Redistribution, hyperproliferation, activation of natural killer cells and CD8 T cells, and cytokine production during first-in-human clinical trial of recombinant human interleukin-15 in patients with cancer

Molecular Aspects and Future Perspectives of Cytokine-Based Anti-cancer Immunotherapy

Cytokine-based immunotherapy is a promising field in the cancer treatment, since cytokines, as proteins of the immune system, are able to modulate the host immune response toward cancer cell, as well as directly induce tumor cell death. Since a low dose monotherapy with some cytokines has no significant therapeutic results and a high dose treatment leads to a number of side effects caused by the pleiotropic effect of cytokines, the problem of understanding the influence of cytokines on the immune cells involved in the pro- and anti-tumor immune response remains a pressing one. Immune system cells carry CD makers on their surface which can be used to identify various populations of cells of the immune system that play different roles in pro- and anti-tumor immune responses. This review discusses the functions and specific CD markers of various immune cell populations which are reported to participate in the regulation of the immune response against the tumor. The results of research studies and clinical trials investigating the effect of cytokine therapy on the regulation of immune cell populations and their surface markers are also discussed. Current trends in the development of cancer immunotherapy, as well as the role of cytokines in combination with other therapeutic agents, are also discussed.

Natural Killer Cells Expanded and Preactivated Exhibit Enhanced Antitumor Activity against Different Tumor Cells in Vitro

One of the emerging treatment strategies for cancer particularly for haematological malignancies is natural killer (NK) cell therapy. However, the availability of a best approach to maximize NK cell anticancer potential is still awaited. It is well established that cytokine-induced memory-like NK cells have the potential to differentiate after a short period of preactivation with interleukins-IL-12, IL-15, and IL-18 and exhibit increased responses to cytokine or activating receptor restimulation for weeks to months after preactivation. We demonstrated that NK cells differentiated from CD34+ cells isolated from cord blood show increased antitumor potential in vitro against different cancer cells. Using flow cytometry, we found that NK cells were able to induce apoptosis in cancer cells in vitro. We further analysed surviving gene expression by quantitative real time PCR and reported that NK cells cause down regulation of survivin gene expression in tumor cells. Therefore, NK cell therapy represents a promising immunotherapy for cancers like AML and other haematological malignancies. It concluded that NK cells can be differentiated from CD34+ cells isolated from cord blood ,are able to induce apoptosis and induce increased antitumor potential in vitro against different cancer cells besides cause downregulation of survivin gene expression in tumor cells. Therefore, NK cell therapy represents a promising immunotherapy for different cancer types and haematological malignancies. Furthers studies are necessary to confirm our findings.

[Mechanisms of radiation-induced lymphopenia and therapeutic impact]

Radiation induced lymphopenia is frequent and can be severe and durable. Although lymphocytes have long been known as highly radiosensitive cells, it is poorly characterized. Radiation-induced lymphopenia seems to affect lymphocyte subpopulations differently and seems to be influenced by radiation modalities. The depth and duration of lymphopenia depend on the location of the irradiation and the volumes of treatment. Importantly, radiation-induced lymphopenia has been associated with poorer prognosis in several tumor types. The knowledge about radiation-induced lymphopenia might lead to a rethinking of the modalities of radiotherapy and new approaches to restore lymphocytes counts.

IL-15 in the Combination Immunotherapy of Cancer

We completed clinical trials of rhIL-15 by bolus, subcutaneous, and continuous intravenous infusions (CIV). IL-15 administered by CIV at 2 mcg/kg/day yielded a 38-fold increase in 10- day number of circulating NK cells, a 358-fold increase in CD56^bright NK cells and a 5.8-fold increase in CD8 T cells. However, IL-15 preparations administered as monotherapy were ineffective, due to actions of immunological checkpoints and due to the lack of tumor specific targeting by NK cells. To circumvent checkpoints, trials of IL-15 in combination with other anticancer agents were initiated. Tumor-bearing mice receiving IL-15 with antibodies to CTLA-4 and PD-L1 manifested marked prolongation of survival compared to mice receiving IL-15 with either agent alone. In translation, a phase I trial was initiated involving IL-15 (rhIL-15), nivolumab and ipilimumab in patients with malignancy (NCT03388632). In rhesus macaques CIV IL-15 at 20 μg/kg/day for 10 days led to an 80-fold increase in number of circulating effector memory CD8 T cells. However, administration of γc cytokines such as IL-15 led to paralysis/depression of CD4 T-cells that was mediated through transient expression of SOCS3 that inhibited the STAT5 signaling pathway. This lost CD4 helper role could be restored alternatively by CD40 agonists. In the TRAMP-C2 prostate tumor model the combination of IL-15 with agonistic anti-CD40 produced additive effects in terms of numbers of TRAMP-C2 tumor specific Spas/SCNC/9H tetramer positive CD8 T cells expressed and tumor responses. A clinical trial is being initiated for patients with cancer using an intralesional anti-CD40 in combination with CIV rhIL-15. To translate IL-15-mediated increases in NK cells, we investigated combination therapy of IL-15 with anticancer monoclonal antibodies including rituximab in mouse models of EL-4 lymphoma transfected with human CD20 and with alemtuzumab (CAMPATH-1H) in a xenograft model of adult T cell leukemia (ATL). IL-15 enhanced the ADCC and therapeutic efficacy of both antibodies. These results provided the scientific basis for trials of IL-15 combined with alemtuzumab (anti-CD52) for patients with ATL (NCT02689453), with obinutuzumab (anti-CD20) for patients with CLL (NCT03759184), and with avelumab (anti-PD-L1) in patients with T-cell lymphoma (NCT03905135) and renal cancer (NCT04150562). In the first trial, there was elimination of circulating ATL and CLL leukemic cells in select patients.

