Use of natural killer cells as immunotherapy for leukaemia

KIR genotype and haplotype repertoire in Kuwaiti healthy donors, hematopoietic cell transplant recipients and healthy family members

The gene complex located on chromosome 19q13.4 encodes the Killer-cell Immunoglobulin-like Receptors (KIRs), which exhibit remarkable polymorphism in both gene content and sequences. Further, the repertoire of KIR genes varies within and between populations, creating a diverse pool of KIR genotypes. This study was carried out to characterize KIR genotypes and haplotypes among 379 Arab Kuwaiti individuals including 60 subjects from 20 trio families, 49 hematopoietic cell transplantation (HCT) recipients and 270 healthy Kuwaiti volunteer HCT donors. KIR Genotyping was performed by a combination of reverse sequence specific oligonucleotide probes (rSSO) and/or Real Time PCR. The frequencies of KIR genes in 270 healthy Kuwaiti volunteer donors were compared to previously reported frequencies in other populations. In addition, we compared the differences in KIR repertoire of patients and healthy donors to investigate the reproducibility of previously reported significant differences between patients with hematological malignancies and healthy donors. The observed frequencies in our cohort volunteer HCT donors was comparable to those reported in neighboring Arab populations. The activating genes KIR2DS1, KIR2DS5 and KIR3DS1 and the inhibitory gene KIR2DL5 were significantly more frequent in patients compared to healthy donors, however, none of the previously reported differences were reproducible in our Kuwaiti cohort. This report is the first description of KIR gene carrier frequency and haplotype characterization in a fairly large cohort of the Kuwaiti population, which may have implications in KIR based HCT donor selection strategies.

Natural Killer Cell Homing and Persistence in the Bone Marrow After Adoptive Immunotherapy Correlates With Better Leukemia Control

Cellular immunotherapy using allogeneic natural killer (NK) cells may overcome chemotherapy-refractory acute myeloid leukemia. Our goal was to document NK cell homing/persistence in the bone marrow following adoptive immunotherapy. Our cohort included 109 patients who received NK cell therapy for refractory acute myeloid leukemia following lymphodepleting conditioning +/- denileukin diftitox, +/- low-dose total body irradiation. We evaluated the NK cell density in bone marrow core biopsies performed an average of 14 days after NK cell transfer using a CD56 immunohistochemical stain. The NK cell density in core biopsies showed only moderate correlation with NK cell percentage in bone marrow aspirates evaluated by flow cytometry (rs=0.48) suggesting that distribution of CD56 cells in the bone marrow niche offers unique insight into NK cell homing. Better leukemia control was associated with increased NK cell density, such that patients with <5% blasts had a higher NK cell density (P=0.01). As well, NK cell density above the median of reference group was significantly associated with morphologic remission of leukemia (P=0.01). Moreover, the NK cell density varied significantly between conditioning protocols. Our findings suggest that the use of low-dose irradiation or CD25-targeting immunocytokine (denileukin diftitox, IL2DT) as part of conditioning results in increased NK cell homing/persistence in the bone marrow. These novel results will help guide future immunotherapy with NK cells.

CD56bright NK cells exhibit potent antitumor responses following IL-15 priming

NK cells, lymphocytes of the innate immune system, are important for defense against infectious pathogens and cancer. Classically, the CD56dim NK cell subset is thought to mediate antitumor responses, whereas the CD56bright subset is involved in immunomodulation. Here, we challenge this paradigm by demonstrating that brief priming with IL-15 markedly enhanced the antitumor response of CD56bright NK cells. Priming improved multiple CD56bright cell functions: degranulation, cytotoxicity, and cytokine production. Primed CD56bright cells from leukemia patients demonstrated enhanced responses to autologous blasts in vitro, and primed CD56bright cells controlled leukemia cells in vivo in a murine xenograft model. Primed CD56bright cells from multiple myeloma (MM) patients displayed superior responses to autologous myeloma targets, and furthermore, CD56bright NK cells from MM patients primed with the IL-15 receptor agonist ALT-803 in vivo displayed enhanced ex vivo functional responses to MM targets. Effector mechanisms contributing to IL-15-based priming included improved cytotoxic protein expression, target cell conjugation, and LFA-1-, CD2-, and NKG2D-dependent activation of NK cells. Finally, IL-15 robustly stimulated the PI3K/Akt/mTOR and MEK/ERK pathways in CD56bright compared with CD56dim NK cells, and blockade of these pathways attenuated antitumor responses. These findings identify CD56bright NK cells as potent antitumor effectors that warrant further investigation as a cancer immunotherapy.

