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Pediatr Blood Cancer 2007;49:615–623 REVIEW Human Natural Killer Cells in Health and Disease Evan Shereck, MD, 1 Prakash Satwani, 1 MD, Erin Morris, Natural killer (NK) cells are an essential component of the innate immune system and play a critical role in tumor immune surveillance. NK cells express their own repertoire of receptors (NKRs) that bind to major histocompatibility class I or class I-like molecules. The balance of signals from stimulation or inhibition of NKRs determines the ability of NK cells to lyse specific targets. In haploidentical stem cell transplantation with purified stem cells, NK cell alloreactivity (killer immunoglobulin-like receptor [KIR] mismatch) has been demonstrated to reduce the risk of relapse in Key words: and Mitchell S. Cairo, MD 1,2,3 * acute myeloid leukemia. There is a need for adequately powered prospective randomized studies to determine the usefulness of NK cells as adoptive immunotherapy, optimal NK cell doses and timing of administration. Further studies are required to determine optimal selection of donors and recipients, both on NKR matching/ mismatching, undergoing haploidentical and unrelated hematopoetic stem cell transplantation. Pediatr Blood Cancer 2007;49: 615–623. ß 2007 Wiley-Liss, Inc. natural killer cell immunology; function; review INTRODUCTION Human natural killer (NK) cells are an essential component of the innate immune system. They have the ability to lyse target cells and to secrete immunoregulatory cytokines [1]. NK cells comprise approximately 10% of all peripheral blood lymphocytes and are characterized by lack of expression of CD3 but have the expression of CD56 [2] and morphology of large granular lymphocytes [3]. NK cells were initially demonstrated by Cudkowicz and Bennett [4,5] by their observation that lethally irradiated mice could mediate rejection of allogeneic or parental strain bone marrow (BM) allografts and later by their ability to mediate spontaneous tumor cytotoxicity in vitro in a major histocompatibility complex (MHC)unrestricted manner [6,7]. NK cells reside in cord blood, peripheral blood, BM, and the spleen where they can protect the host against infectious organisms and malignant transformation [2,6,7]. NK cells are different from other lymphocytes because they do not require specific antigen recognition to lyse tumor cells [1,2,6]. NK Phenotype Mature NK cells are characterized by CD56 expression and the absence of CD3 [8]. NK cells can be classified based on the surface density of CD56 expressed into CD56bright (high density) and CD56dim (low density). Approximately 90% of NK cells are CD56dim, which in the resting state are the more cytotoxic of the two subsets and have high expression of CD16 (Fcg receptor III) and the remaining 10% are CD56bright CD16dim[9]. The CD56dim cells, which in the resting state are the more cytotoxic of the two subsets, have high expression of CD16 which is the Fcg receptor III (FcgRIII), whereas, the CD56bright NK cells are CD16dim. CD16 is responsible for binding to antibody-coated targets and initiating antibody-dependent cellular cytotoxicity (ADCC) [10]. Regulation of NK Cell Development NK cells are derived from CD34þ hematopoietic stem or progenitor cells and undergo maturation primarily in BM (Fig. 1) [11,12]. Interleukin (IL)-15 appears to be the crucial factor for the development of human and murine NK cells [13–15]. Human NK cell development occurs in two phases. In the early phase, an NK progenitor cell (CD34þLin) responds to early acting growth ß 2007 Wiley-Liss, Inc. DOI 10.1002/pbc.21158 1 RN, factors (e.g., Flt-3 ligand or kit ligand) and develops into an NK-cell precursor intermediate with the basic phenotype CD34þ IL-15Rþ (Fig. 1). IL-15 then induces the development of mature NK cells that are CD56bright which lyse tumor target cells and produce immunoregulatory cytokines and chemokines upon stimulation [16]. CD56dim cells are either derived from CD56bright cells in the periphery or might be under the control of other cytokines (e.g., IL-21) [17]. However, with its higher intrinsic