Evaluation of leukaemic contamination in peripheral blood stem cell harvests by reverse transcriptase polymerase chain reaction

Summary. A major issue in autologous blood stem cell transplantation (ABSCT) for leukaemia is whether peripheral blood stem cell (PBSC) harvests are less contaminated with leukaemic cells than bone marrow mononuclear cells (BMMNC). We compared leukaemic contamination in PBSC harvests and BMMNC, obtained simultaneously, by using reverse transcriptase polymerase chain reaction (RT‐PCR) of leukaemia‐specific chimaeric messenger RNA (mRNA), in three patients with Philadelphia chromosome (Ph)‐positive acute lymphoblastic leukaemia (ALL), one with Ph‐positive acute myelogenous leukaemia (AML), and two with acute promyelocytic leukaemia (APL). Our two‐step PCR method employed ‘nested primers’ in the second step and can detect one leukaemic blast diluted into 10 6 HL‐60 cells. In three of four patients with Ph‐positive ALL and AML we detected leukaemic contamination in both PBSC harvests and BMMNC. In the remaining patient with ALL, both PBSC harvests and BMMNC were PCR‐negative. Both PBSC harvests and BMMNC from one patient with APL were PCR‐positive. In contrast, PBSC harvests from another patient with APL, whose BMMNC could not be obtained because of bone marrow necrosis, were PCR‐positive after the first course of consolidation chemotherapy, but became PCR‐negative after the second course. The present study does not support the hypothesis that PBSC harvests are less contaminated by leukaemic cells than BMMNC, but suggests that PBSC harvests are contaminated when BMMNC are contaminated.