CD34 SELECTIONS FROM MYELOMA PERIPHERAL-BLOOD CELL AUTOGRAFTS CONTAINRESIDUAL TUMOR-CELLS DUE TO IMPURITY, NOT TO CD34(+) MYELOMA CELLS

Malignant cells in haemopoietic autografts can contribute to post-tran splant relapse. Engraftment of myeloma patients with CD34(+) periphera l blood progenitors selected from total autografts reduces the number of tumour cells infused by 2.7-4.5 logs. Residual tumour cells detecte d in CD34(+) selected cells map be due to selection impurity or the ex istence of malignant CD34(+) progenitors, In three patients we evaluat ed the CD34 purity and tumour load of total autografts, CD34(+) progen itors selected with immunomagnetic beads and highly purified CD34(+) p rogenitors obtained in two rounds of selection (combining magnetic wit h now cytometry activated cell sorting) to determine the cause of resi dual tumour cells in CD34 selections. Using allele-specific oligonucle otides (ASO) complementary to the unique Ig heavy chain sequence (CDRI II region) of the malignant clone, semi-quantitative, ASO-PCR was capa ble of detecting one malignant cell in 10(4)-10(5) normal white blood cells. Selection of CD34(+) cells from bone marrow (BM) with approxima tely 20% malignant plasma cells resulted in a 1.4 log reduction of tum our burden, Using two-colour now-cytometry we observed CD34(-), BB4(+) malignant plasma cells contaminating this CD34 selection. Prior to so rting, peripheral blood cell autografts (PBCA) contained approximately 0.1% malignant cells. Selection of >99% pure CD34(+) cells using immu nomagnetic beads (Dynal) resulted in an approximate 2 log reduction of malignant cells, but residual tumour cells were still detectable. ASO -PCR detected no malignant cells in >99.9% pure CD34(+) peripheral blo od progenitors obtained with two rounds of selection (combining magnet ic with flow cytometry activated cell sorting). We conclude that CD34( +) malignant cells are not detectable in myeloma PBCA and that residua l tumour cells in CD34 selections are due to contaminating CD34-negati ve cells.