cytotoxicity, more abundant expression of CD16, and absence of a proliferative response, the CD56dim NK cell appears to be more terminally differentiated than the CD56bright NK cell. NK Cell Receptors NK cells do not have the capacity to rearrange genes encoding for antigen recognition. However, NK cells express their own repertoire of several classes of receptors (NKRs) that bind to MHC class I or class I-like molecules or targets that regulate whether NK cells will be activated or inhibited [2,18]. It is the balance of signals from stimulation or inhibition through NKRs that determines the ability of NK cells to lyse specific targets (Fig. 2). NKRs can be classified in a number of ways, such as activating/inhibitory, killer immunoglobulin like receptor (KIR)/C-lectin/other or MHC class I dependent/MHC class I independent/other (Table I) [2,18]. — ————— 1 Department of Pediatrics, Columbia University, New York, New York; 2Department of Medicine, Columbia University, New York, New York; 3Department of Pathology, Columbia University, New York, New York Evan Shereck and Prakash Satwani Contributed equally to this manuscript and should be considered co-primary or first authors. Grant sponsor: Pediatric Cancer Research Foundation; Grant sponsor: Bevanmar Foundation; Grant sponsor: Marisa Fund; Grant sponsor: Scaramella fund. *Correspondence to: Mitchell S. Cairo, Professor of Pediatrics, Medicine and Pathology, Division of Pediatric Hematology and Blood and Marrow Transplantation, Morgan Stanley Children’s Hospital of New York-Presbyterian, Columbia University, 3959 Boardway, CHC 1114, New York, NY 10032. E-mail: [email protected] Received 20 April 2006; Accepted 5 December 2006 616 Shereck et al. Fig. 1. Human natural killer (NK)-cell subset development. NK-cell development can be divided into three discrete stages based on in vitro models. A CD34þ NK-cell progenitor, negative for lineage markers (Lin), that expresses the receptor tyrosine kinases fit-3 and c-kit, and is responsive to fit-3 ligand (FL) and/or c-kit ligand (KL) differentiates into a CD34þ IL-15 receptor (IL-15R)þ NK precursor that is responsive to IL-15 for maturation into a functionally mature CD56bright NK cell. The developmental relationship between CD56bright and CD56dim NK cells has never been established definitively, and CD56dim NK cells have not been generated in vitro. Potential hypotheses for the development of CD56dim NK cells include (a) the existence of a unique CD56dim NK-cell precursor. b: An alternate signal (e.g., a novel cytokine) that could induce the differentiation of CD56dim cells from a common NK-cell precursor: or (c) maturation of CD56bright cells into CD56dim NK cells. Reprinted from Trends in Immunology, Volume 22, Cooper M.A., Fehniger T.A., and Caligiuri M.A., The biology of human natural killer-cell subsets, 633–640, 2001, with permission from Elsevier. Activating NKRs include KIRs, C-lectins, natural cytotoxicity receptors (NCR), and other activating co-receptors (Table I) [2]. Inhibitory receptors on the NK cell surface recognize and engage their ligands, MHC class I molecules (human leukocyte antigen [HLA]) on the surface of the target tumor cell, thereby initiating an inhibitory signal. Activating receptors bind ligands on the target cell surface and trigger NK cell activation and target cell lysis. When inhibitory receptors engage HLA in the absence of an activating receptor/ligand interaction, a net negative signal is generated, resulting in no target cell lysis. Conversely, when activating receptors engage their ligands on target cells in the absence of inhibitory receptor/ligand interaction, a net activation signal is generated, resulting in target cell lysis. This scenario is likely operative in NK alloreactivity in the setting of KIR epitope mismatch (Fig. 2). Another common class of NK receptors is the C-lectin NKG2 family [2,19,20]. There are at least five members of the NKG2 family, including NKG2A, NKG2C, NKG2D, NKG2E, and NKG2F [21,22]. Other than CD94/NKG2A, which is an NK inhibitory receptor, the remaining NKG2 receptors are NK activating receptors (Table