Feeder-free and serum-free in vitro assay for measuring the effect of drugs on acute and chronic myeloid leukemia stem/progenitor cells.

Research on chronic and acute myeloid leukemia (CML/AML) is focused on the development of novel therapeutic strategies to eliminate leukemic stem/progenitor cells that are responsible for drug resistance and disease relapse. Methods to culture hematopoietic stem/progenitor cells (HSPCs) from blood or bone marrow samples are indispensable for investigating disease pathogenesis and delineating drug responses in individual patients. A key challenge in this area is that primary leukemic cells grow poorly in culture or rapidly differentiate and lose their hematopoietic potential. Access to patient samples can also be limiting or cell numbers too low to enable large-scale assays and/or to obtain reproducible quantitative data. Here we describe a feeder cell-free and serum-free liquid culture system for the expansion of CD34+ HSPCs from CML/AML samples and healthy control tissues. Following 7 or 14 days of culture, CD34+ cells are expanded 30- to 65-fold or 400- to 800-fold, yielding a purity of ∼80% and ∼60% CD34+ cells, respectively. This system was adapted to a 96-well format to measure the sensitivity of leukemic and normal HSPCs to cytotoxic drugs after only 7 days. The assay requires only 103 cells per well to determine drug IC50 values and can be performed with uncultured and culture-expanded cells. Importantly, resulting IC50 values strongly correlate with those obtained in the classic colony-forming unit (CFU) assay. Compared with the CFU assay, this novel 96-well liquid-based assay designed specifically for leukemic and normal HSPCs is faster and simpler, with more flexible readout methods for selecting candidates for further drug development.