Impact of Donor Activating KIR Genes on HSCT Outcome in C1-Ligand Negative Myeloid Disease Patients Transplanted with Unrelated Donors-A Retrospective Study

Donor aKIR genes influence the risk of EBV and CMV reactivation after anti-thymocyte globulin-based haploidentical hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) offers the highest curative potential for patients with hematological malignancies. Complications including infection, graft-versus-host disease (GVHD), and relapse reflect delayed or dysregulated immune reconstitution. After transplantation, NK cells rapidly reconstitute and are crucial for immune surveillance and immune tolerance. NK cell function is tightly regulated by killer immunoglobin-like receptors (KIRs). Previous studies have revealed that donor KIRs, especially some activated KIRs (aKIRs) are closely related to transplant outcomes. Here, we performed a retrospective study, including 323 patients who received haploidentical (haplo) HSCT in our center. In univariate analysis, donor KIR2DS1, KIR2DS3 and KIR3DS1 gene protected patients with lymphoid disease from Epstein-Barr virus (EBV) and cytomegalovirus (CMV) reactivation, while donor KIR2DS1, KIR2DS5 and KIR3DS1 gene conferred a higher risk of CMV reactivation for patients with myeloid disease. Multivariate analysis confirmed that donor telomeric (Tel) B/x and KIR2DS3 gene best protected patients with lymphoid disease from EBV (p = 0.017) and CMV reactivation (p = 0.004). In myeloid disease, grafts lacking Tel B/x and KIR2DS5 gene correlated with the lowest risk of CMV reactivation (p = 0.018). Besides, donor aKIR genes did not influence the rates of GVHD, relapse, non-relapse mortality (NRM) and overall survival (OS) in this study. The reactivation of EBV and CMV was associated with poor prognosis of haplo-HSCT. In conclusion, we found that donor aKIR genes might have a synergistic effect on CMV and EBV reactivation after haplo-HSCT. Whether the influence of donor aKIR genes varies with disease types remained to be studied.

Current donor selection strategies for allogeneic hematopoietic cell transplantation

Since the first allogeneic hematopoietic stem cell transplantation (HCT) was performed by Dr. E. Donnall Thomas in 1957, the field has advanced with new stem cell sources, immune suppressive regimens, and transplant protocols. Stem cells may be collected from bone marrow, peripheral or cord blood from an identical twin, a sibling, or a related or unrelated donor, which can be human leukocyte antigen (HLA) matched, mismatched, or haploidentical. Although HLA matching is one of the most important criteria for successful allogeneic HCT (allo-HCT) to minimize graft vs host disease (GVHD), prevent relapse, and improve overall survival, the novel immunosuppressive protocols for GVHD prophylaxis offered improved outcomes in haploidentical HCT (haplo-HCT), expanding donor availability for the majority of HCT candidates. These immunosuppressive protocols are currently being tested with the HLA-matched and mismatched donors to improve HCT outcomes further. In addition, fine-tuning the DPB1 mismatching and discovering the B leader genotype and mismatching may offer further optimization of donor selection and transplant outcomes. While the decision about a donor type largely depends on the patient's characteristics, disease status, and the transplant protocols utilized by an individual transplant center, there are general approaches to donor selection dictated by donor-recipient histocompatibility and the urgency for HCT. This review highlights recent advances in understanding critical factors in donor selection strategies for allo-HCT. It uses clinical vignettes to demonstrate the importance of making timely decisions for HCT candidates.

Donor selection based on NK alloreactivity for patients with hematological malignancies

Natural killer (NK) cells are an important defender against infections and tumors. Their function is regulated by the balance of inhibitory and activating receptors. Among all inhibitory NK receptors: killer immunoglobulin-like receptors (KIR) and CD94/NKG2A recognize human leukocyte antigen (HLA) Class I molecules, allowing NK cells to be 'licensed' to avoid autoreactivity, but be fully functional at the same time. Licensed NK cells can target malignant cells with altered or downregulated/missing 'self' antigens. NK cell attacking malignant cells is one of the mechanisms of graft-versus-leukemia (GVL) effect. Numerous studies have demonstrated that NK cells improve hematopoietic stem cell transplantation (HCT) survival by reducing relapse mortality through GVL effect. Therapeutic strategies, such as adoptive alloreactive NK cell transfer, CAR-NK cells, antibodies against NKG2A and KIR2DL1-3, have been utilized to treat hematological malignancies in HCT. In this review, NK cell functions, NK cell receptors and ligands, as well as common alloreactive NK donor selection algorithms for patients with hematological malignancies in the setting of HCT are discussed. The goal of this review is to provide insights on the controversial results and provide better understanding and resources on how to perform alloreactive donor NK cell selection in HCT.

