Fludarabine Monophosphate Reduces the Incidence and Severity of Graft-Versus-Host Disease in a Murine Model of Bone Marrow Transplantation

To the Editor:

Fludarabine monophosphate is a purine analogue that has been extensively used in the past few years for the treatment of chronic lymphocytic leukemia (CLL) and low-grade non-Hodgkin's lymphoma in particular, with impressive success.1-4 Lately it has also been shown to be effective in combination with other drugs in acute leukemias.5,6 Fludarabine, like other purine analogues, has immunosuppressive activity, inducing long-lasting T-cell lymphopenia in patients when used in the treatment of CLL and other indolent B-cell disorders.7 In addition, isolated reports8,9 indicate that fludarabine, when administered to CLL patients as part of their primary therapy before allogeneic bone marrow transplantation (BMT), may also modulate the host immune system, thereby reducing the severity of graft-versus-host disease (GVHD) encountered in patients undergoing this treatment. Furthermore, transfusion-associated GVHD appears to be more frequent in fludarabine-treated patients, possibly because of the profound CD4⁺ and CD8⁺ T-cell depletion induced by the drug.10 The rare phenomenon of Coombs-positive autoimmune hemolytic anemia reported in CLL patients receiving fludarabine may also relate to fludarabine-induced imbalance of B- and T-cell subsets elicited in these patients.7 10-12 

Recently we examined whether fludarabine is effective in preventing, or modifying, acute GVHD after allogeneic BMT in mice. The experimental protocol was based on allogeneic BMT using C57BL/6 (C57 = marrow donors) and (BALB/C × C57BL/6) F1 (F1 = marrow recipients). The recipient mice were exposed to total body irradiation (750 cGy at 56 cGy/min) after which they received 10 × 10⁶ marrow cells supplemented with 2 × 10⁶ C57 spleen cells. Starting on day +1 fludarabine (0.025 mg/kg) was injected intraperitoneally (IP) twice weekly for 3 weeks. The BMT control mice received IP injections of normal saline according to the same time schedule. Note is made of the prime results. Thus, 2 weeks after transplant, survival of the fludarabine-treated mice and the controls amounted to 71% and 44%, respectively (P = .001, generalized Wilcoxon-Breslow test). Furthermore, no significant weight loss occurred in the mice receiving fludarabine.

Although donor T-cell depletion reduces the incidence of GVHD effectively and facilitates a decrease in the burden of post BMT immunosuppressive therapy, the procedure itself is linked with a higher rate of leukemia relapse and graft rejection.13 Therefore, it seems essential to search for agents that minimize GVHD and GVHD-associated morbidity and mortality. The observation that fludarabine induces unique immunosuppression, as expressed in CD4⁺ and CD8⁺ lymphopenia, immediately upon the first cycle of therapy and persisting after termination of the last treatment10 prompted us to investigate its effect within the context of marrow transplantation in a murine model. Our results indicate that fludarabine may be an immunosuppressive agent capable of ameliorating the severity of acute GVHD. The involvement of fludarabine in engraftment, graft rejection, and graft-versus-leukemia effect is now under investigation in our laboratory.