Human CD4+CD25+ T cells expressing a chimeric antigen receptor against aberrant superoxide dismutase 1 trigger antigen-specific immunomodulation.

BACKGROUND AIMS: Amyotrophic lateral sclerosis (ALS) is a fatal disease associated with motor neuron degeneration, accumulation of aggregated misfolded proteins and neuroinflammation in motor regions of the central nervous system (CNS). Clinical trials using regulatory T cells (Tregs) are ongoing because of Tregs' immunomodulatory function, ability to traffic to the CNS, high numbers correlating with slower disease in ALS and disease-modifying activity in ALS mouse models. In the current study, a chimeric antigen receptor (CAR) was developed and characterized in human Tregs to enhance their immunomodulatory activity when in contact with an ALS protein aggregate. METHODS: A CAR (DG05-28-3z) consisting of a human superoxide dismutase 1 (hSOD1)-binding single-chain variable fragment, CD28 hinge, transmembrane and co-stimulatory domain and CD3ζ signaling domain was created and expressed in human Tregs. Human Tregs were isolated by either magnetic enrichment for CD4+CD25hi cells (Enr-Tregs) or cell sorting for CD4+CD25hiCD127lo cells (FP-Tregs), transduced and expanded for 17 days. RESULTS: The CAR bound preferentially to the ALS mutant G93A-hSOD1 protein relative to the wild-type hSOD1 protein. The CAR Tregs produced IL-10 when cultured with aggregated G93A-hSOD1 proteins or spinal cord explants from G93A-hSOD1 transgenic mice. Co-culturing DG05-28-3z CAR Tregs with human monocytes/macrophages inhibited production of tumor necrosis factor alpha and reactive oxygen species. Expanded FP-Tregs resulted in more robust Tregs compared with Enr-Tregs. FP-Tregs produced similar IL-10 and less interferon gamma, had lower Treg-specific demethylated region methylation and expressed higher FoxP3 and CD39. CONCLUSIONS: Taken together, this study demonstrates that gene-modified Tregs can be developed to target an aggregated ALS-relevant protein to elicit CAR-mediated Treg effector functions and provides an approach for generating Treg therapies for ALS with the goal of enhanced disease site-specific immunomodulation.

Multifunctional mRNA-Based CAR T Cells Display Promising Antitumor Activity Against Glioblastoma.

PURPOSE: Most chimeric antigen receptor (CAR) T-cell strategies against glioblastoma have demonstrated only modest therapeutic activity and are based on persistent gene modification strategies that have limited transgene capacity, long manufacturing processes, and the risk for uncontrollable off-tumor toxicities. mRNA-based T-cell modifications are an emerging safe, rapid, and cost-effective alternative to overcome these challenges, but are underexplored against glioblastoma. EXPERIMENTAL DESIGN: We generated mouse and human mRNA-based multifunctional T cells coexpressing a multitargeting CAR based on the natural killer group 2D (NKG2D) receptor and the proinflammatory cytokines IL12 and IFNα2 and assessed their antiglioma activity in vitro and in vivo. RESULTS: Compared with T cells that either expressed the CAR or cytokines alone, multifunctional CAR T cells demonstrated increased antiglioma activity in vitro and in vivo in three orthotopic immunocompetent mouse glioma models without signs of toxicity. Mechanistically, the coexpression of IL12 and IFNα2 in addition to the CAR promoted a proinflammatory tumor microenvironment and reduced T-cell exhaustion as demonstrated by ex vivo immune phenotyping, cytokine profiling, and RNA sequencing. The translational potential was demonstrated by image-based single-cell analyses of mRNA-modified T cells in patient glioblastoma samples with a complex cellular microenvironment. This revealed strong antiglioma activity of human mRNA-based multifunctional NKG2D CAR T cells coexpressing IL12 and IFNα2 whereas T cells that expressed either the CAR or cytokines alone did not demonstrate comparable antiglioma activity. CONCLUSIONS: These data provide a robust rationale for future clinical studies with mRNA-based multifunctional CAR T cells to treat malignant brain tumors.

Superkine IL-2 and IL-33 Armored CAR T Cells Reshape the Tumor Microenvironment and Reduce Growth of Multiple Solid Tumors.

