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• Absence of KIR2DL1 ligands increases relapse in HLA-matched hematopoietic stem cell transplantation (HSCT) for acute lymphoblastic leukemia (ALL). • This trend is prominent in patients with Ph-negative ALL who experienced acute graft-versus-host disease. • The trend is the opposite of that in our previous report analyzing HSCT for acute myeloid leukemia/chronic myeloid leukemia. 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-CAsn80/CLys80 (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. Image, graphical abstract [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Licensing by self MHC class I ligands is required for proper natural killer (NK) cell response. NK cells with inhibitory killer cell immunoglobulin-like receptors for nonself MHC exhibit transient alloreactivity after hematopoietic stem cell transplantation (HSCT). We analyzed 3866 recipients in the Japan national registry who underwent their first allogeneic HSCT for acute myeloid leukemia (AML) or acute lymphoblastic leukemia (ALL) from HLA-A, -B, and -DRB1 allele-genomatched unrelated donors. By classifying them into 5 independent groups based on HLA-C group matching and assumed donor NK cell status, we found that for HLA-C–matched HSCT for AML in HLA-C1/C1 recipients, in whom transient alloreactivity against HLA-C2–negative leukemic cells was expected, the relapse rate was significantly lower than it was in HLA-C–matched HSCT for AML in HLA-C1/C2 recipients (hazard ratio [HR], .72; P = .011). This difference was not observed in HLA-C–matched HSCT for ALL. Compared with HLA-C–matched HSCT, significantly higher mortality was observed in HLA-C1/C1 AML patients who received transplants from HLA-C–mismatched HLA-C1/C1 donors (HR, 1.37; P = .001) and in HLA-C1/C1 ALL patients who received transplants from HLA-C2–positive donors (HR, 2.13; P = .005). In conclusion, donor selection based on leukemic subtype and donor HLA-C group matching improves transplantation outcome after HLA-C–mismatched HSCT. [ABSTRACT FROM AUTHOR]

• Allogeneic hematopoietic stem cell transplantation is beneficial for patients with mature T cell and natural killer cell neoplasms. • Cord blood transplantation (CBT) resulted in favorable outcomes with a lower risk of relapse. • CBT could be a preferred option, especially for patients with uncontrolled diseases. • Better control of lymphoma at transplantation is a key to improved outcomes. Although allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the key strategy to cure patients with mature T and natural killer (NK) cell lymphomas/leukemia, especially those with relapsed/refractory diseases, there is no consensus strategy for donor selection. We retrospectively analyzed the outcomes of allo-HSCT in 111 patients in 15 Japanese institutions as a multi-institutional joint research project. Thirty-nine patients received bone marrow or peripheral blood stem cell transplantation from related donors (rBMT/rPBSCT), 37 received BMT/PBSCT from unrelated donors (uBMT/uPBSCT), and 35 received cord blood transplantation (CBT). Overall survival (OS) and progression-free survival (PFS) at 4 years were 42% and 34%, respectively. The cumulative incidences of relapse and nonrelapse mortality were 43% and 25%. In multivariate analysis, CBT showed comparable OS with rBMT/rPBSCT (rBMT/rPBSCT versus CBT: hazard ratio [HR], 1.63; P =.264) and better OS compared with uBMT/uPBSCT (HR, 2.99; P =.010), with a trend toward a lower relapse rate (rBMT/rPBSCT versus CBT: HR, 2.60; P =.010; uBMT/uPBSCT versus CBT: HR, 2.05; P =.082). This superiority of CBT was more definite in on-disease patients (OS: rBMT/rPBSCT versus CBT: HR, 5.52; P =.021; uBMT/uPBSCT versus CBT: HR, 6.80; P =.007). Better disease control was also strongly associated with better OS and PFS with lower relapse rate. In conclusion, allo-HSCT is beneficial for the survival of patients with mature T and NK cell lymphomas/leukemia if performed in a timely fashion. Since CBT showed favorable survival with a lower relapse risk, it could be a preferred alternative, especially in on-disease patients. [ABSTRACT FROM AUTHOR]

• All assessable patients with donor HLA-homo to patient HLA-hetero pairs among 5017 single CBT pairs were engrafted neutrophil (38 pairs) and platelets (30 pairs) and revealed a tendency of high incidence of acute GVHD. • Ethnicity-specific conserved extended HLA haplotypes (CEHs) were invariably shared with the same donor HP in 35 pairs. • These findings imply the possibility that HLA-homo iPSC transplantation provides favorable engraftment and accordingly imply the merit of banking iPSC with homozygous major CEHs. Induced pluripotent stem cells (iPSCs) have been applied to clinical regenerative cell therapy. Recently, an iPSC banking system to collect HLA haplotype (HP) homozygous (homo) cells for iPSC transplantation in allogeneic settings was proposed, and tissue transplantation generated from iPSC through banking has just began. We analyzed 5017 single cord blood transplantation (CBT) pairs with HLA-A, -B, -C, -DRB1 allele typing data and found 39 donor HLA homo donor to patient HLA heterozygous (hetero) pairs. Of note, all 39 HLA homo to hetero pairs engrafted neutrophils, except 1 early death pair, and all 30 assessable pairs engrafted platelets. Acute graft-versus-host disease (GVHD) grades II to IV and grades III to IV occurred in 17 and 3 of 38 assessable pairs, respectively. Competing risk regression analysis revealed a favorable risk of neutrophil engraftment and higher risk of acute GVHD compared with HLA-matched CBTs. Thirty-seven of 39 homo to hetero pairs had conserved extended HLA HPs (HP-1, n = 18; HP-2, n = 8; HP-3, n = 7; HP-4, n = 4; HP-5, n = 1) that were ethnicity-specific, and at least 1 of 2 patient HLA-A, -B, -C, and -DRB1 alleles in each locus were invariably shared with the same donor HP in 35 pairs. These findings confirmed our preliminary results with 6 HLA homo CBTs, and a trend of high incidence of acute GVHD was newly observed. Importantly, they imply the possibility that HLA-homo iPSC transplantation provides favorable engraftment and accordingly imply the merit of banking iPSC with homozygous major conserved extended HLA HPs. [ABSTRACT FROM AUTHOR]