Absence of a CD34(-) hematopoietic precursor population in recipients of CD34(+) stem cell transplantation

The purified CD34(+) cell fraction has been used for hematopoietic stem cel l transplantation since they were demonstrated to have long-term reconstitu ting ability. Therefore, the potential effects of CD34(-) stem cells on the clinical course have been a major concern in recipients of CD34(+)-selecte d transplantation. To address this concern, we used an in vitro assay to de termine whether transplant recipients have CD34- precursor population. Lin( -)CD34(-) cells were isolated from bone marrow cells in 11 transplant recip ients including four CD34-selected transplantations, six standard bone marr ow transplantations, and one T cell-depleted marrow transplantation. The fr equency of the Lin-CD34- population in four CD34-enriched transplantation r ecipients was not different from those of normal donors or recipients of ot her modes of transplantation: 0.96 +/- 1.01% (mean +/- s.d., n = 4), 0.45 /- 0.16% (n = 6), and 0.66 +/- 0.59% (n = 7), respectively. However, the Li n-CD34- population obtained from the recipients of CD34-enriched transplant ation acquired neither CD34 expression nor colony-forming activity after 7 days of culture, whereas the cells from all the normal individuals and stan dard BMT recipients were able to differentiate into CD34+ cells accompanied by the emergence of colony-forming activity. We conclude that recipients o f CD34-enriched transplantation appear to have defects in their CD34(-) pre cursor population. The clinical significance of these defects will be deter mined in a life-long follow-up of these patients.