Natural Killer Cell Alloreactivity Research Articles

Activating KIRs exert a crucial role on relapse and overall survival after HLA-identical sibling transplantation

Recognition of HLA-C molecules by killer cell immunoglobulin-like receptors (KIRs) is an important mechanism in the regulation of natural killer (NK) cell activity. Eradication of residual leukaemic cells by alloreactive donor NK cells after haematopoietic stem cell transplantation (HSCT) fulfils a crucial role in the control of relapse. This retrospective study evaluates 83 patients and their related donors. All individuals were typed at low-resolution level to determine their HLA repertoire. KIR genotyping data were obtained by the use of sequence-specific oligonucleotide (SSO) analysis. All data were combined with patient and donor characteristics and post-transplant clinical data. A higher overall survival was seen when KIR2DS1 in the donor was mismatched with the HLA-C group 2 ligand in the patient ( p = 0.03). The number of activating KIRs either in the patient or in the donor was significantly correlated with the occurrence of relapse ( p = 0.003 and p = 0.02, respectively). In addition, the presence of KIR2DS5 in the patient alone or in both the patient and donor was significantly correlated with the occurrence of relapse ( p = 0.004 and p = 0.005, respectively). In conclusion, significant correlations were found for activating KIRs with overall survival and relapse.

NKG2D ligand expression in AML increases in response to HDAC inhibitor valproic acid and contributes to allorecognition by NK-cell lines with single KIR-HLA class I specificities

AbstractThis study exploited alloreactivity of natural killer (NK) cells for augmenting the recognition of human acute myeloid leukemia (AML). To circumvent the inhibitory effect of killer immunoglobulin receptor (KIR) signaling, we generated NK-cell lines with single KIR specificities for major human leukocyte antigen (HLA) class I allotypes. We demonstrated efficient cytolysis of KIR-HLA class I–mismatched primary AML blasts even at low effector-to-target ratios. To define the impact of tumor-associated activating NKG2D-ligands (NKG2D-L), 66 AML patients at diagnosis were analyzed. NKG2D-L were selectively expressed on monoblastic cells in AML M4 and M5 yet absent or weakly expressed on myeloblastic cells in all AML subtypes. Paucity of cell-surface NKG2D-L was not the result of shedding because levels of soluble ULBP1 ligand measured in AML plasma were in the normal range. Notably, purified NKG2D-L+ monoblastic cells were more susceptible to NK-mediated killing than NKG2D-L− myeloblastic cells. Accordingly, induction of cell-surface NKG2D-L by treatment with the histone deacetylase inhibitor, valproic acid, rendered cells more sensitive to NK cytolysis. These data suggest that adoptive transfer of selected populations of alloreactive HLA class I–mismatched NK cells in combination with pharmacologic induction of NKG2D-L merits clinical evaluation as novel approaches to immunotherapy of human AML.

The history and future prospective of haplo-identical stem cell transplantation

Initial attempts at haplo-identical transplantation with T-cell replete bone marrow (BM) were associated with a high transplant-related mortality (TRM), mainly caused by severe graft-versus-host disease (GvHD), and previous efforts to prevent GvHD by ex vivo T-cell depletion of haplo-identical BM were associated with a high risk of graft failure and other complications. Improvements in large-scale T-cell depletion techniques of haplo-identical peripheral mobilized stem cells (PBSC) have overcome the human leukocyte antigen (HLA) barrier by using megadose numbers of stem cells obtained by either highly purified CD34(+) selection or negative depletion of T cells. In addition, recent insights into the role of graft-facilitating and anti-leukemic alloreactive natural killer (NK) cells, the permanent availability of the haplo-identical donor post-transplant and continuous improvements in graft-engineering techniques for the generation of effector cells for post-transplant adoptive transfer, have facilitated the development of strategies to decrease regimen-related toxicity through the use of less intensive preparative regimens, prevent severe infections by rebuilding the immune system and decrease the risk of relapse by exploiting the alloreactivity of donor NK cells and other donor-derived effector cells.

