Immune recovery and immunotherapy after stem cell transplantation in children.

Careful longitudinal studies of the lymphoid cell recovery after stem cell transplantation with other than HLA-identical sibling donors illustrated the prolonged T- and B-cellular immunodeficiency post-SCT, whereas NK-cell recovery was fast. Only low numbers of CD45RO memory T-cells, with a restricted TCR-repertoire, are present in the first 6 months post-SCT. The consequence is an increased risk of viral infections and possibly of leukemia relapse. The latter complication can be prevented by enhancing the anti-leukemic immune reactivity shortly after SCT. Different technical approaches were presented, the majority of them still being in the pre-clinical phase. NK-cell reactivity based on KIR-epitope mismatches between donor and recipient are promising for AML- and CML-, not for ALL-patients. The ALL-blasts may be killed by an antibody-dependent cellular cytotoxicity, using anti-CD19 antibodies, as was shown to be effective in vitro. Also the generation of leukemia-specific CTL's, making use of differences in minor histocompatibility antigens between donor and recipient, is now operational and may be a highly effective approach in a number of leukemic graft recipients.