Dynamic mRNA expression of donor-derived activating KIR genes and their significant effects on clinical outcome after haematopoietic stem cell transplantation

Numerous reports suggest that activating killer immunoglobulin-like receptors (aKIRs) of natural killer (NK) cells, in addition to inhibitory KIRs (iKIRs), play a prognostic role after allogeneic haematopoietic stem cell transplantation (allo-HSCT). We aimed to investigate the association between the dynamic expression of KIRs on NK cells and the outcomes, particularly regarding graft-versus-host disease (GvHD). This study retrospectively enrolled 260 pairs of donors and recipients who had undergone allo-HSCT without in-vitro T cell depletion. The mRNA transcription level of KIRs was determined by quantitative real-time polymerase chain reaction (RT-qPCR). The levels of aKIR transcripts were decreased more than those of iKIRs during the occurrence of GvHD. The transcription levels of KIR2DS2 and KIR2DS4 in the patients developing GvHD, compared with those who were at a tolerance state, showed the most significant decrease in the month at their peak transcription levels (p = 0.03, p = 0.002). Significantly decreased expression of KIR2DS1 (p = 0.02), KIR2DS3 (p = 0.04) and KIR2DS5 (p = 0.04) in the GvHD group was observed when the transcription level reached a maximum. High expression of KIR3DS1 was associated with superior overall survival (OS) (p < 0.001). The expression of KIR2DS4 in the KIR genotype Bx group decreased more during GvHD, particularly at 3M (p = 0.02). These findings suggest that KIR genes are potential post-HSCT biomarkers and dynamic changes in the KIR transcription levels can be detected to better predict the occurrence and evaluate the treatment of GvHD after transplantation.

BSHI guideline: HLA matching and donor selection for haematopoietic progenitor cell transplantation

A review of the British Society for Histocompatibility and Immunogenetics (BSHI) Guideline 'HLA matching and donor selection for haematopoietic progenitor cell transplantation' published in 2016 was undertaken by a BSHI appointed writing committee. Literature searches were performed and the data extracted were presented as recommendations according to the GRADE nomenclature.

Dual effects of natural killer cells in transplantation for leukemia

Natural killer (NK) cells were originally considered to belong to the innate immune system to play a protective role against tumor cells and viral infections. In human, they can recognize self and non-self HLA class 1 as their ligand. So, analyzing the outcomes of allogeneic hematopoietic stem cell transplantation is a good opportunity to know the antitumor effects and regulatory effects of NK cells through HLA class 1 matching and mismatching of donor and recipient. In this review, I looked back on the main analysis results of the past transplants, summarized our reports consisting of many cases in a single ethnic, and showed that NK cells might work oppositely depending on the type of leukemia. New treatment strategies based on these concepts may offer individualized treatment options and ultimately increase offer the possibility of a cure for patients with leukemia.

Dynamic Changes of Inhibitory Killer-Immunoglobulin-Like Receptors on NK Cells after Allogeneic Hematopoietic Stem Cell Transplantation: An Initial Study

Killer-immunoglobulin-like receptors (KIRs) are critical natural killer (NK) cell regulators. The expression of KIRs is a dynamic process influenced by many factors. Their ligands-HLA(Human Leukocyte Antigen) class I molecules-are expressed on all nucleated cells that keep NK cells under control. In hematopoietic stem cell transplantation (HSCT), NK cells play an essential role in relapse protection. In the presented pilot study, we characterized the dynamic expression of inhibitory KIRS (iKIRs), which protect cells against untoward lysis, in donors and patients during the first three months after HSCT using flow cytometry. The expression of all iKIRs was highly variable and sometimes correlated with patients' clinical presentation and therapy regiment. Cyclophosphamide (Cy) in the graft-versus-host disease (GvHD) prevention protocol downregulated KIR2DL1 to just 25% of the original donor value, and the FEAM (Fludarabine + Etoposid + Ara-C + Melphalan) conditioning protocol reduced KIR2DL3. In lymphoid neoplasms, there was a slightly increased KIR2DL3 expression compared to myeloid malignancies. Additionally, we showed that the ex vivo activation of NK cells did not alter the level of iKIRs. Our study shows the influence of pre- and post-transplantation protocols on iKIR expression on the surface of NK cells and the importance of monitoring their cell surface.

