Ex vivo expansion of highly purified NK cells for immunotherapy after haploidentical stem cell transplantation in children

Advances in NK cell therapy for hematologic malignancies: NK source, persistence and tumor targeting

Natural Killer (NK) cells yield promise in therapy of hematologic malignancies. The clinical experience with adoptively transferred allogeneic NK cells over past two decades has revealed safety and minimal risk of CRS or ICANS. Unlike T cells which have to be genetically altered to avoid graft vs host disease (GVHD), HLA mismatched NK cells can be infused without GVHD risk. This makes them ideal for the development of off-the-shelf products. In this review we focus on NK biology relevant to the cancer therapy, the trajectory of NK therapeutics for leukemia, lymphoma, and myeloma; and advantages of the NK cell platform. We will also discuss novel methods to enhance NK cell targeting, persistence, and function in the tumor microenvironment. The future of NK cell therapy depends on novel strategies to realize these qualities.

How I treat high-risk acute myeloid leukemia using preemptive adoptive cellular immunotherapy

Allogeneic hematopoietic stem cell transplantation (alloHSCT) is a potentially curative treatment for patients with high-risk acute leukemias, but unfortunately disease recurrence remains the major cause of death in these patients. Infusion of donor lymphocytes (DLI) has the potential to restore graft-versus-leukemia immunologic surveillance; however, efficacy varies across different hematologic entities. Although relapsed chronic myeloid leukemia, transplanted in chronic phase, has proven remarkably susceptible to DLI, response rates are more modest for relapsed acute myeloid leukemia and acute lymphoblastic leukemia. To prevent impending relapse, a number of groups have explored administering DLI preemptively on detection of measurable residual disease (MRD) or mixed chimerism. Evidence for the effectiveness of this strategy, although encouraging, comes from only a few, mostly single-center retrospective, nonrandomized studies. This article seeks to (1) discuss the available evidence supporting this approach while highlighting some of the inherent challenges of MRD-triggered treatment decisions post-transplant, (2) portray other forms of postremission cellular therapies, including the role of next-generation target-specific immunotherapies, and (3) provide a practical framework to support clinicians in their decision-making process when considering preemptive cellular therapy for this difficult-to-treat patient population.

PRDM1 decreases sensitivity of human NK cells to IL2-induced cell expansion by directly repressing CD25 (IL2RA)

IL2 receptor signaling is crucial for human NK cell activation and gain of effector functions. The molecular mechanisms involved in termination of IL2 activation are largely unknown in human NK cells. PR/SET domain 1 was previously reported to decrease cell growth and increase apoptosis in an IL2-dependent manner in malignant NK cell lines, suggesting the possibility of down-regulation of IL2 signaling pathway gene(s) through direct transcriptional repression. Using ChIP-Seq, we identified a PRDM1 binding site on the first intron of CD25 (IL2RA), which codes for the IL2 receptor subunit regulating sensitivity to IL2 signaling, in primary NK cells activated with engineered K562 cells or IL2. Ectopic expression of PRDM1 down-regulated CD25 expression at transcript and protein levels in two PRDM1 nonexpressing NK cell lines. shRNA-mediated knockdown of CD25 in two malignant NK cell lines led to progressive depletion of NK cells in low IL2 concentrations. By contrast, ectopic CD25 expression in primary human NK cells led to progressive increase in cell number in CD25-transduced cells in low IL2 concentrations. Altogether these results reveal a pivotal role of PRDM1 in inhibition of IL2-induced NK cell expansion through direct repression of CD25 in activated human NK cells. These observations provide additional support for the role of PRDM1 in attenuation of NK cell activation and growth, with implications on neoplastic transformation or NK cell function when it is deregulated.

Selection, Expansion, and Unique Pretreatment of Allogeneic Human Natural Killer Cells with Anti-CD38 Monoclonal Antibody for Efficient Multiple Myeloma Treatment

Cellular immunotherapy is becoming a new pillar in cancer treatment after recent striking results in different clinical trials with chimeric antigen receptor T cells. However, this innovative therapy is not exempt from challenges such as off-tumor toxicity, tumor recurrence in heterogeneous tumors, and affordability. To surpass these limitations, we exploit the unique anti-tumor characteristics of natural killer (NK) cells. In this study, we aimed to obtain a clinically relevant number of allogeneic NK cells derived from peripheral blood (median of 14,050 million cells from a single donor) to target a broad spectrum of solid and liquid tumor types. To boost their anti-tumor activity, we combined allogeneic NK cells with the approved anti-cluster of differentiation 38 (CD-38) monoclonal antibody Daratumumab to obtain a synergistic therapeutic effect against incurable multiple myeloma. The combination therapy was refined with CD16 polymorphism donor selection and uncomplicated novel in vitro pretreatment to avoid undesired fratricide, increasing the in vitro therapeutic effect against the CD-38 positive multiple myeloma cell line by more than 20%. Time-lapse imaging of mice with established human multiple myeloma xenografts revealed that combination therapy of selected and pretreated NK cells with Daratumumab presented tumor volumes 43-fold smaller than control ones. Combination therapy with an allogeneic source of fully functional NK cells could be beneficial in future clinical settings to circumvent monoclonal antibodies' low therapeutic efficiency due to NK cell dysfunctionality in MM patients.

Arming Immune Cells for Battle: A Brief Journey through the Advancements of T and NK Cell Immunotherapy

Simple Summary

This review is intended to provide an overview on the history and recent advances of T cell and natural killer (NK) cell-based immunotherapy. While the thymus was discovered as the origin of T cells in the 1960s, and NK cells were first described in 1975, the clinical application of adoptive cell therapies (ACT) only began in the early 1980s with the first lymphokine activated killer (LAK) cell product for the treatment of cancer patients. Over the past decades, further immunotherapies have been developed, including ACT using cytokine-induced killer (CIK) cells, products based on the NK cell line NK-92 as well as specific T and NK cell preparations. Recent advances have successfully improved the effectiveness of T, NK, CIK or NK-92 cells towards tumor-targeting antigens generated by genetic engineering of the immune cells. Herein, we summarize the promising development of ACT over the past decades in the fight against cancer.

Abstract

The promising development of adoptive immunotherapy over the last four decades has revealed numerous therapeutic approaches in which dedicated immune cells are modified and administered to eliminate malignant cells. Starting in the early 1980s, lymphokine activated killer (LAK) cells were the first ex vivo generated NK cell-enriched products utilized for adoptive immunotherapy. Over the past decades, various immunotherapies have been developed, including cytokine-induced killer (CIK) cells, as a peripheral blood mononuclear cells (PBMCs)-based therapeutic product, the adoptive transfer of specific T and NK cell products, and the NK cell line NK-92. In addition to allogeneic NK cells, NK-92 cell products represent a possible “off-the-shelf” therapeutic concept. Recent approaches have successfully enhanced the specificity and cytotoxicity of T, NK, CIK or NK-92 cells towards tumor-specific or associated target antigens generated by genetic engineering of the immune cells, e.g., to express a chimeric antigen receptor (CAR). Here, we will look into the history and recent developments of T and NK cell-based immunotherapy.

