New Process for Depleting B Cells for Transplant in NHL

NEW ORLEANS—A nonmagnetic method of depleting B cells during purging before autologous peripheral blood stem cell (PBSC) transplantation greatly decreases the nonspecific cell loss that can occur when cells cross a magnet, as in other techniques. The nonmagnetic method is also simple and quick, John Gribben, MD, of Dana-Farber Cancer Institute, said at the 41^st annual meeting of the American Society of Hematology.

Among patients with non-Hodgkin’s lymphoma (NHL), contamination of stem cells with residual tumor has been associated with a high incidence of relapse following autologous PBSC transplantation. Effective purging of tumor cells may improve the results of transplantation, but current methods are technically difficult to perform with large numbers of cells and do not consistently remove all detectable tumor cells, Dr. Gribben explained.

In the new technique, cells are depleted using Eligix High-Density Micropar-ticles (Eligix, Inc., Medford, Mass) coated with anti-CD19 and anti-CD20 monoclonal antibodies in a gravity-mediated system.

4-Log Depletion of B Cells

After being rotated for 5 to 10 minutes, target cells expressing these antigens bind to the microparticle beads and then separate from the other cells. This process is repeated several times and results in a 4-log or greater depletion of B cells and more than 90% recovery of CD34+ cells, Dr. Gribben said.

The phase I trial evaluated engraftment and toxicity after infusion of PBSCs purged in this manner. The study involved nine patients with relapsed B-cell non-Hodgkin’s lymphoma receiving high-dose chemotherapy followed by infusion of autologous PBSCs depleted of B cells.

To be eligible, patients had to be in complete or partial remission, with less than 20% bone marrow involvement. Median age was 50.

The median yield of nontarget cells postdepletion was 84% for CD34+ cells. Following depletion, there was an 82% recovery of CD34+ cells and 81% recovery of CD3+ cells. The median number of CD34+ cells cryopreserved was 3.6 × 106/kg.

Depletion in CD19+ and CD20+ B cells, as assessed by immunocytochemistry, was by more than 2 logs. “B cells were detected in relatively small numbers in patients and were not detected at all in the PBSCs of six patients,” Dr. Gribben observed.

Treatment of PBSCs with the micro-particles was not associated with a delay in engraftment. The median time to neutrophil counts of 500/µL was 10 days. The median day to achieve a platelet count of 20,000/µL unsupported by platelet transfusions was 12. Some mild infusional toxicity occurred, he said.

The investigators concluded that this treatment does not result in a delay to platelet or neutrophil engraftment, there is no significant purging of nontarget cells, and depletion of target cells occurs below the level of detection. A randomized trial is now being planned, he said.