Donor Killer Immunoglobulin-Like Receptor (KIR) Genotype-Patient Cognate KIR Ligand Combination and Antithymocyte Globulin Preadministration Are Critical Factors in Outcome of HLA-C-KIR Ligand-Mismatched T Cell–Replete Unrelated Bone Marrow Transplantation

We previously reported the potent adverse effects of killer immunoglobulin-like receptor (KIR) ligand mismatch (KIR-L-MM) on the outcome of T cell–replete unrelated hematopoietic stem cell transplantation (UR-HSCT) through the Japan Marrow Donor Program. Other UR-HSCT studies have yielded inconsistent results. To address this discrepancy, we evaluated candidate factors contributing to the effects of KIR-L-MM on transplantation outcomes in retrospectively selected hematologic malignancy cases with uniform graft-versus-host disease (GVHD) prophylaxis (n = 1489). KIR-L-MM in the graft-versus-host direction (KIR-L-MM-G) was associated with a higher incidence of acute GVHD (aGVHD; P < .002) and a lower overall survival (OS; P < .0001) only without the preadministration of antithymocyte globulin (ATG). Furthermore, in KIR-L-MM-G, the donor KIR2DS2 gene with the patient cognate C1 ligand was associated with a higher incidence of aGVHD ( P = .012). Multivariate analysis by Cox proportional hazard models suggested that donor 2DS2 and ATG preadministration were critical factors in grade III-IV aGVHD (hazard ratio = 1.96; 95% confidence interval = 1.01-3.80; P = .045, and hazard ratio = 0.56; 95% confidence interval = 0.31-0.99; P = .047, respectively). These results indicate that the adverse effects of KIR-L-MM-G depend on combination of donor-activating KIR genotype-patient cognate KIR ligand type and no ATG preadministration, thereby suggesting the importance of these factors in UR-HSCT and in leukemia treatment using natural killer (NK) cell alloreactivity.

KIR/HLA Ligand Incompatibility in Kidney Transplantation

The polymorphic family of killer-cell immunoglobulin-like receptors (KIRs) consists of activating and inhibitory receptors expressed by natural killer (NK) cells and effector T cells that recognize human leukocyte antigen (HLA) class I ligands. It has been suggested that KIR/HLA incompatibility exerts beneficial effects in hematopoietic stem cell transplantation. To elucidate whether certain receptor-ligand combinations between recipient KIR and donor HLA antigens lead to enhanced alloreactivity of NK cells associated with acute rejection (aRx) after kidney transplantation, we analyzed the entirety of matches/mismatches between KIR genes and known HLA ligands for aRx patients (n=105) compared to patients with stable renal function (n=119). Whereas HLA-C ligand incompatibility between donor and recipient has no influence on aRx, grafts derived from donors homozygous for HLA-C group 2 alleles seem to demonstrate a better outcome (P=0.052). Additionally, a higher number of inhibitory receptors in the recipient's genotype (P=0.042), a significant higher number of matches for the receptors KIR2DL2/DS2 (P=0.004), as well as a higher number of mismatches for KIR2DL3 (P=0.014) could be observed for patients with stable renal function. Our data illustrate that certain KIR/HLA class I ligand combinations between donor and recipient might influence graft short-term outcome after renal transplantation.

Expanded Natural Killer Cells for Cellular Therapy of Acute Myeloid Leukemia.

Approximately half of the patients with acute myeloid leukemia (AML) harbor occult disease during therapy, leading to overt relapse. Novel treatments are needed to advance cure rates. AML cells are sensitive to natural killer (NK) cell cytotoxicity if they express HLA Class I molecules that do not bind killer-inhibitory receptors (KIR) on NK cells. The demonstration that haploidentical NK cells can expand in vivo and exert anti-AML activity when infused after non-myeloablative conditioning (Miller et al., Blood 105: 3051, 2005), provided impetus to further explore their clinical potential and develop ways to increase their efficacy. The success of NK cell therapy depends on: i) mismatch in recipient HLA and donor KIR phenotype, allowing NK cell alloreactivity; ii) infusion of sufficient numbers of NK cells to achieve an effector: target (E:T) ratio that produces a significant leukemia cytoreduction. We found that K562 cells genetically modified to express membrane-bound IL-15 and 4-1BB ligand (K562-mb15-41BBL) induced expansion of human NK cells (Imai et al., Blood 106: 376, 2005). In the present study, we first tested the stimulatory capacity of irradiated K562-mb15-41BBL in 34 additional healthy donors: CD56+ CD3− NK cell expansion after 7–10 days of culture was 5–87 fold (median, 22); after 21 days, NK cells could expand >1000 fold. CD3+ T cells expanded minimally or not at all. NK cells derived from 12 healthy donors were tested against the AML cell lines K562, KG-1, U937 and HL-60. Expanded NK cells were consistently cytotoxic at low E:T ratios. Thus, mean (± SD) cytotoxicity after 4 hrs at 4: 1 was 85.1% ± 8.7% for K562, 83.7% ± 9.4% for KG-1, 78.8% ± 15.2% for U937 and 94.8% ± 5.1% for HL-60. Expanded NK cells were effective even when outnumbered by target cells: at a 0.5: 1 ratio, cytotoxicities were 34.1% ± 14.7% with K562, 51.5% ± 16.5% with KG-1, 24.5% ± 14.8% with U937 and 52.1% ± 9.8% with HL-60. We next tested cytotoxicity of expanded NK cells from 10 donors against primary cells obtained from the bone marrow of 9 newly diagnosed patients with AML. Median cytotoxicity after 4 hrs of culture at a 4: 1 ratio was high, although interdonor variability was observed, with cytoxicities ranging from 22% to 90%. When expanded NK cells were cultured for 7 days with primary AML cells in the presence of bone marrow mesenchymal cells (to prevent spontaneous apoptosis of the AML cells) we could detect cytotoxicity at a 0.01:1 E:T ratio. Expanded NK cells were consistently more cytotoxic than primary NK cells from the same donor. Gene expression studies revealed marked changes in expression of adhesion molecules and cytokine transcripts after expansion. Expanded NK cells exerted considerable antileukemic effect in NOD-SCID-IL2Rgammanull mice engrafted with human AML cells, providing a strong rationale for their clinical testing. To this end, the K562-mb15-41BBL stimulatory cell line is currently being made under cGMP conditions and conditions for large-scale NK cell expansion have been established in support of a pilot protocol in which expanded haploidentical NK cells with be administered to patients with refractory AML.

