A prospective study of positive/negative ex vivo B-cell depletion in patients with chronic lymphocytic leukemia

Objective. Autologous peripheral blood stem cell (PBSC) transplantation is increasingly being used in patients with chronic lymphocytic leukemia (CLL) . As the autografts are frequently contaminated with large numbers of tumor cells, we have prospectively investigated the feasibility and efficacy of ex vivo double purging of PBSC grafts in an open, nonrandomized, single-cen ter phase I/II clinical study. Materials and Methods. Twenty consecutive patients with poor-risk CLL under went uniform stem cell mobilization with chemotherapy and granulocyte colon y-stimulating factor (G-CSF). Double B-cell depletion of the harvested PBSC products was performed using immunomagnetic CD34(+) cell selection (Isolex 300i Nexell, Irvine, CA) followed by a negative step with anti-CD19/20/23/3 7-labeled immunomagnetic beads. The purified PBSC were reinfused after myel oablative treatment with TBI/CY. Results. A total of 25 separation runs was accomplished using collection pr oducts containing 3.4% (1.1-8.1) CD34(+) cells and 1.2% (0.1-42) CD19(+)CD5 (+) CLL cells. After double selection, 33% (15-67) CD34(+) cells were recov ered with a purity of 98.8% (89.1-99.8). CLL cells were undetectable by hig h-resolution flow cytometry in 15 of 25 final products; median purging effi cacy was 5 (4.1-6) log. The CD34(+) content of the 20 final grafts was 4.6 (2.2-6.5) x 10(6)/kg. Rapid and durable engraftment developed in all cases. With a median follow-up of 20 (6-29) months, 17 patients live in complete clinical remission, two have recurrent disease, and one patient died due to pulmonary embolism five months after transplant. Persistence of the leukem ic clone on the molecular level was demonstrated by dot blotting with clone -specific CDR3 probes in an additional five patients. Serious or unexpected infectious complications did not occur. Conclusions. Positive/negative purging with the Isolex system allows prepar ation of highly purified CD34(+) fractions and up to six log of tumor cell depletion in patients with B-CLL and can be safety reinfused after myeloabl ative therapy without affecting hematopoietic engraftment. (C) 2000 Interna tional Society for Experimental Hematology. Published by Elsevier Science I nc.