Double T cell depletion of bone marrow using sequential positive and negative cell immunoaffinity or CD34+ cell selection followed by Campath-1M;: effect on CD34+ cells and progenitor cell recoveries

An advantage of CD34(+) cell selection over antibody purging is that a component allograft is produced comprising a stem cell enriched and an unadsorbed fraction, the latter containing T cells which may be used for posttransplant immunotherapy. Initial reports with PBSC allografts suggested that T cell depletion (TCD) by CD34(+) cell selection and post-graft cyclosporin A +/- methotrexate was insufficient prophylaxis against acute GVHD, We compared sequential TCD (of a CD34(+) cell-selected fraction) using a second (CD2) immunoaffinity step or Campath-1M monoclonal antibody and complement, Since a high stem cell 'dose' enhances engraftment across HLA barriers and improves overall post-transplant outcome, the recovery of CD34(+) cells and progenitors were assessed. Sequential positive (CD34(+)) and negative (CD2+) immunoaffinity selection resulted in a 3.4 log depletion of T cells as compared to a 4.05 log depletion when CD34(+) cell selection was followed by Campath-1M treatment, Recoveries of CD34(+) cells, CFU-GM and BFU-E following double depletion using CD34(+) cell selection plus CD2+ cell depletion were 28, 25 and 17% as compared to 20, 18 and 16% when CD34(+) cells were treated with Campath-1M. The unadsorbed fraction contained 85% of the original T cells, from which donor leukocyte infusions in the range of 10(5) to 10(7) CD3+ cells per kg body weight of the recipient were harvested. Despite the advantages of component allografts, the loss of stem/progenitor cells may restrict sequential TCD steps unless single BM harvests are supplemented and/or replaced with mobilised PBSCs.