An article in Nature Medicine presents early clinical data on in vivo CAR-T cell therapy for multiple myeloma that reveal key mechanistic insights.[original] In vivo CAR-T cells are generated directly in the patient's body, eliminating the need for ex vivo cell processing, complex logistics, and limited manufacturing capacity of traditional methods.[2] This method uses targeted delivery systems such as lentiviral vectors and lipid nanoplasts to introduce CAR genetic material into endogenous T cells.[1][2] Early clinical studies show efficient transduction, sustained CAR expression, and early signs of antitumor activity, confirming proof of concept.[2] In vivo engineering enables faster, more scalable and more globally available immunotherapy compared to ex vivo platforms.[1] Technologies also include in vivo integration of a CAR transgene into the TRAC locus for physiological regulation of expression and sustained antitumor activity in preclinical models.[3] These advances may extend CAR-T therapy to both oncology and autoimmune diseases, such as systemic lupus erythematosus.[2]