From Cancer to Immune-Mediated Diseases and Tolerance Induction: Lessons Learned From Immune Oncology and Classical Anti-cancer Treatment

Success in cancer treatment over the last four decades has ranged from improvements in classical drug therapy to immune oncology. Anti-cancer drugs have also often proven beneficial for the treatment of inflammatory and autoimmune diseases. In this review, we report on challenging examples that bridge between treatment of cancer and immune-mediated diseases, addressing mechanisms and experimental models as well as clinical investigations. Patient-derived tumor xenograft (PDX) (humanized) mouse models represent useful tools for preclinical evaluation of new therapies and biomarker identification. However, new developments using human ex vivo approaches modeling cancer, for example in microfluidic human organs-on-chips, promise to identify key molecular, cellular and immunological features of human cancer progression in a fully human setting. Classical drugs which bridge the gap, for instance, include cytotoxic drugs, proteasome inhibitors, PI3K/mTOR inhibitors and metabolic inhibitors. Biologicals developed for cancer therapy have also shown efficacy in the treatment of autoimmune diseases. In immune oncology, redirected chimeric antigen receptor (CAR) T cells have achieved spectacular remissions in refractory B cell leukemia and lymphoma and are currently under development for tolerance induction using cell-based therapies such as CAR Tregs or NK cells. Finally, a brief outline will be given of the lessons learned from bridging cancer and autoimmune diseases as well as tolerance induction.

Antigen-independent killer cells prepared for adoptive immunotherapy: One source, divergent protocols, diverse nomenclature

Adoptive cell therapy (ACT) using tumor antigen-independent killer cells has been widely used in clinical trials of cancer treatment. Circumventing the need for identification of a particular tumor-associated antigen on tumor cells, the approach has opened possibilities for the extension of ACT immunotherapy to patients with a wide variety of cancer types. Namely, Natural Killer (NK), Lymphokine-activated Killer (LAK) cells and Cytokine-induced killer (CIK) cells are the most commonly used cell types in antigen-independent adoptive immunotherapy of cancer. They all originate from peripheral blood mononuclear cells and share several common features in their killing mechanisms. However, despite broad application in clinical settings, the boundaries between these cell types are not very clearly defined. The current study aims to review different aspects of these cell populations in terms of phenotypical characteristic and preparation media, to clarify how the boundaries are set.

Adoptive cellular immunotherapy for refractory childhood cancers: a single center experience

Prognosis of refractory childhood cancers despite multimodal treatment strategies remains poor. Here, we report a single center experience encountered in 18 patients with refractory solid malignancies treated with adoptive cellular immunotherapy (ACI) from haploidentical or matched donors following hematopoietic stem cell transplantation. While seven patients were in partial and six in complete remission (CR), five patients suffered from relapsed diseases at the time of ACI. 1.5-year probabilities of overall survival (OS) and progression-free survival (PFS) were 19.5% and 16.1% for all patients. Patients in CR showed estimated 1.5-year OS and PFS of 50.1% and 42.7%, respectively. CR was induced or rather sustained in ten children, with two still being alive 9.6 and 9.3 years after ACI. Naïve, central and effector memory T-cells correlated with responses. However, the majority of patients relapsed. Cumulative incidence of relapse was 79.8% at 1.5 years. Acute graft versus host disease (aGVHD) occurred in nine of 18 patients (50%) with aGVHD grade I–II observed in six (33%) and aGVHD grade III seen in three (17%) patients, manageable in all cases.

Altogether, study results indicate that donor-derived ACI at its current state offers palliation but no clear curative benefit for refractory childhood cancers and warrants further improvement.

NK Cell-Based Immunotherapy for Hematological Malignancies

Natural killer (NK) lymphocytes are an integral component of the innate immune system and represent important effector cells in cancer immunotherapy, particularly in the control of hematological malignancies. Refined knowledge of NK cellular and molecular biology has fueled the interest in NK cell-based antitumor therapies, and recent efforts have been made to exploit the high potential of these cells in clinical practice. Infusion of high numbers of mature NK cells through the novel graft manipulation based on the selective depletion of T cells and CD19+ B cells has resulted into an improved outcome in children with acute leukemia given human leucocyte antigen (HLA)-haploidentical hematopoietic transplantation. Likewise, adoptive transfer of purified third-party NK cells showed promising results in patients with myeloid malignancies. Strategies based on the use of cytokines or monoclonal antibodies able to induce and optimize NK cell activation, persistence, and expansion also represent a novel field of investigation with remarkable perspectives of favorably impacting on outcome of patients with hematological neoplasia. In addition, preliminary results suggest that engineering of mature NK cells through chimeric antigen receptor (CAR) constructs deserve further investigation, with the goal of obtaining an "off-the-shelf" NK cell bank that may serve many different recipients for granting an efficient antileukemia activity.

Characterization of human natural killer cells for therapeutic use

As a part of the innate immune system, natural killer (NK) cells are cytotoxic lymphocytes that can exert cytotoxic activity against infected or transformed cells. Furthermore, due to their expression of a functional Fc receptor, they have also been eluded as a major effector fraction in antibody-dependent cellular cytotoxicity. These characteristics have led to multiple efforts to use them for adoptive immunotherapy against various malignancies.  There are now at least 70 clinical trials testing the safety and efficacy of NK cell products around the world in early-phase clinical trials. NK cells are also being tested in the context of tumor retargeting via chimeric antigen receptors, other genetic modification strategies, as well as tumor-specific activation strategies such as bispecific engagers with or without cytokine stimulations. One advantage of the use of NK cells for adoptive immunotherapy is their potential to overcome HLA barriers. This has led to a plethora of sources, such as cord blood hematopoietic stem cells and induced pluripotent stem cells, which can generate comparatively high cytotoxic NK cells to peripheral blood counterparts. However, the variety of the sources has led to a heterogeneity in the characterization of the final infusion product. Therefore, in this review, we will discuss a comparative assessment strategy, from characterization of NK cells at collection to final product release by various phenotypic and functional assays, in an effort to predict potency of the cellular product.