Gene modification strategies for next-generation CAR T cells against solid cancers

Immunotherapies have become the backbone of cancer treatment. Among them, chimeric antigen receptor (CAR) T cells have demonstrated great success in the treatment of hematological malignancies. However, CAR T therapy against solid tumors is less effective. Antigen targeting; an immunosuppressive tumor microenvironment (TME); and the infiltration, proliferation, and persistence of CAR T cells are the predominant barriers preventing the extension of CAR T therapy to solid tumors. To circumvent these obstacles, the next-generation CAR T cells will require more potent antitumor properties, which can be achieved by gene-editing technology. In this review, we summarize innovative strategies to enhance CAR T cell function by improving target identification, persistence, trafficking, and overcoming the suppressive TME. The construction of multi-target CAR T cells improves antigen recognition and reduces immune escape. Enhancing CAR T cell proliferation and persistence can be achieved by optimizing costimulatory signals and overexpressing cytokines. CAR T cells equipped with chemokines or chemokine receptors help overcome their poor homing to tumor sites. Strategies like knocking out immune checkpoint molecules, incorporating dominant negative receptors, and chimeric switch receptors can favor the depletion or reversal of negative T cell regulators in the TME.

Deciphering Natural Killer Cell Homeostasis

Natural killer (NK) cells have a central role within the innate immune system, eliminating virally infected, foreign and transformed cells through their natural cytotoxic capacity. Release of their cytotoxic granules is tightly controlled through the balance of a large repertoire of inhibitory and activating receptors, and it is the unique combination of these receptors expressed by individual cells that confers immense diversity both in phenotype and functionality. The diverse, yet unique, NK cell repertoire within an individual is surprisingly stable over time considering the constant renewal of these cells at steady state. Here we give an overview of NK cell differentiation and discuss metabolic requirements, intra-lineage plasticity and transcriptional reprogramming during IL-15-driven homeostatic proliferation. New insights into the regulation of NK cell differentiation and homeostasis could pave the way for the successful implementation of NK cell-based immunotherapy against cancer.

Phase II Study of Ensituximab, a Novel Chimeric Monoclonal Antibody, in Adults with Unresectable, Metastatic Colorectal Cancer

PURPOSE

Patients with metastatic colorectal cancer refractory to chemotherapy have limited treatment options. Ensituximab (NEO-102) is a novel chimeric mAb targeting a variant of MUC5AC with specificity to colorectal cancer.

PATIENTS AND METHODS

Single-arm, phase II trial assessed the efficacy and safety of ensituximab in patients with advanced, refractory cancer who expressed MUC5AC antigen in tumor tissue. Ensituximab was administered intravenously every 2 weeks with 3 mg/kg as recommended phase II dose (RP2D). A minimum sample size of 43 patients was required on the basis of the assumption that ensituximab would improve median overall survival (OS) by 7 months using a one-sided significance level of 10% and 80% power. Written informed consent was obtained from all patients.

RESULTS

Sixty-three patients with advanced, refractory colorectal cancer were enrolled and 53 subjects were treated in phase II arm. Median age was 58 years and 46% of the patients were female. Among 57 evaluable patients, median OS was 6.8 months. No responses were observed, and stable disease was achieved in 21% of the patients. The most common treatment-related adverse events (AE) at RP2D included fatigue (38%), anemia (30%), nausea (15%), vomiting (11%), increased bilirubin (9%), constipation (8%), decreased appetite (6%), and diarrhea (6%). Serious AEs at least possibly related to ensituximab occurred in 4 patients and included anemia, nausea, increased bilirubin, and hypoxia. No patients discontinued treatment due to drug-related AEs.

CONCLUSIONS

Ensituximab was well tolerated and demonstrated modest antitumor activity in patients with heavily pretreated refractory colorectal cancer.

Targeting tumors with IL-21 reshapes the tumor microenvironment by proliferating PD-1intTim-3-CD8+ T cells

The lack of sufficient functional tumor-infiltrating lymphocytes in the tumor microenvironment (TME) is one of the primary indications for the poor prognosis of patients with cancer. In this study, we developed an Erbitux-based IL-21 tumor-targeting fusion protein (Erb-IL21) to prolong the half-life and improve the antitumor efficacy of IL-21. Compared with Erb-IL2, Erb-IL21 demonstrated much lower toxicity in vivo. Mechanistically, Erb-IL21 selectively expanded functional cytotoxic T lymphocytes but not dysfunctional CD8+ T cells in the TME. We observed that the IL-21-mediated antitumor effect largely depended on the existing intratumoral CD8+ T cells, instead of newly migrated CD8+ T cells. Furthermore, Erb-IL21 overcame checkpoint blockade resistance in mice with advanced tumors. Our study reveals that Erb-IL21 can target IL-21 to tumors and maximize the antitumor potential of checkpoint blockade by expending a subset of tumor antigen-specific CD8+ T cells to achieve effective tumor control.

Staging and Personalized Intervention for Infection and Sepsis

Background: Sepsis is defined as a dysregulated host response to infection, resulting in life-threatening organ dysfunction. It is now understood that this dysregulation not only constitutes excessive inflammation, but also sustained immune suppression. Immune-modulatory therapies thus have great potential for novel sepsis therapies. Here, we provide a review of biomarkers and functional assays designed to immunologically stage patients with sepsis as well as therapies designed to alter the innate and adaptive immune systems of patients with sepsis beneficially. Methods: A search of PubMed/MEDLINE and clinicaltrials.gov was performed between October 1, 2019 and December 22, 2019 using search terms such as "sepsis immunotherapy," "sepsis biomarkers," "sepsis clinical trials," and variations thereof. Results: Despite more than 30 years of research, there is still no Food and Drug Administration (FDA)-cleared biomarker that has proven to be effective in either identifying patients with sepsis who are at an increased risk of adverse outcomes or responsive to specific interventions. Similarly, past clinical trials investigating new treatment strategies have rarely stratified patients with sepsis. Overall, the results of these trials have been disappointing. Novel efforts to properly gauge an individual patient's immune response and choose an appropriate immunomodulatory agent based on the results are underway. Conclusion: Our evolving understanding of the different mechanisms perturbing immune homeostasis during sepsis strongly suggests that future successes will depend on finding the right therapy for the right patient and administering it at the right time. For such a personalized medicine approach, novel biomarkers and functional assays to properly stage the patient with sepsis will be crucial. The growing repertoire of immunomodulatory agents at our disposal, as well as re-appraisal of agents that have already been tested in unstratified cohorts of patients with sepsis, may finally translate into successful treatment strategies for sepsis.