Umbilical Cord Blood and iPSC-Derived Natural Killer Cells Demonstrate Key Differences in Cytotoxic Activity and KIR Profiles

Natural killer (NK) cells derived or isolated from different sources have been gaining in importance for cancer therapies. In this study, we evaluate and compare key characteristics between NK cells derived or isolated from umbilical cord blood, umbilical cord blood hematopoietic stem/progenitor cells, peripheral blood, and induced pluripotent stem cells (iPSCs). Specifically, we find CD56⁺ NK cells isolated and expanded directly from umbilical cord blood (UCB56) and NK cells derived from CD34⁺ hematopoietic stem/progenitors in umbilical cord blood (UCB34) differ in their expression of markers associated with differentiation including CD16, CD2, and killer Ig-like receptors (KIRs). UCB56-NK cells also displayed a more potent cytotoxicity compared to UCB34-NK cells. NK cells derived from iPSCs (iPSC-NK cells) were found to have variable KIR expression, with certain iPSC-NK cell populations expressing high levels of KIRs and others not expressing KIRs. Notably, KIR expression on UCB56 and iPSC-NK cells had limited effect on cytotoxic activity when stimulated by tumor target cells that express high levels of cognate HLA class I, suggesting that in vitro differentiation and expansion may override the KIR-HLA class I mediated inhibition when used across HLA barriers. Together our results give a better understanding of the cell surface receptor, transcriptional, and functional differences between NK cells present in umbilical cord blood and hematopoietic progenitor-derived NK cells which may prove important in selecting the most active NK cell populations for treatment of cancer or other therapies.

Influence of KIR and NK Cell Reconstitution in the Outcomes of Hematopoietic Stem Cell Transplantation

Natural killer (NK) cells play a significant role in immune tolerance and immune surveillance. Killer immunoglobin-like receptors (KIRs), which recognize human leukocyte antigen (HLA) class I molecules, are particularly important for NK cell functions. Previous studies have suggested that, in the setting of hematopoietic stem cell transplantation (HSCT), alloreactive NK cells from the donor could efficiently eliminate recipient tumor cells and the residual immune cells. Subsequently, several clinical models were established to determine the optimal donors who would exhibit a graft-vs. -leukemia (GVL) effect without developing graft-vs. -host disease (GVHD). In addition, hypotheses about specific beneficial receptor-ligand pairs and KIR genes have been raised and the favorable effects of alloreactive NK cells are being investigated. Moreover, with a deeper understanding of the process of NK cell reconstitution post-HSCT, new factors involved in this process and the defects of previous models have been observed. In this review, we summarize the most relevant literatures about the impact of NK cell alloreactivity on transplant outcomes and the factors affecting NK cell reconstitution.

Presence of donor-encoded centromeric KIR B content increases the risk of infectious mortality in recipients of myeloablative, T-cell deplete, HLA-matched HCT to treat AML

The reported influence of donor Killer-cell Immunoglobulin-like Receptor (KIR) genes on the outcomes of haematopoietic cell transplantation (HCT) are contradictory, in part due to diversity of disease, donor sources, era and conditioning regimens within and between different studies. Here, we describe the results of a retrospective clinical analysis establishing the effect of donor KIR motifs on the outcomes of 119 HLA-matched, unrelated donor HCT for adult acute myeloid leukaemia (AML) using myeloablative conditioning (MAC) in a predominantly T-cell deplete (TCD) cohort. We observed that HCT involving donors with at least one KIR B haplotype were more likely to result in non-relapse mortality (NRM) than HCT involving donors with two KIR A haplotypes (p = 0.019). Upon separation of KIR haplotypes into their centromeric (Cen) and telomeric (Tel) motif structures, we demonstrated that the Cen-B motif was largely responsible for this effect (p = 0.001). When the cause of NRM was investigated further, infection was the dominant cause of death (p = 0.006). No evidence correlating donor KIR B haplotype with relapse risk was observed. The results from this analysis confirm previous findings in the unrelated, TCD, MAC transplant setting and imply a protective role for donor-encoded Cen-A motifs against infection in allogeneic HCT recipients.