Ex vivo-expanded highly purified natural killer cells in combination with temozolomide induce antitumor effects in human glioblastoma cells in vitro

Glioblastoma is the leading malignant glioma with a poor prognosis. This study aimed to investigate the antitumor effects of natural killer cells in combination with temozolomide as the standard chemotherapeutic agent for glioblastoma. Using a simple, feeder-less, and chemically defined culture method, we expanded human peripheral blood mononuclear cells and assessed the receptor expression, natural killer cell activity, and regulatory T cell frequency in expanded cells. Next, using the standard human glioblastoma cell lines (temozolomide-sensitive U87MG, temozolomide-resistant T98G, and LN-18), we assessed the ligand expressions of receptors on natural killer cells. Furthermore, the antitumor effects of the combination of the expanded natural killer cells and temozolomide were assessed using growth inhibition assays, apoptosis detection assays, and senescence-associated β-galactosidase activity assays in the glioblastoma cell lines. Novel culture systems were sufficient to attain highly purified (>98%), expanded (>440-fold) CD3⁻/CD56⁺ peripheral blood-derived natural killer cells. We designated the expanded population as genuine induced natural killer cells. Genuine induced natural killer cells exhibited a high natural killer activity and low regulatory T cell frequency compared with lymphokine-activated killer cells. Growth inhibition assays revealed that genuine induced natural killer cells inhibited the glioblastoma cell line growth but enhanced temozolomide-induced inhibition effects in U87MG. Apoptosis detection assays revealed that genuine induced natural killer cells induced apoptosis in the glioblastoma cell lines. Furthermore, senescence-associated β-galactosidase activity assays revealed that temozolomide induced senescence in U87MG. Genuine induced natural killer cells induce apoptosis in temozolomide-sensitive and temozolomide-resistant glioblastoma cells and enhances temozolomide-induced antitumor effects in different mechanisms. Hence, the combination of genuine induced natural killer cells and temozolomide may prove to be a promising immunochemotherapeutic approach in patients with glioblastoma if the antitumor effects in vivo can be demonstrated.

Branched mannans from the mushroom Cantharellus cibarius enhance the anticancer activity of natural killer cells against human cancers of lung and colon

Cantharellus cibarius branched mannans increase natural killer cells NK92 viability and proliferation and enhance their cytotoxicity against lung and colon cancer cells A549 and LS180, at the same time they do not affect lung and colon epithelial cells NL20 and CCD841 CoN.

Continuous and Quantitative Purification of T-Cell Subsets for Cell Therapy Manufacturing Using Magnetic Ratcheting Cytometry

T-cell-based immunotherapies represent a growing medical paradigm that has the potential to revolutionize contemporary cancer treatments. However, manufacturing bottlenecks related to the enrichment of therapeutically optimal T-cell subpopulations from leukopak samples impede scale-up and scale-out efforts. This is mainly attributed to the challenges that current cell purification platforms face in balancing the quantitative sorting capacity needed to isolate specific T-cell subsets with the scalability to meet manufacturing throughputs. In this work, we report a continuous-flow, quantitative cell enrichment platform based on a technique known as ratcheting cytometry that can perform complex, multicomponent purification targeting various subpopulations of magnetically labeled T cells directly from apheresis or peripheral blood mononuclear cell (PBMC) samples. The integrated ratcheting cytometry instrument and cartridge demonstrated enrichment of T cells directly from concentrated apheresis samples with a 97% purity and an 85% recovery of magnetically tagged cells. Magnetic sorting of different T-cell subpopulations was also accomplished on chip by multiplexing cell surface targets onto particles with differing magnetic strengths. We believe that ratcheting cytometry's quantitative capacity and throughput scalability represents an excellent technology candidate to alleviate cell therapy manufacturing bottlenecks.

The Rise of Allogeneic Natural Killer Cells As a Platform for Cancer Immunotherapy: Recent Innovations and Future Developments

Natural killer (NK) cells are critical immune effector cells in the fight against cancer. As NK cells in cancer patients are highly dysfunctional and reduced in number, adoptive transfer of large numbers of cytolytic NK cells and their potential to induce relevant antitumor responses are widely explored in cancer immunotherapy. Early studies from autologous NK cells have failed to demonstrate significant clinical benefit. In this review, the clinical benefits of adoptively transferred allogeneic NK cells in a transplant and non-transplant setting are compared and discussed in the context of relevant NK cell platforms that are being developed and optimized by various biotech industries with a special focus on augmenting NK cell functions.

Natural Killer Cells for Therapy of Leukemia

Clinical application of natural killer (NK) cells against leukemia is an area of intense investigation. In human leukocyte antigen-mismatched allogeneic hematopoietic stem cell transplantations (HSCT), alloreactive NK cells exert powerful anti-leukemic activity in preventing relapse in the absence of graft-versus-host disease, particularly in acute myeloid leukemia patients. Adoptive transfer of donor NK cells post-HSCT or in non-transplant scenarios may be superior to the currently widely used unmanipulated donor lymphocyte infusion. This concept could be further improved through transfusion of activated NK cells. Significant progress has been made in good manufacturing practice (GMP)-compliant large-scale production of stimulated effectors. However, inherent limitations remain. These include differing yields and compositions of the end-product due to donor variability and inefficient means for cryopreservation. Moreover, the impact of the various novel activation strategies on NK cell biology and in vivo behavior are barely understood. In contrast, reproduction of the third-party NK-92 drug from a cryostored GMP-compliant master cell bank is straightforward and efficient. Safety for the application of this highly cytotoxic cell line was demonstrated in first clinical trials. This novel 'off-the-shelf' product could become a treatment option for a broad patient population. For specific tumor targeting chimeric-antigen-receptor-engineered NK-92 cells have been designed.

Cord Blood as a Source of Natural Killer Cells

Cord blood (CB) offers several unique advantages as a graft source for hematopoietic stem cell transplantation (HSCT). The risk of relapse and graft vs. host disease after cord blood transplantation (CBT) is lower than what is typically observed after other graft sources with a similar degree of human leukocyte antigen mismatch. Natural killer (NK) cells have a well-defined role in both innate and adaptive immunity and as the first lymphocytes to reconstitute after HSCT and CBT, and they play a significant role in protection against early relapse. In this article, we highlight the uses of CB NK cells in transplantation and adoptive immunotherapy. First, we will describe differences in the phenotype and functional characteristics of NK cells in CB as compared with peripheral blood. Then, we will review some of the obstacles we face in using resting CB NK cells for adoptive immunotherapy, and discuss methods to overcome them. We will review the current literature on killer-cell immunoglobulin-like receptors ligand mismatch and outcomes after CBT. Finally, we will touch on current strategies for the use of CB NK cells in cellular immunotherapy.

Revving up Natural Killer Cells and Cytokine-Induced Killer Cells Against Hematological Malignancies

Natural killer (NK) cells belong to innate immunity and exhibit cytolytic activity against infectious pathogens and tumor cells. NK-cell function is finely tuned by receptors that transduce inhibitory or activating signals, such as killer immunoglobulin-like receptors, NK Group 2 member D (NKG2D), NKG2A/CD94, NKp46, and others, and recognize both foreign and self-antigens expressed by NK-susceptible targets. Recent insights into NK-cell developmental intermediates have translated into a more accurate definition of culture conditions for the in vitro generation and propagation of human NK cells. In this respect, interleukin (IL)-15 and IL-21 are instrumental in driving NK-cell differentiation and maturation, and hold great promise for the design of optimal NK-cell culture protocols. Cytokine-induced killer (CIK) cells possess phenotypic and functional hallmarks of both T cells and NK cells. Similar to T cells, they express CD3 and are expandable in culture, while not requiring functional priming for in vivo activity, like NK cells. CIK cells may offer some advantages over other cell therapy products, including ease of in vitro propagation and no need for exogenous administration of IL-2 for in vivo priming. NK cells and CIK cells can be expanded using a variety of clinical-grade approaches, before their infusion into patients with cancer. Herein, we discuss GMP-compliant strategies to isolate and expand human NK and CIK cells for immunotherapy purposes, focusing on clinical trials of adoptive transfer to patients with hematological malignancies.

