T cell immune reconstitution after allogeneic bone marrow transplantation in bare lymphocyte syndrome

To study the impact of an MHC class II-negative environment on T cell immun e reconstitution, we have analyzed the phenotypical and functional characte ristics of FACS-sorted cultured CD4(+) and CD8(+) T cells in two Bare Lymph ocyte Syndrome (BLS) patients before and after allo-BMT. A similar analysis was performed in two MHC class II expressing pediatric leukemia patients a fter treatment with an allo-BMT who were included in our study as control. It: was observed that CD4(+) T cells displayed cytolytic alloreactivity in both BLS patients prior to and within the first year after allo-BMT, wherea s such cells mere absent at a later rime-point, in the donors and pediatric leukemia controls. In addition, reduced MWC class II expression was observ ed in CD8(+) T cells of both recipients early after allo-BMT, irrespective of the T cell chimerism pattern. Lack of endogenous MHC class II expression in BLS patients, therefore, results in aberrant T cell selection within th e first year after allo-BMT, analogous to T cell selection before transplan tation. These T cell selection processes seem to be normalized at a later t ime point after allo-BMT probably due to migration and integration of graft -derived MHC class II-positive antigen presenting cells to sites of T cell selection. Human Immunology 61, 898-907 (2000). (C) American Society for Hi stocompatibility and Immunogenetics, 2000. Published by Elsevier Science In c.