Temporal, Quantitative and Functional Characteristics of Single-KIR Positive Alloreactive NK Cell Recovery Account for Impaired Graft Versus Leukemia Activity after Haploidentical HSCT.

Haploidentical Hematopoietic Stem Cell Transplantation (haplo-HSCT) is a promising therapeutic option for patients lacking a fully compatible donor. Due to extensive T cell depletion, Natural Killer (NK) cell activity represents the only immunological protection against disease relapse for the first months after haplo-HSCT. Clinical studies have associated donor-recipient incompatibility for Human Leukocyte Antigen (HLA) ligands of Killer Immunoglobulin-like Receptors (KIR), with a marked anti-leukemic activity. Alloreactive donor NK cells carrying a single KIR whose ligand is missing in the recipient mediate a potent graft vs. leukemia effect, resulting in reduced incidence of relapse and increased Overall Survival (OS). These exciting results have recently been challenged by conflicting clinical and biological data from different groups. In the present study, we have characterized reconstitution of NK cells, in particular of alloreactive single-KIR+ NK cells, in 58 patients who received CD34+ selected haplo-HSCT for high-risk hematologic malignancies. One month after haplo-HSCT CD56bright/CD56dim NK cell subsets were subverted in their proportions and phenotypic features, accounting for enrichment in maturation intermediates. We show that CD25 and CD117 deregulation by CD56bright, and NKG2A and CD62L by CD56dim, are intrinsic to NK cell physiologic differentiation and support a sequential CD56bright-to-CD56dim NK cell maturation. Consistently, the in vitro functional potential of these maturation intermediates against leukemic blasts was heavily impaired, both in terms of cytotoxicity and of cytokine release. Full mature receptor repertoire reconstitution took at least three months. Alloreactive single-KIR+ NK cells had highly variable frequency ranging from less than 1% to more than 30% of NK cells circulating at 90–120 days after transplantation, independently from predicted NK alloreactivity. Importantly, out of three patients with predicted NK alloreactivity, none had a relative expansion of alloreactive single-KIR+ cells, accounting for less than 1% of circulating NK cells in two of them. As demonstrated by flow cytometric analysis of NK cell CD107a mobilization in response to the HLA class I negative target 721.221, single-KIR+ NK cells at three months after haplo-HSCT showed a not yet fully developed functional reactivity, which was recovered to donor-levels only at later time-points. In line with these observations, clinical outcome of haplo-HSCT was not affected in any way by the presence of donor NK alloreactivity. The incidence of relapse was virtually identical in patients transplanted from alloreactive or non-alloreactive donors. Taken together, our data shed new light onto the kinetics of NK cell differentiation in vivo and suggest that NK alloreactivity could be best exploited by the use of mature donor single-KIR+ selected alloreactive NK cells.

NK-Cell Reconstitution after HLA-Identical Blood and Marrow Transplantations for CML: The Recovery of NKG2D Is Inversely Correlated with NKG2A and It Promotes the GVL Effect.

