Peripheral blood monoclonal B-cells predict the event free survival in multiple myeloma

Reinfusion of myeloma progenitor cells may contribute to relapse of multipl e myeloma after autologous stem cell transplantation. The aim of our study was to investigate whether monoclonal B-cells are present in the apheresis product and to evaluate the clinical relevance of these cells. Leukapheresi s products of 55 patients were purged with anti-B-cell-Monoclonal antibodie s (MoAbs) and immunobeads. Monoclonal B-cells were found in 85% of patients within the B-cell population. In one third of all myeloma patients, the ma jority of B-cells was represented by monoclonal myeloma progenitor B-cells, whereas in two thirds of patients monoclonal cells only represented a smal l part of the entire B-cell population. As shown by sequence analysis, mono clonal precursor B-cells and malignant plasma cells had the identical genet ic CDR III sequence. The purging efficacy. using a negative selection syste m, was a median of 3 logs (range 1,5-3,5). No statistical difference in the purging efficacy was found when 3. 4 or 5 MoAbs against B-cells antigens w ere used. However, a tumor specific signal could be detected in the purged harvest of all patients. when the highly sensitive ASO-PCR approach was use d. Furthermore, we found a direct correlation between the amount of remaini ng monoclonal cells after negative selection and the event free survival of myeloma patients. 10/15 patients with a median of 30 x 10(3) monoclonal ce lls in the purged product relapsed at a median of 1,4 years. whereas only 6 /24 patients with an oligoclonal pattern including a low number of remainin g monoclonal cells relapsed at a median of 2,2 years. The event free surviv al (EFS) was statistically different between the two groups (p = 0.014).