Fewer Circulating Natural Killer Cells 28 Days After Double Cord Blood Transplantation Predicts Inferior Survival and IL-15 Response

Natural Killer (NK) cell immune reconstitution after double umbilical cord blood transplantation (dUCBT) is rapid and thought to be involved in graft vs. leukemia (GvL) reactions. To investigate the role of NK cell recovery on clinical outcomes, the absolute number of NK cells at Day 28 after dUCBT was determined and patients with low numbers of NK cells had inferior two year disease-free survival (hazard ratio 1.96; p=0.04). A detailed developmental and functional analysis of the recovering NK cells was performed to link NK recovery and patient survival. The proportion of NK cells in each developmental stage was similar for patients with low, medium, and high Day 28 NK cell numbers. As compared to healthy controls, patients post-transplant showed reduced NK functional responses upon K562 challenge (CD107a, IFN-γ, and TNFα); however, there were no differences based on Day 28 NK cell number. Patients with low NK numbers had 30% less STAT5 phosphorylation in response to exogenous IL-15 (p=0.04) and decreased Eomes expression (p=0.025) compared to patients with high NK numbers. Decreased STAT5 phosphorylation and Eomes expression may be indicative of reduced sensitivity to IL-15 in the low NK cell group. Incubation of patient samples with IL-15 superagonist (ALT803) increased cytotoxicity and cytokine production in all patient groups. Thus, clinical interventions, including administration of IL-15 early after transplantation may increase NK cell number and function and, in turn, improve transplantation outcomes.

Genetically re-engineered K562 cells significantly expand and functionally activate cord blood natural killer cells: Potential for adoptive cellular immunotherapy

Natural killer (NK) cells play a significant role in reducing relapse in patients with hematological malignancies after allogeneic stem cell transplantation, but NK cell number and naturally occurring inhibitory signals limit their capability. Interleukin-15 (IL-15) and 4-1BBL are important modulators of NK expansion and functional activation. To overcome these limitations, cord blood mononuclear cells (CB MNCs) were ex vivo expanded for 7 days with genetically modified K562-mbIL15-41BBL (MODK562) or wild-type K562 (WTK562). NK cell expansion; expression of lysosome-associated membrane protein-1 (LAMP-1), granzyme B, and perforin; and in vitro and in vivo cytotoxicity against B-cell non-Hodgkin lymphoma (B-NHL) were evaluated. In vivo tumor growth in B-NHL-xenografted nonobese diabetic severe combined immune deficient (NOD-scid) gamma (NSG) mice was monitored by tumor volume, cell number, and survival. CB MNCs cultured with MODK562 compared with WTK562 demonstrated significantly increased NK expansion (thirty-fivefold, p < 0.05); LAMP-1 (p < 0.05), granzyme B, and perforin expression (p < 0.001); and in vitro cytotoxicity against B-NHL (p < 0.01). Xenografted mice treated with MODK562 CB experienced significantly decreased B-NHL tumor volume (p = 0.0086) and B-NHL cell numbers (p < 0.01) at 5 weeks and significantly increased survival (p < 0.001) at 10 weeks compared with WTK562. In summary, MODK562 significantly enhanced CB NK expansion and cytotoxicity, enhanced survival in a human Burkitt's lymphoma xenograft NSG model, and could be used in the future as adoptive cellular immunotherapy after umbilical CB transplantation. Future directions include expanding anti-CD20 chimeric receptor-modified CB NK cells to enhance B-NHL targeting in vitro and in vivo.

