Allogeneic hematopoietic transplantation and natural killer cell recognition of missing self

Engineering antigen-specific primary human NK cells against HER-2 positive carcinomas

NK cells are promising effectors for tumor adoptive immunotherapy, particularly when considering the targeting of MHC class I low or negative tumors. Yet, NK cells cannot respond to many tumors, which is particularly the case for nonhematopoietic tumors such as carcinomas or melanoma even when these cells lose MHC class I surface expression. Therefore, we targeted primary human NK cells by gene transfer of an activating chimeric receptor specific for HER-2, which is frequently overexpressed on carcinomas. We found that these targeted NK cells were specifically activated upon recognition of all evaluated HER-2 positive tumor cells, including autologous targets, as indicated by high levels of cytokine secretion as well as degranulation. The magnitude of this specific response correlated with the level of HER-2 expression on the tumor cells. Finally, these receptor transduced NK cells, but not their mock transduced counterpart, efficiently eradicated tumor cells in RAG2 knockout mice as visualized by in vivo imaging. Taken together, these results indicate that the expression of this activating receptor overrides inhibitory signals in primary human NK cells and directs them specifically toward HER-2 expressing tumor cells both in vitro and in vivo.

Xenotransplantation: role of natural immunity

Hyperacute rejection, mediated by natural anti-Galalpha1,3Galbeta1,4GlcNAc (alphaGal) antibodies and the classically activated complement pathway, was identified as the first major barrier to the survival of porcine organs in humans. Subsequently, discordant pig-to-nonhuman primate and concordant rodent models revealed key roles for T and B lymphocytes in the second form of rejection, acute vascular rejection (AVR) or delayed xenograft rejection (DXR). As significant progress was made in strategies to circumvent or suppress xenoreactivity of the adaptive immune system, it became clear that, apart from natural antibodies, other innate immune system elements actively participate in AVR/DXR and represent a barrier to xenograft acceptance that may be particularly difficult to overcome. Observations in pig-to-primate and semi-discordant and concordant rodent models indicate that Natural Killer (NK) cells play a more prominent role in xenograft than in allograft rejection. Several mechanisms through which human NK cells recognize porcine endothelial cells have been elucidated and these appear to be more diverse than those involved in NK cell alloreactivity. Further, it has been demonstrated that human macrophages and neutrophils can directly recognize pig derived cells and can mediate direct xenograft damage. Here, we review the recent progress in the understanding of the xenoreactivity of the natural immune system, focussing on preclinical pig-to-(non)human primate systems, and discuss the proposed strategies to overcome these barriers.

NK cell-mediated targeting of human cancer and possibilities for new means of immunotherapy

Insights into the molecular basis for natural killer (NK) cell recognition of human cancer have been obtained in recent years. Here, we review current knowledge on the molecular specificity and function of human NK cells. Evidence for NK cell targeting of human tumors is provided and new strategies for NK cell-based immunotherapy against human cancer are discussed. Based on current knowledge, we foresee a development where more cancers may be subject to treatment with drugs or other immunomodulatory agents affecting NK cells, either directly or indirectly. We also envisage a possibility that certain forms of cancers may be subject to treatment with adoptively transferred NK cells, either alone or in combination with other therapeutic interventions.

Human natural killer cells

Natural killer (NK) cells were discovered more than 30 years ago. NK cells are large granular lymphocytes that belong to the innate immune system because unlike T or B lymphocytes of the adaptive or antigen-specific immune system, NK cells do not rearrange T-cell receptor or immunoglobulin genes from their germline configuration. During the past 2 decades there has been a substantial gain in our understanding of what and how NK-cells "see," lending important insights into their functions and purpose in normal immune surveillance. The most recent discoveries in NK-cell receptor biology have fueled translational research that has led to remarkable results in treating human malignancy.