Natural killer (NK) cell alloreactivity is reported to mediate strong graft versus leukemia (GVL) effect in patients after allogeneic stem-cell transplantation. NKG2D receptors recognize human MHC class Ichain related A and B (MICA/B) and UL16-binding protein 1∼4(ULBP 1∼4) on target cells, thereby regulating NK cell activity. To examine the recovery of NKG2D, NKG2A and other receptors expression by NK cells, we used flow cytometry to evaluate samples from 11 chronic myeloid leukemia patients and their donors in the year following unmanipulated HLA completely matched peripheral blood stem cells plus bone marrow transplantation. Peripheral blood mononuclear cells from patients and their donors were tested in standard 51Cr release assays against cultured K562 targets to determine the cytotoxicity of the NK cells in the same intervals. There is no mismatched immunoglobulin-like receptor (KIR) ligand in both GVH and HVG direction. The reconstitution of KIR2DL1 (CD158a) after this transplantation protocol was very slow and these receptors didn't reach normal value in the year and KIR2DL2 (CD158b) was much better. The NKG2D increased and the NKG2A decreased quickly at the same time after engraftment, and used linear regression analysis we demonstrated that NKG2A recovery was inversely correlated with NKG2D recovery in the year following transplantation. The ratio of NKG2D/NKG2A was directly associated with the capacity of NK-cell cytotoxicity. Thus, the reconstitution of NKG2D makes contribution to the recovery of the NK cytotoxicity. These results reveals that the NK cells generated after HLA matched blood plus bone morrow transplantation of CML patients are promoted at an immature state characterized by specific phenotypic features and enhanced functioning, having potential impact for immune responsiveness and transplantation outcome.

Transplantation of T-Cell Depleted Peripheral Blood Haematopoietic Stem Cells from an HLA-Disparate Family Donor for Children with Hematological Malignancies.

Transplantation of T-cell depleted peripheral blood hematopoietic stem cells (PBHSCT) from an HLA-disparate relative has been reported to cure a significant proportion of adults with hematological malignancies, especially if transplanted for myeloid leukemia from a natural killer (NK)-alloreactive donor. Information on effectiveness of this type of allograft for children is limited. We analysed 47 patients (26 M, 21 F; median age 8 years, range 2–21) given PBHSCT from an HLA-mismatched relative between January 1998 and April 2007 for acute lymphoblastic leukemia (ALL; N.23), acute myeloid leukemia (AML; N.17) and myelodysplastic syndrome (MDS; N.7). Only 4 out of 40 patients with acute leukemia were transplanted in 1st remission; in 14 cases the allograft was performed in presence of active disease. In 29 and 18 cases, the donor did or did not display NK-alloreactivity against the recipient, respectively. All patients were given T-cell depleted CD34+ cells, positively selected using the CliniMacs device (Miltenyi Biotech), after a myeloablative regimen. After January 2005, patients received T-cell lines or clones to accelerate immune recovery against the most frequent and life-threatening pathogens (EBV, CMV, Adenovirus, Aspergillus). No pharmacological immune suppression was given after PBHSCT. Primary and secondary graft failure occurred in 1 patient each at day +15 and +65, respectively. Both patients were successfully re-transplanted from the same donor. For engrafted patients, median time to neutrophil and platelet recovery was 12 (range, 9–16) and 13 days (range, 7–20), respectively. Incidence of grade III-IV acute and extensive chronic GVHD were 6% and 3%, respectively. Cumulative incidence of transplantation mortality of overall cohort was 25% (95%, CI 14–43); 10% (95%, CI 3–37) for patients who received the allograft after January 2005 and 35% (95%, CI 20–61) for those transplanted before (p<0.05). Ten out of the 47 patients experienced relapse at a median of 126 days after PBHSCT (range 55–220), the overall cumulative incidence of relapse being 25% (95% CI 15–45). With a median follow-up of 16 months (range 4–108), the 5-year estimate of disease-free survival (DFS) for the whole cohort was 50% (95%, CI 34–66); 70% (95%, CI 49–90), 20% (95%, CI 0–39) and 75% (95%, CI 33–100) in patients with ALL, AML and MDS, respectively (p<0.01). In children with acute leukaemia who did or did not receive the allograft from an NK-alloreactive donor, the cumulative incidence of relapse was 17% and 50%, respectively (p<0.05), while the DFS probability was 64% (95%, CI 46–83) and 17% (95%, CI 0–39), respectively (p<0.05). The DFS of the 18 patients with ALL transplanted from an NK-alloreactive donor was 81% (95%, CI 61–100). Donor-derived alloreactive NK cells emerged in the early phase after PBHSCT and persisted over time. T-cell depleted PBHSCT from an HLA-disparate relative is a valuable option for children with hematological malignancies needing an allograft, especially if affected by ALL. Outcome of patients transplanted from an NK-alloreactive donor is very encouraging.

