Allo-Reactive NK Cells after HLA-Matched Allogeneic Hematopoietic Stem Cell Transplantation.

Allo-reactive natural killer (NK) cells frequently occur early after haplo-mismatch hematopoietic stem cell transplantation (HSCT) with killer cell immunoglobuline-like receptor (KIR)-ligand mismatch in graft versus host (GvH) direction. Clinical data and experiments in mice indicate a beneficial influence on relapse rates, graft acceptance and Graft-versus-Host disease (GvHD). We determined the incidence of allo-reactive donor type NK cells after HLA A-, B-, DR-, DQ-matched allogeneic HSCT on a functional level. Clinical course, chimerism (PCR), immune-reconstitution (FACS) and frequencies of functional active and allo-reactive NK cells (ELISpot) were longitudinal determined in 19 patients so far. Patients (pts) suffered for high risk AML (7 pts), CML failing cytogenetic response to imatinib (3 pts), poor risk ALL (2 pts), relapse/refractory high-grade NHL (6 pts) and Multiple Myeloma (13q-) (1 pt). All patients received myeloablative conditioning regimens and GvHD-prophylaxis with cyclosporine A or tacrolimus and short course mycophenolat mofetil without in vivo or ex vivo T cell depletion. Chimerism analyses ensured hematopoietic reconstitution from donor type in 19/19 patients. In 3/19 patients NK cell activity was absent even against HLA class I negative control target cells. Absence of functional active NK cells correlates with severe acute GvHD accompanied by high doses of glucocorticosteroid medication. In all other patients we detected at least once functional active NK cells in peripheral blood. In 4/19 cases we detected allo-reactive NK cells after HSCT at days (d) +28, +68, +128 (case 19), d +56 (case 8), d +355 (case 1) and d +379 (case 13). Two cases were transplanted in KIR-ligand mismatch in GvH direction (donors HLA-C^Asn80 and -C^Lys80, recipients missing HLA-C^Lys80). Allo-reactive NK cells were absent in all patients with known complete KIR-ligand match. Flow cytometry data on reconstitution of NK cell repertoire showed individual heterogeneous results. After median observation time post HSCT of 268 d (31–902) 3 patients died due to relapse. None of the patients with NK cell allo-reactivity experienced relapse. This is the first proof of circulating functionally active, allo-reactive NK cells after HLA-A, -B, -DR and -DQ matched HSCT. We detected NK cell allo-reactivity in all donor-recipient pairs with KIR-ligand (HLA-C) mismatch in GvH direction. After haplo-mismatch HSCT and T cell depletion NK cell allo-reactivity is restricted early after transplantation (within 3 months). In contrast, we detected late onset (>1 year) of NK cell allo-reactivity after one-locus (HLA-C) mismatch HSCT without T cell depletion of the grafts.