Preservation of Immune Repertoire by Selective Depletion of Haploidentical Grafts

Activated T cells are relatively more sensitive to the effects of cyclophosphamide compared to resting T cells. Following nonmyeloablative conditioning, both donor and host T cells are exposed to alloantigens, resulting in activation and proliferation of T cells capable of host-versus-graft and graft-versus-host reactions. Expansion of the alloreactive clones occurs in the first 3 days after transplant, at which point cyclophosphamide is given to deplete activated T cells. Hematopoietic stem cells and resting T cells are relatively resistant to cyclophosphamide, which preserves T cells that recognize viral antigens and enhances immune reconstitution.

Flow cytometric analysis of CD34⁺ positively selected stem cells and CD3/19 negatively depleted PBSCs. Although the CD34⁺ population is homogenous without any contaminating non-T/B-cells, the CD3/19 depleted PBSC's contain large numbers of non- T/B-cells, including CD34⁺ stem cells, NK cells, and myeloid cells.

The NK activity of PBSCs without and with overnight stimulation with IL-2 and IL-15 against the standard target cell line K562 is shown.