Chimeric-antigen receptor (CAR) T-cell therapy has shown remarkable efficacy against hematologic tumors. Yet, CAR T-cell therapy has had little success against solid tumors due to obstacles presented by the tumor microenvironment (TME) of these cancers. Here, we show that CAR T cells armored with the engineered IL-2 superkine Super2 and IL-33 were able to promote tumor control as a single-agent therapy. IFNγ and perforin were dispensable for the effects of Super2- and IL-33-armored CAR T cells. Super2 and IL-33 synergized to shift leukocyte proportions in the TME and to recruit and activate a broad repertoire of endogenous innate and adaptive immune cells including tumor-specific T cells. However, depletion of CD8+ T cells or NK cells did not disrupt tumor control, suggesting that broad immune activation compensated for loss of individual cell subsets. Thus, we have shown that Super2 and IL-33 CAR T cells can promote antitumor immunity in multiple solid tumor models and can potentially overcome antigen loss, highlighting the potential of this universal CAR T-cell platform for the treatment of solid tumors.

Engineering a natural ligand-based CAR: directed evolution of the stress-receptor NKp30.

B7H6, a stress-induced ligand which binds to the NK cell receptor NKp30, has recently emerged as a promising candidate for immunotherapy due to its tumor-specific expression on a broad array of human tumors. NKp30 can function as a chimeric antigen receptor (CAR) extracellular domain but exhibits weak binding with a fast on and off rate to B7H6 compared to the TZ47 anti-B7H6 single-chain variable fragment (scFv). Here, directed evolution using yeast display was employed to isolate novel NKp30 variants that bind to B7H6 with higher affinity compared to the native receptor but retain its fast association and dissociation profile. Two variants, CC3 and CC5, were selected for further characterization and were expressed as soluble Fc-fusion proteins and CARs containing CD28 and CD3ς intracellular domains. We observed that Fc-fusion protein forms of NKp30 and its variants were better able to bind tumor cells expressing low levels of B7H6 than TZ47, and that the novel variants generally exhibited improved in vitro tumor cell killing relative to NKp30. Interestingly, CAR T cells expressing the engineered variants produced unique cytokine signatures in response to multiple tumor types expressing B7H6 compared to both NKp30 and TZ47. These findings suggest that natural CAR receptors can be fine-tuned to produce more desirable signaling outputs while maintaining evolutionary advantages in ligand recognition relative to scFvs.

A Chimeric Antigen Receptor That Binds to a Conserved Site on MICA.

The NKG2D ligand MHC class I chain-related protein A (MICA) is expressed on many varieties of malignant cells but is absent from most normal tissues, and thus represents a potential target for chimeric Ag receptor (CAR) T cell-based therapeutics. However, there are more than 100 alleles of MICA, so the ability to target a conserved site is needed for a therapy to be used in most patients. In this study, we describe a fully human anti-MICA CAR created by fusing the single-chain fragment variable B2 to the full length DAP10 protein and the traditional CD3ζ signaling domain. Human T cells expressing the B2 CAR killed MICA-positive tumor cells, produced IFN-γ when in contact with MICA-positive tumor cells or plate-bound MICA protein, and inhibited PANC-1 growth in a mouse xenograft model. To localize B2's epitope on MICA, we used novel computational methods to model potential binding modes and to design mutational variants of MICA testing these hypotheses. Flow cytometry using a commercial anti-MICA/MICB Ab indicated that the variant proteins were expressed at high levels on transduced P815 cell lines. One variant protein (R38S/K40T/K57E) showed reduced staining with a B2-IgG1 fusion protein compared with controls and did not induce IFN-γ production by human T cells expressing the B2 CAR. These results show antitumor activity of MICA-specific CAR T cells and indicate an essential role for a conserved site in the exposed loop involving aa 38-57 of MICA. This study describes a novel MICA-specific CAR and discusses its potential use as a cancer therapeutic.

Toxicity Induced by a Bispecific T Cell-Redirecting Protein Is Mediated by Both T Cells and Myeloid Cells in Immunocompetent Mice.

