Demonstration of donor origin of CD34+ HLA-DR- bone marrow cells after allogeneic peripheral blood transplantation with a long follow-up.

Peripheral blood progenitor cells (PBPC) are increasingly being used to perform allogeneic transplants (allo-PBPCT). An important issue regarding allo-PBPCT is the potential for long-term engraftment of human PBPC. A subset of bone marrow (BM) cells displaying the immunophenotype CD34+ HLA-DR- has functional properties associated with pluripotential stem cells. We studied the origin (donor vs recipient) of CD34+ HLA-DR- hematopoietic cells from patients having received allo-PBPCT and with a long follow-up (14+ to 21+ months). Chimeric status was determined after amplification by polymerase chain reaction (PCR) of short tandem repeat sequences (PCR-STR). Four patients (acute myeloid leukemia (n = 3), acute lymphoid leukemia (n = 1) were studied. CD34+ HLA-DR- cells from bone marrow aspirates were isolated by flow cytometry cell sorting. The mean percentage of CD34+ cells among the total nucleated BM cells from the four patients was 0.6+/-0.2% (mean +/- s.d.) (range, 0.31-1.27%). The CD34+ HLA-DR- cells accounted for 1.54+/-0.54 (range, 0.9-2.05%) of the CD34+ BM cells. The purity of the CD34+ HLA-DR- cells analyzed after sorting was higher than 94% in all sorted fractions. PCR-STR of these cells showed donor origin in all patients. The origin of CD34+ HLA-DR- bone marrow cells in patients treated with allo-PBPCT has not so far been analyzed. These results provide further evidence that G-CSF-mobilized PBPC contains cells which are capable of sustained long-term engraftment.