New avenues for melanoma immunotherapy: Natural Killer cells?

Human solid malignant tumours may be particularly resistant to conventional therapies. Among solid tumours, immunological features of cutaneous melanoma have been well characterized in the past and today melanoma patients are routinely treated with the anti-immune checkpoints immunotherapy that has completely changed metastatic melanoma treatment and prognosis. Two cytotoxic cell populations may lead to the physical elimination of tumour cell targets: cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. Tumour recognition by CTLs depends on major histocompatibility complex (MHC) class I molecules, while NK cells recognize tumours expressing low or null levels of MHC class I molecules. Despite this well-established complementarity, NK cells are still left behind in the optimization of innovative immunotherapy approaches. NK cells are members of innate lymphoid cells (ILCs) that play a critical role in early host defence against invading pathogens and transformed cells. Recent findings suggest that NK cell frequencies directly correlate with the overall survival of ipilimumab-treated melanoma patients. Furthermore, in vitro and in vivo evidences indicate that NK cells can selectively kill cancer stem cells, reducing tumour size and delaying metastatic progression. The aim of this review is to provide a survey of the evidences indicating NK cells as an excellent candidate to complement the newest solid tumour immunotherapy approaches.

Functional and mechanistic advantage of the use of a bifunctional anti-PD-L1/IL-15 superagonist

BACKGROUND

Anti(α)-programmed cell death-1 (PD-1)/programmed death-ligand 1 (PD-L1) monotherapy fails to provide durable clinical benefit for most patients with carcinoma. Recent studies suggested that strategies to reduce immunosuppressive cells, promote systemic T-cell responses and lymphocyte trafficking to the tumor microenvironment (TME) may improve efficacy. N-809 is a first-in-class bifunctional agent comprising the interleukin (IL)-15 superagonist N-803 fused to two αPD-L1 domains. Thus, N-809 can potentially stimulate effector immune cells through IL-15 and block immunosuppressive PD-L1. Here, we examined the antitumor efficacy and immunomodulatory effects of N-809 versus N-803+αPD-L1 combination.

METHODS

The ability of N-809 to block PD-L1 and induce IL-15-dependent immune effects was examined in vitro and in vivo. Antitumor efficacy of N-809 or N-803+αPD-L1 was evaluated in two murine carcinoma models and an extensive analysis of immune correlates was performed in the tumor and tumor-draining lymph node (dLN).

RESULTS

We demonstrate that N-809 blocks PD-L1 and induces IL-15-dependent immune effects. N-809 was well-tolerated and reduced 4T1 lung metastasis, decreased MC38 tumor burden and increased survival versus N-803+αPD-L1. Compared with N-803+αPD-L1, N-809 enhanced natural killer (NK) and CD8+ T-cell activation and function in the dLN and TME, relating to increased gene expression associated with interferon and cytokine signaling, lymphoid compartment, costimulation and cytotoxicity. The higher number of TME CD8+ T cells was attributed to enhanced infiltration, not in situ expansion. Increased TME NK and CD8+ T-cell numbers correlated with augmented chemokine ligands and receptors. Moreover, in contrast to N-803+αPD-L1, N-809 reduced immunosuppressive regulatory T cells (Treg), monocytic myeloid-derived suppressor cells (M-MDSC) and M2-like macrophages in the TME.

CONCLUSIONS

Our results suggest that N-809 functions by a novel immune mechanism to promote antitumor efficacy. Foremost, N-809 enhances intratumoral lymphocyte numbers by increasing trafficking via altered chemokine levels in the TME and chemokine receptor expression on CD8+ T cells and NK cells. In addition, N-809 reduces immunosuppressive and pro-tumorigenic immune cells in the TME, including Treg, M2-like macrophages and M-MDSC. Overall, these novel effects of N-809 promote an inflamed TME, leading to lower tumor burden and increased survival. These results provide mechanistic insight and rationale supporting the potential clinical study of N-809 in patients with carcinoma.

Novel CD19-targeted TriKE restores NK cell function and proliferative capacity in CLL

Chronic lymphocytic leukemia (CLL) is characterized by chronic clonal expansion of mature CD19-expressing B lymphocytes and global dysfunction of immune effectors, including natural killer (NK) cells. CLL remains incurable, and novel approaches to refractory CLL are needed. Our group has previously described trispecific killer engager (TriKE) molecules that redirect NK cell function against tumor cells. TriKE reagents simultaneously bind an activating receptor on NK cells, CD16, and a tumor antigen while also providing an NK cell expansion signal via an interleukin-15 moiety. Here we developed the novel CD19-targeting 161519 TriKE. We demonstrate that 161519 TriKE induced killing of a CD19-expressing Burkitt's lymphoma cell line and examined the impact on primary CLL targets using healthy donor and patient NK cells. 161519 TriKE induced potent healthy donor NK cell activation, proliferation, and directed killing. Furthermore, 161519 TriKE rescued the inflammatory function of NK cells obtained from CLL patient peripheral blood samples. Finally, we show that 161519 TriKE induced better directed killing of CLL in vitro when compared with rituximab. In conclusion, 161519 TriKE drives a potent activating and proliferative signal on NK cells, resulting in enhanced NK cell expansion and CLL target killing. Our findings indicate the potential immunotherapeutic value of 161519 TriKE in CLL.