I). Target cell ligands for NKG2D are different than other NKRs and include two families of ligands, MHC class I chainrelated antigens (MIC) and UL16 binding proteins (ULBPs) [23,24]. MIC expression by several malignant solid tumors and leukemias as recently demonstrated [2]. We have also demonstrated expression of NKG2D ligands such as ULBP 1, 2, 3 and/or MIC A and B in pediatric acute lymphoblastic leukemia, chronic myeloid leukemia, non-Hodgkin lymphoma, and neuroblastoma cell lines [25]. Pediatr Blood Cancer DOI 10.1002/pbc The NCRs, which are NK activating receptors, have no apparent specificity for MHC class I molecules. Three NCRs have been identified that appear to be expressed on all NK cell subsets, including NKp46, NKp44, and NKp30 [18,26,27]. NKp44 is not expressed on resting NK cells but is significantly upregulated after IL-2 stimulation and is also expressed on gamma/delta T cells [28]. Lastly, there are a number of other NK receptors known as coreceptors, which appear to activate NK cells after initial NKR binding, and they include CD16 (FcgRIII), CD2, LFA-1, 2B4, Nkp80, and CD40 ligand [2]. NK cells can be activated by various cytokines such as interferon-g(IFN-g), IL-2, IL-12, IL-15, or IL-18, increasing their number and cytotoxic activity and thereby killing a broader spectrum of targets, including some that are generally not affected by NK cells. This is probably related to the change in cytokine environment that can induce specific molecules on both NK as well as target cells to support cell adhesion and to mediate cytolysis of NK cell-resistant targets [29]. The resistance of cancer cells to NK cell activity can be overcome by genetic modification resulting in transduction of chimeric receptors on NK cells targeted against specific ligands on malignant cells. The stimulatory signals triggered by the receptors on contact with target cells can induce powerful cytotoxicity against NK-resistant leukemic cell lines [30]. Mechanisms of NK Cytotoxicity When NK cells fail to interact with the MHC class I molecule and the activating receptor is activated, NK cell mediated lysis will occur Natural Killer Cells in Health and Disease 617 Fig. 2. Regulation of NK cell response by activating and inhibitory receptors. Inhibitory receptors (e.g., inhibitory KIR, CD94/NKG2A) recognize and engage their ligands, MHC class I molecules (HLA), on the surface of the target tumor cell, thereby initiating an inhibitory signal. Activating receptors (e.g., activating KIR, CD94/NKG2C, NKG2D) bind ligands on the target cell surface and trigger NK cell activation and target cell lysis. A: When inhibitory receptors engage HLA in the absence of an activating receptor/ligand interaction, a net negative signal is generated, resulting in no target cell lysis. B: Conversely, when activating receptors engage their ligands on target cells in the absence of inhibitory receptor/ ligand interaction, a net activation signal is generated, resulting in target cell lysis. This scenario is likely operative in NK alloreactivity in the setting of KIR epitope mismatch. More complex physiologic scenarios are shown in C and D with both inhibitory and activating receptor/ligand signals being generated when an NK cell interacts with a target cell. C: Here, the activating receptor/ligand interactions predominate over weaker inhibitory receptor/ligand signals with the net result of NK cell activation and target cell lysis. This net result may occur when activation receptors and ligands are upregulated, thereby amplifying the net activation signal to exceed the inhibitory signal. For example, the activating ligands MICA/B and ULBPs are expressed highly in stressed or transformed cells, thereby activating NKG2D/P13K pathways that are not susceptible to inhibitory signals. Alternatively, when expression of self-MHC class I ligands is decreased in the setting of viral infection or transformation, the net signal may be positive, also resulting in target cell lysis. D: Here, inhibitory receptor/ligand interactions result in a net negative signal that prevents NK cell lysis of the target cell. This process