AbstractThe polymorphic minor histocompatibility antigen HA‐1 induces powerful T‐cell alloreactivities with important consequences for graft‐vs‐tumor activity and development of graft‐vs‐host disease in patients after human leukocyte antigen‐matched stem‐cell transplantation (SCT). In view of possible translational animal studies, we analyzed the evolutionary conservation of the diallelic HA‐1 locus in four mammalian species. Our results show that rodents do not encode the HA‐1H allele, neither show polymorphism in this position on the HA‐1 gene. Contrariwise, the HA‐1H allele is present in non‐human primate species and dogs. Interestingly, both the HA‐1H T‐cell epitope and its non‐immunogenic counterpart HA‐1R are present in the latter species. Thus, the HA‐1 allelic polymorphism is conserved in evolution in primates and dogs.