Targeting an essential viral oncoprotein with an IL-7-enhanced mRNA vaccine induces durable immunity to Merkel cell...

Although mRNA technologies have reinvigorated cancer vaccine development, the identification of strong antigens with consistent tumor cell expression and generation of durable antigen-specific CD8⁺ T cell memory remain key challenges. We identified the Merkel cell carcinoma (MCC) large T antigen (LTA) as an optimal vaccine target, essential for tumor cell survival and immunogenic in a cancer with high unmet clinical need. We developed an mRNA vaccine to MCC-LTA in murine studies and patient samples. We showed that antigen loss develops rapidly and causes resistance in mouse models when immunogenic, but non-essential antigens are targeted. To improve T cell response durability, we co-encoded LTA and IL-7, co-localizing proliferative and memory signals spatially and temporally with antigen exposure. IL-7-containing mRNA vaccines improved antigen-specific T cell expansion, memory differentiation, and tumor control. We propose that the principles of antigen essentiality and memory signal co-encoding may be adapted to improve the efficacy of mRNA therapeutics.