Researchers at UC San Francisco and collaborators reported a dual‑vector approach that enables precise, site‑specific integration of large DNA payloads into T cells directly in vivo, producing functional CAR‑T cells without ex vivo manufacturing. Published results showed durable engraftment and antitumor activity in humanized mouse models, including efficacy against solid tumors. The study represents a technical advance over prior in vivo strategies by combining cell specificity with locus targeting to reduce off‑target integration risks. Investigators framed the method as a potential shortcut to eliminate complex manufacturing and reduce costs; they cautioned translation will require careful safety testing and regulatory scrutiny because permanent genomic insertion in vivo raises risk‑management questions.