FATE OF CONTAMINATING T(14-18)(-CELLS DURING EX-VIVO EXPANSION OF CD34-SELECTED HEMATOPOIETIC PROGENITOR CELLS() LYMPHOMA)

The use of ex vivo expanded CD34-selected hematopoietic progenitor cel ls (HPCs) for autologous stem cell support or gene therapy is a major area of research and is likely to increase in the future. At present, little is known about the fate of contaminating malignant cells during ex vivo expansion of CD34-selected HPCs. We established a competitive polymerase chain reaction (PCR) titration assay to determine the numb er of residual lymphoma cells before and after selection and ex vivo e xpansion of CD34-selected HPCs in patients with t(14;18) translocation carrying non-Hodgkin's lymphoma, Seven bone marrow (BM) and 2 mobiliz ed peripheral blood progenitor cell samples from 8 patients without hi stologic BM involvement at the time of the harvest were analyzed by co mpetitive PCR titration assay and determined to contain between less t han or equal to 10 and 4,000 lymphoma cells/ 10(6) mononuclear cells ( MNCs). Immunoadsorption enriched CD34(+) cells from a mean of 5% (rang e, 1% to 9%) to a mean of 88% (range, 76% to 94%) of MNCs and resulted in a 1 to 4 log depletion of contaminating tumor cells, Two HPC sampl es became PCR negative after CD34 selection, whereas 7 samples still c ontained less than or equal to 10 to 200 residual lymphoma cells/10(6) MMCs. CD34-selected cells were consecutively expanded in suspension c ulture in the presence of stem cell factor, interleukin-1 beta (IL-1 b eta), IL-3, and IL-6. The mean increase of cells was 13-fold (range, 4 - to 22-fold) at day 7 and 65-fold (range, 43- to 110-fold) at day 14 of culture. Expansion resulted predominantly in myelomonocytic differe ntiation, whereas B-cell antigen-expressing cells became undetectable. Six of the seven PCR-positive CD34-selected samples became PCR-negati ve for the t(14; 18) translocation at day 7 and/or 14 of expansion. On e PCR-positive and one PCR-negative CD34-selected sample were PCR-posi tive after ex vivo expansion, but the number of residual lymphoma cell s remained at the limit of detection. We conclude that CD34 selection does not eliminate contaminating lymphoma cells in the majority of t(1 4;18)(+) HPC harvests. However, during ex vivo expansion of CD34-selec ted HPCs, residual t(14;18)(+) lymphoma cells do not proliferate and b ecome undetectable by PCR in the majority of cases. (C) 1996 by The Am erican Society of Hematology.