may occur constantly as NK cells survey normal host tissues. Not shown is the scenario of absence of both inhibitory and activating signals that results in no NK cell activation. From: Farag SS, Fehniger TA, Ruggeri L, Velardi A, and Caligiuri MA. Natural killer cell receptors: new biology and insights into the graft-versus-leukemia effect. Blood 2002; 100:1935–1947. Copyright American Society of Hematology, used with permission. [31]. For example, when CMV invades a host cell it causes downregulation of MHC class I molecules, which stops the inhibition of cell killing that usually occurs [31]. After activation, lysosome-like vesicles containing perforin, serine esterases, and sulfated proteoglycans are secreted toward the target cell. Perforin causes pore formation in the target cell causing an osmotic lysis of the target cell [32]. The serine esterases, including granzymes, stimulate apoptosis [1,33]. Tumor necrosis factor-a (TNF-a) activates a target cell endonuclease which degrades genomic DNA [1]. Proteoglycans appear to protect the granzymes from inactivation by protease inhibitors [34]. Whether NK cells kill their targets with perforin or recruit other cells by producing cytokines, the NK cells seem to require Pediatr Blood Cancer DOI 10.1002/pbc stimulation by conventional dendritic cells. Andoniou et al. [35] demonstrated that NK cells alone with CMV or NK cells with dendritic cells not exposed to CMV were not enough for the NK cells to mount a response. Only when the NK cells were placed with CMV and dendritic cells exposed to CMV was the cytotoxic function enhanced and IFN-g produced [35]. The dendritic cells can enhance NK cell cytotoxicity directly by activating the NKG2D receptor or indirectly by producing IFN-g [35]. The dendritic cells also produce IL-12 and IL-18 which enhance IFN-g production by NK cells [35]. After stimulation with cytokines, the CD56bright are able to produce IFN-g, TNF-a, and granulocyte-macrophage colony stimulating factor [36]. These cytokines provide positive feedback 618 Shereck et al. TABLE I. Human Activating and Inhibitory NK Cell Receptors (NKR) and Their Corresponding Ligands Type Killer immunoglobulin receptors C-type lectin receptors Natural cytotoxicity receptors Activating receptor Activating receptor ligand specificity Inhibitory receptors Inhibitory receptor ligand specificity KIR2DS1 Group 2 HLA-CAsn77 Lys80 KIR2DL1 (CD158a) Group 2 HLA-C Asn77Lys80 KIR2DS2 KIR2DL4 KIR2DS4 KIR2DS5 KIR3DS1 CD94/NKG2C CD94/NKG2E/H NKG2D NKp46, NKp44, NKp30 Group 1 HLA-CSer 77 Asn80 HLA-G Unknown Unknown Unknown HLA-E Unknown MIC-A, MIC-B, ULBP-1, 2 & 3 Unknown KIR2DL2 (CD158b) KIR2DL3 (CD158b) KIR3DL1 KIR3DL2 KIR3DL7 CD94/NKG2A/B CIRU CIRU Unknown Group 1 HLA-C Ser77Asn80 Group 1 HLA-C Ser77Asn80 HLA-Bw4 HLA-A3, -A11 Unknown HLA-E CIRU CIRU CIRU KIR, killer immunoglobulin like receptor; NK, natural killer; HLA, human leukocyte antigen; MIC, MHC class I chain related antigens; ULBP, UL16 binding proteins; KIR, killer immunoglobulin like receptor; CIRU, corresponding inhibitory receptor unknown. to macrophages and other antigen presenting cells for more efficient control of infection [8]. NK cells can also act independently of perforin by NK celldependent death receptor mediated apoptosis. These molecules and receptors are part of the TNF family of ligands and receptors. Two of these ligands, the FAS (APO-1, CD95) ligand (FasL) [37] and TNF-related apoptosis-inducing ligand (TRAIL/APO-2L) [38], are found on NK cells and both have corresponding receptors on the target cell. In a resting state NK cells intracellularly express significant levels of FasL [39]. However, after activation of the NK1.1 (CD161) receptor, FasL is upregulated on the cell surface in a dose-dependent fashion [39]. Oshimi et al. [40] demonstrated that target cells with high levels of Fas underwent apoptosis when placed in a calcium free medium that inhibits the use of perforin after NK cells were added. These apoptotic changes were not seen when an anti-Fas monoclonal antibody (Mab) was added [40]. TRAIL has been shown to play an important role in tumor surveillance [41]. Role of NK Cells in Adoptive Cellular Immunotherapy Several investigators have used immunotherapy with IL-2 alone or in combination with activated NK cells in patients with various malignant hematologic diseases and breast cancer [42–44]. Rosenberg et al. treated 25 adult patients with refractory metastatic cancer with systemic administration of autologous lymphokine activated killer cells (ex-vivo expanded) and IL-2. Although this approach induced nearly 15–20% partial and complete responses (CR) in their initial trials, subsequent studies showed that a similar anti-tumor effect could be achieved with high-dose IL-2 alone [45,46]. Several non-randomized trials with different patient eligibility and experimental designs have been performed with the aim of evaluating the safety and efficacy of immunotherapy with IL2 with and without autologous hematopoietic stem cell transplant (HSCT) in adult patients with lymphoma and breast cancer. These trials have suggested a potential clinical benefit using an IL-2 based immunotherapy approach [47–50]. An immuno-targeting approach has been tested in pediatric patients with refractory neuroblastoma. Using immunotherapy with Pediatr Blood Cancer DOI 10.1002/pbc a Mab targeting a tumor-associated antigen, GD2, has been shown to be uniformly expressed by neuroblastoma cells. Therapeutic responses have been obtained in Phase I and Phase II studies using murine IgG3 Mab, 3F8 [51], murine IgG2 Mab, 14G2a [52,53] and human-mouse chimeric Mab, ch14.18 [54,55]. The biological activities of ch14.18 are mediated by complement dependent cytotoxicity [55] and ADCC, in part mediated by innate cellular immunity of NK cells. Various non-randomized studies have been conducted in children with refractory solid tumors and hematological malignancies using IL-2. In these studies only small number of patients achieved clinical remission [56–62]. In a recently conducted Phase III trial (CCG-2961) for newly diagnosed children with acute myeloid leukemia (AML) administration of IL-2 had no impact on overall survival and disease free survival (P ¼ 0.606) [63]. Role of NK Cells in Allogeneic Stem Cell Transplantation Cure of leukemia by allogeneic HSCT relies on the action of donor T-cells in the allograft, which is vital for promoting engraftment, eradicating malignant cells (graft-versus- leukemia [GVL] effect), and reconstituting immunity. Unfortunately, donor T cells also mediate GVHD. In full haplotype-mismatched transplantation a high dose (approximately 20 106 CD34þ cells/kg) of purified hematopoietic stem cells from NK alloreactive donors are infused. The transplanted stem cells quickly give rise to NK cells. The potential beneficial role of NK cells in haploidentical stem cell transplant (haplo-SCT) is possible through the following theoretical mechanisms: (1) targeting host T lymphocytes that may result in lower rates of graft rejection; (2) targeting host dendritic cells resulting in decrease antigen presentation by host dendritic cells and hence decreasing the risk of GVHD; (3) targeting leukemic cells which may decrease relapse; and (4) improving immune reconstitution which may decrease the risk of opportunistic infections [64,65]. Donor selection for haplo-SCT requires a search for the donor who is able to mount donor-versus-recipient NK cell alloreactivity. Natural Killer Cells in Health and Disease Search for haploidentical NK alloreactive donors may require extension from the immediate family to other family members such as aunts, uncles, and cousins. While patients who express the three major HLA class I KIR ligands may not find an alloreactive donor, patients who express one or two of these ligands may [66]. Ruggeri et al. [67] demonstrated that donor-versus-recipient NK cell alloreactivity reduced the risk of leukemia relapse in 57 AML patients at high risk of relapse, while improving engraftment and protecting against GVHD. Similarly, in children with acute leukemia, HSCT from haploidentical donors with potential for NK cell alloreactivity was reported to decrease the risk of relapse [68]. An updated analysis of 93 haplo-SCT for