CD34 augmentation improves allogeneic T cell-depleted bone marrow engraftment

T cell depletion (TCD) performed by elutriation has decreased the incidence of acute and chronic graft-versus-host disease (GvHD) following bone marrow transplantation (BMT). However, as with all forms of TCD, patients may experience graft failure (10%), delayed engraftment, and mixed chimerism. Because 66%-75% of the CD34+ cells coseparate with the small lymphocytes, which are removed by elutriation, we designed a phase I trial in HLA-identical siblings to determine if the readdition of these previously lost small CD34+ cells would improve elutriation's engraftment kinetics. CD34+ cells were isolated from the small cell fraction of 10 consecutive donor grafts and infused into the recipients along with the TCD graft. The positively selected product had a mean T cell content of 1.2 × 10⁵/kg and was 80% CD34+, doubling the CD34+ content of the graft. All patients engrafted promptly with a median time to 500 neutrophils/mm³, untransfused 50,000 platelets/mm³, and discharge from the hospital of 19 (range 10-25), 24 (14-52), and 24 (18-29) days, respectively. Acute GvHD occurred in 2 patients, and no patient had chronic GvHD. Augmenting stem cell dose may be an efficient and safe alternative for overcoming TCD-associated delayed engraftment and graft failure, rather than increasing immunosuppression.