Growth kinetics and blast-colony forming cell binding capacity of aplastic anaemic stromal cells.

The kinetics of bone marrow cell growth and a special function of stromal cells (the capability of binding blast colony forming cells) were studied in patients with aplastic anaemia (AA). All 10 patients studied showed faster growth of bone marrow stromal cells. The time for a confluent stromal layer formation was 24.5 days for AA bone marrow as opposed to 33.0 days for normal bone marrow. This faster growth rate could also be observed if normal bone marrow cells, depleted of plastic non-adherent fraction, were plated, suggesting that at least one of the reasons for altered stromal cell growth kinetics in AA is the changes in the ratio of plastic adherent/non-adherent cells. Functionally, i.e. in supporting the growth of normal bone marrow blast colonies, AA stromal layers did not differ from that of normal stromal layers, independently of the clinical state of the disease (AA or SAA; in one patient before or after ATG treatment; in two patients after successful allogenic bone marrow transplantation). Moreover, in some AA patients this blast colony forming cell binding function of AA stromal layers could also be detected in samples cultured without hydrocortisone (i.e. in the absence of fat cells), suggesting that AA stroma also differs qualitatively from normal stroma without inducing a defective microenvironment for stem cell homing.