Role of KIRs and KIR ligands in hematopoietic transplantation

This review focuses on recent research demonstrating the role alloreactive natural killer (NK) cells play in adoptive immunotherapy of leukemia in allogeneic hematopoietic transplantation. For patients with hematologic malignancies and an indication to allogeneic hematopoietic transplantation who do not have a matched sibling donor, unrelated donor, or cord blood transplants are almost always available (as long as the patient's ethnicity is represented in the donor registries). However, up to one half of patients relapse and do not make it to transplant during the time required for the donor search, completion of donor HLA typing, bone marrow harvest, and shipment. Donor-versus-recipient NK cell alloreactivity is effected by a functional repertoire of 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. It improves outcomes of HLA haplotype-mismatched ('haploidentical') transplants by controlling acute myeloid leukemia relapse without causing graft-versus-host disease. It is hoped the dramatic improvements afforded by the discovery of the role of NK cell alloreactivity will extend the use of haploidentical transplants, as the donors are, unlike the unrelated, immediately available family members.

Hematopoietic SCT from partially HLA-mismatched (HLA-haploidentical) related donors

Hematopoietic SCT from a partially HLA-mismatched (HLA-haploidentical) first-degree relative offers the benefits of rapid and near universal donor availability but also the risks that result from traversing the HLA barrier; namely, graft failure, severe GVHD and prolonged immunodeficiency. Improvements over the last 10 years in conditioning regimens, graft engineering and pharmacological immunoprophylaxis of GVHD have substantially reduced the morbidity and mortality of HLA-haploidentical SCT. Highly immunosuppressive but nonmyeloablative conditioning extends the availability of HLA-haploidentical SCT to elderly hematologic malignancy patients lacking HLA-matched donors and permits recovery of autologous hematopoiesis in the event of graft failure. Current regimens for HLA-haploidentical SCT are associated with a 2-year non-relapse mortality of 20+/-5%, relapse of 35+/-15% and overall survival of 50+/-20%. Major developmental areas include harnessing natural killer cell alloreactivity to reduce the risk of disease relapse and improving immune reconstitution by delayed infusions of lymphocytes selectively depleted of alloreactive cells. Hematologic malignancy patients who lack suitably matched related or unrelated donors can now be treated with HLA-haploidentical related donor or unrelated umbilical cord blood SCT. Future clinical trials will assess the relative risks and benefits of these two graft sources.

A pilot study of allogeneic cellular therapy for patients with advanced hematologic malignancies

Allogeneic hematopoietic stem cell transplantation provides curative therapy for some patients with advanced hematologic malignancies. Disease response after allogeneic transplant is, at least in part, mediated by donor immune cells. In this report we describe a cellular therapy using haploidentical peripheral blood stem cells administered after very low dose total body irradiation (TBI) (100cGy). The donor cells were anticipated to be rejected, so no graft-versus-host (GVHD) prophylaxis was used. Patients with persistent disease beyond 8 weeks could be further treated with infusions of irradiated haploidentical donor cells. Of the 10 patients enrolled in the study, durable engraftment of allogeneic cells was seen in one patient. Two patients with resistant relapsed acute myelogenous leukemia (AML) had a disease response. Analysis of T cell reactivity from one patient who achieved a complete response but did not have durable engraftment of donor cells indicated that disease response was associated with the generation of host-derived anti-leukemic cytotoxic CD8+ T cells that reacted with an AML-associated proteinase 3 epitope. Results from this patient suggest that allogeneic therapy induced a host anti-tumor response associated with cytotoxic T cells reactive with a low affinity self-antigen.

Functions of natural killer cells

Natural killer (NK) cells are effector lymphocytes of the innate immune system that control several types of tumors and microbial infections by limiting their spread and subsequent tissue damage. Recent research highlights the fact that NK cells are also regulatory cells engaged in reciprocal interactions with dendritic cells, macrophages, T cells and endothelial cells. NK cells can thus limit or exacerbate immune responses. Although NK cells might appear to be redundant in several conditions of immune challenge in humans, NK cell manipulation seems to hold promise in efforts to improve hematopoietic and solid organ transplantation, promote antitumor immunotherapy and control inflammatory and autoimmune disorders.

