How reliable are in vitro clonal cultures? Some comments based on hemopoietic cultures.

Clonal cultures in semisolid medium have proved invaluable in analyzing hemopoietic subpopulations and in detecting their specific growth regulators. However, they can be subject to certain deficiencies that an investigator must take care to exclude. These include inabilities of the particular culture system to detect the true stem cells under study or to allow self-generation of clonogenic cells or a full expression of their differentiation potential. Clonal cultures, like conventional cultures, can be subject to significant cell-cell interactions, complicating attempts to characterize the action of a test regulatory molecule. Culture data need to be supplemented by a variety of other data before they can be regarded as valid evidence that a regulatory molecule detected in vitro is likely to function in a similar manner in vivo.