Unfractionated peripheral blood stem cell autografts and CD34(+)-enriched autografts have similar long-term culture initiating capacity in multiple myeloma

CD34+-enriched peripheral blood stem cells (PBSC) are increasingly being us ed as an autograft in patients with multiple myeloma (MM). The rationale fo r the use of the CD34+-enriched fraction in MM is the ability to obtain a g raft with a significant reduction of contamination by plasma cells. However , the effect of such a manipulation on the proliferating potential of the e ngrafted cells is not known. We wished to study, as part of a randomized tr ial comparing the outcome in MM patients transplanted with either CD34+-enr iched cells or unfractionated PBSC, the primitive hematopoietic cell conten t of the autografts using longterm culture initiating cell (LTC-IC) assays in 7 MM patients. In 3 patients CD34+cell-enriched fraction was compared to unfractionated PBSC whereas in the remaining 4 patients the LTC-IC assay w as performed on total PBSC. The mean percentage of CD34+ cells of the CD34 selected fraction in three patients was 82% (range 71%-96%) whereas the sa me percentage in PBSC varied from 0.6% to 10% in 4 patients (mean: 4.2%). O ut of three patients transplanted with CD34+ cell fraction, two patients we re found to have a very similar LTC-IC generating potential in their CD34versus PBSC fractions as this was assessed by the clonogenic cell output at week+5 per 10(4) CD34+ cells initiating the culture (PBSC: 92 and 168 and CD34+ fraction: 102 and 16(1), respectively) whereas one patient had a slig htly different values (PBSC: 51 and CD34+ fraction: 103). When the PBSC fra ction was compared in all 7 patients, the LTC-IC generation potential was v ery heterogenous, varying from 1.4 to 168. To determine if the selection pr ocedure influences the numbers of LTC-IC's in both fractions, we have perfo rmed limiting dilution assays to determine both the frequency of distributi on of hematopoietic colonies and the frequency of LTC-IC's in two patients. The frequency of distribution of hematopoietic colonies was linear in both CD34+ and PBSC fractions as was the frequency of LTC-IC when the correctio ns were made with regard to the CD34+ cell-content of the cultures (1/20). Our results indicate that the CD34+ selection procedure used in all three p atients (Ceprate) is not deleterious for the generation of LTC-IC's and the se findings support the rationale for the use of this procedure in multiple myeloma for the purposes of tumor depletion.