Combined IL-15 and IL-12 drives the generation of CD34+-derived natural killer cells with superior maturation and alloreactivity potential following adoptive transfer

Adoptive transfer of allogeneic natural killer (NK) cells represents a promising treatment approach against cancer, including acute myeloid leukemia (AML). Previously, we reported a cytokine-based culture method for the generation of NK cell products with high cell number and purity. In this system, CD34⁺ hematopoietic progenitor cells (HPC) were expanded and differentiated into NK cells under stroma-free conditions in the presence of IL-15 and IL-2. We show that combining IL-15 with IL-12 drives the generation of more mature and highly functional NK cells. In particular, replacement of IL-2 by IL-12 enhanced the cytolytic activity and IFNγ production of HPC-NK cells toward cultured and primary AML cells in vitro, and improved antileukemic responses in NOD/SCID-IL2Rγnull (NSG) mice bearing human AML cells. Phenotypically, IL-12 increased the frequency of HPC-NK cells expressing NKG2A and killer immunoglobulin-like receptor (KIR), which were more responsive to target cell stimulation. In addition, NK15/12 cell products demonstrated superior maturation potential, resulting in >70% positivity for CD16 and/or KIR within 2 weeks after infusion into NSG mice. We predict that higher functionality and faster in vivo maturation will favor HPC-NK cell alloreactivity toward malignant cells in patients, making this cytokine combination an attractive strategy to generate clinical HPC-NK cell products for cancer adoptive immunotherapy.

"No donor"? Consider a haploidentical transplant

Haploidentical stem cell transplantation (HaploSCT) is an attractive option for patients requiring a hematopoietic stem cell transplant who do not have an HLA-matched donor, because it is cheaper, can be performed faster, and may extend transplantation to virtually all patients in need. Significant advances have been made in the recent decade with dramatic improvement in treatment outcomes. Historically, overcoming the HLA-incompatibility barrier has been a significant limitation to the expansion of this form of transplant. While ex vivo T-cell depletion effectively prevented the development of acute GVHD, it was associated with a higher treatment-related mortality, in excess of 40% in some series, due to a significant delay in recovery of the adaptive immune system. Newer methods have successfully maintained the memory T cells in the graft and/or selectively depleted alloreactive T cells, and are associated with improved treatment outcomes. Post-transplant cyclophosphamide for GVHD prevention has proven very effective in controlling GVHD with lower incidence of infectious complications and treatment-related mortality-as low as 7% at 1 year-and has become the new standard in how this transplant is performed. Here, we reviewed the current experience with this approach and various other strategies employed to control alloreactivity in this setting, including selective depletion of T cells from the graft, as well as we discuss post-transplantation therapy to prevent disease relapse and improve immunologic reconstitution.

Role of NKG2D, DNAM-1 and natural cytotoxicity receptors in cytotoxicity toward rhabdomyosarcoma cell lines mediated by resting and IL-15-activated human natural killer cells

Children with advanced stages (relapsed/refractory and stage IV) of rhabdomyosarcoma (RMS) have a poor prognosis despite intensive chemotherapy and autologous stem cell rescue, with 5-year survival rates ranging from 5 to 35 %. Development of new, additional treatment modalities is necessary to improve the survival rate. In this preclinical study, we investigated the potential of resting and cytokine-activated natural killer (NK) cells to lyse RMS cell lines, as well as the pathways involved, to explore the eventual clinical application of (activated) NK cell immunotherapy. RMS cell lines (n = 3 derived from embryonal RMS and n = 2 derived from alveolar RMS) were susceptible to cytolysis mediated by resting NK cells, and this susceptibility was significantly increased using IL-15-activated NK cells. Flow cytometry and cytolytic assays were used to define the activating and inhibitory pathways of NK cells involved in recognizing and lysing RMS cells. NKG2D and DNAM-1 receptor-ligand interactions were essential in cytolysis by resting NK cells, as simultaneous blocking of both pathways resulted in almost complete abrogation of the cytotoxicity. In contrast, combined blocking of DNAM-1 and NKG2D only led to partial reduction of the lytic activity of IL-15-activated NK cells. In this respect, residual lysis was, at least partly, mediated by pathways involving the natural cytotoxicity receptors NKp30 and NKp46. These findings support further exploration of NK cell-based immunotherapy as adjuvant modality in current treatment strategies of RMS.

Advantages and applications of CAR-expressing natural killer cells

In contrast to donor T cells, natural killer (NK) cells are known to mediate anti-cancer effects without the risk of inducing graft-versus-host disease (GvHD). In order to improve cytotoxicity against resistant cancer cells, auspicious efforts have been made with chimeric antigen receptor (CAR) expressing T- and NK cells. These CAR-modified cells express antigen receptors against tumor-associated surface antigens, thus redirecting the effector cells and enhancing tumor-specific immunosurveillance. However, many cancer antigens are also expressed on healthy tissues, potentially leading to off tumor/on target toxicity by CAR-engineered cells. In order to control such potentially severe side effects, the insertion of suicide genes into CAR-modified effectors can provide a means for efficient depletion of these cells. While CAR-expressing T cells have entered successfully clinical trials, experience with CAR-engineered NK cells is mainly restricted to pre-clinical investigations and predominantly to NK cell lines. In this review we summarize the data on CAR expressing NK cells focusing on the possible advantage using these short-lived effector cells and discuss the necessity of suicide switches. Furthermore, we address the compliance of such modified NK cells with regulatory requirements as a new field in cellular immunotherapy.

Immunophenotypic and functional characterization of ex vivo expanded natural killer cells for clinical use in acute lymphoblastic leukemia patients

The management of acute lymphoblastic leukemia (ALL) patients has witnessed profound changes in recent years. Nonetheless, most patients tend to relapse, underlining the need for new therapeutic approaches. The anti-leukemic potential of natural killer (NK) cells has over the years raised considerable interest. In this study, we developed an efficient method for the expansion and activation of NK cells isolated from healthy donors and ALL patients for clinical use. NK cell products were derived from peripheral blood mononuclear cells of 35 healthy donors and 4 B-lineage ALL by immunomagnetic CD3 T cell depletion followed by CD56 cell enrichment. Isolated NK cells were expanded and stimulated in serum-free medium supplemented with irradiated autologous feeder cells and autologous plasma in the presence of clinical grade interleukin (IL)-2 and IL-15 for 14 days. Healthy donor NK cells expanded on average 34.9 ± 10.4 fold and were represented, after expansion, by a highly pure population of CD3(-)CD56(+) cells showing a significant upregulation of natural cytotoxicity receptors, activating receptors and maturation markers. These expanded effectors showed cytolytic activity against K562 cells and, most importantly, against primary adult B-lineage ALL blasts. NK cells could be efficiently isolated and expanded-on average 39.5 ± 20.3 fold-also from primary B-lineage ALL samples of patients in complete remission. The expanded NK cells from these patients showed a significantly increased expression of the NKG2D- and DNAM1-activating receptors and were cytotoxic against K562 cells. These data provide the basis for developing new immunotherapeutic strategies for the management of ALL patients.