Killer-cell immunoglobulin-like receptor assessment algorithms in haemopoietic progenitor cell transplantation: current perspectives and future opportunities

Natural killer cells preferentially target and kill malignant and virally infected cells. Both these properties present compelling clinical utility in the field of haemopoietic progenitor cell transplantation (HPCT), potentially promoting a graft vs leukaemia effect in the absence of graft vs host disease and protecting against cytomegalovirus activation. Killer Ig-like receptors (KIR) play a central role in the cytotoxic action of natural killer cells, providing opportunity for improving transplantation outcomes by prioritising potential donors with optimal characteristics. Numerous algorithms for assessing KIR gene content as part of HPCT donor selection protocols exist, but no single model has been found to be universally applicable in all transplant centres. This review summarises several of the predominant strategies in KIR assessment algorithms, discussing their basic scientific principles, clinical utility and benefits to post-transplant outcomes. Finally, the review will consider how future donor selection protocols could develop towards unifying the concepts of KIR proteomics and genetics for optimising patient care.

Study of KIR gene expression at the mRNA level in specific donor-derived NK cells after allogeneic HSCT

The function of natural killer (NK) cells after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is regulated by the balance between inhibitory KIRs (iKIRs) and activating KIRs (aKIRs). However, few studies have examined the subsequent expression of KIR genes unique to the donor. We defined the set of KIR genes expressed only in the donor and designed a method for measuring the expression of these KIR genes by quantitative real-time polymerase chain reaction (RT-qPCR) based on genetic cloning techniques. In this study, we evaluated the recovery pattern of KIR genes in 252 donor-recipient pairs. The expression of each KIR unique to the donor was in line with that of KIR genes shared by the donor and recipient, such as KIR2DS1, KIR3DS1, KIR2DS4, or KIR2DS3. The timing of the peak mRNA expression of aKIRs unique to the donor was inconsistent but occurred within the first 3 months posttransplantation, whereas the peak mRNA expression of iKIRs was consistently observed in the third month after transplantation. The expression of KIR2DL2 in the third month posttransplantation was significantly higher in the transplant recipients than in the donors (p = 0.01). The KIR2DL1 and KIR3DL1 levels in the transplant recipients in the second and third months posttransplantation were also obviously higher than the donor levels (p < 0.0001). Thus, these observations should be considered when attempting to predict the correlation between mRNA expression and prognosis after allo-HSCT.

Increased Relapse Risk of Acute Lymphoid Leukemia in Homozygous HLA-C1 Patients after HLA-Matched Allogeneic Transplantation: A Japanese National Registry Study

Natural killer (NK) cells expressing killer cell immunoglobulin-like receptors (KIRs) can recognize specific HLA class I molecules as their ligands. By studying a large Japanese transplant registry, we compared transplant outcomes between patients heterozygous for HLA-C^Asn80/C^Lys80 (HLA-C1/C2) and those homozygous for HLA-C1 (HLA-C1/C1) among patients who had undergone HLA-matched hematopoietic stem cell transplantation (HSCT). A high frequency of KIR2DL1 with strong HLA-C2 binding capacity and a low frequency of HLA-C2 and KIR haplotype B are characteristic of the Japanese population. In our previous report, HLA-C1/C1 patients with myeloid leukemia were less likely to relapse than HLA-C1/C2 patients. We newly assessed 2884 patients with acute lymphoblastic leukemia (ALL) who received HLA-matched allogeneic HSCT and analyzed their leukemia relapses by using adjusted competing-risk methods. HLA-C1/C1 patients with ALL experienced significantly higher relapse rates than HLA-C1/C2 patients (hazard ratio [HR] = 1.55, P = .003), contrary to our results in patients with myeloid leukemia. We allocated patients with ALL to several subgroups and found a higher frequency of relapse (HR >1.8) in the HLA-C1/C1 group than in the HLA-C1/C2 group among patients with Ph-negative ALL, those who had no cytomegalovirus reactivation, those who received transplants from donors who were aged 41 years or older, and those who experienced acute graft-versus-host disease, especially if it required systemic treatment. One interpretation of our results is that KIR2DL1-positive NK cells disrupt T cells, antigen-presenting cells, or both from working efficiently in transplant immunity in HLA-C1/C1 patients with ALL. Another is that KIR2DS1-positive NK cells directly attack HLA-C2-positive ALL blasts in HLA-C1/C2 patients. Whether HLA-C2 can cause recurrence to decrease or increase in patients depending on the disease (ALL or myeloid leukemia) will be a very important finding. We hope that our results will provide clues to the real mechanisms behind relapse after transplantation in patients with different HLA profiles.

