Chimerism analysis of cell-free DNA in patients treated with hematopoietic stem cell transplantation may predict early relapse in patients with hematologic malignancies

Background: We studied DNA chimerism in cell-free DNA (cfDNA) in patients treated with HSCT.Methods: Chimerism analysis was performed on CD3+ cells, polymorphonuclear (PMN) cells, and cfDNA using 16 small tandem repeat loci. The resulting labeled PCR-products were size-fractionated and quantified.Results: Analyzing samples from 191 patients treated with HSCT for nonneoplastic hematologic disorders demonstrated that the cfDNA chimerism is comparable to that seen in PMN cells. Analyzing leukemia patients (N = 126) showed that, of 84 patients with 100% donor DNA in PMN, 16 (19%) had evidence of clinical relapse and \u3e10% recipient DNA in the plasma. Additional 16 patients of the 84 (19%) showed \u3e10% recipient DNA in plasma, but without evidence of relapse. Eight patients had mixed chimerism in granulocytes, lymphocytes, and plasma, but three of these patients had \u3e10% recipient DNA in plasma compared to PMN cells and these three patients had clinical evidence of relapse. The remaining 34 patients showed 100% donor DNA in both PMN and lymphocytes, but cfDNA showed various levels of chimerism. Of these patients 14 (41%) showed laboratory or clinical evidence of relapse and all had \u3e10% recipient DNA in cfDNA.Conclusion: Monitoring patients after HSCT using cfDNA might be more reliable than cellular DNA in predicting early relapse