You Have Got a Fast CAR: Chimeric Antigen Receptor NK Cells in Cancer Therapy

The clinical success stories of chimeric antigen receptor (CAR)-T cell therapy against B-cell malignancies have contributed to immunotherapy being at the forefront of cancer therapy today. Their success has fueled interest in improving CAR constructs, identifying additional antigens to target, and clinically evaluating them across a wide range of malignancies. However, along with the exciting potential of CAR-T therapy comes the real possibility of serious side effects. While the FDA has approved commercialized CAR-T cell therapy, challenges associated with manufacturing, costs, and related toxicities have resulted in increased attention being paid to implementing CAR technology in innate cytotoxic natural killer (NK) cells. Here, we review the current landscape of the CAR-NK field, from successful clinical implementation to outstanding challenges which remain to be addressed to deliver the full potential of this therapy to more patients.

Glypican-3-Specific CAR T Cells Coexpressing IL15 and IL21 Have Superior Expansion and Antitumor Activity against Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the fourth most common cause of cancer-related death in the world, and curative systemic therapies are lacking. Chimeric antigen receptor (CAR)-expressing T cells induce robust antitumor responses in patients with hematologic malignancies but have limited efficacy in patients with solid tumors, including HCC. IL15 and IL21 promote T-cell expansion, survival, and function and can improve the antitumor properties of T cells. We explored whether transgenic expression of IL15 and/or IL21 enhanced glypican-3-CAR (GPC3-CAR) T cells' antitumor properties against HCC. We previously optimized the costimulation in GPC3-CARs and selected a second-generation GPC3-CAR incorporating a 4-1BB costimulatory endodomain (GBBz) for development. Here, we generated constructs encoding IL15, IL21, or both with GBBz (15.GBBz, 21.GBBz, and 21.15.GBBz, respectively) and examined the ability of transduced T cells to kill, produce effector cytokines, and expand in an antigen-dependent manner. We performed gene-expression and phenotypic analyses of GPC3-CAR T cells and CRISPR-Cas9 knockout of the TCF7 gene. Finally, we measured GPC3-CAR T-cell antitumor activity in murine xenograft models of GPC3+ tumors. The increased proliferation of 21.15.GBBz T cells was at least in part dependent on the upregulation and maintenance of TCF-1 (encoded by TCF7) and associated with a higher percentage of stem cell memory and central memory populations after manufacturing. T cells expressing 21.15.GBBz had superior in vitro and in vivo expansion and persistence, and the most robust antitumor activity in vivo These results provided preclinical evidence to support the clinical evaluation of 21.15.GPC3-CAR T cells in patients with HCC.

Mechanisms of Leukemia Immune Evasion and Their Role in Relapse After Haploidentical Hematopoietic Cell Transplantation

Over the last decade, the development of multiple strategies to allow the safe transfer from the donor to the patient of high numbers of partially HLA-incompatible T cells has dramatically reduced the toxicities of haploidentical hematopoietic cell transplantation (haplo-HCT), but this was not accompanied by a similar positive impact on the incidence of post-transplantation relapse. In the present review, we will elaborate on how the unique interplay between HLA-mismatched immune system and malignancy that characterizes haplo-HCT may impact relapse biology, shaping the selection of disease variants that are resistant to the “graft-vs.-leukemia” effect. In particular, we will present current knowledge on genomic loss of HLA, a relapse modality first described in haplo-HCT and accounting for a significant proportion of relapses in this setting, and discuss other more recently identified mechanisms of post-transplantation immune evasion and relapse, including the transcriptional downregulation of HLA class II molecules and the enforcement of inhibitory checkpoints between T cells and leukemia. Ultimately, we will review the available treatment options for patients who relapse after haplo-HCT and discuss on how a deeper insight into relapse immunobiology might inform the rational and personalized selection of therapies to improve the largely unsatisfactory clinical outcome of relapsing patients.

Unleashing Natural Killer Cells in the Tumor Microenvironment-The Next Generation of Immunotherapy?

The emergence of immunotherapy for cancer treatment bears considerable clinical promise. Nevertheless, many patients remain unresponsive, acquire resistance, or suffer dose-limiting toxicities. Immune-editing of tumors assists their escape from the immune system, and the tumor microenvironment (TME) induces immune suppression through multiple mechanisms. Immunotherapy aims to bolster the activity of immune cells against cancer by targeting these suppressive immunomodulatory processes. Natural Killer (NK) cells are a heterogeneous subset of immune cells, which express a diverse array of activating and inhibitory germline-encoded receptors, and are thus capable of directly targeting and killing cancer cells without the need for MHC specificity. Furthermore, they play a critical role in triggering the adaptive immune response. Enhancing the function of NK cells in the context of cancer is therefore a promising avenue for immunotherapy. Different NK-based therapies have been evaluated in clinical trials, and some have demonstrated clinical benefits, especially in the context of hematological malignancies. Solid tumors remain much more difficult to treat, and the time point and means of intervention of current NK-based treatments still require optimization to achieve long term effects. Here, we review recently described mechanisms of cancer evasion from NK cell immune surveillance, and the therapeutic approaches that aim to potentiate NK function. Specific focus is placed on the use of specialized monoclonal antibodies against moieties on the cancer cell, or on both the tumor and the NK cell. In addition, we highlight newly identified mechanisms that inhibit NK cell activity in the TME, and describe how biochemical modifications of the TME can synergize with current treatments and increase susceptibility to NK cell activity.

Synergistic Combination of Oncolytic Virotherapy and Immunotherapy for Glioma

PURPOSE

We hypothesized that the combination of a local stimulus for activating tumor-specific T cells and an anti-immunosuppressant would improve treatment of gliomas. Virally encoded IL15Rα-IL15 as the T-cell activating stimulus and a prostaglandin synthesis inhibitor as the anti-immunosuppressant were combined with adoptive transfer of tumor-specific T cells.