Natural killer cells: diversity in search of a niche

Over the years, the enigmatic lifestyle of natural killer (NK) cells has fascinated immunologists. Elucidating the principles governing NK cell biology is a constant source of surprise, as these lymphocytes often break the rules of lymphocyte 'behavior' established by their T and B cell counterparts. In this Focus issue, experts address how NK cells have secured a fundamental place in the immune system, how they 'see' their targets and how they participate in and influence immune responses. We now need to understand how environmental 'niches' condition the generation and function of distinct NK cell subsets in vivo. Ultimately, we can hope that unraveling the mysteries of how these atypical lymphocytes function will have an impact on human disease therapies.

Antiviral NK cell responses in HIV infection: II. viral strategies for evasion and lessons for immunotherapy and vaccination

As is the case in other viral infections, humans respond to HIV infection by activating their NK cells. However, the virus uses several strategies to neutralize and evade the host's NK cell responses. Consequently, it is not surprising that NK cell functions become compromised in HIV-infected individuals in early stages of the infection. The compromised NK cell functions also adversely affect several aspects of the host's antiviral adaptive immune responses. Researchers have made significant progress in understanding how HIV counters NK cell responses of the host. This knowledge has opened new avenues for immunotherapy and vaccination against this infection. In the first part of this review article, we gave an overview of our current knowledge of NK cell biology and discussed how the genes encoding NK cell receptors and their ligands determine innate genetic resistance/susceptibilty of humans against HIV infections and AIDS. In this second part, we discuss NK cell responses, viral strategies to counter these responses, and finally, their implications for anti-HIV immunotherapy and vaccination.

Methylprednisolone induces preferential and rapid differentiation of CD34+ cord blood precursors toward NK cells

Previous studies showed that methylprednisolone (MePDN) down-regulates the surface expression of activating NK receptors and sharply inhibits the NK cytotoxicity both in vitro and in vivo. Since MePDN is administered to patients undergoing hemopoietic stem cell transplant to treat acute graft versus host disease (GvHD), we analyzed whether it could also inhibit the NK cell differentiation from CD34(+) hemopoietic cell precursors, thus interfering with the development of effector cells with anti-leukemic potential. We show that MePDN promotes the in vitro differentiation of CD161+CD56+/- immature NK cells by inducing a rapid expression of NKp46, NKG2D, DNAX-accessory molecule 1 (DNAM-1), leukocyte function-associated antigen-1 and NKG2A and an efficient cytolytic activity. This phenotypic and functional NK cell maturation occurred more rapidly than in parallel control cultures performed in the absence of MePDN. In addition, MePDN induced CD33+CD161-CD56- myeloid precursors to switch toward NK cells. It is also of note that immature NK cells when cultured in the absence (but not in the presence) of MePDN produced high amounts of IL-8. These data indicate that MePDN can accelerate the in vitro NK cell differentiation, thus revealing a dichotomous effect on immature versus mature NK cells; in addition, interference with the in vitro development of myeloid cells occurred. These effects should be further investigated in hemopoietic stem cell transplanted patients receiving steroids to treat GvHD.

IFN-gamma mediates the rejection of haematopoietic stem cells in IFN-gammaR1-deficient hosts

BACKGROUND

Interferon-gamma receptor 1 (IFN-gammaR1) deficiency is a life-threatening inherited disorder, conferring predisposition to mycobacterial diseases. Haematopoietic stem cell transplantation (HSCT) is the only curative treatment available, but is hampered by a very high rate of graft rejection, even with intra-familial HLA-identical transplants. This high rejection rate is not seen in any other congenital disorders and remains unexplained. We studied the underlying mechanism in a mouse model of HSCT for IFN-gammaR1 deficiency.

