Expansion of haematopoietic stem cells in vitro: a challenge to stem cell biologists

Expansion of haematopoietic stem cells from various sources has gained importance so as to provide a clinically potential graft, which shows ideal growth kinetics, resulting in reduction of the period of neutropenia and thrombocytopenia in any autologous or allogenic transplant setting. Expansion also facilitates transduction of genes for gene therapy. This review examines the various means employed to achieve the expansion of stem cells, and the criteria used to score the extent of expansion based on how stem cells are identified. It tries to analyse the ideal manner in which expansion should be carried out, with emphasis that expansion should not be at the expense of loss of stemness. It also attempts to judge the roles played by the stromal elements and cytokines, which are both part of the complex microenvironment, which in vivo has a strict regulation on haematopoiesis.