Reprogramming Human Cancer Cells into Antigen Presentation

Cancer progression entails close crosstalk between tumor cells and immune system. Recent advances in understanding mutual tumor-immune interactions translated into the development of cancer immunotherapy, changing the cancer treatment paradigm. Nevertheless, despite achieving long-term effect even in advanced malignancies, only a minor subset of patients responds to immunotherapy. The activation of the immune system, as well as good response to the immunotherapy strongly depends on tumor immunogenicity and effective presentation of tumor-associated antigens by conventional dendritic cells type 1 (cDC1). However, downregulation of antigen-presentation machinery and cDC1 exclusion represent major mechanisms of cancer immune evasion, leading to immunotherapy failure. Previously, we identified a combination of 3 transcription factors, PU.1, IRF8, and BATF3 (PIB) that instructed direct reprogramming of fibroblasts into cDC1-like cells endowed with the ability to present and cross-present antigens. Here, we hypothesize that cDC1-direct reprogramming employing PIB transcription factors can impose antigen-presentation directly in human tumor cells, generating functional tumor-antigen presenting cells (tumor-APCs) able to prime antigen-specific T cell responses.

Here, we used a large panel of human cell lines (>30) derived from leukemia and multiple solid tumors including glioblastoma, melanoma, breast, pancreatic, ovarian, prostate, head and neck, and lung adenocarcinoma and evaluated dendritic cell reprogramming efficiency. Enforced expression of PIB induced a cDC1-phenotype in tumor cells, as demonstrated by an emerging CD45+HLA-DR+ population and the activation of the cDC1-markers CD11c, CD141, and CLEC9A. Induced cells showed global transcriptional reprogramming towards cDC1 fate imposing a tumor-APC signature in cancer cells at varying efficiencies ranging between 0.2±0.1% to 94.5±7.6% according to the tumor cell of origin. PIB induces rapid transcriptomic and epigenetic rewiring of cancer cells towards cDC1-fate, activating antigen presentation and processing machinery. This reprogramming process is asynchronous and leads to the generation of intermediate populations with active tumor-APC gene expression signatures. Furthermore, tumor-APCs upregulated expression of HLA-ABC and the co-stimulatory molecules CD40, CD80, and CD86, suggesting the acquired ability to prime immune-effectors. Functionally, tumor-APCs secrete pro-inflammatory cytokines including IL12p70, TNFα, CXCL10, and IL-29 upon TLR3/4 stimulation with Poly:IC and LPS, are competent in phagocytosis of dead cells and proteins, and can activate antigen-specific CD8+ T-cells. Importantly, cDC1-cell fate adoption was accompanied by downregulation of proliferation and diminished tumorigenicity, as evidenced by the loss of anchorage-independent growth. Importantly, cDC1-reprogramming was efficient in primary tissues obtained from head and neck, breast, urothelial and pancreatic carcinoma, as well as melanoma patients. Notably, PIB-mediated cDC1 reprogramming of tumor cells is substantially augmented when combined with a histone deacetylase inhibitor, valproic acid.

In summary, PIB expression imposes cDC1 fate and function in a broad range of human cancer cells suggesting a capacity to elicit anti-tumor responses by orchestrating innate and adaptive immunity. Our strategy combines cDC1 antigen-processing and presenting abilities with the endogenous generation of tumor-antigens. This approach merges cell fate reprogramming with cancer immunotherapy, paving the way for the development of novel gene therapy for cancer.