The assessment of the hemopoietic reservoir after immunosuppressive therapy (is) or bone marrow transplantation (bmt) in severe aplastic anemia

We investigated the naemopoietic reservoir in 43 Severe Aplastic Anemia (SAA) patients following immunosuppression (IS) (n=15) or bone marrow transplantation (BMT) (n=28), at a median interval of 5 years (range 2-20} from treatment All patients had normal blood counts, good marrow cellularity and normal numbers of colony forming unit-granulo macrophages (CFU-GM), Burst forming unit-erythroid (BFU-E) and colony forming unit-granuio erythroid megakanocyte macrophages (CFU-GEMM) numbers were reduced when compared to normal controls. However, the most pronounced defect was observed at the level of long term cultureinitiating cells (LTC-IC) which significantly differed from controls (p<0 00001) both for IS and BMT patients Their number did not improve with time and was not affected by transplant or treatment-related variables. When IS patients were compared to BMT we found comparable numbers of CFU-GEMM (p=0.8) and LTC-IC (p=0 9) but lower numbers of BFU-E and CFU-GM (p=0 05 and p=0 004 respectively), suggestive of a persistent suppressive mechanism These data indicate that LTC-IC numbers are severely reduced in BMT and IS patients, contradicting the common believe that the former are fully reconstituted as compared to the latter In addition, the number of mature cells and committed progenitors does not seem to reflect the real size of the haemopoietic reservoir and few stem cells may be sufficient to guarantee normal haemopoiesis long term.