LONG-TERM BONE-MARROW CULTURES IN APLASTIC-ANEMIA

The long-term bone marrow culture (LTBMC) system provides an in vitro physiological model for the study of stromal cell mediated haemopoiesi s in patients with aplastic anaemia. The two aspects of haemopoiesis - stromal and stem cell function - can be analysed separately using a m odification of LTBMC with cross-over studies. Patients with aplastic a naemia universally demonstrate defective stem cell function in terms o f reduced or absent marrow repopulating ability, reflecting a deficien cy of long-term culture initiating cells. Defects in stromal cell func tion, as assessed by the ability of aplastic anaemia stroma to support normal generation of haemopoietic progenitors, are not common, but ma y conceal an isolated deficiency of a particular growth factor in some patients due to the overlapping nature of haemopoietic growth factor activities. The stem cell abnormality in aplastic anaemia reflects a d eficiency in cell numbers, as well as dysfunction in certain cases. An increased level of apoptosis in aplastic anaemia marrow CD34(+) cells exists, and this correlates well with disease severity. LTBMC studies demonstrate that more of the haemopoietic cells are nonviable (apopto tic and dead) compared with normal controls, and this correlates with reduced colony (CFU-GM) generation. An increase in apoptosis among pri mitive haemopoietic cells may contribute to the stem cell defect in ap lastic anaemia. Haemopoietic growth factors such as G-CSF, when given after immunosuppressive therapy such as antilymphocyte globulin and cy closporin for aplastic anaemia, may act partly by reducing the increas ed level of apoptosis, resulting in improved stem cell survival.