The so-called hematopoietic stem cells from mouse and human bone marrow can be induced in vitro to form colonies, provided that the appropriate hormones (colony stimulating factors, CSFs) and culture conditions have been selected. Such hematopoietic colony cultures are of interest for in vitro cytotoxicity testing of a great number of drugs. In fact, it has been increasingly recognized that serious side effects of many drugs involve injury to hematopoietic organs. Moreover, several hormones and inhibitors (including chalones) that regulate hematopoiesis have attracted clinical interest and their identity can be determined by such in vitro cultures. Therefore hematopoietic stem cells seem to provide identified targets to assay for either stimulatory, inhibitory, or cytotoxic drug effects.