EXPERIMENTAL DESIGN

Two oncolytic poxviruses, vvDD vaccinia virus and myxoma virus, were each engineered to express the fusion protein IL15Rα-IL15 and a fluorescent protein. Viral gene expression (YFP or tdTomato Red) was confirmed in the murine glioma GL261 in vitro and in vivo. GL261 tumors in immunocompetent C57BL/6J mice were treated with vvDD-IL15Rα-YFP vaccinia virus or vMyx-IL15Rα-tdTr combined with other treatments, including vaccination with GARC-1 peptide (a neoantigen for GL261), rapamycin, celecoxib, and adoptive T-cell therapy.

RESULTS

vvDD-IL15Rα-YFP and vMyx-IL15Rα-tdTr each infected and killed GL261 cells in vitro. In vivo, NK cells and CD8⁺ T cells were increased in the tumor due to the expression of IL15Rα-IL15. Each component of a combination treatment contributed to prolonging survival: an oncolytic virus, the IL15Rα-IL15 expressed by the virus, a source of T cells (whether by prevaccination or adoptive transfer), and prostaglandin inhibition all synergized to produce elimination of gliomas in a majority of mice. vvDD-IL15Rα-YFP occasionally caused ventriculitis-meningitis, but vMyx-IL15Rα-tdTr was safe and effective, causing a strong infiltration of tumor-specific T cells and eliminating gliomas in 83% of treated mice.

CONCLUSIONS

IL15Rα-IL15-armed oncolytic poxviruses provide potent antitumor effects against brain tumors when combined with adoptive T-cell therapy, rapamycin, and celecoxib.

NK Cell-Based Immunotherapy in Renal Cell Carcinoma

Natural killer (NK) cells are cytotoxic lymphocytes that are able to kill tumor cells without prior sensitization. It has been shown that NK cells play a pivotal role in a variety of cancers, highlighting their relevance in tumor immunosurveillance. NK cell infiltration has been reported in renal cell carcinoma (RCC), the most frequent kidney cancer in adults, and their presence has been associated with patients’ survival. However, the role of NK cells in this disease is not yet fully understood. In this review, we summarize the biology of NK cells and the mechanisms through which they are able to recognize and kill tumor cells. Furthermore, we discuss the role that NK cells play in renal cell carcinoma, and review current strategies that are being used to boost and exploit their cytotoxic capabilities.

Cytokines as potential combination agents with PD-1/PD-L1 blockade for cancer treatment

Immunotherapy has caused a paradigm shift in the treatment of several malignancies, particularly the blockade of programmed death-1 (PD-1) and its specific receptor/ligand PD-L1 that have revolutionized the treatment of a variety of malignancies, but significant durable responses only occur in a small percentage of patients, and other patients failed to respond to the treatment. Even those who initially respond can ultimately relapse despite maintenance treatment, there is considerable potential for synergistic combinations of immunotherapy and chemotherapy agents with immune checkpoint inhibitors into conventional cancer treatments. The clinical experience in the use of cytokines in the clinical setting indicated the efficiency of cytokine therapy in cancer immunotherapy. Combinational approaches to enhancing PD-L1/PD-1 pathways blockade efficacy with several cytokines such as interleukin (IL)-2, IL-15, IL-21, IL-12, IL-10, and interferon-α (IFN-α) may result in additional benefits. In this review, the current state of knowledge about PD-1/PD-L1 inhibitors, the date in the literature to ascertain the combination of anti-PD-1/PD-L1 antibodies with cytokines is discussed. Finally, it is noteworthy that novel therapeutic approaches based on the efficient combination of recombinant cytokines with the PD-L1/PD-1 blockade therapy can enhance antitumor immune responses against various malignancies.

Immunotherapy in sepsis - brake or accelerate?

Sepsis, a life threating syndrome characterized by organ failure after infection, is the most common cause of death in hospitalized patients. The treatment of sepsis is generally supportive in nature, involving the administration of intravenous fluids, vasoactive substances and oxygen plus antibiotics to eliminate the pathogen. No drugs have been approved specifically for the treatment of sepsis, and clinical trials of potential therapies have failed to reduce mortality - suggesting that new approaches are needed. Abnormalities in the immune response elicited by the pathogen, ranging from excessive inflammation to immunosuppression, contribute to disease pathogenesis. Although hundreds of immunomodulatory agents are potentially available, it remains unclear which patient benefits from which immune therapy at a given time point. Results indicate the importance of personalized therapy, specifically the need to identify the type of intervention required by each individual patient at a given point in the disease process. To address this issue will require using biomarkers to stratify patients based on their individual immune status. This article reviews recent and ongoing clinical investigations using immunostimulatory or immunosuppressive therapies against sepsis including non-pharmacological and novel preclinical approaches.

NK cells for cancer immunotherapy

Natural killer (NK) cells can swiftly kill multiple adjacent cells if these show surface markers associated with oncogenic transformation. This property, which is unique among immune cells, and their capacity to enhance antibody and T cell responses support a role for NK cells as anticancer agents. Although tumours may develop several mechanisms to resist attacks from endogenous NK cells, ex vivo activation, expansion and genetic modification of NK cells can greatly increase their antitumour activity and equip them to overcome resistance. Some of these methods have been translated into clinical-grade platforms and support clinical trials of NK cell infusions in patients with haematological malignancies or solid tumours, which have yielded encouraging results so far. The next generation of NK cell products will be engineered to enhance activating signals and proliferation, suppress inhibitory signals and promote their homing to tumours. These modifications promise to significantly increase their clinical activity. Finally, there is emerging evidence of increased NK cell-mediated tumour cell killing in the context of molecularly targeted therapies. These observations, in addition to the capacity of NK cells to magnify immune responses, suggest that NK cells are poised to become key components of multipronged therapeutic strategies for cancer.