Influence of autologous dendritic cells on the in-vitro expansion and functions of peripheral blood NK cells

CONTEXT

Allogeneic reactive NK cells were previously shown to exert a graft-versus-leukemia (GVL) effect during allogeneic hematopoietic stem cell transplantation, as well as reduce the incidence of graft-versus-host disease (GVHD).

OBJECTIVE

We used autologous immature DCs as feeder cells for the in-vitro expansion of NK cells and studied the function of the NK cell cultures.

MATERIALS AND METHODS

NK cells were cultured for 15 days in the presence of autologous, immature DCs. Fold expansion, killing activity and expression of IFN-γ, perforin and granzyme B were evaluated.

RESULTS

The highest NK cell expansion efficiency was observed when the ratio of NK cells:DCs was 2:1 and when cells were cultured in a contact-dependent manner. The killing activity of NK cells was highest when the NK:DC ratio was 10:1. NK cell cultures exhibited a significant upregulation in the mRNA expression of IFN-γ, perforin and granzyme B when the ratio of NK cells to DCs was 10:1.

DISCUSSION

We successfully amplified NK cells using autologous immature DCs derived from human peripheral monocytes after induction as feeder cells. The use of autologous immature DCs for ex-vivo expansion of NK cells can be clinically applied to overcome limitations, such as the small number of NK cells in peripheral blood, and the high cost of NK cell sorting. Transfusion of allogeneic reactive NK cells has been suggested as a potential adjunctive therapeutic strategy after transplantation.

CONCLUSION

Autologous immature DCs can be used as feeder cells for ex-vivo expansion of functional NK cells.

A dual-targeting triplebody mediates preferential redirected lysis of antigen double-positive over single-positive leukemic cells

The single-chain triplebody HLA-ds16-hu19 consists of three single-chain Fv (scFv) antibody fragments connected in a single polypeptide chain. This protein with dual-targeting capacity mediated preferential lysis of antigen double positive(dp) over single-positive (sp) leukemic cells by recruitment of natural killer (NK) cells as effectors. The two distal scFv modules were specific for the histocompatibility protein HLA-DR and the lymphoid antigen CD19, the central one for the Fc gamma receptor CD16. In antibody-dependent cellular cytotoxicity (ADCC) experiments with a mixture of leukemic target cells comprising both HLA-DR sp HuT-78 or Kasumi-1 cells and (HLA-DR plus CD19) dp SEM cells, the triplebody mediated preferential lysis of the dp cells even when the sp cells were present in ≤ 20-fold numerical excess.The triplebody promoted equal lysis of SEM cells at 2.5-fold and 19.5-fold lower concentrations than the parental antibodies specific for HLA-DR and CD19, respectively. Finally, the triplebody also eliminated primary leukemic cells at lower concentrations than an equimolar mixture of bispecific single-chain Fv fragments (bsscFvs) separately addressing each target antigen (hu19-ds16 and HLA-ds16). The increased selectivity of targeting and the preferential lysis of dp over sp cells achieved by dual-targeting open attractive new perspectives for the use of dual-targeting agents in cancer therapy.

Immunotherapeutic strategies against mucormycosis in haematopoietic stem cell transplantation

Mucormycoses remain a serious complication in patients undergoing allogeneic haematopoietic stem cell transplantation (HSCT). In these patients, mortality rates of mucormycosis reach up to 90%, which is due, at least in part, to the severe and prolonged immunosuppression after transplantation. Although prolonged neutropaenia is one of the most important risk factors for mucormycosis, other cell populations, such as CD4(+) T cells may also provide critical defence mechanisms against this infection. The management of mucormycosis includes antifungal therapy, surgery and, most importantly, the control of the underlying predisposing conditions, such as the correction of an impaired immune system. Here, we review the current data of granulocytes, antifungal T cells and natural killer cells regarding their activity against mucormycetes and regarding a potential immunotherapeutic approach. It is hoped that further animal studies and clinical trials assessing immunotherapeutic strategies will ultimately improve the poor prognosis of allogeneic HSCT recipients suffering from mucormycosis.

Interleukin-2-stimulated natural killer cells are less susceptible to mycophenolate mofetil than non-activated NK cells: possible consequences for immunotherapy

In a clinical phase I/II trial, pediatric patients with high-risk malignancies were treated with ex vivo IL-2-stimulated donor natural killer (NK) cells after transplantation with haploidentical stem cells. To evaluate the potential negative effects of the immunosuppressive drug mycophenolate mofetil (MMF) used for immunotherapy, the functionality and signaling of ex vivo NK cells was investigated. Our results show that during NK cell expansion, long-term (9 days) incubation with mycophenolic acid (MPA), the active metabolite of MMF, in therapeutically relevant concentrations led to the severe inhibition of NK cell proliferation. This correlated with a significantly reduced cytokine/chemokine secretion and the inhibited acquisition of surface receptors regarding cytotoxicity (e.g., NKp30, NKp44, NKp46, NKG2D), adhesion/migration (e.g., ICAM-1/CD54, LFA-1/CD11a, CD62L, CXCR3) and activation (e.g., CD25). Moreover, MPA prevented phosphorylation of the central signaling molecules STAT-3/-4/-5, AKT and ERK1/2. In contrast, short-term (24 h) MPA incubation of IL-2-stimulated NK cells had no or only marginal effects on the activated NK cell phenotype, including receptor expression, cytokine/chemokine secretion and intracellular signaling. Further, short-term MPA incubation only moderately affected the highly cytotoxic activity of previously IL-2-stimulated NK cells. In conclusion, while long-term MPA incubation significantly compromised ex vivo NK cell functionality, previously IL-2-activated NK cells seemed to be rather resistant to short-term MPA treatment. This finding supports the use of IL-2-activated NK cells as immunotherapy, especially for patients treated with MMF after haploidentical stem cell transplantation.

