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.

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Aspergillus and cytomegalovirus are major causes of morbidity/mortality after haploidentical hematopoietic transplantation. The high degree of mismatching makes cell immunotherapy impossible as it would result in lethal graft-versus-host disease (GvHD). We generated large numbers of donor T-cell clones specific for Aspergillus or cytomegalovirus antigens. We identified clones potentially responsible for causing GvHD by screening them for cross-reactivity against recipient mononuclear cells. Nonrecipient reactive, pathogen-specific clones were infused soon after transplantation. They were CD4 ؉ and produced high levels of interferon-␥ and low levels of interleukin-10. In 46 control transplant recipients who did not receive adoptive therapy, spontaneous pathogen-specific T cells occurred in low frequency 9 to 12 months after transplantation and displayed a nonprotective low interferon-␥/high interleukin-10 production phenotype.

In haploidentical transplants that are KIR ligand mismatched in the GvH direction, functional donor NK-cells that express as their sole inhibitory receptor for self, a KIR for the HLA-class-I group which is absent in the recipient, sense the missing expression of the self class-I ligand on allogeneic targets and mediate alloreactions. In a limited series of transplants donor-vs-recipient NK-cell alloreactivity reduced the risk of AML relapse and markedly improved EFS (Ruggeri L, Science 2002). Here, we analyzed 112 AML patients transplanted from NK-alloreactive (n=51) or non-NK-alloreactive (n=61) haploidentical donors. NK-alloreactive donors possessed: HLA-class-I KIR ligand(s) which were missing in the recipients, KIR gene(s) for missing self recognition on recipient targets, and alloreactive NK-clones against recipient targets. Transplantation from NK-alloreactive donors was associated with: significantly lower relapse rate in patients transplanted in CR (3% vs 47%) (P<0.003); decrease infectious mortality which was more evident in patients transplanted in relapse (P=0.1); better EFS in patients transplanted in relapse (34% vs 6%, P=0.04) and in remission (67% vs 18%, P=0.02); reduced risk of relapse or death (relative risk vs non-NK-alloreactive donor: 0.48 [95% CI 0.29–0.78], P<0.001). Recently, an additional algorithm, termed the “missing ligand” model, has been proposed for predicting favorable outcomes not only in haploidentical (Leung W, JI 2004; JI 2005) but also in matched sibling (Hsu KC, Blood 2005) and in unrelated donor transplants (Hsu KC, BBMT 2006). The “missing-ligand” model includes all donor-recipient pairs in whom there is a mismatch between KIR(s) in the donor and HLA molecule(s) in the recipient. Consequently, the model includes all KIR ligand-mismatched transplants because they are all associated with a missing KIR ligand in the recipient, and KIR ligand-matched transplants from donors possessing “extra” KIR(s) for which neither donor nor recipient have HLA ligand(s). Therefore, in the same series of patients we tested the “missing ligand” model. The first step was to divide our 61 non-NK alloreactive (KIR ligand-matched) donor-recipient pairs according to the number of KIR ligands in donor and recipient, i.e., three KIR ligands (29 patients; 15 in remission, 14 in relapse at transplant) vs fewer than three (32 patients; 16 in remission, 16 in relapse at transplant). EFS did not differ in each sub-group. Both curves indicated worse survival than after transplantation from NK-alloreactive donors. The second step was to group the above 32 “missing ligand” transplants and all 51 KIR ligand-mismatched transplants (which corresponded to all our NK-alloreactive transplants). We analyzed EFS in this pool of 83 patients (46 in remission, 37 in relapse at transplant) against EFS in 29 patients with no missing ligand (15 in remission, 14 in relapse at transplant). No significant difference emerged. EFS in the “missing ligand” cohort was worse than after transplantation from NK-alloreactive donors. Therefore, the present analysis leaves no doubt that KIR ligand mismatches, i.e., donor NK cell recognition of “missing self” on recipient targets, are essential for triggering powerful NK cell alloreactions that impact beneficially on transplantation outcomes.

IntroductionInvasive aspergillosis (IA) is the leading cause of both nosocomial pneumonia and death in recipients of allogeneic hematopoietic stem cell (HSC) transplants given myeloablative 1,2 or nonmyeloablative 3 conditioning. Despite advances in early diagnosis 4 and new antifungal agents, 2 the majority of cases of IA remain undiagnosed and untreated at the individual's death. The most important risk factor for IA has historically been neutropenia. However, recent studies on the epidemiology of IA in recipients of an HSC transplant indicate a reduced neutropenia-related infection and an increased "late-onset" infection, in concomitance with the occurrence of graft-versus-host disease. 5,6 These findings, together with the occurrence in nonneutropenic patients, 2,7 attest to the importance of specific defects in both the innate and adaptive immune effector mechanisms in the pathogenesis of the disease. [8][9][10][11][12][13] The recent evidence that, in healthy individuals and in patients surviving IA, a significant antigen-specific proliferation of interferon ␥ (IFN-␥)-producing T cells occurred 14 confirms the crucial role of a T helper (T H )1 reactivity in the control of infection. 9,10,15 Dendritic cells (DCs) orchestrate the overall antifungal immune resistance in the lungs. 10,16,17 A dense network of DCs has been described in the respiratory tracts. 18 The evidence that pulmonary DCs, through production of interleukin 10 (IL-10), mediate unresponsiveness to respiratory antigens, 19 suggests that the ability of DCs to instruct the appropriate T-cell responses to the invading pathogens may be affected by local immunoregulatory events. In the case of Aspergillus, by using distinct pattern recognition receptors, including Toll-like receptors (TLRs), murine pulmonary DCs were able to finely discriminate between conidia and hyphae of Aspergillus in terms of induction of adaptive T H responses. 16,17 A protective T H 1-mediated resistance was induced on vaccination with Aspergillus antigens and the TLR-9 ligand CpG oligodeoxynucleotide as adjuvant. 17 These results suggest that the proper manipulation of DC functioning in vivo may translate into beneficial effects in fungal infections.Recent evidence suggests the utility of DCs pulsed with Candida albicans in adoptive transfer experiments. The ability of Candida-pulsed DCs to prime for T H 1-and T H 2-cell activation correlated with the occurrence of resistance and susceptibility to the fungus. 20 In addition, transfecting DCs with fungal RNA was also an effective way to induce antifungal protective immunity in vivo. 21 In the current study we assessed the utility of Aspergilluspulsed DCs in conferring antifungal resistance in vivo. Ex vivo DCs were pulsed with conidia, hyphae, or fungal RNA and adoptively transferred into mice that were recipients of allogeneic HSC transplants. 22 Parameters of infection and immunity were then evaluated on the infection with the fungus. Materials and methods MiceFemale, 8-to 10-week-old inbred BALB/c, C57BL6, and C3H/HeJ m...

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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.

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