Engineering strategies to overcome the current roadblocks in CAR T cell therapy

T cells genetically engineered to express chimeric antigen receptors (CARs) have proven — and impressive — therapeutic activity in patients with certain subtypes of B cell leukaemia or lymphoma, with promising efficacy also demonstrated in patients with multiple myeloma. Nevertheless, various barriers restrict the efficacy and/or prevent the widespread use of CAR T cell therapies in these patients as well as in those with other cancers, particularly solid tumours. Key challenges relating to CAR T cells include severe toxicities, restricted trafficking to, infiltration into and activation within tumours, suboptimal persistence in vivo, antigen escape and heterogeneity, and manufacturing issues. The evolution of CAR designs beyond the conventional structures will be necessary to address these limitations and to expand the use of CAR T cells to a wider range of malignancies. Investigators are addressing the current obstacles with a wide range of engineering strategies in order to improve the safety, efficacy and applicability of this therapeutic modality. In this Review, we discuss the innovative designs of novel CAR T cell products that are being developed to increase and expand the clinical benefits of these treatments in patients with diverse cancers.

Chimeric antigen receptor (CAR) T cell therapy, the first approved therapeutic approach with a genetic engineering component, holds substantial promise in the treatment of a range of cancers but is nevertheless limited by various challenges, including toxicities, intrinsic and acquired resistance mechanisms, and manufacturing issues. In this Review, the authors describe the innovative approaches to the engineering of CAR T cell products that are providing solutions to these challenges and therefore have the potential to considerably improve the safety and effectiveness of treatment.

Chimeric antigen receptor (CAR) T cells have induced remarkable responses in patients with certain haematological malignancies, yet various barriers restrict the efficacy and/or prevent the widespread use of this treatment.

Investigators are addressing these challenges with engineering strategies designed to improve the safety, efficacy and applicability of CAR T cell therapy.

CARs have modular components, and therefore the optimal molecular design of the CAR can be achieved through many variations of the constituent protein domains.

Toxicities currently associated with CAR T cell therapy can be mitigated using engineering strategies to make CAR T cells safer and that potentially broaden the range of tumour-associated antigens that can be targeted by overcoming on-target, off-tumour toxicities.

CAR T cell efficacy can be enhanced by using engineering strategies to address the various challenges relating to the unique biology of diverse haematological and solid malignancies.

Strategies to address the manufacturing challenges can lead to an improved CAR T cell product for all patients.

Role of IL-15 Signaling in the Pathogenesis of Simian Immunodeficiency Virus Infection in Rhesus Macaques

Although IL-15 has been implicated in the pathogenic hyperimmune activation that drives progressive HIV and SIV infection, as well as in the generation of HIV/SIV target cells, it also supports NK and T cell homeostasis and effector activity, potentially benefiting the host. To understand the role of IL-15 in SIV infection and pathogenesis, we treated two cohorts of SIVmac239-infected rhesus macaques (RM; Macaca mulatta), one with chronic infection, the other with primary infection, with a rhesusized, IL-15-neutralizing mAb (versus an IgG isotype control) for up to 10 wk (n = 7-9 RM per group). In both cohorts, anti-IL-15 was highly efficient at blocking IL-15 signaling in vivo, causing 1) profound depletion of NK cells in blood and tissues throughout the treatment period; 2) substantial, albeit transient, depletion of CD8+ effector memory T cells (TEM) (but not the naive and central memory subsets); and 3) CD4+ and CD8+ TEM hyperproliferation. In primary infection, reduced frequencies of SIV-specific effector T cells in an extralymphoid tissue site were also observed. Despite these effects, the kinetics and extent of SIV replication, CD4+ T cell depletion, and the onset of AIDS were comparable between anti-IL-15- and control-treated groups in both cohorts. However, RM treated with anti-IL-15 during primary infection manifested accelerated reactivation of RM rhadinovirus. Thus, IL-15 support of NK cell and TEM homeostasis does not play a demonstrable, nonredundant role in SIV replication or CD4+ T cell deletion dynamics but may contribute to immune control of oncogenic γ-herpesviruses.

Rapid isolation and enrichment of mouse NK cells for experimental purposes

Natural killer (NK) cells have shown to play a critical, but as yet poorly defined, role in the process by which the immune system controls tumor progression. Indeed, NK cell-based immunotherapy, particularly NK cell adoptive transfer therapy, has become a very attractive cancer weapon against multiple types of cancers such as metastatic and hematological cancers. Unfortunately, the implementation of these therapies has been challenged by the existence of immunosuppression mechanisms that have prevented NK cell functionality. Additionally, the development of protocols to obtain purified and functional NK cells has faced some difficulties due to the limitations in the numbers of cells that can be obtained and the development of an exhaustion phenotype with impaired proliferative and functional capabilities during lengthy ex vivo NK cell expansion protocols. Thus, the development of new strategies to obtain a rapid expansion of highly functional NK cells without the appearance of exhaustion is still much needed. This is particularly true in the case of mouse NK cells, a surrogate commonly used to evaluate NK cell biology and human NK cell-based immunotherapeutic alternatives. Here, we describe a feasible and rapid protocol to produce strongly activated mouse NK cells in vivo taking advantage of the hydrodynamic delivery of a plasmid that contains interleukin-15, a cytokine known to cause NK cell expansion and activation, fused with the binding domain of the IL-15Rα ("sushi" domain) and apolipoprotein A-I.

A magnetic SERS immunosensor for highly sensitive and selective detection of human carboxylesterase 1 in human serum samples

Hepatocellular carcinoma (HCC) is a common and lethal cancer. New serum markers for detecting HCC are urgently needed. Human carboxylesterase 1 (hCE1) is an important member of the serine hydrolase superfamily and is closely related to the occurrence of HCC. It can be used as a good serum marker for early diagnosis of HCC. Here, we developed a surface enhanced Raman scattering (SERS)- based magnetic immunosensor that specifically recognizes and detects trace amounts of hCE1 in human serum via a sandwich structure consisting of a SERS tags, magnetic supporting substrates, and target antigen (hCE1). The SERS tags are 4-mercaptobenzoic acid (4-MBA)-labeled AgNPs, and the SERS supporting substrates are composed of a raspberry-like morphology of Fe₃O₄@SiO₂@AgNPs magnetic nanocomposites surface-functionalized with a hCE1 antibody. The prepared SERS magnetic immunosensor exhibits excellent selectivity and extremely high sensitivity for hCE1 detection. The SERS signal and logarithm of hCE1 concentration presented a wide linear response range of 0.1 ng mL^-1 to 1.0 mg mL^-1, and the detection limit of hCE1 was 0.1 ng mL^-1. The results indicate that the immunosensor can be used for the rapid determination of hCE1 in human serum without a complicated sample pre-treatment. Furthermore, the immunosensor has good reproducibility and stability, and has a promising prospect for the quantitative detection of other tumor markers in early clinical diagnosis.