Opportunities and limitations of natural killer cells as adoptive therapy for malignant disease

Although natural killer (NK) cells can be readily generated for adoptive therapy with current techniques, their optimal application to treat malignant diseases requires an appreciation of the dynamic balance between signals that either synergize with or antagonize each other. Individuals display wide differences in NK function that determine their therapeutic efficacy. The ability of NK cells to kill target cells or produce cytokines depends on the balance between signals from activating and inhibitory cell-surface receptors. The selection of NK cells with a predominant activating profile is critical for delivering successful anti-tumor activity. This can be achieved through selection of killer immunoglobulin-like receptor-mismatched NK donors and by use of blocking molecules against inhibitory pathways. Optimum NK cytotoxicity may require licensing or priming with tumor cells. Recent discoveries in the molecular and cellular biology of NK cells inform in the design of new strategies, including adjuvant therapies, to maximize the cytotoxic potential of NK cells for adoptive transfer to treat human malignancies.

HPV16 CTL epitope peptide-activated dendritic cell and natural killer co-culture for therapy of cervical cancer in an animal model

There is increasing evidence that natural killer (NK) cells play an important role in antitumor immunity following dendritic cell (DC) vaccination. Little is known, however, about the optimal stimulation of DCs by epitopes and NK interactions for cytotoxicity in tumors. In this study, DC cells activated by the HPV16E7.49-57 epitope and LPS were co-cultured with NK cells in vitro, and then used ot immunize mice to study CTL activity of TC-1, which constitutively expresses HPV16E6E7, with an LDH release assay. Cytotoxicity in mice immunized with DC loaded with epitope HPVE7.49-57 vaccine co-cultured with NK was enhanced significantly (p<0.01). In conclusion, talk-across between DC and NK cells enhances their functions, also improving cytotoxicity againsttumor cells, suggesting that activated DC-NK by epitopes has potential application for cancer-specific immuno-cellular therapy.

Allele-level haplotype frequencies and pairwise linkage disequilibrium for 14 KIR loci in 506 European-American individuals

The immune responses of natural killer cells are regulated, in part, by killer cell immunoglobulin-like receptors (KIR). The 16 closely-related genes in the KIR gene system have been diversified by gene duplication and unequal crossing over, thereby generating haplotypes with variation in gene copy number. Allelic variation also contributes to diversity within the complex. In this study, we estimated allele-level haplotype frequencies and pairwise linkage disequilibrium statistics for 14 KIR loci. The typing utilized multiple methodologies by four laboratories to provide at least 2x coverage for each allele. The computational methods generated maximum-likelihood estimates of allele-level haplotypes. Our results indicate the most extensive allele diversity was observed for the KIR framework genes and for the genes localized to the telomeric region of the KIR A haplotype. Particular alleles of the stimulatory loci appear to be nearly fixed on specific, common haplotypes while many of the less frequent alleles of the inhibitory loci appeared on multiple haplotypes, some with common haplotype structures. Haplotype structures cA01 and/or tA01 predominate in this cohort, as has been observed in most populations worldwide. Linkage disequilibrium is high within the centromeric and telomeric haplotype regions but not between them and is particularly strong between centromeric gene pairs KIR2DL5∼KIR2DS3S5 and KIR2DS3S5∼KIR2DL1, and telomeric KIR3DL1∼KIR2DS4. Although 93% of the individuals have unique pairs of full-length allelic haplotypes, large genomic blocks sharing specific sets of alleles are seen in the most frequent haplotypes. These high-resolution, high-quality haplotypes extend our basic knowledge of the KIR gene system and may be used to support clinical studies beyond single gene analysis.