AML included 40 recipients (25 transplanted in remission, 15 in relapse) who received HSCT from haploidentical donors who were able to mount donor-versus-recipient NK alloreactions and 53 AML recipients (26 transplanted in remission, 27 in relapse) who received HSCT from haploidentical donors who were unable to mount donorversus-recipient NK alloreactions [69]. The analysis confirms that grafts from NK alloreactive donors enhance engraftment and appear to protect against GVHD. The probability of relapse was 15% for the 40 patients transplanted from NK alloreactive donors versus 68% for the 53 patients transplanted from non-NK alloreactive donors (P < 0.005). The probability of survival was correspondingly much better after NK alloreactive donor transplantation (55% vs. 12%, P < 0.005). In 62 haploidentical transplants in patients with leukemia, Bishara et al. demonstrated that potential NK alloreactivity in the GVHD direction (MHC class I KIR ligand is absent in the recipient but present in the donor) was associated with an increased incidence of severe GVHD and poorer patient survival. Furthermore, this approach had no impact on engraftment or leukemic relapse and that lack of extensive T-cell depletion in haploSCT was associated with high GVHD rates and diminished the benefits of NK cell alloreactivity [70]. T cells in the allograft may affect NK cell reconstitution in vivo. In 77 patients with chronic myeloid leukemia who received allografts from unrelated donors, Cooley et al. demonstrated that NK cells expressed fewer KIRs and produced more IFN-g after unmanipulated BM compared to T-cell depleted transplants. Increased NK cell IFN-g production correlated with more acute GVHD and decreased KIR expression correlated with inferior survival [71]. Nguyen et al. [72] demonstrated that NK cells generated after haplomismatched SCT are blocked at an immature state characterized by specific phenotypic features and impaired functioning. Leung et al. demonstrated that the NK cells derived from highly purified CD34þ cells acquired a donor-specific pattern of KIR expression independent of self-HLA within the first 3 months of transplantation. However, subsets of NK cells may express only one of the KIRs which may potentially provide alloreactivity if the corresponding ligand was absent in the recipient’s cells. These findings might help to select a perfect mismatch donor on the basis of a single evaluation of the donor’s KIR repertoire before transplantation [68]. NK cell alloreactivity may be expected to occur in >60% of unrelated donor transplants with one or more HLA allele-level mismatches [73]. However, it remains to be determined whether alloreactive donor-derived NK cells display GVL reactions after unmodified unrelated HSCT. Some of the retrospective studies have failed to demonstrate any advantage of transplantation from unrelated donors with the potential to exert NK cell alloreactivity Pediatr Blood Cancer DOI 10.1002/pbc 619 (Table II) [74–76]. These reports lacked functional assessment of donor-versus-recipient NK cell alloreactivity, utilized heterogeneous conditioning regimens, immunosuppressive therapy, and infused smaller stem cell doses. Other studies have documented an increased GVL effect in transplants from unrelated donors, this theoretically had the potential to exert NK cell alloreactivity (Table II) [77–80]. Donor NK Cell Infusion Donor lymphocyte infusion is limited by the development of acute and chronic GVHD in up to 60% of the patients, which has been associated with significant morbidity and mortality. Several groups have investigated the preparation and infusion of purified, T-cell-depleted, donor NK lymphocytes with the aim to consolidate engraftment and induce GVL effects in patients after HSCT from haploidentical or other donors. Despite demonstrating CRs in some studies, most of these investigations include small numbers of patients with short follow-up. Hence, it is difficult to assess the potential benefit of this approach. However, these studies demonstrated that ex vivo purification of donor NK cells from leukapheresis products is technically