Bispecific T cell engagers have demonstrated clinical efficacy; however, their use can be accompanied by severe toxicity. Mechanistic understanding of these toxicities is limited by a lack of suitable immunocompetent preclinical models. In this study, we describe an immunocompetent mouse tumor model that exhibits bispecific T cell engager-induced toxicity and recapitulates key features similar to those in human cytokine release syndrome. In this study, toxicity occurred between the second and fourth injections of an NK Group 2D bispecific T cell engager protein. Symptoms were transient, peaking 3-4 h after treatment and resolving by 8 h. Mice developed weight loss, elevated plasma cytokines, a significant reduction in spleen white pulp, and lymphocyte infiltration in the liver. Systemic cellular immune changes also occurred; notably, an increase in CD8+ T cell activation, an increase in myeloid cells in the blood, and a population of Ly-6Cint monocytes (CD11b+Ly-6G-F4/80-) emerged in the liver and spleens of bispecific protein-treated mice. IFN-γ was primarily produced by CD8+ T cells in the spleen and was required for the observed changes in both T cell and myeloid populations. Rag deficiency, IFN-γ deficiency, or depletion of either CD4+ or CD8+ T cells prevented toxicity, whereas perforin deficiency, GM-CSF deficiency, or modulation of the myeloid population through clodronate-mediated depletion showed a partial abrogation of toxicity. Together, these findings reveal that T cell activation by a bispecific T cell engager leads to changes in the host myeloid cell population, both of which contribute to treatment induced toxicity in immunocompetent mice.

Phase I Trial of Autologous CAR T Cells Targeting NKG2D Ligands in Patients with AML/MDS and Multiple Myeloma.

NKG2D ligands are widely expressed in solid and hematologic malignancies but absent or poorly expressed on healthy tissues. We conducted a phase I dose-escalation study to evaluate the safety and feasibility of a single infusion of NKG2D-chimeric antigen receptor (CAR) T cells, without lymphodepleting conditioning in subjects with acute myeloid leukemia/myelodysplastic syndrome or relapsed/refractory multiple myeloma. Autologous T cells were transfected with a γ-retroviral vector encoding a CAR fusing human NKG2D with the CD3ζ signaling domain. Four dose levels (1 × 106-3 × 107 total viable T cells) were evaluated. Twelve subjects were infused [7 acute myeloid leukemia (AML) and 5 multiple myeloma]. NKG2D-CAR products demonstrated a median 75% vector-driven NKG2D expression on CD3+ T cells. No dose-limiting toxicities, cytokine release syndrome, or CAR T cell-related neurotoxicity was observed. No significant autoimmune reactions were noted, and none of the ≥ grade 3 adverse events were attributable to NKG2D-CAR T cells. At the single injection of low cell doses used in this trial, no objective tumor responses were observed. However, hematologic parameters transiently improved in one subject with AML at the highest dose, and cases of disease stability without further therapy or on subsequent treatments were noted. At 24 hours, the cytokine RANTES increased a median of 1.9-fold among all subjects and 5.8-fold among six AML patients. Consistent with preclinical studies, NKG2D-CAR T cell-expansion and persistence were limited. Manufactured NKG2D-CAR T cells exhibited functional activity against autologous tumor cells in vitro, but modifications to enhance CAR T-cell expansion and target density may be needed to boost clinical activity.

Manufacturing development and clinical production of NKG2D chimeric antigen receptor-expressing T cells for autologous adoptive cell therapy.

BACKGROUND AIMS: Adoptive cell therapy employing natural killer group 2D (NKG2D) chimeric antigen receptor (CAR)-modified T cells has demonstrated preclinical efficacy in several model systems, including hematological and solid tumors. We present comprehensive data on manufacturing development and clinical production of autologous NKG2D CAR T cells for treatment of acute myeloid leukemia and multiple myeloma (ClinicalTrials.gov Identifier: NCT02203825). An NKG2D CAR was generated by fusing native full-length human NKG2D to the human CD3ζ cytoplasmic signaling domain. NKG2D naturally associates with native costimulatory molecule DAP10, effectively generating a second-generation CAR against multiple ligands upregulated during malignant transformation including MIC-A, MIC-B and the UL-16 binding proteins. METHODS: CAR T cells were infused fresh after a 9-day process wherein OKT3-activated T cells were genetically modified with replication-defective gamma-retroviral vector and expanded ex vivo for 5 days with recombinant human interleukin-2. RESULTS: Despite sizable interpatient variation in originally collected cells, release criteria, including T-cell expansion and purity (median 98%), T-cell transduction (median 66% CD8+ T cells), and functional activity against NKG2D ligand-positive cells, were met for 100% of healthy donors and patients enrolled and collected. There was minimal carryover of non-T cells, particularly malignant cells; both effector memory and central memory cells were generated, and inflammatory cytokines such as granulocyte colony-stimulating factor, RANTES, interferon-γ and tumor necrosis factor-α were selectively up-regulated. CONCLUSIONS: The process resulted in production of required cell doses for the first-in-human phase I NKG2D CAR T clinical trial and provides a robust, flexible base for further optimization of NKG2D CAR T-cell manufacturing.

