The authors describe a prospective study of the transplantation of genetically modified allogeneic beta cells into the forearm of a man with long-term type 1 diabetes mellitus, while the patient was not receiving any immunosuppression[3]. Cells were engineered using CRISPR–Cas12b and lentiviral transduction to reduce recognition by the recipient's immune system[3]. After transplantation, no measurable alloimmune or antibody responses against the genotyped cells were demonstrated during the 12-week follow-up[1][3]. C-peptide measurements showed stable and glucose-responsive insulin secretion during the observed period[3]. PET imaging and functional tests confirmed the survival and metabolic activity of the graft at the implantation site[1][3]. The study registration reported that four adverse events occurred, none of which were serious or attributable to the study intervention[3]. According to the authors, this is a proof of concept that genotyped allogeneic beta cells can survive and function without systemic immunosuppression over a 12-week timeframe[1][3].