CONDITIONING THE LEUKEMIC PATIENT BEFORE ALLOGENEIC BMT - VALUE OF INTENSIFYING IMMUNOSUPPRESSION IN THE CONTEXT OF DIFFERENT LEVELS OF T-LYMPHOCYTE DEPLETION OF THE GRAFT

We have studied the value of additional immune suppression in BMT cond itioning regimens in 45 patients with leukemia and 4 with myelodysplas tic syndrome allografted between 1984 and 1991. A dose of 6 Gy total l ymphoid irradiation (TLI) was delivered to 12 of 24 and 15 of 25 patie nts conditioned with 10 Gy and 12 Gy total body irradiation (TBI), res pectively. Thirteen patients also received methylprednisolone (MP) bef ore BMT to enhance immunosuppression. Differences in immunosuppression between the TBI with or without TLI or MP regimens and the influence of different levels of graft T cell depletion were measured in terms o f transplant rejection, and complete versus mixed chimerism. The treat ment-related complications were evaluated in terms of GVHD and inciden ce of pneumonitis. The overall transplant rejection rate was 6% (3 of 49). Complete chimerism was not significantly modified by increasing t he TBI dose or by additional TLI (p > 0.10) but was more often seen in patients receiving MP given as pre-transplant immunosuppressor booste r (p = 0.01). The incidence of GVHD was only influenced by the level o f T cell depletion (p = 0.003). All 49 patients received a TBI lung do se in the range 9.5-10 Gy. A crude pneumonitis range of 19% (9 of 47 e valuable patients) was found. Neither the addition of TLI, MP nor the T cell depletion influenced the lung toxicity rate (p > 0.10) but pneu monitis was more frequent in patients with GVHD (p = 0.005).