Phase I-II Trial of Adoptive Immunotherapy with Haploidentical KIR Ligand-Mismatched Natural Killer Cells in High Risk Acute Myeloblastic Leukemia Patients.

Natural killer (NK) cells play a critical role in innate immunity and are relevant for the immune control of tumors. Their effector function is regulated by a number of activating and inhibitory receptors, termed killer immunoglobulin receptors (KIRs). In haploidentical T-cell depleted transplantation the donor/recipient KIR mismatch significantly impacts on tumor cell killing, particularly in acute myeloid leukemia (AML). Therefore, haploidentical KIR-mismatched NK cells may be used as adoptive immunotherapy for high risk AML patients in non-transplantation settings. Thirty-one high risk AML patients entered a phase I-II study of NK-cell based immunotherapy and were screened for the avalilability of one haploidentical KIR ligand mismatched donor. Ten of them resulted as having one suitable donor. NK cells were enriched from steady-state leukaphereses by using a double-step immunomagnetic separation system (Miltenyi Biotec, Germany), consisting in1.depletion of CD3+ T cells followed by2.positive selection of CD56+ NK cells, and then cryopreserved.CD56+ NK cells were enriched from 8.28±3.7% to 85.9±3.2% (recovery 67.9±15%, viability >92%). So far, 8 patients (1 partial remission, 4 progressions and 3 complete remissions) received NK cell infusion which was preceeded by immunosuppressive chemotherapy, including fludarabine 125 mg/m2 and cyclophosphamide 4g/m2. AML patients received 6 subcutaneous injections of interleukin 2 (IL-2) after adoptive immunotherapy. The median number of reinfused NK cells was 3.6 × 106/Kg and contaminating CD3+ T cells were always less than 1×105/Kg. NK cells were capable to kill NK-sensitive K562 cells in a flow-cytometry-based cytotoxicity assay. The procedure was well-tolerated and no significant toxicity, including GVHD, related to NK cell infusion was observed. The patient in partial remission obtained a complete remission, which lasted for 6 months; among the 4 patients with active/progressive disease 2 patients showed the persistence of disease and one patient died during the aplastic phase. The 3 patients in complete remission are stable after 5, 3 and 4 months of follow up. By using a RT-PCR-based chimerism assay, we demonstrated the presence of adoptively transferred NK cells in 2/4 patients with a peak in circulating NK cell number at day 12 after infusion. Functional biological studies demonstrated the presence of alloreactive NK cell clones in all the donors (at the frequencies of 11 ± 4%) and in 3/4 patients (at the frequences of 16 ± 5%) only at day 3 after infusion of NK cells. In summary, a two-step enrichment of CD56+ NK cells allows the collection of a suitable number of target cells to be used as adoptive immunotherapy in AML patients. Infusion of cryopreserved NK cells is feasible and safe and adoptively transferred NK cells can be detected in the peripheral blood after infusion.

Stromal Cells Support a Myeloid Pathway of Human NK Cell Differentiation.

