In Vivo CAR-T Therapy Moves Toward Scalable, Off-the-Shelf Cancer Treatment

Conventional ex vivo CAR-T cell therapy has transformed hematological oncology but faces profound barriers to broader adoption. Manufacturing requires weeks of leukapheresis, T cell activation, viral transduction, and GMP-grade expansion — a process costing hundreds of thousands of dollars per patient, inducing T cell exhaustion, and delaying treatment for patients with aggressive disease. Approximately 40% of DLBCL patients who initially respond to CD19-directed CAR-T therapy relapse, often as CAR-T cells exhaust and tumor cells escape via antigen downregulation. Solid tumors present additional obstacles including dense stromal matrices, dysfunctional vasculature, metabolically hostile microenvironments rich in TGF-β, Tregs, and MDSCs, and heterogeneous antigen expression that facilitates immune escape.

In vivo CAR-T therapy addresses these limitations by delivering CAR-encoding genetic payloads directly into endogenous T lymphocytes inside the patient. Pioneering proof-of-concept was established in 2017 using synthetic DNA nanocarriers to program leukemia-specific T cells in situ, and in 2018 using engineered lentiviral vectors. The approach bypasses apheresis, ex vivo expansion, and lymphodepleting chemotherapy entirely, compressing the treatment timeline from weeks to days and potentially slashing costs dramatically.

Three major delivery platforms are reviewed in depth. Engineered lentiviral and gamma-retroviral vectors provide stable genomic integration and durable CAR expression but carry risks of insertional oncogenesis and immunogenicity. Adeno-associated viral vectors offer a strong safety profile and tissue tropism versatility but have limited cargo capacity. Lipid nanoparticles (LNPs) delivering CAR-encoding mRNA provide transient, tunable expression with no genomic integration risk, though mRNA-based CAR expression is short-lived and LNPs can trigger inflammatory reactogenicity. Emerging platforms include implantable biomaterial scaffolds that locally concentrate vectors at tumor sites and ultrasound-mediated sonoporation enabling spatiotemporally controlled T cell transfection.

Early-phase clinical trials in relapsed/refractory multiple myeloma and B-cell malignancies have demonstrated meaningful antitumor responses generated through in vivo T cell reprogramming, with some trials proceeding without preconditioning chemotherapy — a notable departure from conventional practice. The ability to administer repeated doses also transforms CAR-T from a one-time cellular product into a titratable pharmacotherapy, enabling chronic treatment regimens not feasible with current ex vivo products.

Significant challenges gatekeep widespread adoption. Achieving selective in vivo targeting of T cells without off-target transduction of other immune or non-immune cells remains technically demanding. The immunosuppressive TME continues to blunt efficacy in solid tumors. Antigen escape and tumor heterogeneity require multi-antigen targeting strategies. Safety risks including vector genotoxicity, LNP reactogenicity, cytokine release syndrome, and immune effector cell-associated neurotoxicity syndrome must be carefully managed. Regulatory frameworks for these novel agents are still evolving. Future progress will require refined vector tropism engineering, tunable safety switches, synergistic combination regimens, and robust biomarker-guided patient selection.