Improving the outcome of leukemia by natural killer cell-based immunotherapeutic strategies

Blurring the boundary between innate and adaptive immune system, natural killer (NK) cells are widely recognized as potent anti-leukemia mediators. Alloreactive donor NK cells have been shown to improve the outcome of allogeneic stem-cell transplantation for leukemia. In addition, in vivo transfer of NK cells may soon reveal an important therapeutic tool for leukemia, if tolerance to NK-mediated anti-leukemia effects is overcome. This will require, at a minimum, the ex vivo generation of a clinically safe NK cell product containing adequate numbers of NK cells with robust anti-leukemia potential. Ideally, ex vivo generated NK cells should also have similar anti-leukemia potential in different patients, and be easy to obtain for convenient clinical scale-up. Moreover, optimal clinical protocols for NK therapy in leukemia and other cancers are still lacking. These and other issues are being currently addressed by multiple research groups. This review will first describe current laboratory NK cell expansion and differentiation techniques by separately addressing different NK cell sources. Subsequently, it will address the mechanisms known to be responsible for NK cell alloreactivity, as well as their clinical impact in the hematopoietic stem cells transplantation setting. Finally, it will briefly provide insight on past NK-based clinical trials.

Ex vivo generation of highly purified and activated natural killer cells from human peripheral blood

Adoptive immunotherapy using natural killer (NK) cells has been a promising treatment for intractable malignancies; however, there remain a number of difficulties with respect to the shortage and limited anticancer potency of the effector cells. We here established a simple feeder-free method to generate purified (>90%) and highly activated NK cells from human peripheral blood-derived mononuclear cells (PBMCs). Among the several parameters, we found that CD3 depletion, high-dose interleukin (IL)-2, and use of a specific culture medium were sufficient to obtain highly purified, expanded (∼200-fold) and activated CD3(-)/CD56(+) NK cells from PBMCs, which we designated zenithal-NK (Z-NK) cells. Almost all Z-NK cells expressed the lymphocyte-activated marker CD69 and showed dramatically high expression of activation receptors (i.e., NKG2D), interferon-γ, perforin, and granzyme B. Importantly, only 2 hours of reaction at an effector/target ratio of 1:1 was sufficient to kill almost all K562 cells, and the antitumor activity was also replicated in tumor-bearing mice in vivo. Cytolysis was specific for various tumor cells, but not for normal cells, irrespective of MHC class I expression. These findings strongly indicate that Z-NK cells are purified, expanded, and near-fully activated human NK cells and warrant further investigation in a clinical setting.

Clinical grade purification and expansion of natural killer cells

Natural killer (NK) cells have been shown to have important functions in anti-tumor responses and therefore have been used as adoptive immunotherapy for cancer. Here, we review the current methods of ex vivo activation, enrichment, expansion, and shipment of clinical NK cell products.

Clinical grade purification and expansion of NK cell products for an optimized manufacturing protocol

Allogeneic natural killer (NK) cells are used for adoptive immunotherapy after stem cell transplantation. In order to overcome technical limitations in NK cell purification and activation, the following study investigates the impact of different variables on NK cell recovery, cytotoxicity, and T-cell depletion during good manufacturing practice (GMP)-grade NK cell selection. Forty NK cell products were derived from 54 unstimulated donor leukaphereses using immunomagnetic CD3 T-cell depletion, followed by a CD56 cell enrichment step. For T-cell depletion, either the depletion 2.1 program in single or double procedure (D2.1_1depl, n = 18; D2.1_2depl, n = 13) or the faster depletion 3.1 (D3.1, n = 9) was used on the CliniMACS instrument. Seventeen purified NK cell products were activated in vitro by IL-2 for 12 days. The whole process resulted in a median number of 7.59 × 10⁸ CD56⁺CD3⁻ cells with both purity and viability of 94%, respectively. The T-cell depletion was significantly better using D2.1_1depl/2depl compared to D3.1 (log 4.6/log 4.9 vs. log 3.7; p < 0.01) and double procedure in two stages led always to residual T cells below 0.1%. In contrast D3.1 was superior to D2.1_1depl/2depl with regard to recovery of CD56⁺CD3⁻ NK cells (68% vs. 41%/38%). Concomitant monocytes and especially IL-2 activation led to increased NK cell activity against malignant target cells compared to unstimulated NK cells, which correlated with both up-regulation of natural cytotoxicity receptors and intracellular signaling. Overall, wide variations in the NK cell expansion rate and the distribution of NK cell subpopulations were found. In conclusion, our results indicate that GMP-grade purification of NK cells might be improved by a sequential processing of T-cell depletion program D2.1 and D3.1. In addition NK cell expansion protocols need to be further optimized.

Cellular therapy following allogeneic stem-cell transplantation

Allogeneic hematopoietic stem-cell transplantation (HSCT) is the most effective approach for many patients with hematologic malignancies. Unfortunately, relapse remains the most common cause of death after allogeneic HSCT, and the prognosis of relapsed disease is poor for most patients. Induction of a graft-versus-leukemia (GVL), or graft-versus-tumor, effect through the use of donor leukocyte infusion (DLI), or donor lymphocyte infusion, has been remarkably successful for relapsed chronic myelogenous leukemia. Unfortunately, response to DLI in other hematologic malignancies is much less common and depends on many factors including histology, pace and extent of relapse, and time from HSCT to relapse. Furthermore, graft-versus-host disease (GVHD) is common after DLI and often limits successful immunotherapy. Ultimately, manipulations to minimize GVHD while preserving or enhancing GVL are necessary to improve outcomes for relapse after allogeneic HSCT.

Advances in haploidentical stem cell transplantation

Hematopoietic stem cell transplantation from haploidentical donors is an attractive method of transplantation due to the immediate donor availability, ease of stem cell procurement and the possibility to collect additional donor cells for cellular therapy, if needed. Historically, maintaining T-cells in the graft has been associated with very high rates of graft-versus-host disease, while T-cell depleted haploidentical transplantation has been limited by a higher incidence of graft rejection and delayed immune reconstitution post-transplant. Recent approaches attempt to maintain the T-cells in the graft while effectively preventing the development of graft-versus-host disease post-transplant. Selective depletion of alloreactive T-cells post-transplant using high-dose post-transplant cyclophosphamide is under investigation as a promising alternative in haploidentical transplantation. While engraftment has improved and graft-versus-host disease is controlled with this approach, future directions should focus on optimizing conditioning regimens and the prevention of disease relapse post-transplant.

Pre-emptive immunotherapy with purified natural killer cells after haploidentical SCT: a prospective phase II study in two centers

Adoptive immunotherapy with allogeneic purified natural killer (NK) cell products might exert graft-versus-tumor alloreactivity with little risk of GVHD. In a prospective phase II study in two centers, we administered purified NK cell products to high-risk patients treated with haploidentical T-cell-depleted SCT. Sixteen patients received a total of 29 NK cell infusions on days +3, +40 and +100 after transplantation. Median doses (and ranges) of infused NK- and T-cells per product were 1.21 (0.3-3.8) × 10(7)/kg and 0.03 (0.004-0.72) × 10(5)/kg, respectively. With a median follow-up of 5.8 years 4/16 patients are alive. Cause of death was relapse in five, GVHD in three, graft failure in three, and transplant related neurotoxicity in one patient. Four patients developed acute GVHDgrade II, all receiving a total of 0.5 × 10(5) T cells/kg. Compared with historical controls, NK cell infusions had no apparent effect on the rates of graft failure or relapse. Adoptive transfer of allogeneic NK cells is safe and feasible, but further studies are needed to determine the optimal dose and timing of NK cell therapy. Moreover, NK cell activation/expansion may be required to attain clinical benefit, while careful consideration must be given to the number of T cells infused.