Natural killer (NK) cells belong to the lymphocyte lineage; however a myeloid origin has been debated in the past based on nascent experimental evidence. We studied the in vitro development of human NK cells from UCB-derived CD34+ cells following culture with cytokines (IL15, IL7, SCF, FLT3L, IL3) on a murine fetal stromal cell line EL08.1D2 (Blood , 2006; 108: 3824–3833). We investigated the differential requirement of CD34+ subsets for stromal cell support. Limiting dilution experiments showed that CD34+ cells negative for phenotypic markers of NK commitment (CD7, CD161, integrin B7, CD122, CD45RA) absolutely require stromal cells and/or addition of hydrocortisone (HC) to differentiate into functional NK cells. Without stromal cells or HC those progenitors give rise to myeloid lineage cells, but not NK cells. Thus, we hypothesized that stromal cells could instruct myeloid precursors to convert to the NK lineage. Indeed, CD56+ cells generated in stroma supported cultures frequently co-express CD33 and CD13. To determine whether myeloid cells developing from CD34+ cells after 2–3 wk cultures could give rise to NK cells, we FACS sorted the CD56−CD33+CD13high and CD56−CD14+ populations. Such CD33+CD13high and CD14+ cells express macrosialin (CD68) and acquire lyzozyme (by FACS), confirming their myeloid characteristics. Sorted cells cultured further in cytokines alone (IL15, IL7, SCF, FLT3L) did not give rise to NK cells. However, in the presence of cytokines, stromal cells and HC, NK cells were generated. To exclude the possibility of NK cell contamination, CD33+CD13high and CD14+ cells were isolated from cultures of CD34+ cells in conditions not supportive of NK cell development (GM-CSF, IL3, FLT3L, SCF, without stroma, IL15 or IL7). Such cells gave the same results as above (i.e., NK cells developed only with stroma and HC). In additional studies, a fraction (∼16%) of CFU-GM colonies isolated from methylocellulose cultures could generate NK cells only in the presence of stromal cells, HC and cytokines, but not cytokines alone. As more of a definitive marker of the monocytic lineage, we used the surface expression of M-CSF receptor (CD115) on hematopoietic precursors. CD56−CD117+CD115+ and CD56−CD117+CD115− fractions were FACS sorted from 2–3 wk cultures of CD34+ cells. While both populations could differentiate into NK cells, only the CD115+ monocytic precursors required stromal cells. Quantitatively the CD117+CD115− cells were the main source of NK cells in this culture system. Notably the NK cells derived from CD115+ precursors were remarkably different, showing significantly higher expression of Killer Immunoglobulin-like Receptors (KIR: CD158a, CD158b and CD158e) than their CD115− derived counterparts (52% vs 15% KIR+, n=3, p=0.002). With respect to the repertoire of HLA-specific inhibitory receptors, NK cells derived from monocytic precursors resemble the dominant fraction of peripheral blood NK cells, including potentially alloreactive NK cells (KIR+CD94/NKG2A−). Collectively we present evidence that NK cells can be derived from developmental intermediates of the monocytic lineage and this differentiation pathway is dependent upon interaction with stroma. Our data indicate that the developmental trajectory shapes the pattern of inhibitory receptor expression on mature NK cells. Such findings have bearing on our understanding of NK cell biology, post transplant NK cell reconstitution and could explain the paucity of recognized immature NK cell leukemias coinciding with the occurrence of AML variants with NK specific antigen expression.

KIR Gene and KIR Ligand Analysis to Predict Graft Rejection After Renal Transplantation

The identification of transplant patients at high risk for rejection after reduction of immunosuppression would allow minimization of immunosuppression and avoidance of side effects in low-risk patients. Next to T cells, innate natural killer (NK) cells may contribute to graft rejection. NK cell activation depends on the balance between activating and inhibitory signals, delivered by self-human leukocyte antigens (HLA) through binding of killer-cell immunoglobulin receptors (KIR). In transplantation, KIR and/or HLA mismatching may lead to NK cell activation. In this study, we have evaluated whether acute rejection after reduction of immunosuppression after renal transplantation was associated with peripheral blood NK cell frequencies or with predicted NK cell alloreactivity based on KIR gene and ligand analysis. HLA and KIR genotyping was used to analyze the presence of single KIR genes and haplotypes, and to predict NK cell alloreactivity based on the "missing self" and "missing ligand" hypothesis. NK cell frequencies were analyzed using flow cytometry. No association was found between NK cell alloreactivity based on KIR gene analysis or peripheral blood NK cell subset frequencies and the occurrence of acute rejection after reduction of immunosuppression. Our data suggest that in a setting where immunosuppression is reduced, prior analysis of NK cell reactivity cannot identify patients at risk for subsequent graft rejection.

