POSITIVE SELECTION OF HEMATOPOIETIC CD34(-CELLS PROVIDES INDIRECT PURGING OF CD34(-) LYMPHOID-CELLS AND THE PURGING EFFICIENCY IS INCREASEDBY ANTI-CD2 AND ANTI-CD30 IMMUNOTOXINS() STEM)

Human CD34(+) hematopoietic cells were purified using the avidin-bioti n immunoabsorption technique. The selected population showed 78.6 +/- 3% CD34(+) cells and the overall recovery of CD34(+) cells, CFU-GM and BFU-E from the starting population was 34 +/- 5%, 71 +/- 4% and 67 +/ - 2% respectively. Hematopoietic progenitor cell purification also res ulted in 3 log of normal T cell depletion from the bone marrow (BM) by immunofluorescence analysis. Moreover, when unseparated BM cells were mixed with the CD34(-) lymphoma cell lines D430B and Raji, the remova l of greater than 3 log of tumor cells from the enriched CD34(+) cell fraction was demonstrated. To increase the neoplastic cell purging, se veral immunotoxins (IT) containing the ribosome-inactivating protein ( RIP) saporin and directed toward the lymphoid-associated antigens CD30 and CD2 were prepared. Our experiments showed only a minimal toxicity of the immunoconjugates on colony-forming cells (CFC) derived from pu rified CD34(+) cells. Conversely, all the ITs were very effective in i nhibiting protein synthesis and growth of normal and neoplastic lympho id cells. Further experiments demonstrated that the sequential combina tion of CD34(+) cells purification and IT treatment resulted in 5 or m ore log of tumor cell purging with no additional loss of BM progenitor cells.