Characterization and Potential Applications of Dog Natural Killer Cells in Cancer Immunotherapy

Natural killer (NK) cells of the innate immune system are a key focus of research within the field of immuno-oncology based on their ability to recognize and eliminate malignant cells without prior sensitization or priming. However, barriers have arisen in the effective translation of NK cells to the clinic, in part because of critical species differences between mice and humans. Companion animals, especially dogs, are valuable species for overcoming many of these barriers, as dogs develop spontaneous tumors in the setting of an intact immune system, and the genetic and epigenetic factors that underlie oncogenesis appear to be similar between dogs and humans. Here, we summarize the current state of knowledge for dog NK cells, including cell surface marker phenotype, key NK genes and genetic regulation, similarities and differences of dog NK cells to other mammals, especially human and mouse, expression of canonical inhibitory and activating receptors, ex vivo expansion techniques, and current and future clinical applications. While dog NK cells are not as well described as those in humans and mice, the knowledge of the field is increasing and clinical applications in dogs can potentially advance the field of human NK biology and therapy. Better characterization is needed to truly understand the similarities and differences of dog NK cells with mouse and human. This will allow for the canine model to speed clinical translation of NK immunotherapy studies and overcome key barriers in the optimization of NK cancer immunotherapy, including trafficking, longevity, and maximal in vivo support.

Skeletal muscle as potential central link between sarcopenia and immune senescence

As our population grows older, age-related pathologies are becoming more prevalent. Deterioration of skeletal muscle and the immune system manifests as sarcopenia and immune senescence respectively. The disease burden of these pathologies emphasizes the need for a better understanding of the underlying mechanisms. Skeletal muscle has emerged as a potent regulator of immune system function. As such, skeletal muscle might be the central integrator between sarcopenia and immune senescence in an aging biological system. Therapeutic approaches targeting skeletal muscle might be able to restore both muscle and immune system function. In this review, we therefore outline the current - however still fragmentary - knowledge about the potential communication pathways of muscle and immune system, how they are affected by aging of skeletal muscle and discuss possible treatment strategies. The review intends to be hypothesis-generating and should thereby stimulate further research in this important scientific field.

Engineering for Success: Approaches to Improve Chimeric Antigen Receptor T Cell Therapy for Solid Tumors

While impressive clinical responses have been observed using chimeric antigen receptor (CAR) T cells targeting CD19+ hematologic malignancies, limited clinical benefit has been observed using CAR T cells for a variety of solid tumors. Results of clinical studies have highlighted several obstacles which CAR T cells face in the context of solid tumors, including insufficient homing to tumor sites, lack of expansion and persistence, encountering a highly immunosuppressive tumor microenvironment, and heterogeneous antigen expression. In this review, we review clinical outcomes and discuss strategies to improve the antitumor activity of CAR T cells for solid tumors.

Natural killer cells and cancer therapy, what we know and where we are going

Natural killer (NK) cells are among the significant components of innate immune system and they have come to the first line of defense against tumor cells developing inside the body. CD56lo/CD16+ NK cells are highly cytotoxic and CD56hi NK cells can produce cytokines and perform a regulatory function. Specific features of NK cells have made them a unique choice for cancer immunotherapy. Simple interventions like cytokine-injection to boost the internal NK cells were the first trials to target these cells. Nowadays, many other types of intervention are under investigation, such as adoptive NK cell immunotherapy. In this paper, we will discuss the biology and function of NK cells in cancer immunosurveillance and therapeutic approaches against cancer via using NK cells.

NK Cell Plasticity in Cancer

Natural killer (NK) cells are critical immune components in controlling tumor growth and dissemination. Given their innate capacity to eliminate tumor cells without prior sensitization, NK-based therapies for cancer are actively pursued pre-clinically and clinically. However, recent data suggest that tumors could induce functional alterations in NK cells, polarizing them to tumor-promoting phenotypes. The potential functional plasticity of NK cells in the context of tumors could lead to undesirable outcomes of NK-cell based therapies. In this review, we will summarize to-date evidence of tumor-associated NK cell plasticity and provide our insights for future investigations and therapy development.

The Role of Natural Killer Cells as a Platform for Immunotherapy in Pediatric Cancers

PURPOSE OF REVIEW

We aim to review the most recent findings in the use of NK cells in childhood cancers.

RECENT FINDINGS

Natural killer cells are cytotoxic to tumor cells. In pediatric leukemias, adoptive transfer of NK cells can bridge children not in remission to transplant. Interleukins (IL2, IL15) can enhance NK cell function. NK cell-CAR therapy has advantages of shorter life span that lessens chronic toxicities, lower risk of graft versus host disease when using allogeneic cells, ability of NK cells to recognize tumor cells that have downregulated MHC to escape T cells, and possibly less likelihood of cytokine storm. Cytotoxicity to solid tumors (rhabdomyosarcoma, Ewing's sarcoma, neuroblastoma) is seen with graft versus tumor effect in transplant and in combination with antibodies. Challenges lie in the microenvironment which is suppressive for NK cells. NK cell immunotherapy in childhood cancers is promising and recent works aim to overcome challenges.