NK cell alloreactivity and allogeneic hematopoietic stem cell transplantation

As only 60% of leukaemia patients find a matched donor, the Perugia Bone Marrow Transplant Centre developed transplantation from HLA haplotype-mismatched family donors to provide a cure for more patients [F. Aversa, A. Tabilio, A. Terenzi, et al., Successful engraftment of T-cell-depleted haploidentical "three-loci" incompatible transplants in leukemia patients by addition of recombinant human granulocyte colony-stimulating factor-mobilized peripheral blood progenitor cells to bone marrow inoculum, Blood 84 (1994) 3948–3955] [F. Aversa, A. Tabilio, A. Velardi, et al., Treatment of high-risk acute leukemia with T-cell-depleted stem cells from related donors with one fully mismatched HLA haplotype, N. Engl. J. Med. 339 (1998) 1186–1193] [F. Aversa, A. Terenzi, A. Tabilio, et al., Full haplotype-mismatched hematopoietic stem-cell transplantation: a phase II study in patients with acute leukemia at high risk of relapse, J. Clin. Oncol. 23 (2005) 3447–3454]. HLA-mismatches trigger donor vs. recipient NK cell alloreactivity which improves engraftment, protects from GvHD and reduces relapse in AML patients [L. Ruggeri, M. Capanni, E. Urbani, et al., Effectiveness of donor natural killer cell alloreactivity in mismatched hematopoietic transplants, Science 295 (2002) 2097–2100], [L. Ruggeri, A. Mancusi, M. Capanni, E. Urbani, A. Carotti, T. Aloisi, M. Stern, D. Pende, K. Perruccio, E. Burchielli, F. Topini, E. Bianchi, F. Aversa, M.F. Martelli, A. Velardi, Donor natural killer cell allorecognition of missing self in haploidentical hematopoietic transplantation for acute myeloid leukemia: challenging its predictive value, Blood, in press]. We are using murine transplant models to determine whether NK cell alloreactivity can be exploited to reduce transplant-related mortality (TRM) which remains a major issue. Data from these on-going studies show pre-transplant infusion of alloreactive NK cells: (1) ablates AML cells, (2) kills recipient T cells, permitting a reduced toxicity conditioning regimen, and (3) ablates the recipient dendritic cells (DCs) which trigger GvHD, thus protecting from GvHD while permitting a higher T cell content in the graft. We are designing a clinical haploidentical transplant trial using alloreactive NK cells in the conditioning regimen, with the aim of reducing TRM and improving outcomes and overall survival.

Patients benefit from the addition of KIR repertoire data to the donor selection procedure for unrelated haematopoietic stem cell transplantation

Killer cell immunoglobulin-like receptors (KIRs) expressed on donor natural killer (NK) cells are important for induction of NK cell alloreactivity in haematopoietic stem cell transplantation (HSCT). Current criteria in the selection procedure of an unrelated donor do not account for this potential NK alloresponse. In this study the KIR gene repertoire of 21 HSCT patients and all their potential, unrelated donors ( N = 64) has been identified by the sequence-specific priming (SSP) procedure. KIR genotype characteristics are correlated with HLA and clinical data. These data show that for 16 cases an HLA compatible alternative donor was available. Among those 16 were 8 donors with a favourable predicted NK alloreactivity directed against the leukaemic cells. In conclusion, it is feasible and clinically relevant to add the KIR repertoire to the unrelated donor selection procedure.

Rapid natural killer cell recovery determines outcome after T-cell-depleted HLA-identical stem cell transplantation in patients with myeloid leukemias but not with acute lymphoblastic leukemia

Natural killer (NK) cells are the first lymphocytes to recover after allogeneic stem cell transplantation (SCT) and can exert powerful graft-versus-leukemia (GVL) effects determining transplant outcome. Conditions governing NK cell alloreactivity and the role of NK recovery in sibling SCT are not well defined. NK cells on day 30 post-transplant (NK30) were measured in 54 SCT recipients with leukemia and donor and recipient killer immunoglobulin-like receptor (KIR) genotype determined. In univariate analysis, donor KIR genes 2DL5A, 2DS1, 3DS1 (positive in 46%) and higher numbers of inhibitory donor KIR correlated with higher NK30 counts and were associated with improved transplant outcome. NK30 counts also correlated directly with the transplant CD34 cell dose and inversely with the CD3+ cell dose. In multivariate analysis, the NK30 emerged as the single independent determinant of transplant outcome. Patients with NK30 >150/microl had less relapse (HR 18.3, P=0.039), acute graft-versus-host disease (HR 3.2, P=0.03), non-relapse mortality (HR 10.7, P=0.028) and improved survival (HR 11.4, P=0.03). Results suggest that T cell-depleted SCT might be improved and the GVL effect enhanced by selecting donors with favorable KIR genotype, and by optimizing CD34 and CD3 doses.

Reconstitution of Natural Killer Cell Receptor Repertoires after Unmanipulated HLA-Mismatched/Haploidentical Blood and Marrow Transplantation: Analyses of CD94:NKG2A and Killer Immunoglobulin-Like Receptor Expression and Their Associations with Clinical Outcome

