CD34 POSITIVE PBPC EXPANDED EX-VIVO MAY NOT PROVIDE DURABLE ENGRAFTMENT FOLLOWING MYELOABLATIVE CHEMORADIOTHERAPY REGIMENS

We have previously demonstrated that CD34(+) cells, selected from peri pheral blood progenitor cells (PBPC), can be expanded in ex vivo cultu re and can be infused in tandem with unmanipulated PBPC with little or no toxicity, In this study, four patients (two non-Hodgkin's lymphoma (NHL), two multiple myeloma (MM)) received myeloablative conditioning prior to stem cell rescue using ex vivo expanded cells alone, The two patients with NHL received cyclophosphamide and total body irradiatio n (CY/TBI) and the two patients with MM, busulphan and melphalan (Bu/M ), One case received an inadequate CFU-GM dose, despite expansion, and in one case the expanded cells were contaminated, No definitive concl usions may therefore be drawn concerning engraftment in these two case s. However, the other two cases received high doses of committed proge nitors, Following infusion of the expanded material, all four patients failed to show sustained neutrophil engraftment and none showed evide nce of platelet engraftment, Back-up, unmanipulated PBPC were therefor e infused on days 14, 34, 32 and 28 and subsequently all four cases ac hieved satisfactory engraftment of both neutrophils and platelets, In conclusion, we feel that, CD34(+) cells, expanded ex vivo using the co nditions described in this report, may not provide durable engraftment following fully myeloablative conditioning.