Imbalance of Genes Encoding Natural Killer Immunoglobulin-Like Receptors and Human Leukocyte Antigen in Patients With Biliary Cancer

BACKGROUND & AIMS

Bile duct tumors are rare and have poor prognoses. Natural killer (NK) cells are frequent in human liver and infiltrate these tumors but do not control their progression. Responses of NK cells are regulated by NK immunoglobulin-like receptors (KIRs), which interact with HLA class I ligands. We aimed to characterize the features of the KIR gene loci and their ligands in patients with bile duct cancer (BDC).

METHODS

We performed combined multidimensional characterization of genes that encode KIRs and their ligands in blood samples from patients with BDC from Sweden, followed for up to 8 years after diagnosis (n = 148), in 2 geographically matched cohorts of healthy individuals from Northern Europe (n = 204 and n = 900), and in healthy individuals from 6 geographically unrelated populations (n = 2917). We used real-time polymerase chain reaction, RNA sequencing, immunohistochemistry, and flow cytometry to evaluate NK-cell presence, as well as KIR and KIR-ligand expression in bile duct tumors and control tissues.

RESULTS

Patients with bile duct tumors had multiple alterations at the KIR gene loci. KIR loci are grouped into genotypes that encode more inhibitory (group A) and more activating (group B) receptors, which can be subdivided into centromeric and telomeric fragments. Patients with BDC had a lower prevalence of KIR2DL3, which was linked to disequilibrium in centromeric A/B and B/B genotypes, compared with control individuals. The associations between KIRs and KIR ligands differed between patients with BDC and control individuals; patients had an altered balance between activating and inhibitory KIRs. KIR-positive NK cells infiltrated biliary tumors that expressed matched KIR ligands.

CONCLUSIONS

In a multidimensional analysis of DNA from blood samples of patients with BDC in Europe, we found patients to have multiple alterations at the KIR and HLA gene loci compared with control individuals. These alterations might affect NK-cell tumor surveillance. NK cells from bile duct tumors expressed KIRs and were found in tumors that expressed cognate ligands. This should be considered in development of immune-based therapies for BDC.

Donor KIR2DS1 reduces the risk of transplant related mortality in HLA-C2 positive young recipients with hematological malignancies treated by myeloablative conditioning

Background

Recognition of HLA-C2 group alleles on recipient cells by activating killer immunoglobulin like receptors, KIR2DS1 on donor natural killer cells may lead to increased graft-versus-leukemia effect or immunomodulation in patients treated by allogeneic hematopoietic stem cell transplantation (allo-HSCT) influencing disease free and overall survival (OS).

Objective

In the present study, 314 consecutive, allo-HSCT recipient and donor pairs were included with retrospective donor KIR-genotyping and clinical parameters analyzes.

Results

After a median follow-up of 23.6 months, recipients with HLA-C2 group allele (rC2) showed improved (p = 0.046) OS if transplanted with KIR2DS1 positive donors (d2DS1) compared to those without one or both of this genetic attribute. Within the myeloablative conditioning (MAC) subgroup (n = 227), rC2 homozygous+d2DS1 patients (n = 14) showed a 5 years OS of 93% followed by rC2 heterozygous+d2DS1 patients (n = 48, 65%) compared to rC2 and/or d2DS1 negatives (47%, p = 0.018). Multivariate analyses indicated rC2+d2DS1 positivity as an independent predictor of OS (HR:0.47, 0.26–0.86, p = 0.014) besides donor type, presence of CMV-reactivation or chemoresistant disease. Among MAC-treated patients, the combined rC2+d2DS1 presence was associated with a markedly decreased cumulative incidence of transplant related mortality (p = 0.0045).