The effect of natural killer (NK) cell alloreactivity on the outcome of haploidentical hematopoietic stem cell transplantation (HSCT), with or without in vitro T cell depletion, remains controversial. Killer immunoglobulin-like receptors (KIRs) recognize human leukocyte antigen C and B epitopes on target cells, thereby regulating NK cell activity. To examine the recovery of CD94:NKG2A and KIR (CD158a, CD158b, and CD158e) expression by NK cells, we used flow cytometry to evaluate samples from 24 patients and their donors before and in the year following unmanipulated HLA-haploidentical/mismatched blood and marrow transplantation. Linear regression analysis demonstrated that NKG2A recovery was inversely correlated with CD158b recovery in the year following transplant. The doses of T cell subgroups CD4 + and CD8 + were inversely associated with CD158a and CD158e expression during the 2 months following transplantation. Moreover, patients with grades II-IV acute graft-versus-host disease (aGVHD) or who received “high” doses of T cells (>1.37 × 10 8/kg) showed delayed recovery of KIRs during the 2 months following transplantation. Univariate analysis showed that patients with high CD94 expression by day 60 (>90%) or who received donors with high CD94 expression (>80%) were associated with higher transplantation-related mortality ( P = .006 or .067, respectively) and poorer leukemia-free survival ( P = .012 or .094, respectively). Thus, the occurrence of aGVHD or the receipt of high doses of T cells in the allograft altered KIR reconstitution. Furthermore, high levels of CD94 expression in donors or in recipients by day 60 might be a good predictor for poor prognosis.

Functional dichotomy of NK cells in organ transplantation

Evaluation of: Yu G, Xu X, Vu MD, Kilpatrick ED, Li XC. NK cells promote transplant tolerance by killing donor antigen-presenting cells. J. Exp. Med. 203, 1851–1858 (2006).Natural killer (NK) cells have the potential to display different functional activities after transplantation. The traditional view is that NK cells have the capacity to contribute to rejection by facilitating the activation/differentiation of leukocytes that destroy the graft. By contrast, in the article under review, a novel role for NK cells was identified in the setting of costimulation blockade where alloreactive NK cells of recipient origin were found to have the capacity to kill donor-derived antigen-presenting cells, thereby reducing T-cell priming and promoting long-term skin graft acceptance.

Natural killer cell alloreactivity in allogeneic hematopoietic transplantation

This review will focus on the translation of natural killer cell recognition of missing self into the clinical practice of allogeneic hematopoietic transplantation and discuss how it has opened innovative perspectives in the cure of leukemia. Allogeneic hematopoietic stem cell transplantation from a human leukocyte antigen-matched sibling can cure leukemia but 75% of patients do not have a matched donor, one alternative source of stem cells includes full haplotype mismatched family members. As haploidentical transplantation must be extensively T cell depleted to prevent lethal graft-versus-host disease, it cannot rely on donor T cells for the graft-versus-leukemia effect. Mismatched transplantation, however, triggers alloreactivity mediated by natural killer cells which is based upon 'missing self recognition'. Recent studies using preclinical murine models of haploidentical transplantation demonstrated that conditioning with alloreactive natural killer cells ablates the recipient immune system and leukemia cells. In the clinical setting of mismatched hematopoietic stem cell transplantation, donor versus recipient natural killer cell alloreactivity has been associated with better outcome, particularly in patients with acute myeloid leukemia who are transplanted in remission. Given the benefits of natural killer cell alloreactivity, it is expected that it will encourage greater use of haploidentical transplants for the large numbers of leukemia patients without matched donors.

Human natural killer cells in health and disease

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 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.

Detrimental Effect of Natural Killer Cell Alloreactivity in T-replete Hematopoietic Cell Transplantation (HCT) for Leukemia Patients

In hematopoietic cell transplantation (HCT), natural killer cell alloreactivity conferred by inhibitory ligands of killer immunoglobulin-like receptors (iKIRLs) may result in beneficial or detrimental outcomes. More data may contribute to resolution of this complex issue. We analyzed 378 primary allogeneic transplants with T-replete grafts for acute lymphoblastic leukemia (n = 101), acute myeloid leukemia and myelodysplastic syndrome (n = 149), and chronic myeloid leukemia (n = 128). The cohort was divided into 3 groups: in group 1, HLA class I matched at the antigen level (n = 260); in group 2, HLA class I mismatched at the antigen level (n = 57); and in group 3, HLA class I and iKIRLs mismatched (n = 61). One-year overall survival (OS) across groups 1 (59%), 2 (49%), and 3 (30%) was significantly different ( P = .002). In contrast to group 2, group 3 had statistically lower OS ( P = .05) and event-free survival ( P = .01). Relapse and relapse-free mortality appeared to contribute to the low OS in group 3. The detrimental effect of natural killer alloreactivity was also evident when HLA-matched transplants were analyzed for patients lacking iKIRLs. One-year OS in patients lacking the HLA-Cw group 1 or 2 iKIRL was significantly lower than that in patients having the iKIRLs (55% vs 67%, n = 246, P = .01). Our observations indicate that, in T-replete unrelated HCT, iKIRL mismatches and the absence of iKIRLs confer higher risk to patients after HCT.