Residual clonable host cell detection for predicting engraftment of T cell depleted BMTs

Rejection of T-depleted BMTs is predominantly mediated by alloreactive host T cells. A low but significant number of radiochemoresistant clonable T cells can be detected following a conventional cytoreductive protocol given prior to T-depleted BMT. Elimination of these cells increases the engraftment rate. We found no clonable T cells at the end of the conditioning regimen in 100 ml of peripheral blood from 47 patients who received an HLA-identical T-depleted BMT. None rejected the graft and none displayed mixed chimerism. In addition, although no clonable T cells were detected in nine patients who received a mismatched BMT, two rejected their graft. However, in three mismatched patients, who for clinical reasons received a modified pre-BMT schedule, the presence of host clonable T cells was associated with immunological rejection. These findings suggest that the detection of clonable T cells should prove a valuable indicator for optimising immunosuppression prior to T-depleted BMT.