Antonella Mancusi

Survival after T cell–depleted haploidentical stem cell transplantation is improved using the mother as donor

We hypothesized that transplacental leukocyte trafficking during pregnancy, which induces long-term, stable, reciprocal microchimerism in mother and child, might influence outcome of patients with acute leukemia given parental donor haploidentical hematopoietic stem cell transplantation (HSCT). We analyzed the outcome of 118 patients who received transplants for acute leukemia in 2 centers. Patients received highly T cell-depleted haploidentical grafts after myelo-ablative conditioning. Five-year event-free survival was better in patients who received transplants from the mother than from the father (50.6% +/- 7.6% vs 11.1% +/- 4.2%; P < .001). Better survival was the result of both reduced incidence of relapse and transplantation-related mortality. The protective effect was seen in both female and male recipients, in both lymphoid and myeloid diseases; it was more evident in patients receiving transplants in remission than in chemotherapy-resistant relapse. Incidences of rejection and acute graft-versus-host disease were not significantly influenced. Multivariate analysis confirmed donor sex in parental donor transplantation as an independent prognostic factor for survival (hazard ratio, father vs mother = 2.36; P = .003). In contrast, in a control cohort of patients who received transplants from haploidentical siblings, donor sex had no influence on outcome. Although obtained in a retrospective analysis, these data suggest that the mother of the patient should be preferred as donor for haploidentical HSCT.

Natural killer cell allorecognition of missing self in allogeneic hematopoietic transplantation: a tool for immunotherapy of leukemia

Donor-versus-recipient natural killer (NK) cell alloreactivity has been established as a key therapeutic element in HLA haplotype mismatched hematopoietic transplants in adult AML and pediatric ALL and as a possible beneficial effector in cord blood transplant for AML. It is effected by functional NK cells which express inhibitory killer cell immunoglobulin-like receptor(s) (KIR) for self-class I ligand(s), sense missing expression of donor KIR ligand(s) in the recipient and mediate alloreactions. At present NK cell allotherapy for leukemia is deployed through stem cell transplantation (and ensuing NK cell reconstitution) across KIR ligand mismatches. Studies have been performed to infuse NK cells for immunotherapy outside the fields of transplantation and/or harness the function of endogenous NK cells in patients with hematological malignancies.

Human leukocyte antigens A23, A24, and A32 but not A25 are ligands for KIR3DL1.

Inhibitory killer cell immunoglobulin receptors (KIR) bind to major histocompatibility complex antigens. Concise knowledge of KIR ligands allows prediction of natural killer (NK)-cell alloreactivity after hematopoietic stem cell transplantation. KIR3DL1 binds to the Bw4 epitope on HLA-B antigens. Although the same epitope is also found on 4 HLA-A antigens (HLA-A23/24/25/32), these are not currently regarded as KIR3DL1 ligands. We show that expression of HLA A*2301, A*2402, or A*3201 but not HLA A*2501 protects target cells from lysis by KIR3DL1(+) NK cells. KIR3DL1(+) NK cells from donors expressing the Bw4 epitope on an HLA-A antigen only are fully functional and capable of lysing Bw4(-) target cells. HLA A25 differs at amino acid 90, close to the serologic Bw4 epitope, from A23/24/32 and from Bw4(+) HLA-B antigens. These data suggest that HLA-A antigens should be taken into consideration when assessing the potential for NK alloreactivity after hematopoietic stem cell transplantation.

Natural killer cell alloreactivity in allogeneic hematopoietic transplantation.

Purpose of review 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 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. Summary 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.

Haploidentical hematopoietic transplantation from KIR ligand–mismatched donors with activating KIRs reduces nonrelapse mortality

Because activating killer cell immunoglobulinlike receptors (KIRs) are heterogeneously expressed in the population, we investigated the role of donor activating KIRs in haploidentical hematopoietic transplants for acute leukemia. Transplants were grouped according to presence vs absence of KIR-ligand mismatches in the graft-vs-host direction (ie, of donor-vs-recipient natural killer [NK]-cell alloreactivity). In the absence of donor-vs-recipient NK-cell alloreactivity, donor activating KIRs had no effects on outcomes. In the 69 transplant pairs with donor-vs-recipient NK-cell alloreactivity, transplantation from donors with KIR2DS1 and/or KIR3DS1 was associated with reduced risk of nonrelapse mortality, largely infection related (KIR2DS1 present vs absent: hazard ratio [HR], 0.25; P = .01; KIR3DS1 present vs absent: HR, 0.18; P = .006), and better event-free survival (KIR2DS1 present vs absent: HR, 0.31; P = .011; KIR3DS1 present vs absent: HR, 0.30; P = .008). Transplantation from donors with KIR2DS1 and/or KIR3DS1 was also associated with a 50% reduction in infection rate (P = .003). In vitro analyses showed that KIR2DS1 binding to its HLA-C2 ligand upregulated inflammatory cytokine production by alloreactive NK cells in response to infectious challenges. Because ∼40% of donors able to exert donor-vs-recipient NK-cell alloreactivity carry KIR2DS1 and/or KIR3DS1, searching for them may become a feasible, additional criterion in donor selection.

Killer-cell immunoglobulin-like receptors reactivity and outcome of stem cell transplant.

