Researchers reported an intraperitoneal delivery method using mRNA lipid nanoparticles to program CAR macrophages in situ, boosting antitumor activity in peritoneal cancer models. The approach enables transient in‑body generation of engineered macrophages without ex vivo cell manufacturing, potentially lowering cost and logistic barriers for adoptive cell therapies. Preclinical results showed enhanced tumor clearance in the peritoneal compartment and favorable safety signals in animal models; investigators highlighted the LNP platform’s adaptability for other CAR constructs. The method could shorten development timelines for solid‑tumor cell therapy programs if translational toxicology and delivery in humans prove manageable.