• immune reconstitution;
  • haploidentical;
  • CD34+ stem cell transplantation;
  • T-cell repertoire diversity;
  • CDR3 size spectratyping

Transplantation of haematopoietic stem cells from human leucocyte antigen (HLA)-disparate parental donors presents a promising new approach for the treatment of patients lacking a HLA-matched donor. Success against major obstacles such as graft-versus-host disease (GvHD) and graft rejection has recently been demonstrated, so that immune reconstitution is one of the prime factors that determines the long-term prognosis following transplantation. Twenty children transplanted with megadoses of highly purified CD34+ haematopoietic stem cells after rigorous T-cell depletion were prospectively monitored for their immune reconstitution during the first post-transplant year. Natural killer (NK) cells showed a marked increase on d +30. T and B cells began to reconstitute on d +72 and +68 respectively. During extended follow-up, their numbers and proliferative capacity upon mitogen stimulation continually increased. Early reconstituting T cells were predominantly of a primed, activated phenotype with severely skewed T-cell receptor (TCR)-repertoire complexity. Naive T cells emerged 6 months post transplantation, paralleled by an increase in TCR-repertoire diversity. All patients self-maintained sufficient immunoglobulin levels after d +200. This study demonstrates that paediatric recipients of highly purified, haploidentical stem cells are able to reconstitute functioning T-, B- and NK-cell compartments within the first post-transplant year. This, together with the absence of significant GvHD, provides a strong indication for this approach to be considered in children who lack a HLA-matched donor.