GCT-conditioned medium: an unsuitable stimulus for monitoring granulocyte--macrophage colony-forming cells in cryopreserved bone marrow.

Assays of granulocyte-macrophage colony-forming cells provide a means of testing the viability of cryopreserved bone marrow cells intended for autologous transplantation. We have compared two different sources of granulocyte-macrophage colony-stimulating activity, giant cell tumor-conditioned medium (GCT-CM) and peripheral blood leukocyte feeder layers, to determine whether the former is a suitable substitute for leukocyte feeder layers in the assay. The results show that GCT-CM, while providing a comparable stimulus to that provided by leukocyte feeder layers for colony formation by fresh bone marrow samples, is an inadequate stimulus when cryopreserved bone marrow samples are cultured. GCT-CM is not therefore suitable for use in monitoring cryopreserved bone marrow, since there is gross underestimation of the number of colony-forming cells present when this stimulus is used. The results suggest that great care should be taken when selecting alternative sources of granulocyte-macrophage colony-stimulating activity for culture of cryopreserved material.