HEMATOPOIETIC-CELL TRANSPLANTATION IN THE TWITCHER MOUSE - THE EFFECTS OF PRETRANSPLANT CONDITIONING WITH GRADED DOSES OF BUSULFAN

The effects of congenic hematopoietic cell transplantation (HCT; trans plantation of bone marrow and spleen cells) after graded doses of busu lfan (BU), a myeloablative but nonimmunosuppressive alkylating agent, were evaluated in the twitcher mouse model of human galactosylceramida se deficiency, a demyelinating sphingo-lipid storage disease. C57BL/6 twitcher mice (immunophenotype Ly-5.1) were given 10 to 50 mg/kg of BU or total-body irradiation (9.0 Gy) at age nine days and HCT from cong enic Ly-5.2 donors 24 hr later. The 30-day post-HCT survival, an indic ator of tolerance of the preparative regimen, was at least 83% in twit cher mice given 45 mg/kg or less of BU, was 50% in recipients of 50 mg /kg BU and 75% in TBI-conditioned twitchers. The lifespan of twitcher mice given HCT after 10 or 20 mg/kg of BU was similar to that of untre ated twitchers (median survival, 42 days; range, 30-47). In contrast, mice transplanted after 35 to 50 mg/kg of BU had significantly prolong ed survival (median, 82 days; range, 56-208) and stabilization of hind limb paralysis, similar to TBI-conditioned recipients. Post-HCT repopu lation by donor Ly-5.2 cells was determined by flow cytometry. Thirty days after HCT, only 11-15% of lymphohematopoietic cells in blood, bon e marrow, and spleens were of Ly-5.2 donor origin in twitcher mice tra nsplanted after 10 mg/kg of BU but 60-80% were of Ly-5.2 donor origin in mice transplanted after higher doses of BU. These levels further in creased to 70-90% by 90 days after HCT, comparable to that seen after TBI. Levels of galactosylceramidase in livers, spleens, and brains of twitchers transplanted after 35-50 mg/kg of BU or after TBI increased to 30-116% of normal control values by 90 days after HCT. Conditioning for HCT with as little as 35 mg/kg of BU provides minimal peri-transp lant mortality, rapid and sustained establishment of donor lymphohemat opoiesis, replacement of lysosomal hydrolase, and prolonged survival i n this murine model of human sphingolipidosis.