Myeloma cell contamination of peripheral blood stem cell grafts in patients with multiple myeloma treated by high-dose therapy.

In order to assess the contamination with malignant cells of peripheral blood stem cell (PBSC) transplants used to support high-dose therapy in multiple myeloma (MM), we used the immunoglobulin heavy chain gene radioactive fingerprinting polymerase chain reaction (PCR) method to detect clonal cells in PBSC from 10 patients. The sensitivity of the technique allowed the detection of one clonal cell among 10(4) normal blood mononuclear cells. A clonal band was detected in 4 of 11 leukaphereses samples. The level of contamination was low because a clonal band could never be identified on ethidium bromide-stained agarose gels whose sensitivity is between 1 and 5%. The use of granulocyte-colony stimulatory factor (G-CSF) in combination with chemotherapy in three cases did not seem to increase the contamination of PBSC grafts; in one patient, G-CSF was used during a second course of leukapheresis which was free of detectable clonal cells whereas the first one performed after chemotherapy alone contained clonal cells. Thus, PBSC grafts may rarely be completely devoid of clonal potentially malignant cells but the level of contamination is much lower than in BM grafts. Whether graft contamination is an important adverse prognostic factor for patients with MM undergoing intensive treatment and autografting is still unsettled.