Contamination of hematopoietic stem cells (HSCs) with tumor cells has been associated with increased incidence of relapse in patients with non-Hodgkin's lymphoma following autologous HSC transplantation. Effective purging of tumor cells may improve the results of HSC transplantation, but current methods of purging are technically difficult to perform with large numbers of cells and do not consistently remove all detectable cells. We report a pilot clinical trial in which 10 patients with relapsed B-cell non-Hodgkin's lymphoma received high-dose chemotherapy followed by infusion of autologous HSCs depleted of B-cells by high-density microparticles (HDM) coated with anti-CD19 and anti-CD20 monoclonal antibodies (BCell-HDM). HSCs were mobilized with cyclophosphamide and granulocyte colony-stimulating factor. In 6 of the 10 patients, B-cells were detectable by immunocytochemical analysis of the apheresis products prior to treatment. Following treatment with the BCell-HDM, no B-cells were detected in the products from 5 of these patients, a result representing a median depletion of >2.2 logs (range, >0.4 to >5.1 logs). The median recovery of nontarget cells postdepletion was 73% for CD34 cells and 78% for CD3+ cells. All patients received high-dose cyclophosphamide, BCNU (carmustine), and etoposide prior to reinfusion of their B-cell-depleted autologous HSCs. The median number of CD34+ cells cryopreserved was 3.6 x 10(6) cells/kg (range, 2.2-10.1 x 10(6) cells/kg). Engraftment was rapid in all cases, with a median time to achieve an absolute neutrophil count of 0.5 x 10(9)/L of 10 days (range, 8-11 days). The median time to achieve a platelet count of 20 x 10(9)/L unsupported by platelet transfusion was 11.5 days (range, 8-17 days). This nonmagnetic negative-depletion technology is simple, rapid, and effective in depleting target cells to undetectable levels, with excellent recovery of nontarget cells.