Large-scale ex vivo expansion and characterization of natural killer cells for clinical applications

BACKGROUND AIMS

Interest in natural killer (NK) cell-based immunotherapy has resurged since new protocols for the purification and expansion of large numbers of clinical-grade cells have become available.

METHODS

We have successfully adapted a previously described NK expansion method that uses K562 cells expressing interleukin (IL)-15 and 4-1 BB Ligand (BBL) (K562-mb15-41BBL) to grow NK cells in novel gas-permeable static cell culture flasks (G-Rex).

RESULTS

Using this system we produced up to 19 × 10(9) functional NK cells from unseparated apheresis products, starting with 15 × 10(7) CD3(-) CD56 (+) NK cells, within 8-10 days of culture. The G-Rex yielded a higher fold expansion of NK cells than conventional gas-permeable bags and required no cell manipulation or feeding during the culture period. We also showed that K562-mb15-41BBL cells up-regulated surface HLA class I antigen expression upon stimulation with the supernatants from NK cultures and stimulated alloreactive CD8 (+) T cells within the NK cultures. However, these CD3 (+) T cells could be removed successfully using the CliniMACS system. We describe our optimized NK cell cryopreservation method and show that the NK cells are viable and functional even after 12 months of cryopreservation.

CONCLUSIONS

We have successfully developed a static culture protocol for large-scale expansion of NK cells in the gas permeable G-Rex system under good manufacturing practice (GMP) conditions. This strategy is currently being used to produce NK cells for cancer immunotherapy.

Engineering lymph node homing of ex vivo-expanded human natural killer cells via trogocytosis of the chemokine receptor CCR7

Natural killer (NK) cells have gained significant attention in adoptive immunotherapy for cancer. Consequently, novel methods of clinical-grade expansion of NK cells have emerged. Subsets of NK cells express a variety of chemokine receptors. However, to expand the scope of adoptively transferred NK cell homing to various malignancies, expression of corresponding chemokine receptors on NK cells is essential. Here, we have explored the use of trogocytosis as a tool to transiently express the chemokine receptor CCR7 on expanded human NK cells with the aim to enhance their homing to lymph nodes. We generated a K562-based "donor" cell line expressing CCR7, Clone9.CCR7, to transfer CCR7 onto NK cells via trogocytosis. CCR7 expression occurred in 80% of expanded NK cells within 1 hour after coculture with Clone9.CCR7. After removal of the donor cells from the coculture, the CCR7 expression on NK cells steadily declined to baseline levels by 72 hours. The acquired CCR7 receptors mediated in vitro migration of NK cells toward CCL19 and CCL21 and increased the lymph node homing by 144% in athymic nude mice. This is the first report on exploiting trogocytosis to rapidly and transiently modify lymphocytes, without direct genetic intervention, for adoptive transfer.

Progress in haploidentical stem cell transplantation

Haploidentical stem cell transplantation is an attractive form of transplantation because of the immediate donor availability, ease of stem cell procurement, and the possibility to further collect donor cells for cellular therapy. Historically, maintaining T cells in the graft has been associated with very high rates of graft-versus-host-disease (GVHD), whereas T cell-depleted haploidentical transplantation has been limited by a higher incidence of graft rejection and nonrelapse mortality related to infectious complications as a result of delayed immune reconstitution posttransplantation. Recent approaches have attempted to eliminate the alloreactive T cells to prevent GVHD posttransplantation. Administration of high-dose cyclophosphamide early posttransplantation in combination with tacrolimus and mycophenolate mofetil has produced engraftment and GVHD rates similar to HLA-matched sibling transplants, suggesting that the most important barriers against successful haploidentical transplantation can be overcome. Future directions should focus on optimizing conditioning regimens for different diseases and prevention of disease relapse posttransplantation.

Optimization of the use of Calcineurin inhibitors in liver transplantation

Calcineurin inhibitors (CNIs), such as cyclosporin A and tacrolimus, are the cornerstone of maintenance immunosuppressive regimens in liver transplantation. CNIs prevent rejection by inhibition of calcineurin, via which lymphocyte proliferation and interleukin (IL)-2 production is prevented. Tacrolimus is now the first-choice immunosuppressant after liver transplantation, since it is associated with fewer episodes of rejection than cyclosporin A. In this review we will discuss interindividual differences, which influence tacrolimus metabolism. Because of these factors and the narrow therapeutic index of tacrolimus, monitoring of drug trough levels is necessary. Furthermore, we will discuss studies concerning conversion from the tacrolimus twice daily to tacrolimus once daily formulation in stable LT patients. Due to adverse effects of CNIs, such as chronic renal failure, hypertension, de novo malignancy and new-onset diabetes mellitus, CNI minimization strategies have been developed, which will be discussed too.

Membrane-bound IL-21 promotes sustained ex vivo proliferation of human natural killer cells

NK cells have therapeutic potential for a wide variety of human malignancies. However, because NK cells expand poorly in vitro, have limited life spans in vivo, and represent a small fraction of peripheral white blood cells, obtaining sufficient cell numbers is the major obstacle for NK-cell immunotherapy. Genetically-engineered artificial antigen-presenting cells (aAPCs) expressing membrane-bound IL-15 (mbIL15) have been used to propagate clinical-grade NK cells for human trials of adoptive immunotherapy, but ex vivo proliferation has been limited by telomere shortening. We developed K562-based aAPCs with membrane-bound IL-21 (mbIL21) and assessed their ability to support human NK-cell proliferation. In contrast to mbIL15, mbIL21-expressing aAPCs promoted log-phase NK cell expansion without evidence of senescence for up to 6 weeks of culture. By day 21, parallel expansion of NK cells from 22 donors demonstrated a mean 47,967-fold expansion (median 31,747) when co-cultured with aAPCs expressing mbIL21 compared to 825-fold expansion (median 325) with mbIL15. Despite the significant increase in proliferation, mbIL21-expanded NK cells also showed a significant increase in telomere length compared to freshly obtained NK cells, suggesting a possible mechanism for their sustained proliferation. NK cells expanded with mbIL21 were similar in phenotype and cytotoxicity to those expanded with mbIL15, with retained donor KIR repertoires and high expression of NCRs, CD16, and NKG2D, but had superior cytokine secretion. The mbIL21-expanded NK cells showed increased transcription of the activating receptor CD160, but otherwise had remarkably similar mRNA expression profiles of the 96 genes assessed. mbIL21-expanded NK cells had significant cytotoxicity against all tumor cell lines tested, retained responsiveness to inhibitory KIR ligands, and demonstrated enhanced killing via antibody-dependent cell cytotoxicity. Thus, aAPCs expressing mbIL21 promote improved proliferation of human NK cells with longer telomeres and less senescence, supporting their clinical use in propagating NK cells for adoptive immunotherapy.