NOD2 Polymorphisms and Their Impact on Haematopoietic Stem Cell Transplant Outcome

Haematopoietic stem cell transplantation (HSCT) is a valuable tool in the treatment of many haematological disorders. Advances in understanding HLA matching have improved prognoses. However, many recipients of well-matched HSCT develop posttransplant complications, and survival is far from absolute. The pursuit of novel genetic factors that may impact on HSCT outcome has resulted in the publication of many articles on a multitude of genes. Three NOD2 polymorphisms, identified as disease-associated variants in Crohn's disease, have recently been suggested as important candidate gene markers in the outcome of HSCT. It was originally postulated that as the clinical manifestation of inflammatory responses characteristic of several post-transplant complications was of notable similarity to those seen in Crohn's disease, it was possible that they shared a common cause. Since the publication of this first paper, numerous studies have attempted to replicate the results in different transplant settings. The data has varied considerably between studies, and as yet no consensus on the impact of NOD2 SNPs on HSCT outcome has been achieved. Here, we will review the existing literature, summarise current theories as to why the data differs, and suggest possible mechanisms by which the SNPs affect HSCT outcome.

A perspective on the selection of unrelated donors and cord blood units for transplantation

Selection of a suitable graft for allogeneic hematopoietic stem cell transplantation involves consideration of both donor and recipient characteristics. Of primary importance is sufficient donor-recipient HLA matching to ensure engraftment and acceptable rates of GVHD. In this Perspective, the National Marrow Donor Program and the Center for International Blood and Marrow Transplant Research provide guidelines, based on large studies correlating graft characteristics with clinical transplantation outcomes, on appropriate typing strategies and matching criteria for unrelated adult donor and cord blood graft selection.

Umbilical cord blood immunology: relevance to stem cell transplantation

Because of its easier accessibility and less severe graft-versus-host disease, umbilical cord blood (UCB) has been increasingly used as an alternative to bone marrow for hematopoietic stem cell transplantation. Naiveté of UCB lymphocytes, however, results in delayed immune reconstitution and infection-related mortality in transplant recipients. This review updates the phenotypic and functional deficiencies of various immune cell populations in UCB compared with their adult counterparts and discusses clinical implications and possible therapeutic strategies to improve the outcome of stem cell transplantation.

Cellular therapies in acute lymphoblastic leukemia

ALL remains a difficult disease to treat. In the adult setting, most patients will ultimately die of their disease, whereas in the pediatric setting, relapsed and refractory disease remains a therapeutic challenge. Cellular therapy through allo-HSCT remains an option for these patients, and recent advances in alternative forms of allo-HSCT, including unrelated donor transplants, UCB transplants, and haploidentical transplants, have expanded the numbers of patients eligible for allo-HSCT but have not improved outcomes when compared with HLA-matched related allo-HSCTs. In light of this persistent failure, several novel adoptive cellular approaches are being investigated to treat patients with ALL. The use of enriched WT-1–specific donor T cells to treat patients with ALL is currently under investigation in phase I trials at several centers. Treatment of ALL with genetically modified T cells targeted to the CD19 antigen through the expression of a CD19-specific CAR also have entered phase I clinical trials at several centers. Similarly, a clinical trial treating patients with ALL with genetically modified NK cells targeted to the CD19 antigen has recently opened for accrual. Collectively, these ongoing and anticipated trials provide a promising role for adoptive cellular therapies in the treatment of ALL. What remains to be seen is whether this promise will either translate into improved outcomes for these patients or provide significant insights on which to design second-generation adoptive cell therapeutic clinical trials for ALL in the future.

Production of cytotoxic, KIR-negative NK cells from CD34+ cord blood cells with the use of Notch signaling

The use of natural killer (NK) cells as cell therapy against acute leukemia is an active area of investigation. The optimal source of cytotoxic NK cells for therapeutic use is presently unknown. With funds from the National Blood Foundation, the author's lab has developed in vitro culture systems that use the Notch receptor ligand Delta4 for the differentiation and expansion of functional NK cells from CD34+ cord blood hematopoietic progenitor cells. These Notch-induced NK (N-NK) cells display a predominantly immature, CD56(bright) surface phenotype, with expression of activating receptors important for leukemia cell recognition and killing, but with an absence of inhibitory receptors that bind major histocompatibility complex (MHC) class I, making them free of restriction by self-MHC. They are capable of directly killing hematopoietic tumor cell lines and primary leukemia cells in vitro. Thus, cytotoxic, HLA-independent N-NK cells may represent a novel cell therapy for hematopoietic malignancy.

