EFFECTIVE MOBILIZATION OF PERIPHERAL-BLOOD PROGENITOR CELLS WITH DEXA-BEAM AND G-CSF - TIMING OF HARVESTING AND COMPOSITION OF THE LEUKAPHERESIS PRODUCT

The mini-BEAM regimen (BCNU, etoposide, cytarabine, melphalan) and its modification 'Dexa-BEAM' are effective salvage protocols for relapsed Hodgkin's disease and non-Hodgkin's lymphoma. Since many patients wit h relapsed lymphoma are eligible for high-dose chemotherapy with autol ogous stem cell rescue, we were interested in the suitability of these second line regimens for mobilising peripheral blood progenitor cells (PBPC). The kinetics of PBPC were studied in 15 patients treated with Dexa-BEAM and granulocyte colony-stimulating factor (G-CSF). Leukocyt es started to rise from <0.5 nL-1 on day 18 (16-22) after Dexa-BEAM, a nd exceeded 10 nL-1 on day 20 (18-28). Peripheral blood CFU-GM peaked on day 21 (19-28) and declined slowly thereafter; the median leukocyte count was 18.7 nL-1 (12.2-60) on the day of CFU-GM-peak. The maximum number of CFU-GM circulating in peripheral blood was inversely correla ted to the duration of leukopenia after Dexa-BEAM. Measurement of CD34 + cells with the monoclonal antibody 8G12-PE (HPCA-2) predicted the nu mber of CFU-GM precisely in both peripheral blood and leukapheresis pr oducts (r = 0.90-0.95). Two to six leukapheresis procedures yielded 6. 39 x 10(8) mononuclear cells kg-1 (1.82-13.49) containing 44.4 x 10(4) CFU-GM kg-1 (2.2-213.8). Immunophenotypical analysis revealed that th e percentage of CD19 + B cells was very low in all collection products (less than 1%). Nine patients were autografted with PBPC (15.4-213.8 x 10(4) CFU-GM kg-1) after myeloablative chemotherapy and experienced rapid and sustained engraftment (Platelets > 50 nL-1 on day +13 [9-22] ). We conclude that PBPC can be mobilised effectively by Dexa-BEAM plu s G-CSF. An adequate timing of PBPC collection (when the leukocyte cou nt has exceeded 10 nL-1) and evaluation of the progenitor content of t he leukapheresis products with 8G12-PE will allow to minimise the numb er of leukaphereses.