Objective: We aimed to create a molecular assay to monitor erythroid (red blood cell [RBC]) engraftment in any patient following allogeneic hematopoietic stem cell transplantation, independent of disease-specific mutations.
Materials and methods: We identified 10 common single nucleotide polymorphisms (SNPs), expressed by genes encoding RBC antigens and structural proteins. These SNPs were polymerase chain reaction-amplified from total RNA extracted from peripheral blood, which contains nucleated erythroid progenitors. Mixing studies validated that each SNP can quantitatively measure donor/recipient DNA and RNA.
Results: We directly genotyped 23 patients who underwent hematopoietic stem cell transplantation and their human leukocyte antigen-matched donors and found a median of three informative SNPs (i.e., discordant between donor and recipient) per pair. By using the informative RBC SNPs to quantify donor-derived RBC transcripts, we compared rates of RBC engraftment in 13 patients with hemoglobinopathies vs donor mononuclear cell (white blood cell [WBC]) engraftment. Consistent with known ineffective erythropoiesis associated with hemoglobinopathies, we detected up to threefold greater RBC-specific compared to overall WBC engraftment in five of eight patients who were mixed chimeras by transplant day 30. The remaining three of eight who received ABH-incompatible grafts, demonstrated at least 0.5-fold lower RBC compared to WBC engraftment that was related to persistence of host-derived anti-isohemagglutinin antibodies.
Conclusion: This RNA-based assay can be used to monitor RBC-specific engraftment regardless of a patient's specific hemoglobin mutation or even diagnosis. We propose that panels of expressed SNPs informative for other cell lineages can be created to comprehensively assess the impact of novel stem cell-based therapies on lineage-specific engraftment.