METHODS AND FINDINGS

We demonstrated that HSCT with cells from a syngenic C57BL/6 Ifngr1+/+ donor engrafted well and restored anti-mycobacterial immunity in naive, non-infected C57BL/6 Ifngr1-/- recipients. However, Ifngr1-/- mice previously infected with Mycobacterium bovis bacillus Calmette-Guérin (BCG) rejected HSCT. Like infected IFN-gammaR1-deficient humans, infected Ifngr1-/- mice displayed very high serum IFN-gamma levels before HSCT. The administration of a recombinant IFN-gamma-expressing AAV vector to Ifngr1-/- naive recipients also resulted in HSCT graft rejection. Transplantation was successful in Ifngr1-/- x Ifng-/- double-mutant mice, even after BCG infection. Finally, efficient antibody-mediated IFN-gamma depletion in infected Ifngr1-/- mice in vivo allowed subsequent engraftment.

CONCLUSIONS

High serum IFN-gamma concentration is both necessary and sufficient for graft rejection in IFN-gammaR1-deficient mice, inhibiting the development of heterologous, IFN-gammaR1-expressing, haematopoietic cell lineages. These results confirm that IFN-gamma is an anti-haematopoietic cytokine in vivo. They also pave the way for HSCT management in IFN-gammaR1-deficient patients through IFN-gamma depletion from the blood. They further raise the possibility that depleting IFN-gamma may improve engraftment in other settings, such as HSCT from a haplo-identical or unrelated donor.

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.

The alloimmune response to the human platelet antigen-1a is not related to maternal-fetal killer immunoglobulinlike receptor/HLA-Cw combinations

BACKGROUND

Human platelet antigen (HPA)-1a fetomaternal alloimmune thrombocytopenia, responsible in the most severe cases for fetal or neonatal intracranial hemorrhages leading to death or survival with neurologic sequelae, was shown to be restricted to the human leukocyte antigen (HLA) Class II DRB3*0101-encoded molecule. Whereas more than 90 percent of alloimmunized mothers display the DRB3*0101 allele, the positive predictive value of the presence of DRB3*0101 is only 35 percent. Additional genetic risk factors may exist of which elucidation could improve the undertaking of incompatible pregnancies in at-risk families, encouraging an antenatal screening. Interactions of killer immunoglobulinlike receptors (KIRs) on maternal decidual NK cells with HLA-Cw molecules on fetal trophoblasts were reported as one of the mechanisms involved in the fetomaternal tolerance during pregnancy.

STUDY DESIGN AND METHODS

Genotyping was performed of 16 KIR genes in HPA-1a-negative/DRB3*0101-positive alloimmunized mothers and in HPA-1a-negative/DRB3*0101-positive nonimmunized mothers as well as HLA-Cw genotyping in thrombocytopenic children and their nonaffected siblings.

RESULTS

No particular KIR genes or KIR genotypes were observed in the alloimmunized or nonimmunized mothers. Distribution of HLA-Cw genes in affected infants and nonaffected siblings did not reveal any HLA-Cw specificity associated with triggering or modulation of the HPA-1a alloimmunization. No maternal KIR/fetal HLA-Cw combinations were demonstrated in association with a detrimental or a protective effect on the HPA-1a alloimmunization.

CONCLUSION

Maternal KIR/fetal HLA-Cw gene combinations that are involved in the fetomaternal tolerance do not appear to play a role in the HPA-1a alloimmunization.

Haematopoietic stem cell transplantation: can our genes predict clinical outcome?

Haematopoietic stem cell transplantation (HSCT) is currently the only curative treatment for many patients with malignant and non-malignant haematological diseases. The success of HSCT is greatly reduced by the development of complications, which include graft-versus-host disease (GVHD), relapse and infection. Human leukocyte antigen (HLA) matching of patients and donors is essential, but does not completely prevent these complications; non-HLA genes may also have an impact upon transplant outcome. Polymorphisms within genes that are associated with an individual's capability to mount an immune response to alloantigen and infectious pathogens and/or response to drugs (pharmacogenomics) are all currently being studied for their association with HSCT outcome. This review summarises the potential role of non-HLA polymorphisms in predicting HSCT outcome, from studies on retrospective transplant cohorts of HLA-identical siblings and matched unrelated donors. The clinical relevance and interpretation of non-HLA genetics, and how these could be used alongside clinical risk factors in HSCT, are also discussed.

