Clonal analysis by the HUMARA assay of BM and MNBCs from 3 patients. HUMARA alleles were amplified by PCR in the absence (−) or in the presence (+) of Hpa II. The ratio of digested DNA/undigested DNA allows to correct for the potential preferential amplification of one allele over the other that occurs frequently. Shadow bands result from slippage of DNA polymerase during PCR amplification. In patient no. 68, both the pre-ABMT BM sample (BM-PRE) and the last available BM (BM-LAST) showed balanced methylation patterns, consistent with polyclonal hematopoiesis before and after ABMT. In patient no. 59, the pre-ABMT BM sample, the last available BM sample, and the MNBC control sample showed an inbalanced methylation pattern, with the predominance of the upper allele, consistent with a skewed XIP. In patient no. 27, the pre-ABMT BM sample showed a balanced methylation pattern (polyclonal hematopoiesis), but subsequent BM samples obtained after ABMT (BM-1 and BM-2) showed a progressive predominance of the upper allele. Thess results are consistent with the development of clonal hematopoiesis after ABMT. See text for definitions of skewed XIP, polyclonal hematopoeisis, and clonal hematopoiesis.