Purpose of reviewThis review focuses on advances in the field of natural killer (NK) cell alloreactivity as a form of immunotherapy in the setting of allogeneic haematopoietic transplantation. Recent findingsRecent research has focused on mechanisms underlying the acquisition of function by NK cells after haematopoietic transplantation, on the therapeutic impact of NK-cell alloreactivity in various forms of transplantation and in adoptive immunotherapy. Finally, studies have highlighted the role of NK-cell responses in viral infections after transplantation. SummaryDonor-versus-recipient NK-cell alloreactivity is established as a key therapeutic element in human leukocyte antigen haplotype-mismatched haematopoietic transplants in adult acute myeloid leukaemia (AML) and paediatric acute lymphoblastic leukaemia (ALL). NK-cell allotherapy for leukaemia is deployed through stem cell transplantation (and ensuing NK-cell reconstitution) across killer-cell immunoglobulin-like receptor ligand mismatches. Donor-derived NK cells were also reported to respond to cytomegalovirus by acquiring features that are reminiscent of the specificity and memory of adaptive (T-cell) immune responses. As NK cells are the earliest immune cells to recover after transplant, this observation suggests they may contribute to controlling viral reactivation early after transplant.

Natural killer cell alloreactivity and haplo-identical hematopoietic transplantation

In haplo-identical hematopoietic transplantation, donor vs. recipient natural killer (NK) cell alloreactivity derives from a mismatch between donor NK clones bearing inhibitory killer cell Ig-like receptors (KIR) for self-HLA class I molecules and their HLA class I ligands (KIR ligands) on recipient cells. When faced with mismatched allogeneic targets, these NK clones sense the missing expression of self-HLA class I alleles and mediate alloreactions. KIR ligand mismatches in the GvH direction trigger donor vs. recipient NK cell alloreactions, which improve engraftment, do not cause GvHD and control relapse in AML patients . The mechanism whereby alloreactive NK cells exert their benefits in transplantation has been elucidated in mouse models. The infusion of alloreactive NK cells ablates (i) leukemic cells, (ii) recipient T cells that reject the graft and (iii) recipient DC that trigger GvHD, thus protecting from GvHD.

Effects of anti-NKG2A antibody administration on leukemia and normal hematopoietic cells

Natural killer cells are key cells of the innate immune system. Natural killer cell receptor repertoires are diversified by a stochastic expression of killer-cell-immunoglobulin-like receptors and lectin-like receptors such as NKG2 receptors. All individuals harbor a subset of natural killer cells expressing NKG2A, the inhibitory checkpoint receptor for HLA-E. Most neoplastic and normal hematopoietic cells express HLA-E, the inhibitory ligand of NKG2A. A novel anti-human NKG2A antibody induced tumor cell death, suggesting that the antibody could be useful in the treatment of cancers expressing HLA-E. We found that immunodeficient mice, co-infused with human primary leukemia or Epstein-Barr virus cell lines and NKG2A+ natural killer cells, pre-treated with anti-human NKG2A, were rescued from disease progression. Human NKG2A+ natural killer cells reconstituted in immunodeficient mice after transplantation of human CD34+ cells. These natural killer cells are able to kill engrafted human primary leukemia or Epstein-Barr virus cell lines by lysis after intraperitoneal administration of anti-human NKG2A. Thus, this anti-NKG2A may exploit the anti-leukemic action of the wave of NKG2A+ natural killer cells recovering after hematopoietic stem cell transplants or adoptive therapy with natural killer cell infusions from matched or mismatched family donors after chemotherapy for acute leukemia, without the need to search for a natural killer cell alloreactive donor.

Natural killer cell alloreactivity in haploidentical hematopoietic stem cell transplantation.

Natural killer (NK) cells are primed to kill by several activating receptors. NK cell killing of autologous cells is prevented because NK cells coexpress inhibitory receptors (killer cell immunoglobulin-like receptors [KIR]) that recognize groups of (self) major histocompatibility complex class I alleles. Because KIRs are clonally distributed, the NK cell population in any individual are constituted of a repertoire with a variety of class I specificities. NK cells in the repertoire mediate alloreactions when the allogeneic targets do not express the class I alleles that block them. After haploidentical hematopoietic transplantation, NK cell-mediated donor-versus-recipient alloresponses reduce the risk of relapse in acute myeloid leukemia patients while improving engraftment and protecting against graft-versus-host disease. High-resolution molecular HLA typing of recipient and donor, positive identification of donor KIR genes, and, in some cases, functional assessment of donor NK clones identify haploidentical donors who are able to mount donor-versus-recipient NK alloreactions.

Clinical impact of natural killer cell reconstitution after allogeneic hematopoietic transplantation.

Although the optimal donor for allogeneic hematopoietic stem cell transplantation is a human leukocyte antigen (HLA)-matched sibling, 75% of patients do not have a match and alternatives are matched unrelated volunteers, unrelated umbilical cord blood units, and full HLA-haplotype-mismatched family members. This review will focus on the open issues of allogeneic hematopoietic transplantation and on the benefits of natural killer (NK) cell alloreactivity and its underlying mechanisms. Donor-versus-recipient NK cell alloreactivity derives from a mismatch between inhibitory receptors for self major histocompatibility complex (MHC) class I molecules on donor NK clones and the MHC class I ligands on recipient cells. These NK clones sense the missing expression of the self MHC class I allele on the allogeneic targets (“missing self”) and mediate alloreactions. Here, we review the translation of NK cell allorecognition into the clinical practice of allogeneic hematopoietic transplantation and discuss how it has opened innovative perspectives in the cure of leukemia.