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Background Solid tumors such as breast, lung, pancreatic, colorectal, and ovarian cancers contribute to nearly half of all cancer-related mortality in the U.S. Despite advances in surgery, targeted agents, and immunotherapies, durable responses remain limited. Both ex vivo and in vivo chimeric antigen receptor (CAR) therapies have shown curative potential in hematologic malignancies, but translation to solid tumors remains challenging. Key hurdles include transient CAR expression, antigen heterogeneity, immunosuppressive microenvironments, manufacturing complexity, and long-term safety concerns. A critical need exists for new CAR platforms that enable scalable, repeatable, and durable immune reprogramming.Methods Velvet Therapeutics is developing a next-generation in vivo CAR therapy platform using biodegradable nanoparticles to deliver non-integrating minicircle DNA (mcDNA) encoding CAR constructs directly into immune cells in vivo. This approach eliminates the need for ex vivo cell manipulation and allows repeat dosing to sustain CAR expression over time. The proprietary CAR-X architecture is engineered to activate both adaptive and innate immunity, enhancing tumor clearance and limiting antigen escape.Results Intravenous administration of luciferase-encoding DNA nanoparticles led to gene expression primarily in the thymus, lymph nodes, and lungs, while sparing the liver. Luciferase expression was observed in both T cells and antigen-presenting cells (APCs). As an in vivo proof of concept, we delivered a fully murine CD19-targeting STAR-CAR (STAR-mCD19) to C57BL/6 mice via two biweekly IV doses. Treated animals showed rapid and sustained depletion of CD20+ B cells in blood and spleen by day 7, persisting through day 21. T cell expansion suggested systemic immune activation. Liver (GGT, ALT, AST) and kidney (BUN) function remained within normal ranges, and body weights were stable, indicating a favorable safety profile.To test efficacy against a solid tumor antigen, we evaluated a human STAR-TROP2 CAR-X construct in vitro. Transfected PBMCs displayed strong, antigen-specific cytotoxicity against TROP2+ HEK293 and SAOS-2 cells, with no killing of antigen-negative or irrelevant CAR controls. These cells secreted high levels of IFN-γ, IL-2, GM-CSF, and TNF-α, without elevating Th2 associated IL-4, IL-5, IL-13 which can lead to antibody response, indicating coordinated, long term re-dosable anti-tumor immune activation.Conclusions These findings establish proof of concept for safe, effective in vivo delivery of mcDNA-encoded STAR-CARs. This platform supports durable immune engagement and tumor specificity and holds promise for scalable, re-dosable CAR therapies targeting solid tumors. Ongoing in vivo studies are assessing anti-tumor efficacy in in vivo models.