KIR2DS1 genotype predicts for complete cytogenetic response and survival in newly diagnosed chronic myeloid leukemia patients treated with imatinib

Natural killer (NK) cells are expanded in chronic myeloid leukemia (CML) patients on tyrosine kinase inhibitors (TKI) and exert cytotoxicity. The inherited repertoire of killer immunoglobulin-like receptors (KIR) may influence response to TKI. We investigated the impact of KIR-genotype on outcome in 166 chronic phase CML patients on first-line imatinib treatment. We validated our findings in an independent patient group. On multivariate analysis, KIR2DS1 genotype (RR=1.51, P=0.03) and Sokal risk score (low-risk RR=1, intermediate-risk RR=1.53, P=0.04, high-risk RR=1.69, P=0.034) were the only independent predictors for failure to achieve complete cytogenetic response (CCyR). Furthermore, KIR2DS1 was the only factor predicting shorter progression-free (PFS) (RR=3.1, P=0.03) and overall survival (OS) (RR=2.6, P=0.04). The association between KIR2DS1 and CCyR, PFS and OS was validated by KIR genotyping in 174 CML patients on first-line imatinib in the UK multi-center SPIRIT-1 trial; in this cohort, KIR2DS1(+) patients had significantly lower 2-year probabilities of achieving CCyR (76.9 vs 87.9%, P=0.003), PFS (85.3 vs 98.1%, P=0.007) and OS (94.4 vs 100%, P=0.015) than KIR2DS1(-) patients. The impact of KIR2DS1 on CCyR was greatest when the ligand for the corresponding inhibitory receptor, KIR2DL1, was absent (P=0.00006). Our data suggest a novel role for KIR-HLA immunogenetics in CML patients on TKI.

Good manufacturing practice-compliant cell sorting and large-scale expansion of single KIR-positive alloreactive human natural killer cells for multiple infusions to leukemia patients

BACKGROUND AIMS

Alloreactive natural killer (NK) cells are potent effectors of innate anti-tumor defense. The introduction of NK cell-based immunotherapy to current treatment options in acute myeloid leukemia (AML) requires NK cell products with high anti-leukemic efficacy optimized for clinical use.

METHODS

We describe a good manufacturing practice (GMP)-compliant protocol of large-scale ex vivo expansion of alloreactive NK cells suitable for multiple donor lymphocyte infusions (NK-DLI) in AML. CliniMACS-purified NK cells were cultured in closed air-permeable culture bags with certified culture medium and components approved for human use [human serum, interleukin (IL)-2, IL-15 and anti-CD3 antibody] and with autologous irradiated feeder cells.

RESULTS

NK cells (6.0 ± 1.2 x 10(8)) were purified from leukaphereses (8.1 ± 0.8 L) of six healthy donors and cultured under GMP conditions. NK cell numbers increased 117.0 ± 20.0-fold in 19 days. To reduce the culture volume associated with expansion of bulk NK cells and to expand selectively the alloreactive NK cell subsets, GMP-certified cell sorting was introduced to obtain cells with single killer immunoglobulin-like receptor (KIR) specificities. The subsequent GMP-compliant expansion of single KIR+ cells was 268.3 ± 66.8-fold, with a contaminating T-cell content of only 0.006 ± 0.002%. The single KIR-expressing NK cells were cytotoxic against HLA-mismatched primary AML blasts in vitro and effectively reduced tumor cell load in vivo in NOD/SCID mice transplanted with human AML.

CONCLUSIONS

The approach to generating large numbers of GMP-grade alloreactive NK cells described here provides the basis for clinical efficacy trials of NK-DLI to complement and advance therapeutic strategies against human AML.