Advances in the use of natural receptor- or ligand-based chimeric antigen receptors (CARs) in haematologic malignancies.

Chimeric antigen receptors (CAR)-T cell therapy has recently made promising advances towards treatment of B-cell malignancies. This approach makes use of an antibody-derived single chain variable fragment (scFv)-based CAR to target the CD19 antigen. Currently scFvs are the most common strategy for creation of CARs, but tumor cells can also be targeted using non-antibody based approaches with designs focused on the interaction between natural receptors and their ligands. This emerging strategy has been used in unique ways to target multiple tumor types, including solid and haematological malignancies. In this review, we will highlight the performance of receptor-ligand combinations as designs for CARs to treat cancer, with a particular focus on haematologic malignancies.

T-bet promotes potent antitumor activity of CD4+ CAR T cells.

Chimeric antigen receptor (CAR) therapy has shown promise against B cell malignancies in the clinic. However, limited success in patients with solid tumors has prompted the development of new CAR strategies. In this study, a B7H6-specific CAR was combined with different variants of T-bet, a transcription factor that acts as the master regulator to induce a Th1 phenotype in CD4+ T cells, to create more effective CAR T cells. Skewing CD4+ CAR T cells into a Th1 improved CAR T cell functional activity while promoting a robust proinflammatory response against B7H6-expressing tumors. The expression of T-bet with the B7H6-specific CAR in CD4+ T cells conferred higher expression of the CAR, elevated secretion of Th1 and proinflammatory cytokines, and improved cellular cytotoxicity against B7H6-expressing tumor cells. In vivo, CD4+ T cells co-expressing a B7H6-specific CAR and T-bet improved the survival of RMA-B7H6 lymphoma-bearing mice. Thus, CD4+ CAR T cells with increased T-bet expression have the potential to modify the tumor microenvironment and the immune response to better treat solid and hematologic cancers.

Chimeric antigen receptors with human scFvs preferentially induce T cell anti-tumor activity against tumors with high B7H6 expression.

B7H6 is emerging as a promising tumor antigen that is known to be expressed on a wide array of tumors and is reported to stimulate anti-tumor responses from the immune system. As such, B7H6 presents a good target for tumor-specific immunotherapies. B7H6-specific chimeric antigen receptors (CAR) based on a murine antibody showed successful targeting and elimination of tumors expressing B7H6. However, mouse single chain variable fragments (scFvs) have the potential to induce host anti-CAR responses that may limit efficacy, so human scFvs specific for B7H6 were selected by yeast surface display. In this study, we validate the functionality of these human scFvs when formatted into chimeric antigen receptors. The data indicate that T cells expressing these B7H6-specific human scFvs as CARs induced potent anti-tumor activity in vitro and in vivo against tumors expressing high amounts of B7H6. Importantly, these human scFv-based CARs are sensitive to changes in B7H6 expression which may potentially spare non-tumor cells that express B7H6 and provides the foundation for future clinical development.

NKG2D-Based CAR T Cells and Radiotherapy Exert Synergistic Efficacy in Glioblastoma.

Chimeric antigen receptor (CAR) T-cell therapy is an emerging immunotherapy against several malignancies including glioblastoma, the most common and most aggressive malignant primary brain tumor in adults. The challenges in solid tumor immunotherapy comprise heterogenously expressed tumor target antigens and restricted trafficking of CAR T cells to and impaired long-term persistence at the tumor site, as well as the unaddressed integration of CAR T-cell therapy into conventional anticancer treatments. We addressed these questions using a NKG2D-based chimeric antigen receptor construct (chNKG2D) in fully immunocompetent orthotopic glioblastoma mouse models. ChNKG2D T cells demonstrated high IFNγ production and cytolytic activity in vitro Upon systemic administration in vivo, chNKG2D T cells migrated to the tumor site in the brain, did not induce adverse events, prolonged survival, and cured a fraction of glioma-bearing mice. Surviving mice were protected long-term against tumor rechallenge. Mechanistically, this was not solely the result of a classical immune memory response, but rather involved local persistence of chNKG2D T cells. A subtherapeutic dose of local radiotherapy in combination with chNKG2D T-cell treatment resulted in synergistic activity in two independent syngeneic mouse glioma models by promoting migration of CAR T cells to the tumor site and increased effector functions. We thus provide preclinical proof-of-concept of NKG2D CAR T-cell activity in mouse glioma models and demonstrate efficacy, long-term persistence, and synergistic activity in combination with radiotherapy, providing a rationale to translate this immunotherapeutic strategy to human glioma patients.Significance: These findings provide evidence for synergy of conventional anticancer therapy and CAR T cells and heralds future studies for other treatment combinations. Cancer Res; 78(4); 1031-43. ©2017 AACR.