Good news, bad news for missing-self recognition by NK cells: autoimmune control but viral evasion

In this issue of Immunity, Voigt et al. (2007) and Lu et al. (2007) extend the understanding of the consequences of missing-self recognition in immune evasion and immune cell regulation via NKRP-1 and CD94-NKG2A inhibitory receptors, respectively.

Mucosal challenge with cell-associated or cell-free feline immunodeficiency virus induces rapid and distinctly different patterns of phenotypic change in the mucosal and systemic immune systems

The majority of human immunodeficiency virus type 1 (HIV-1) infections occur via mucosal transmission through contact with genital secretions containing cell-associated and cell-free virus. However, few studies have assessed whether exposure to cells, HIV-1 infected or uninfected, plays a role in the sexual transmission of HIV-1. This study examined phenotypic changes in mucosal and systemic lymphoid tissue 24 hr after vaginal exposure to in vitro equilibrated infectious doses of cell-associated or cell-free feline immunodeficiency virus, uninfected heterologous cells, or medium alone. We found that even at this early time-point, mucosal exposure to virus induced substantial alterations in the phenotype and distribution of leucocytes, particularly in the tissues of the mucosal immune system. Second, we found that the type of virus inoculum directly influenced the phenotypic changes seen. Vaginal exposure to cell-free virus tended to induce more generalized phenotypic changes, typically in the peripheral immune system (blood and systemic lymph nodes). In contrast, exposure to cell-associated virus was primarily associated with phenotypic shifts in the mucosal immune system (gut and mucosal/draining lymph nodes). In addition, we found that exposure to uninfected heterologous cells also induced alterations in the mucosal immune system. These data suggest that significant immune changes occur within the first 24 hr of virus exposure, well before substantial replication would be anticipated. As the mucosal immune system, and particularly the gut, is an early and persistent target for lentiviral replication, these findings have substantial implications for HIV-1 pathogenesis and vaccine development.

Allorecognition and the alloresponse: clinical implications

The artificial transfer of tissues or cells between genetically diverse individuals elicits an immune response that is adaptive and specific. This response is orchestrated by T lymphocytes that are recognizing, amongst others, major histocompatibility complex (MHC) molecules expressed on the surface of the transferred cells. Three pathways of recognition are described: direct, indirect and semi-direct. The sets of antigens that are recognized in this setting are also discussed, namely, MHC protein products, the MHC class I-related chain (MIC) system, minor histocompatibility antigens and natural killer cell receptor ligands. The end product of the effector responses are hyperacute, acute and chronic rejection. Special circumstances surround the situation of pregnancy and bone marrow transplantation because in the latter, the transferred cells are the ones originating the immune response, not the host. As the understanding of these processes improves, the ability to generate clinically viable immunotherapies will increase.

Prospects for the use of NK cells in immunotherapy of human cancer

Current insights into the molecular specificities that regulate natural killer (NK)-cell function suggest that it might be possible to design NK-cell-based immunotherapeutic strategies against human cancer. Here, we describe evidence for NK-cell targeting of human tumours and address crucial questions that, in our opinion, require consideration for the development of successful NK-cell-based therapies. Appropriately used, we predict that NK cells will have a role, both directly and in combination with other treatment modalities, in future treatment of cancer.

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.

Stromal-cell regulation of natural killer cell differentiation

Natural killer (NK) cells are bone-marrow-derived lymphocytes that play a crucial role in host defense against some viral and bacterial infections, as well as against tumors. Their phenotypic and functional maturation requires intimate interactions between the bone marrow stroma and committed precursors. In parallel to the identification of several phenotypic and functional stages of NK cell development, recent studies have shed new light on the role of stromal cells in driving functional maturation of NK cells. In this review, we provide an overview of the role of bone marrow microenvironment in NK cell differentiation.