IL-15 and type I interferon are required for activation of tumoricidal NK cells by virus-infected dendritic cells

There is increasing evidence that natural killer (NK) cells play an important role in antitumor immunity following dendritic cell (DC) vaccination. Little is known, however, about the optimal stimulation of DCs that favors NK activation in tumor-bearing hosts. In this study, we demonstrate that treatment with toll-like receptor (TLR) ligands and infection with a mutant vesicular stomatitis virus (VSV-ΔM51) both induced DC maturation. Further, inoculation of these DCs led to robust NK-mediated protection against tumor challenge. Strikingly, only VSV-ΔM51-infected DCs were capable of suppressing the growth of established tumors, suggesting that additional signals provided by viral infection may be required to activate tumoricidal NK cells in tumor-bearing hosts. VSV-ΔM51 infection of DCs induced greater type I interferon (IFN I) production than TLR ligand treatment, and disruption of the IFN I pathway in DCs eliminated their ability to induce NK activation and tumor protection. However, further studies indicated that IFN I alone was not sufficient to activate NK cells, especially in the presence of a tumor, and DC-derived IL-15 was additionally required for tumoricidal NK activation. These results suggest that induction of IFN I by VSV-ΔM51 allows DCs to overcome tumor-associated immunosuppression and facilitate IL-15-mediated priming of tumoricidal NK cells. Thus, the mode of DC maturation should be carefully considered when designing DC-based cancer immunotherapies.

Haematopoietic transplants combining a single unrelated cord blood unit and mobilized haematopoietic stem cells from an adult HLA-mismatched third party donor. Comparable results to transplants from HLA-identical related donors in adults with acute leukaemia and myelodysplastic syndromes

We describe results of the strategy, developed by our group, of co-infusion of mobilized haematopoietic stem cells as a support for single-unit unrelated cord blood transplant (dual CB/TPD-MHSC transplants) for treatment of haematological malignancies in adults, and a comparative analysis of results obtained using this strategy and transplants performed with mobilized haematopoietic stem cells from related HLA-identical donors (RTD) for treatment of adults with acute leukaemia and myelodysplastic syndromes. Our data show that the dual CB/TPD-MHSC transplant strategy results in periods of post-transplant neutropenia, final rates of full donor chimerism and transplant-related mortality rates comparable to those of the RTD. Final survival outcomes are comparable in adults transplanted because of acute leukaemia, with different incidences of the complications that most influence these: a higher incidence of infections related to late recovery of protective immunity dependent on T cell functions, and a lower incidence of serious acute graft-versus-host disease and relapses. Recent advances in cord blood transplant techniques allow allogeneic haematopoietic stem cell transplantation (HSCT) to be a viable option for almost every patient who may benefit from this therapeutic approach. Development of innovative strategies to improve the post-transplant recovery of T cells function is currently the main challenge to further improving the possibilities of unrelated cord blood transplantation.

MHC class I-deficient natural killer cells acquire a licensed phenotype after transfer into an MHC class I-sufficient environment

In MHC class I-deficient hosts, natural killer (NK) cells are hyporesponsive to cross-linking of activation receptors. Functional competence requires engagement of a self-major histocompatability complex (MHC) class I-specific inhibitory receptor, a process referred to as "licensing." We previously suggested that licensing is developmentally determined in the bone marrow. In this study, we find that unlicensed mature MHC class I-deficient splenic NK cells show gain-of-function and acquire a licensed phenotype after adoptive transfer into wild-type (WT) hosts. Transferred NK cells produce WT levels of interferon-γ after engagement of multiple activation receptors, and degranulate at levels equivalent to WT NK cells upon coincubation with target cells. Only NK cells expressing an inhibitory Ly49 receptor specific for a cognate host MHC class I molecule show this gain-of-function. Therefore, these findings, which may be relevant to clinical bone marrow transplantation, suggest that neither exposure to MHC class I ligands during NK development in the BM nor endogenous MHC class I expression by NK cells themselves is absolutely required for licensing.

Quality assessment of cellular therapies: the emerging role of molecular assays

Cellular therapies are becoming increasingly important in treating cancer, hematologic malignancies, autoimmune disorders, and damaged tissue. These therapies are becoming more effective and are being used more frequently, but they are also becoming more complex. As a result, quality testing is becoming an increasingly important part of cellular therapy. Cellular therapies should be tested at several points during their production. The starting material, intermediate products and the final product are usually analyzed. Products are evaluated at critical steps in the manufacturing process and at the end of production prior to the release of the product for clinical use. In addition, the donor of the starting biologic material is usually evaluated. The testing of cellular therapies for stability, consistency, comparability and potency is especially challenging. We and others have found that global gene and microRNA expression analysis is useful for comparability testing and will likely be useful for potency, stability and consistency testing. Several examples of the use of gene expression analysis for assessing cellular therapies are presented.

