CD34(+) selection of autologous peripheral blood stem cells for transplantation following sequential cycles of high-dose therapy and mobilisation in multiple myeloma

A potential problem of autologous transplantation in the treatment of multi ple myeloma (MM) is the infusion of tumor cells, CD34(+) selection has been used to purge autografts in MM and it is also possible to reduce tumour ce ll contamination of autografts by cytotoxic drug therapy prior to periphera l blood stem cell (PBSC) collection. To evaluate the effectiveness of a pro tocol combining multiple cycles of high-dose therapy and CD34(+) selection to reduce tumour contamination of PBSC autografts, 34 MM patients were ente red on a treatment schedule comprising two sequential cycles of mobilisatio n, CD34(+) selection, and transplantation following high-dose therapy. In t he second cycle of mobilisation there was a five-fold reduction in tumour c ontamination of the stem cell harvest (0.5 x 10(6)/kg) compared with the fi rst cycle (2.5 x 10(6)/kg). In the 97 CD34(+) selection procedures performe d a median of 185 x 10(8) mononuclear cells (R-INC) were processed yielding a median of 0.98 x 10(8) CD34(+)-enriched cells. CD34(+) cells were enrich ed 68-fold from 1.3% to 88.6%. The median yield of CD34(+) cells was 42.2%. Following CD34(+) selection the tumour cell contamination of the leukapher esis product was reduced by a median of 2.7 logs. This study demonstrates t hat in multiple myeloma a significant reduction ill the malignant contamina tion of stem cell autografts can be achieved by combining the in vivo purgi ng effect of cytotoxic therapy with in vitro purging by CD34(+) selection.