| The effect of nonmyeloablative procedures on the pace of post-transplant immune reconstitution is unknown. The aim of this work was to investigate the immune status of patients with leukemia following non-myeloablative allogeneic peripheral blood stem cell transplantation (NST). Ten adult underwent NST from HLA-identical (n=8) or part of antigen-matched sibling donors were enrolled in the study. Patients were analyzed 1, 3 and 12 months after transplant. Recovery of T-, B-, and NK-lymphocyte subsets, immunoglobulin levels, proliferative in vitro response to mitogens, as well as cytotoxic activities, was investigated.Results demostrated that the absolute number of CD3+and CD8+T cells, B lymphocytes, as well as the proliferative response to T-cell mitogens, recovered with time after transplantation.CD8+T cell and B cell recovered to the normal range by 3 months.CD4+T cell counts remained below normal up to 1 year after transplantation. Recovery of NK cell number and innate cytotoxic activities was fast. IgG and IgM levels were within normal range at 1 month post transplant. We suggest the different behavior inthe immune reconstitution of CDS subset after NST may be favored by an extrathymic origin of these cells, while CD44 subset recovery which is thymus-dependent is impaired in adult population. We conclude that stem cell engraftment following nonmyeloablative conditioning may result in early immune reconstitution. We speculate that NST may lead to faster development of effective immune responses against residual host-type malignant and abnormal non-malignant hematopoietic cells.
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