Aplastic anemia: lack of increase of in vitro colony formation after T cell depletion with monoclonal antibodies and complement.

To detect suppressor T cells to hematopoietic stem cells, growth of granulocyte-macrophage colony-forming cells (CFU-GM) and burst-forming unit (BFU-E) was compared before and after treatment of bone marrow cells with anti-T monoclonal antibodies and complement in 29 patients with aplastic anemia. The anti-T monoclonal antibodies used were 35.1 (CD2), Tp120 (CD6) and ATL27 (not clustered). Treatment of normal bone marrow with anti-T monoclonal antibodies and complement resulted in complete (greater than 99%) lysis of T cells with negligible effects on colony growth. Preincubation of marrow samples with monoclonal antibodies and complement did not enhance CFU-GM or BFU-E colony growth in patients with aplastic anemia. Using this assay, there was no evidence of T cell-mediated inhibition of colony proliferation in any of 29 patients.