potentially identified a novel cytotoxic CD8+CD11c+GR-1+ population. Additionally, the expansion of tumor-reactive TCRs was attributed to DNA-PKi’s ability to both expand and diversify the number of neoantigen transcripts resulting in a broader neoantigen expression profile. RNA-seq identified 27 unique neoantigens as potential novel targets in melanoma immunotherapy. TILs isolated from B16 tumors were co-cultured with dendritic cells transfected with tandem-mini genes, each encoding ~10 neoantigens, and T cells were analyzed by flow cytometry to quantify the TCRβ repertoire and functional response to neoantigens. We demonstrate combination treatment with NU7441, STING-L and CD40 agonist enhance antitumor responses through increased myeloid cell infiltration and sensitization of tumor cells to T cell-mediated killing from an expanded CD8+TCRβ repertoire. Supported by R01CA207913 NCI BX004935-01, VA, Merit Award P30CA046934, NCI Leukemia and Lymphoma Society Department of Defense Gates Grubstake University of Colorado Anschutz Medical Campus Cancer League of Colorado