NK Cells Rapidly Reject Allogeneic Bone Marrow in the Spleen Through a Perforin‐ and Ly49D‐Dependent, but NKG2D‐Independent Mechanism

Abstract

We have used a sensitive and specific in vivo killing assay to monitor the kinetics, anatomic location and mechanisms controlling NK-mediated rejection of Balb/c bone marrow by C57BL/6 natural killer (NK) cells. We find that NK killing of fully allogeneic bone marrow is a rapid, highly efficient process, leading to substantial rejection of transplanted marrow within 6 h of transplant and elimination of 85% of the transplanted cells within 2 days. NK-mediated rejection occurred predominantly in the spleen, with sparing of rejection in the bone marrow and lymph nodes. Rejection was dependent on Perforin gene function, but was independent of interferon-gamma. Finally, rejection of Balb/c bone marrow by B6 NK cells required signaling through the Ly49D receptor, but occurred despite blockade of NKG2D, which distinguishes these results from previous studies using semiallogeneic transplant pairs. These results identify NK cells as highly active mediators of bone marrow rejection, and suggest that inhibiting NK function early during transplantation may increase the efficiency of engraftment and allow successful engraftment of limiting doses of donor bone marrow.

HOXB4-Transduced Embryonic Stem Cell-Derived Lin−c-kit+ and Lin−Sca-1+ Hematopoietic Progenitors Express H60 and Are Targeted by NK Cells

“…These results are consistent with our recently published data on HPC engraftment in immunocompetent mice (30). We therefore concluded that NK cells regulate HPC engraftment early after transplant, consistent with the reported rapid kinetics of NK cell-mediated rejection of transplanted allogeneic bone marrow cells (26,31). To rule out that the effects of lethal irradiation were confounding our engraftment data, we characterized both the percentage and absolute numbers of NK cells in peripheral blood, spleen, and bone marrow in nonirradiated and irradiated Rag2 Ϫ/Ϫ mice.…”

“…In this study, we used the unique characteristics of Rag2 Ϫ/Ϫ (B and T cell deficient) and Rag2 Ϫ/Ϫ ␥ c Ϫ/Ϫ (B, T, and NK cell deficient) mice to assess the ability of NK cells to regulate ES-derived HPC engraftment. We demonstrate that NK cells rapidly reject HPCs within the first 24 h post transplant, comparable to the rejection kinetics observed in allogeneic bone marrow transplantation (26). Although a subpopulation of HPCs survives the NK cell response, engraftment is transient, suggesting lack of self renewal properties.…”

“…One possible explanation for the observed decline of HPC-derived cells in Rag2 Ϫ/Ϫ recipients is that NK cells continue to eliminate HPCs at late time points post transplant; however, this scenario is unlikely because it has been demonstrated that NK cells only play a role in the rejection of allogeneic bone marrow within the first week post transplant (26,31). The simplest alternate explanation is that the subpopulation of HPCs deleted by NK cells early post transplant contains the long-term hematopoietic progenitors capable of maintaining permanent engraftment, while the engrafting population is comprised of mature progenitors that have limited self-renewal capacity.…”

NKG2D gene polymorphism has a significant impact on transplant outcomes after HLA-fully-matched unrelated bone marrow transplantation for standard risk hematologic malignancies

“…33,34 Alloreactive NK cells reduced the risk of relapse of acute myeloid leukemia without increasing the incidence of GVHD, resulting in a marked improvement of event-free survival in a series of haploidentical transplant recipients. 35,36 In HLA-identical sibling transplants, the absence of HLA-C and HLA-B ligand for donor-inhibitory killer immunoglobulin-like receptors (KIR) provided benefits in terms of survival and relapse of patients with acute myeloid leukemia and myelodysplastic syndrome in recipients of T-cell-depleted SCT.…”

The requirement for NKG2D in NK cell–mediated rejection of parental bone marrow grafts is determined by MHC class I expressed by the graft recipient

“…1 Many of the same activating receptors that NK cells use to police for pathogens and tumors are involved in the rejection of bone marrow (BM) transplants. [7][8][9][10] The rejection of BM is also influenced by inhibitory signals received by interactions with donor MHC class I. 11,12 In fully allogeneic transplants, the donor BM is not matched with the recipient's MHC; therefore, some NK cells in the recipient will not be inhibited by the allogeneic MHC class I on the donor BM cells and will reject the graft.…”