Computationally-driven identification of antibody epitopes.

Understanding where antibodies recognize antigens can help define mechanisms of action and provide insights into progression of immune responses. We investigate the extent to which information about binding specificity implicitly encoded in amino acid sequence can be leveraged to identify antibody epitopes. In computationally-driven epitope localization, possible antibody-antigen binding modes are modeled, and targeted panels of antigen variants are designed to experimentally test these hypotheses. Prospective application of this approach to two antibodies enabled epitope localization using five or fewer variants per antibody, or alternatively, a six-variant panel for both simultaneously. Retrospective analysis of a variety of antibodies and antigens demonstrated an almost 90% success rate with an average of three antigen variants, further supporting the observation that the combination of computational modeling and protein design can reveal key determinants of antibody-antigen binding and enable efficient studies of collections of antibodies identified from polyclonal samples or engineered libraries.

Development of unique cytotoxic chimeric antigen receptors based on human scFv targeting B7H6.

As a stress-inducible natural killer (NK) cell ligand, B7H6 plays a role in innate tumor immunosurveillance and is a fairly tumor selective marker expressed on a variety of solid and hematologic cancer cells. Here, we describe the isolation and characterization of a new family of single chain fragment variable (scFv) molecules targeting the human B7H6 ligand. Through directed evolution of a yeast surface displayed non-immune human-derived scFv library, eight candidates comprising a single family of clones differing by up to four amino acid mutations and exhibiting nM avidities for soluble B7H6-Ig were isolated. A representative clone re-formatted as an scFv-CH1-Fc molecule demonstrated specific binding to both B7H6-Ig and native membrane-bound B7H6 on tumor cell lines with a binding avidity comparable to the previously characterized B7H6-targeting antibody, TZ47. Furthermore, these clones recognized an epitope distinct from that of TZ47 and the natural NK cell ligand NKp30, and demonstrated specific activity against B7H6-expressing tumor cells when expressed as a chimeric antigen receptor (CAR) in T cells.

Exploiting natural killer group 2D receptors for CAR T-cell therapy.

Chimeric antigen receptors (CARs) are genetically engineered proteins that combine an extracellular antigen-specific recognition domain with one or several intracellular T-cell signaling domains. When expressed in T cells, these CARs specifically trigger T-cell activation upon antigen recognition. While the clinical proof of principle of CAR T-cell therapy has been established in hematological cancers, CAR T cells are only at the early stages of being explored to tackle solid cancers. This special report discusses the concept of exploiting natural killer cell receptors as an approach that could broaden the specificity of CAR T cells and potentially enhance the efficacy of this therapy against solid tumors. New data demonstrating feasibility of this approach in humans and supporting the ongoing clinical trial are also presented.

NKG2D Ligand-Targeted Bispecific T-Cell Engagers Lead to Robust Antitumor Activity against Diverse Human Tumors.

Two new bispecific T-cell engaging (BiTE) molecules with specificity for NKG2D ligands were developed and functionally characterized. One, huNKG2D-OKT3, was derived from the extracellular portion of the human NKG2D receptor fused to a CD3ε binding single-chain variable fragment (scFv), known as OKT3. NKG2D has multiple ligands, including MICA, which are expressed by a variety of malignant cells. A second molecule, B2-OKT3, was created in the tandem scFv BiTE format that targets MICA on tumor cells and CD3ε on human T cells. Both BiTEs specifically activated T cells to kill human tumor cell lines. Cytotoxicity by B2-OKT3, but not huNKG2D-OKT3, is blocked by soluble rMICA. The huNKG2D-OKT3 induced greater T-cell cytokine production in comparison with B2-OKT3. No T-cell pretreatment was required for IFNγ production upon coculture of B2-OKT3 or huNKG2D-OKT3 with T cells and target cells. The effector memory T-cell compartment was the primary source of IFNγ, and culture of T cells and these BiTEs with plate-bound rMICA showed ligand density-dependent production of IFNγ from both CD4+ and CD8+ T cells. There was 2-fold more IFNγ produced per CD8+ T cell and 5-fold greater percentage of CD8+ T cells producing IFNγ compared with CD4+ T cells. In addition, both BiTEs elicited significant antitumor responses against human metastatic melanoma tumor samples using autologous or healthy donor T cells. These data demonstrate the robust antitumor activity of these NKG2D ligand-binding bispecific proteins and support their further development for clinical use. Mol Cancer Ther; 16(7); 1335-46. ©2017 AACR.