Clinical production and therapeutic applications of alloreactive natural killer cells

Recent advances have improved our understanding of natural killer (NK) cell-mediated alloreactivity after hematopoietic cell transplantation (HCT) or with adoptive transfer. NK cells contribute to a graft-versus-leukemia effect and may play a role in preventing graft-versus-host disease or controlling infectious diseases after allogeneic HCT. New discoveries in NK cell biology, including characterization of NK cell receptors and their interactions with self-HLA molecules and a better understanding of the mechanism of NK cell education have led to the development of novel strategies to exploit NK cell alloreactivity against tumors. While early studies using autologous NK cells lacked efficacy, the use of adoptively transferred NK cells to treat hematopoietic malignancies has been expanding. The production of allogeneic donor NK cells requires efficient removal of T- and B cells from clinical-scale leukapheresis collections. The goal of this chapter is to review NK cell biology, NK cell receptors, the use of NK cells as therapy and then to discuss the clinical decisions resulting in our current good manufacturing practices processing and activation of human NK cells for therapeutic use.

IL-2 stimulated but not unstimulated NK cells induce selective disappearance of peripheral blood cells: concomitant results to a phase I/II study

In an ongoing clinical phase I/II study, 16 pediatric patients suffering from high risk leukemia/tumors received highly purified donor natural killer (NK) cell immunotherapy (NK-DLI) at day (+3) +40 and +100 post haploidentical stem cell transplantation. However, literature about the influence of NK-DLI on recipient's immune system is scarce. Here we present concomitant results of a noninvasive in vivo monitoring approach of recipient's peripheral blood (PB) cells after transfer of either unstimulated (NK-DLI(unstim)) or IL-2 (1000 U/ml, 9-14 days) activated NK cells (NK-DLI(IL-2 stim)) along with their ex vivo secreted cytokine/chemokines. We performed phenotypical and functional characterizations of the NK-DLIs, detailed flow cytometric analyses of various PB cells and comprehensive cytokine/chemokine arrays before and after NK-DLI. Patients of both groups were comparable with regard to remission status, immune reconstitution, donor chimerism, KIR mismatching, stem cell and NK-DLI dose. Only after NK-DLI(IL-2 stim) was a rapid, almost complete loss of CD56(bright)CD16(dim/-) immune regulatory and CD56(dim)CD16(+) cytotoxic NK cells, monocytes, dendritic cells and eosinophils from PB circulation seen 10 min after infusion, while neutrophils significantly increased. The reduction of NK cells was due to both, a decrease in patients' own CD69(-) NCR(low)CD62L(+) NK cells as well as to a diminishing of the transferred cells from the NK-DLI(IL-2 stim) with the CD56(bright)CD16(+/-)CD69(+)NCR(high)CD62L(-) phenotype. All cell counts recovered within the next 24 h. Transfer of NK-DLI(IL-2 stim) translated into significantly increased levels of various cytokines/chemokines (i.e. IFN-γ, IL-6, MIP-1β) in patients' PB. Those remained stable for at least 1 h, presumably leading to endothelial activation, leukocyte adhesion and/or extravasation. In contrast, NK-DLI(unstim) did not cause any of the observed effects. In conclusion, we assume that the adoptive transfer of NK-DLI(IL-2 stim) under the influence of ex vivo and in vivo secreted cytokines/chemokines may promote NK cell trafficking and therefore might enhance efficacy of immunotherapy.

Clinical-grade generation of active NK cells from cord blood hematopoietic progenitor cells for immunotherapy using a closed-system culture process

Natural killer (NK) cell-based adoptive immunotherapy is a promising treatment approach for many cancers. However, development of protocols that provide large numbers of functional NK cells produced under GMP conditions are required to facilitate clinical studies. In this study, we translated our cytokine-based culture protocol for ex vivo expansion of NK cells from umbilical cord blood (UCB) hematopoietic stem cells into a fully closed, large-scale, cell culture bioprocess. We optimized enrichment of CD34⁺ cells from cryopreserved UCB units using the CliniMACS system followed by efficient expansion for 14 days in gas-permeable cell culture bags. Thereafter, expanded CD34⁺ UCB cells could be reproducibly amplified and differentiated into CD56⁺CD3⁻ NK cell products using bioreactors with a mean expansion of more than 2,000 fold and a purity of >90%. Moreover, expansion in the bioreactor yielded a clinically relevant dose of NK cells (mean: 2×10⁹ NK cells), which display high expression of activating NK receptors and cytolytic activity against K562. Finally, we established a versatile closed washing procedure resulting in optimal reduction of medium, serum and cytokines used in the cell culture process without changes in phenotype and cytotoxic activity. These results demonstrate that large numbers of UCB stem cell-derived NK cell products for adoptive immunotherapy can be produced in closed, large-scale bioreactors for the use in clinical trials.

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.

Mechanisms of tumor and viral immune escape from natural killer cell-mediated surveillance

Human natural killer (NK) cells recognize and efficiently eliminate MHC class I low or negative malignant targets and virally infected host cells, without requirement for prior sensitization. However, viruses and various tumor cells display elaborate adaptations to evade and overcome immunosurveillance. The current review focuses on escape mechanisms of viruses and malignantly transformed 'stressed' cells to evade from NK cell cytotoxicity. A general overview of recent clinical studies using allogeneic donor NK cells is given, summarizing first data about a possible benefit for patients suffering from high-risk leukemia and solid tumors. Finally, the review discusses the future perspectives and hypotheses aiming to improve therapeutic NK cell strategies against tumor immune escape mechanisms.

Natural killer cells and tumor control

PURPOSE OF REVIEW

After hematopoietic cell transplantation (HCT) donor-derived natural killer (NK) cells kill tumor cells to prevent relapse and mediate other beneficial clinical effects including control of infections without inducing graft-vs.-host disease (GVHD). Understanding the determinants of NK cell alloreactivity and function will support improvements in the design of HCT and adoptive cellular therapies.

RECENT FINDINGS

Refinements to the model of NK cell education or licensing have been made which will inform strategies to develop functional alloreactive NK cells for therapeutic use. Differences in NK cell function have been shown to be dependent on the nature of the stimuli. Recent advances have been made in our understanding of the role of activating NK receptors on education and outcome after HCT. The use of adoptively transferred NK cells to treat hematopoietic malignancies has been expanding. New approaches to modulate target sensitivity to NK cell-mediated killing are under development.

SUMMARY

NK cells play an important role in the therapeutic efficacy of HCT, with effects on control of infections, GVHD, engraftment and relapse prevention. Recent advances in our understanding of NK cell biology will support improvements in our ability to exploit NK cells to treat cancer.