COLLECTION, TUMOR CONTAMINATION, AND ENGRAFTMENT KINETICS OF HIGHLY PURIFIED HEMATOPOIETIC PROGENITOR CELLS TO SUPPORT HIGH-DOSE THERAPY INMULTIPLE-MYELOMA

Unfractionated peripheral blood stem cell (PBSC) grafts contain measur able quantities of myeloma cells and are therefore a potential source of relapse posttransplantation. In contrast, fluorescence-activated ce ll sorting (FACS)-sorted CD34(+) Thy(1)(+) Lin(-) peripheral blood cel ls are substantially enriched for stem cell activity, yet contain virt ually no clonal myeloma cells. A study was performed in patients with symptomatic myeloma, who had received 12 months or less of preceding s tandard chemotherapy, to evaluate the feasibility of large scale purif ication of primitive hematopoietic stem cells in order to study engraf tment kinetics posttransplantation and the degree of tumor cell contam ination of this cell population, based on polymerase chain reaction (P CR) analysis for the patient-specific complementarity-determining regi on III (CDR III). PBSC were mobilized with high dose cyclophosphamide and granulocyte-macrophage colonystimulating factor (GM-CSF). A combin ation of elutriation and chemical lysis was used to deplete PBSC colle ctions of monocytes, granulocytes, erythrocytes, and platelets. Subseq uently, CD34(+) Thy(1)(+) Lin-progenitor cells were purified with high speed cell sorting. Of the 10 evaluable patients, nine met the requir ed minimum criteria of greater than or equal to 7.2 x 10(5) cells/kg t o support tandem transplants. After high dose melphalan (200 mg/m(2)) eight engrafted successfully, although granulocyte (absolute neutrophi l count [ANC] >0.5 x 10(9)/L, 16 days) and platelet recovery (platelet s > 50 x 10(9)/L, 39 days) was substantially delayed when compared wit h unmanipulated PBSC grafts; one patient required infusion of a reserv e graft because of lack of evidence of engraftment by day +28. Three p atients proceeded to a second graft with high dose melphalan and total body irradiation; two required infusion of a reserve graft and both d ied of infectious complications; one showed delayed, but complete, eng raftment after this myeloablative regimen. Two of the nine evaluable p atients attained a clinical complete remission (CR). The grafts from t hree patients were tested for tumor contamination and contained no det ectable clonal myeloma cells. Larger quantities of purified cells may be required to resolve the problem of delayed engraftment. (C) 1998 by The American Society of Hematology.