Mechanisms of Acute Toxicity in NKG2D Chimeric Antigen Receptor T Cell-Treated Mice.

Targeting cancer through the use of effector T cells bearing chimeric Ag receptors (CARs) leads to elimination of tumors in animals and patients, but recognition of normal cells or excessive activation can result in significant toxicity and even death. CAR T cells based on modified NKG2D receptors are effective against many types of tumors, and their efficacy is mediated through direct cytotoxicity and cytokine production. Under certain conditions, their ligands can be expressed on nontumor cells, so a better understanding of the potential off-tumor activity of these NKG2D CAR T cells is needed. Injection of very high numbers of activated T cells expressing CARs based on murine NKG2D or DNAM1 resulted in increased serum cytokines (IFN-γ, IL-6, and MCP-1) and acute toxicity similar to cytokine release syndrome. Acute toxicity required two key effector molecules in CAR T cells-perforin and GM-CSF. Host immune cells also contributed to this toxicity, and mice with severe immune cell defects remained healthy at the highest CAR T cell dose. These data demonstrate that specific CAR T cell effector mechanisms and the host immune system are required for this cytokine release-like syndrome in murine models.

Regulatory T cell-based therapies for autoimmunity.

Autoimmune disorders are long-term diseases that adversely affect the quality of life for patients, and they are one of the top ten leading causes of death. While each autoimmune disorder is unique, they all are caused by a breakdown of tolerance against endogenous proteins. This leads to auto-inflammatory events that promote the destruction of organs in a humoral and cellular immune mediated manner. Treatment options for autoimmunity can involve the use of chemical and biologic agents that suppress inflammation. While these treatment options for patients have shown to be beneficial in autoimmunity, they can result in patients being vulnerable to opportunistic infections. Newer therapies aim to identify methods to specifically block auto-inflammatory immune cells while allowing for an intact immune response to other antigens. T regulatory (Treg) cells are a subtype of the adoptive immune cell that is capable of suppressing inflammatory events in an antigen-specific manner, but they are often poorly functioning within autoimmune patients. Treg cells have been well characterized for their immune modulating capabilities and preclinical and early clinical studies support their therapeutic potential for antigen-specific immune suppression. This review will examine the current understanding of Treg cell function and the therapeutic potential of enhancing Treg cells in patients with inflammatory disorders.

Signaling in Effector Lymphocytes: Insights toward Safer Immunotherapy.

Receptors on T and NK cells systematically propagate highly complex signaling cascades that direct immune effector functions, leading to protective immunity. While extensive studies have delineated hundreds of signaling events that take place upon receptor engagement, the precise molecular mechanism that differentially regulates the induction or repression of a unique effector function is yet to be fully defined. Such knowledge can potentiate the tailoring of signal transductions and transform cancer immunotherapies. Targeted manipulations of signaling cascades can augment one effector function such as antitumor cytotoxicity while contain the overt generation of pro-inflammatory cytokines that contribute to treatment-related toxicity such as "cytokine storm" and "cytokine-release syndrome" or lead to autoimmune diseases. Here, we summarize how individual signaling molecules or nodes may be optimally targeted to permit selective ablation of toxic immune side effects.

Designing multivalent proteins based on natural killer cell receptors and their ligands as immunotherapy for cancer.

INTRODUCTION: Natural killer (NK) cells are an important component of the innate immune system that play a key role in host immunity against cancer. NK cell recognition and activation is based on cell surface receptors recognizing specific ligands that are expressed on many types of tumor cells. Some of these receptors are capable of activating NK cell function while other receptors inhibit NK cell function. Therapeutic approaches to treat cancer have been developed based on preventing NK cell inhibition or using NK cell receptors and their ligands to activate NK cells or T cells to destroy tumor cells. AREAS COVERED: This article describes the various strategies for targeting NK cell receptors and NK cell receptor ligands using multivalent proteins to activate immunity against cancer. EXPERT OPINION: NK cell receptors work in synergy to activate NK cell effector responses. Effective anti-cancer strategies will need to not only kill tumor cells but must also lead to the destruction of the tumor microenvironment. Immunotherapy based on NK cells and their receptors has the capacity to accomplish this through triggering lymphocyte cytotoxicity and cytokine production.