CRISPR-Cas9-driven antigen conversion of clinically relevant blood group systems

The common practice of blood transfusion entirely relies on blood donations from the population. Ensuring blood group compatibility between a donor and a recipient is paramount to prevent critical adverse reactions. Finding compatible blood can be challenging given the high diversity of blood group antigens, especially for chronically transfused patients at higher risk of alloimmunization owing to repeated exposures to foreign RBCs. In addition, due to the immunogenicity of the ABO blood group and the highly polymorphic nature of the Rhesus (Rh) system, they both remain of prime importance in transfusion medicine. Cultured red blood cells (cRBCs) may eventually provide an alternative for blood donations-at least in some circumstances. Combining cRBCs with blood group gene editing could broaden transfusion accessibility by making antigen expression compatible with rare phenotypes, thus meeting the needs of more patients. Starting from mobilized, erythroid-primed hematopoietic stem and progenitor cells (HSPCs), we used virus- and selection-free, CRISPR-Cas9-mediated knockouts to produce erythroid cells devoid of AB and Rh antigen. The approach yielded almost complete conversion to O- and RhNull phenotypes, as determined by standard hemagglutination and flow cytometry analyses. Combined with robust cRBC protocols, these clinically relevant phenotypic changes could eventually expand the accessibility of blood transfusion for specific and unmet clinical needs.