Conclusion

The combination of rC2+d2DS1 may be a favorable genetic constellation in allo-HSCT with MAC potentially reducing transplant related mortality.

Selecting the Best Donor for Haploidentical Transplant: Impact of HLA, Killer Cell Immunoglobulin-Like Receptor Genotyping, and Other Clinical Variables

The use of post-transplant cyclophosphamide (PTCy)-based haploidentical (haplo) transplant is increasing worldwide. However, because multiple potential haplo donors are usually available, data-driven guidance is clearly needed to help transplant centers prioritize donors. To that end, we retrospectively analyzed 208 consecutive donor-recipient pairs receiving PTCy-based haplo transplant at a single institution. Median recipient and donor age were 52 years (range, 19 to 75) and 38 years (range, 15 to 73), peripheral blood stem cell was the stem cell source in 66%, and myeloablative conditioning was used in 41%. Median follow-up for surviving patients was 33 months (range, 7 to 130). Donor variables analyzed included age, sex, relationship, cytomegalovirus (CMV) status, ABO compatibility, HLA disparity, and several natural killer (NK) alloreactivity models. Multivariate Cox analysis was used to adjust for known patient, disease, and transplant covariates. Donor characteristics independently associated with improved survival included presence of HLA-DR mismatch, HLA-DP nonpermissive mismatch, killer cell immunoglobulin-like receptor (KIR) receptor-ligand mismatch, and KIR B/x haplotype with KIR2DS2. Donor characteristics associated with inferior survival included parental donor relationship and the use of a CMV-seronegative donor for a CMV-seropositive patient. Increased HLA disparity (≥4/10 HLA allelic mismatches [graft-versus-host direction]) resulted in relapse protection at the expense of increased nonrelapse mortality with no associated survival effect. We further propose a donor risk factor scoring system to permit a more evidence-based selection algorithm for potential haplo donors. This large, single-institution analysis demonstrates the importance of HLA-DR/HLA-DP disparity, NK alloreactivity, and other clinical variables in the haplo donor selection process and suggests that KIR and HLA-DP genotyping should be performed routinely for haplo donor selection.

NK cell therapy for hematologic malignancies

Natural killer (NK) cells are part of the innate immune system and represent the first line of defense against infections and tumors. In contrast to T cells, NK cells do not require prior antigen sensitization to induce cytotoxicity and do not cause graft-versus-host disease. These, along with other advantages, make NK cells an attractive candidate for adoptive cellular therapy. Herein, we describe the mechanisms of NK cell cytotoxicity, which is governed by an intricate balance between various activating and inhibitory receptors, including the killer cell immunoglobulin-like receptors (KIRs). We illustrate the advantages of NK alloreactivity as demonstrated in various types of hematopoietic stem cell transplants (HSCT), such as haploidentical, human leukocyte antigen-matched related or unrelated donor and umbilical cord blood transplant. We elaborate on different models used to predict NK cell alloreactivity in these studies, which are either based on the absence of the ligands for inhibitory KIRs, presence of activating NK cell receptors and KIR genes content in donors, or a combination of these. We will review clinical studies demonstrating anti-tumor efficacy of NK cells used either as a stand-alone immunotherapy or as an adjunct to HSCT and novel genetic engineering strategies to improve the anti-tumor activity of NK cells.

Selected biological issues affecting relapse after stem cell transplantation: role of T-cell impairment, NK cells and intrinsic tumor resistance

The graft vs. leukemia (GvL) effect as a method of preventing relapse is well described after allogeneic hematopoietic cell transplantation (HCT), but the mechanisms to this effect and how tumor sometimes develops resistance to GvL are just beginning to be understood. This article reviews and expands upon data presented at the Third International Workshop on Biology, Prevention and Treatment of Relapse after Stem Cell Transplantation held in Hamburg, Germany, in November 2016. We first discuss in detail the role that T-cell impairment early after HCT plays in relapse by looking at data from T cell-depleted approaches as well as the clear role that early T-cell recovery has shown in improving outcomes. We then review key findings regarding the role of specific KIR donor/recipient pairings that contribute to relapse prevention after HCT for several tumor types. Finally, we discuss a unique mouse model following the development of tumor resistance to GvL. Detailed molecular characterization of events marking the development of tumor resistance to the immunotherapy of GvL may help in developing future strategies to overcome immune escape.

