Minimal HLA Disparity and KIR Ligand Compatibility in Host Versus Graft Direction May Facilitate Donor Engraftment Following In Vivo and Ex Vivo T Cell Depleted (TCD) Nonmyeloablative Haploidentical Stem Cell Transplantation for Hematologic Malignancies.

Mixed chimerism (MC) can be induced in mice across MHC barriers using nonmyeloablative conditioning and T cell depletion. Delayed donor lymphocyte infusions (DLI) convert this MC state to full donor hematopoiesis and impart a powerful graft versus tumor effect without inducing GVHD. Based on this principle, we developed a clinical trial with a goal of inducing a GVH-free mixed chimeric platform for delayed cellular immunotherapy via DLI following nonmyeloablative haploidentical HSCT. This study analyzed graft outcomes in 13 patients who received in vivo and ex vivo TCD, haploidentical (HLA 1–3 Ag mismatched) HSCT for refractory hematologic malignancies (NHL, n=7; CLL, n=1; HD, n=3; CML, n=1; MDS, n=1). Conditioning consisted of MEDI-507 (siplizumab, an anti-CD2 mAb) for in vivo T cell depletion of both the host and donor, cyclophosphamide, fludarabine, thymic irradiation, and a brief course of cyclosporine. An earlier cohort of 4 patients did not receive fludarabine. All patients received ex vivo TCD of G-CSF-mobilized peripheral blood stem cells using a CD34+ cell-selection device. A median of 7.38 x 10⁶ (3.19 x 10⁶ to 1.49 x 10⁷) CD 34+ cells/kg and a median of 5.24 x 10⁴ (6.31 x 10² to 1.61 x 10⁵) CD3+ cells/kg were given. DLI was given as early as 5 weeks in patients without evidence of GVHD. Inhibitory killer immunoglobulin-like receptor (KIR)-HLA epitope mismatches (missing ligand) in the GVH and HVG (host versus graft) directions were assessed based on HLA and KIR genotyping of patients and their donors. Natural killer (NK) cells recovered relatively early, despite the presence of circulating MEDI-507. Split lineage MC was observed in each case, with a predominance of early donor myeloid chimerism and a lower percentage of donor T cell chimerism. Four of the 13 patients eventually lost their grafts despite DLI, including 2 who were not conditioned with fludarabine. Five patients spontaneously achieved full donor chimerism (FDC) and 4 converted to FDC following DLI. The spontaneous chimerism group had significantly fewer HLA mismatches in the HVG direction. Four out of the 5 had only one mismatch, whereas the patients who had graft loss or required DLI had at least two mismatches (p=0.007 by Fisher’s exact test). This finding remained significant when the subgroup of patients not conditioned with fludarabine was excluded from the analysis (p=0.048). Spontaneous FDC was also associated with the presence of graft HLA-C group 1 (HLA-C^Asn80) ligand for host NK cell inhibitory receptor KIR2DL2/3 (KIR-L match/compatible, 4 out of 4 evaluable patients) while this graft HLA ligand tended to be absent in the group that lost the graft or required DLI to achieve chimerism (KIR-L mismatch, 5 out of 8 patients) (p=0.08 by Fisher’s exact test). There was no significant relationship between donor KIR and host HLA types in the GVH direction for predicting engraftment. While these observations are preliminary given the heterogeneity of the conditioning regimens and the small number of patients, the data suggest that the lesser degree of HLA mismatching and the presence of KIR ligand compatibility in the HVG direction may influence donor engraftment following nonmyeloablative TCD haploidentical HSCT and warrant further study.