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-center phase I/II clinical study.
Materials and methods: Twenty consecutive patients with poor-risk CLL underwent uniform stem cell mobilization with chemotherapy and granulocyte colony-stimulating factor (G-CSF). Double B-cell depletion of the harvested PBSC products was performed using immunomagnetic CD34(+) cell selection (Isolex300i Nexell, Irvine, CA) followed by a negative step with anti-CD19/20/23/37-labeled immunomagnetic beads. The purified PBSC were reinfused after myeloablative treatment with TBI/CY.
Results: A total of 25 separation runs was accomplished using collection products 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 recovered with a purity of 98.8% (89.1-99. 8). CLL cells were undetectable by high-resolution flow cytometry in 15 of 25 final products; median purging efficacy 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 leukemic 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 preparation 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 myeloablative therapy without affecting hematopoietic engraftment.