Introduction

Treatment of patients with aplastic anemia aims to improve peripheral blood counts so that the patients no longer require transfusions and are not at risk of opportunistic infections. In contrast to bone marrow transplantation, where the defective organ is replaced by healthy marrow, immunosuppressive treatment will not cure the disease but rather aims to eliminate the ‘autoaggressive’ cells responsible for the aplastic marrow resulting in pancytopenia. Today, immunosuppressive regimens for aplastic anemia include antilymphocyte globulin (ALG) and cyclosporin. In the present chapter the term ALG is used for all antilymphocyte serums, antilymphocyte and antithymocyte globulin (ATG). The use of ALG goes back to Mathé's early studies. He used ALG as a conditioning regimen before marrow infusion for four accidentally irradiated patients (Mathé et al., 1970). Although no engraftment was observed, two of the four patients survived, presenting with autologous regeneration of hemopoiesis. Similar observations were made by Speck and Kissling, in a study of rabbits with benzene-induced aplasia (Speck and Kissling, 1971). Control animals died, whereas animals treated with ALG and infusion of HLA-haploidentical marrow recovered autologous bone marrow function. These observations clearly indicate that ALG alone is not sufficient to allow engraftment of allogeneic marrow. Nevertheless, recovery of hemopoiesis seemed possible after treatment with ALG. The evidence that autologous reconstitution can occur under experimental and clinical circumstances uncovered new possibilities for treating patients with aplastic anemia.