Summary:reported. 8 To date, however, chimerism of CSF mononuclear cells after BMT has not been systematically studied. In this study we have evaluated donor-recipient To evaluate the chimeric status of mononuclear cells in the CSF after allogeneic BMT, cells were analyzed by chimerism on the CSF cells in pediatric ALL patients who underwent sex-mismatch allo-BMT with TBI regimens. FISH using satellite DNA probes for human X and Y chromosomes. CSF cells were obtained from five pediatric ALL patients who received BMT from sexmismatched donors. All patients received TBI-containPatients and methods ing conditioning regimens. We found that CSF cells showed complete donor type in 19-97 days after BMT,Patients' characteristics when complete donor type hematopoiesis was observed.Five patients with childhood ALL who underwent sexThe rapid entry of the donor leukocytes into the brain mismatched allo-BMT (four from siblings, and one from may exert beneficial effects to eradicate the residual an unrelated donor) were investigated ( Table 1). The CNS leukemic cells and prevent a CNS relapse in ALL median age at BMT was 2 years (range 1-9 years). All patients after BMT.patients were high-risk ALL; three patients had a MLL Keywords: chimerism; CSF; allo-BMT; FISH; TBI gene rearrangement, which was demonstrated either by Southern analysis or FISH, one had a Ph chromosome, and the remaining case had CNS relapse. Disease status before There has been considerable interest in the replacement of BMT was 2nd CR in two cases, 1st CR in one case, and host tissue leukocytes by donor cells after allogeneic BMT active disease in 1st relapse in two cases. (allo-BMT). There are several ways to detect donor-The conditioning regimens consisted of TBI 12 Gy/Bu recipient cell chimerism; cytogenetic markers, RBC anti-280 mg/m 2 /l-PAM 210 mg/m 2 for three cases, TBI gens, HLA type, and DNA polymorphisms. 1 The fluor-12 Gy/Ara-C 18 g/m 2 for one case, and TBI 12 Gy/CY escence in situ hybridization (FISH) technique, using sex 120 mg/kg for one case. The number of transfused bone chromosome-specific probes, is a simple and quantitative marrow cells was 3.4-9.0 × 10 8 /kg. GVHD prophylaxis way to detect mixed chimerism following sex-mismatched was CsA alone in two cases, and CsA and short course BMT, particularly in cases where small samples for exam-MTX in three cases. ination are available. Although there have been several Chromosome analysis on bone marrow cells was perforrefined studies on this issue, they were mostly carried out med with a routine G-banding technique or by FISH before, on peripheral blood cells, or bone marrow cells. [2][3][4][5] and 19-31 days after BMT. Recently, it was reported that there exists great disparity on the chimeric status between peripheral blood cells and FISH analysis on CSF mononuclear cells tissue leukocytes. 6,7 Twenty-five to 100% of alveolar macrophages were of recipient origin about a month after Repeat lumbar punctures were performed to examine CNS allo-BMT, and 25-40% of intestinal mucosal mononuclear...