Xu, J. R. | bioRxiv Science

bioRxiv2026

An immunocompetent model of MCPyV-driven Merkel cell carcinoma reveals tumor evolution under immune selection

Merkel cell carcinoma (MCC) is a neuroendocrine skin tumor that is frequently driven by integration of Merkel cell polyomavirus (MCPyV). In MCC, the MCPyV genome is truncated, but expression of the viral tumor antigens, truncated large tumor antigen (LTT) and small tumor antigen (sT), is maintained and drives uncontrolled proliferation. We introduced constitutive expression of the MCPyV T antigens (TAs) into primary mouse dermal fibroblasts (MDFs) to determine whether these cells are susceptible to MCPyV-driven transformation. TA expression alone in MDFs induced key MCC markers, cytokeratin-20 (CK20) and Sry-box transcription factor 2 (SOX2), and promoted anchorage-independent growth indicative of cellular transformation. Subcutaneous implantation of TA-transformed fibroblasts produced high-grade MCC-like tumors that grew persistently in immunodeficient NSG mice but not in immunocompetent C57BL/6 mice. Serial in vivo passaging of the tumor cell line enhanced tumor growth, reduced expression of p53-target genes and MHC-1, and was accompanied by a shift in T antigen isoform expression, with decreased LTT and increased sT expression. Our data demonstrate that MCPyV-driven tumors acquire immune-evasive adaptions during tumor progression in vivo and suggest that the anti-tumor immune response exerts selective pressure in MCC that favors expression of sT rather than LTT. The model established in this study provides a unique platform for studying evolution of MCPyV-driven tumors under immune pressure and identifying mechanisms of immune evasion in MCC that could be used to develop new therapeutic strategies. Significance StatementMCPyV tumor antigen expression transforms mouse dermal fibroblasts to generate MCC-like tumors. Serial in vivo passaging reveals tumor evolution under immune pressure, providing a model to study immune evasion mechanisms in MCC.

cancer biology↗

bioRxiv2022

Lipid nanoparticles delivering constitutively active STING mRNA as a novel anti-cancer therapeutic approach

Treating immunosuppressive tumors represents a major challenge in cancer therapies. Activation of STING signaling has shown remarkable potential to invigorate the immunologically cold tumor microenvironment (TME). However, we and others have shown that STING is silenced in many cancers, including pancreatic ductal adenocarcinoma (PDAC) and Merkel cell carcinoma (MCC), both of which are associated with an immune-dampened TME. In this study, we applied mRNA lipid nanoparticles (LNP) to deliver a permanently active gain-of-function STINGR284S mutant into PDAC and MCC cells. Expression of STINGR284S induces cytokines and chemokines crucial for promoting intratumoral infiltration of CD8+ T cells and, importantly, also leads to robust cancer cell death while avoiding T cell entry and toxicity. Our studies demonstrated that mRNA-LNP delivery of STINGR284S could be explored as a novel therapeutic tool to reactivate antitumor response in an array of STING-deficient cancers while overcoming the toxicity and limitations of conventional STING agonists.

bioengineering↗