Homozygous HLA-C1 is Associated with Reduced Risk of Relapse after HLA-Matched Transplantation in Patients with Myeloid Leukemia

Natural killer (NK) cells assume graft-versus-leukemia alloreactivity after hematopoietic stem cell transplantation (HSCT) through their inhibitory killer cell immunoglobulin-like receptors (KIRs). KIR2D family members recognize HLA-C alleles with Asn80 (HLA-C1) or Lys80 (HLA-C2). The predominance of HLA-C1 over HLA-C2 and the frequent presence of KIR2DL1 are characteristic of Japanese people. We compared clinical outcomes among homozygous HLA-C1 (HLA-C1/C1) patients and heterozygous HLA-C1/C2 patients who underwent HLA-matched HSCT for hematologic malignancies by assessing the data of 10,638 patients from the Japanese national registry. HLA-C1/C1 recipients had a lower rate of relapse than HLA-C1/C2 recipients after transplantation for acute myelogenous leukemia (AML) (hazard ratio [HR], .79; P = .006) and chronic myelogenous leukemia (CML) (HR, .48; P = .025), but not for acute lymphoblastic leukemia (HR, 1.36), lymphoma (HR, .97), or low-grade myelodysplastic syndrome (HR, 1.40). We then grouped AML and CML patients together and divided them into several subgroups. Advantages of HLA-C1/C1 recipients over HLA-C1/C2 recipients regarding relapse were observed irrespective of donor relation (related: HR, .79, P = .069; unrelated: HR, .77, P = .022), preparative regimen (myeloablative: HR, .79, P = .014; reduced intensity: HR, .73, P = .084), and occurrence of acute graft-versus-host disease (yes: HR, .70, P = .122; no, HR .71, P = .026) or cytomegalovirus reactivation (reactivated: HR .67,P = .054; nonreactivated: HR .71, P = .033); however, these advantages were not observed in recipients with a delay in achieving complete chimerism (HR, 1.06). The advantage of decreasing relapse and extending relapse-free survival of C1/1 over C1/2 KIR-ligand status was most pronounced in T cell-depleted HSCT (HR, .27; P < .001 and HR, .30; P = .002, respectively) and in children age <15 years (HR, .29; P < .001 and HR .31; P < .001, respectively). Our findings represent an important mechanism responsible for the immunity against HLA-C2-negative myeloid leukemia cells after HLA-matched transplantation.

The effect of killer cell immunoglobulin-like receptor genotype on outcome of hematopoietic stem cell transplantation from matched sibling

The alloreactivity of natural killer (NK) cell after allogeneic hematopoietic stem cell transplantation (AHSCT) is regulated by the interaction between donor killer immunoglobulin-like receptors (KIRs) and recipient human leukocyte antigen (HLA)-class I molecules. The aim was to identify KIR genes, haplotypes and their HLA-class I ligands and to investigate their association with transplantation outcome. The study included 65 patient/donor pairs who received AHSCT from HLA-matched identical siblings. KIR genotyping was done for donors using reverse sequence specific oligonucleotide probes (rSSO) coupled with luminex technology, while HLA-C genotyping was performed in patients using rSSO strip assay. In multivariate analysis, KIR2DS4 was associated with significant reduced incidence of relapse (p = .002). A trend towards reduced incidence of relapse was also observed with more than two KIR B motifs (p = .09), whereas a significant increased relapse was associated with homozygous HLA-C2 ligand compared to combined C1/C2 and C1/C1 (p = .04). Activating KIR2DS3 was associated with rapid leukocyte engraftment (p = .02). While, KIR 2DL5 was associated with decreased CMV infection (p = .03) and better platelets engraftment (p = .05). KIR genes, haplotypes and HLA-C alleles have an impact on HSCT outcome. Better selection of donors with favorable KIR genotype can improve HLA-matched sibling HSCT outcome especially for AML patients.