Comparison of donor chimerism following myeloablative and nonmyeloablative allogeneic hematopoietic SCT.

Surveillance of hematopoietic chimerism following hematopoietic SCT (HSCT) with nonmyeloablative (NMA) preparative regimens is standard to assess the need for clinical intervention. Monitoring of donor chimerism following HSCT with myeloablative (MA) preparative regimens is, however, not considered useful because engraftment is thought to occur rapidly and consistently. This study compares the timing of donor hematopoietic cell engraftment in patients undergoing NMA conditioning with fludarabine and TBI with those receiving MA conditioning with BU- or TBI-based regimens. Achievement of ≥ 90% donor leukocyte chimerism occurred rapidly and consistently in all three groups and time to achievement of ≥ 90% donor T cells was similar among the three groups (P = 0.57). Achievement of ≥ 90% donor leukocyte chimerism was not associated with risk of acute or chronic GVHD, graft rejection, relapse or all cause mortality in multivariate analyses. Donor T-cell chimerism of ≥ 90% was significantly associated with development of extensive chronic GVHD. The value of routine surveillance of chimerism following any of the preparative regimens used in this study should be reevaluated.