Allogeneic haematopoietic stem cell transplantation: individualized stem cell and immune therapy of cancer

The year 2009 marked the fiftieth anniversary of the first successful allogeneic haematopoietic stem cell transplant (HSCT). The field of HSCT has pioneered some of the most exciting areas of research today. HSCT was the original stem cell therapy, the first cancer immune therapy and the earliest example of individualized cancer therapy. In this Timeline article we review the history of the development of HSCT and major advances made in the past 50 years. We highlight accomplishments made by researchers who continue to strive to improve outcomes for patients and increase the availability of this potentially life-saving therapy for patients with otherwise incurable malignancies.

Acquisition, preparation, and functional assessment of human NK cells for adoptive immunotherapy

Human natural killer (NK) cells, a subset of peripheral blood lymphocytes that lack a T- or B-cell receptor, play a crucial role in the innate immune response to viruses and malignant cells. NK cells differentiate infected or malignant cells from normal cells by a complex balance between activating and inhibitory receptor-ligand interactions. Unlike T cells, NK cells do not proliferate in vitro in response to simple crosslinking of a single activating receptor. While many methods to study T-cell function and phenotype can also be applied to NK cells, this chapter addresses methods that are unique to the preparation and assessment of human NK cells for immunotherapy.

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.

Cellular therapies in acute lymphoblastic leukemia

The majority of adult patients with acute lymphoblastic leukemia (ALL) will die from the disease. Although the prognosis for pediatric patients is significantly better than for adult patients with ALL, the prognosis for patients with relapsed or refractory disease is poor in all cases. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) from a related donor offers a significant therapeutic benefit for pediatric patients, although the benefit of this therapy to adults with ALL is less established. Because most patients lack a suitable related donor, alternative approaches to allo-HSCT, including umbilical cord blood, and unrelated and haploidentical allo-HSCT, have been investigated in the clinical setting. Although treatment with donor-derived T-cells, so-called 'donor lymphocyte infusion', has demonstrated poor outcomes in patients with relapsed ALL following HSCT, modified adoptive T-cell regimens, including the infusion of enriched tumor-targeted donor T-cells and genetically targeted T-cells, are currently under clinical investigation. In addition, the resistance of ALL tumor cell lines to NK-cell-mediated lysis may be overcome by the genetic modification of NK cells to target ALL tumor cell antigens, and this approach will be evaluated in an upcoming clinical trial. Whether these novel adoptive cell therapies will ultimately result in improved clinical outcomes remains to be determined.

Bone marrow transplantation: new approaches to immunosuppression and management of acute graft-versus-host disease

PURPOSE OF REVIEW

Acute graft-versus-host disease (GVHD) significantly limits the application and the success of allogeneic hematopoietic stem cell transplantation (HSCT). Novel therapies that target the aberrant immune response underlying GVHD are reviewed with particular emphasis on immunomodulatory agents currently incorporated into clinical trials. In addition, regenerative stromal cellular therapy (RSCT) is discussed as an emerging form of novel GVHD therapy.

RECENT FINDINGS

Knowledge for transplant immunology, particularly as it relates to underlying pathophysiology of GVHD, has dramatically increased over the last decade. As a result, new immunomodulatory therapies have been used to treat steroid-refractory GVHD. However, their success has been limited by their lack of clinical experience during HSCT as well as by their associated toxicity profiles. RSCT uniquely offers the potential to enhance donor-derived hematopoiesis and immunity and to ameliorate adverse sequelae associated with GVHD.

SUMMARY

An exciting era incorporating the use of cellular therapeutics during HSCT has arrived. As the experience and understanding for cellular therapies, in general, and RSCT, in particular, increases, so too will their success in benefiting the HSCT recipient beyond limitations of current pharmaceutical agents.