feasible and that large numbers of CD56þ highly CD3 depleted cells can be obtained. These purified NK cells have been infused without immediate adverse events and without inducing GVHD. Clinical data on efficacy are very limited. Whether NK donor lymphocyte infusion will prevent graft rejection and/or promote a GVL effect requires additional studies. Future Considerations Adequately powered prospective and/or randomized studies are required to determine the usefulness of NK cells as adoptive immunotherapy, optimal NK cell doses, and timing of administration. Furthermore, appropriate selection of donors and recipients based on NKR matching/mismatching following haploidentical and unrelated HSCT, requires further study. The use of NK cells as adoptive immunotherapy will help to better define the clinical impact of NK cell alloreactivity, including the importance of KIR and other NKR matching and mismatching. Whether these cells should be used preemptively or as salvage treatment is unknown. Purging and enrichment technology using magnetic beads for clinical application is technologically feasible but expensive. Strategies for blocking KIR-MHC class I Ag interaction so that inhibitory receptors are not activated should be further tested. Other approaches might include the induction of activating receptors and its ligands on malignant cells, infusion of autologous genetically engineered NK cells to recognize specific tumor receptors and costimulation of NK cells through dendritic cell activation [81]. Other considerations should include the investigation of various cytokines (IL-15, IL-18, and IL-21) to increase in vivo or ex vivo expansion and activation of NK cells. There is a need to better understand the mechanisms that impact KIR expression and influence of T cells on NK cell repertoire after unmanipulated BM and haplo-SCT. Further understanding of the biology of NK cells and the mechanisms that govern target cell sensitivity and resistance, together with clinical investigations, will hopefully result in optimal exploitation of this class of cytotoxic cells for the benefit of leukemia patients and possibly patients with other malignancies [82]. Pediatr Blood Cancer DOI 10.1002/pbc CML, ALL, AML, MDS, others CML, AML, MDS CML, ALL, AML, MDS, MM, NHL CML AML, MDS, CML CML, ALL, AML, MDS [100] [102] [103] [116] [106] [99] 66 89 49 49 103 113 112 48 29 20 15 62 KIR ligand incompatibility (Group B) (n) NA 2.3 vs. 6.3 4 vs. 7 8 vs. 0 10 vs. 13 7 vs. 8 Graft Failure Group A vs. B % TCD 100 vs. 100 None ATG 20 vs. 13 ATG 100 vs. 100 None TCD 37 vs. 29 TCD/ATG Group A vs. B % 15 vs. 24 58 vs. 55 49 vs. 52 43 vs. 30 46 vs. 69 50 vs. 61 Grade II-IV AGVHD Group A vs. B % NA 11 vs. 4 20 vs. 0 21 vs. 6 30 vs. 60 12 vs. 9 Relapse rate Group A vs. B % NA 53 vs. 58 52 vs. 66 48 vs. 87 46 vs. 33 40 vs. 32 5-year OS Group A vs. B % Unrelated donors, Retrospective study. Heterogeneous patients and conditioning and immunosuppression, includes pediatric patients Unrelated donors, Retrospective study. Older patients Unrelated donors, Prospective study. Younger patients Unrelated donors, Prospective study. Decreased RR with KIR incompatibility but no survival advantage Unrelated donors, Prospective study. Decreased RR with KIR incompatibility but no survival advantage Matched sibling donors only AML and MDS patients with inhibitory KIR mismatch had significantly higher DFS and OS Remarks CML, chronic myeloid leukemia; ALL, acute lymphoblastic leukemia; AML, acute myeloid leukemia; MDS, myelodysplastic syndrome; MM, multiple myeloma; NHL, non-Hodgkin’s lymphoma; KIR, killer immunoglobulin like receptor; aGVHD, acute graft-versus-host disease; OS, overall survival; RR, relapse rate; ATG, anti-thymocyte globulin; TCD, T cell depletion; DFS, disease free survival; NA, not available. Diagnosis Study No KIR ligand incompatibility (Group A) (n) TABLE II. Outcomes of Non-Haploidentical Myeloablative Allogeneic Stem Cell Transplantation in Recipients With and Without Killer Immunoglobulin-Like Receptor Ligand Incompatibility 620 Shereck et al. 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