Rethinking preclinical models for genetically engineered porcine red blood cell xenotransfusion.

Genetically engineered porcine red blood cells (pRBCs) are emerging as a potential supplementary source of oxygen-carrying cells for transfusion medicine. Triple-knockout (TKO) pigs lacking major carbohydrate xenoantigens, including Gal, Neu5Gc, and Sd(a), have substantially reduced human antibody binding in vitro, and additional expression of human protective molecules such as CD55 and CD47 may further improve compatibility. However, the translational development of pRBC xenotransfusion is now constrained less by donor engineering alone than by the absence of an appropriate in vivo evaluation model. Old World nonhuman primates have historically served as essential preclinical models in xenotransplantation, but their cytidine monophosphate-N-acetylneuraminic acid hydroxylase (CMAH)-positive background and natural antibody repertoires may exaggerate immune barriers to TKO pRBCs that are not fully representative of humans. New World nonhuman primates, brain-dead human models, and eventually carefully regulated early-phase human studies each offer distinct advantages and limitations. In this Commentary, we argue that pRBC xenotransfusion requires a purpose-specific translational framework rather than reliance on a single preclinical model. Such a framework should integrate standardized compatibility testing, in vitro human assays, animal-based safety stress-testing, and, where ethically and legally feasible, short-term human reference models.