NKT Cells Coexpressing a GD2-Specific Chimeric Antigen Receptor and IL15 Show Enhanced In Vivo Persistence and Antitumor Activity against Neuroblastoma

PURPOSE

Vα24-invariant natural killer T cells (NKT) are attractive carriers for chimeric antigen receptors (CAR) due to their inherent antitumor properties and preferential localization to tumor sites. However, limited persistence of CAR-NKTs in tumor-bearing mice is associated with tumor recurrence. Here, we evaluated whether coexpression of the NKT homeostatic cytokine IL15 with a CAR enhances the in vivo persistence and therapeutic efficacy of CAR-NKTs.

EXPERIMENTAL DESIGN

Human primary NKTs were ex vivo expanded and transduced with CAR constructs containing an optimized GD2-specific single-chain variable fragment and either the CD28 or 4-1BB costimulatory endodomain, each with or without IL15 (GD2.CAR or GD2.CAR.15). Constructs that mediated robust CAR-NKT cell expansion were selected for further functional evaluation in vitro and in xenogeneic mouse models of neuroblastoma.

RESULTS

Coexpression of IL15 with either costimulatory domain increased CAR-NKT absolute numbers. However, constructs containing 4-1BB induced excessive activation-induced cell death and reduced numeric expansion of NKTs compared with respective CD28-based constructs. Further evaluation of CD28-based GD2.CAR and GD2.CAR.15 showed that coexpression of IL15 led to reduced expression levels of exhaustion markers in NKTs and increased multiround in vitro tumor cell killing. Following transfer into mice bearing neuroblastoma xenografts, GD2.CAR.15 NKTs demonstrated enhanced in vivo persistence, increased localization to tumor sites, and improved tumor control compared with GD2.CAR NKTs. Importantly, GD2.CAR.15 NKTs did not produce significant toxicity as determined by histopathologic analysis.

CONCLUSIONS

Our results informed selection of the CD28-based GD2.CAR.15 construct for clinical testing and led to initiation of a first-in-human CAR-NKT cell clinical trial (NCT03294954).

Natural Killer Cell-Mediated Cellular Therapy of Hematological Malignancies

Our understanding on the mechanisms of graft versus tumor/leukemia (GvT/GvL) and graft versus host (GvH) effects has tremendously evolved within the past decades. During the search for a mechanism that augments GvT/GvL without increasing GvH effects, natural killer (NK) cells have clearly attracted attention. Current approaches of NK cell immunotherapy for hematological malignancies involve using methods for in vivo potentiation of NK cell proliferation and activity; adoptive transfer of NK cells from autologous and allogeneic sources [cord blood mononuclear cells, peripheral blood mononuclear cells, CD34⁺ stem cells] and NK cell lines; and genetic modification of NK cells. Several cytokines, including interleukin-2 and interleukin-15 take part in the development of NK cells and have been shown to boost NK cell effects both in vivo and ex vivo. Monoclonal antibodies directed towards certain targets, including stimulating CD16, blockade of NK cell receptors, and redirection of cytotoxicity to tumor cells via bi- or tri-specific engagers may promote NK cell function. Despite the relative disappointment with autologous NK cell infusions, the future holds promise in adoptive transfer of allogeneic NK cells and the development of novel cellular therapeutic strategies, such as chimeric antigen receptor-modified NK cell immunotherapy. In this review, we summarize the current status of NK cell-related mechanisms in the therapy of hematologic malignancies, and discuss the future perspectives on adoptive NK cell transfer and other novel cellular immunotherapeutic strategies.

Immunotherapy of Melanoma: Facts and Hopes

Melanoma is among the most sensitive of malignancies to immune modulation. Although multiple trials conducted over decades with vaccines, cytokines, and cell therapies demonstrated meaningful responses in a small subset of patients with metastatic disease, a true increase in overall survival (OS) within a randomized phase III trial was not observed until the development of anti-CTLA-4 (ipilimumab). Further improvements in OS for metastatic disease were observed with the anti-PD-1-based therapies (nivolumab, pembrolizumab) as single agents or combined with ipilimumab. A lower bound for expected 5-year survival for metastatic melanoma is currently approximately 35% and could be as high as 50% for the nivolumab/ipilimumab combination among patients who would meet criteria for clinical trials. Moreover, a substantial fraction of long-term survivors will likely remain progression-free without continued treatment. The hope and major challenge for the future is to understand the immunobiology of tumors with primary or acquired resistance to anti-PD-1 or anti-PD-1/anti-CTLA-4 and to develop effective immune therapies tailored to individual patient subsets not achieving long-term clinical benefit. Additional goals include optimal integration of immune therapy with nonimmune therapies, the development and validation of predictive biomarkers in the metastatic setting, improved prognostic and predictive biomarkers for the adjuvant setting, understanding mechanisms of and decreasing toxicity, and optimizing the duration of therapy.

Interleukin-15 Enhances Anti-GD2 Antibody-Mediated Cytotoxicity in an Orthotopic PDX Model of Neuroblastoma

PURPOSE

Immunotherapy with IL2, GM-CSF, and an anti-disialoganglioside (GD2) antibody significantly increases event-free survival in children with high-risk neuroblastoma. However, therapy failure in one third of these patients and IL2-related toxicities pose a major challenge. We compared the immunoadjuvant effects of IL15 with those of IL2 for enhancing antibody-dependent cell-mediated cytotoxicity (ADCC) in neuroblastoma.

EXPERIMENTAL DESIGN

We tested ADCC against neuroblastoma patient-derived xenografts (PDX) in vitro and in vivo and examined the functional and migratory properties of NK cells activated with IL2 and IL15.

RESULTS

In cell culture, IL15-activated NK cells induced higher ADCC against two GD⁺ neuroblastoma PDXs than did IL2-activated NK cells (P < 0.001). This effect was dose-dependent (P < 0.001) and was maintained across several effector-to-tumor ratios. As compared with IL2, IL15 also improved chemotaxis of NK cells, leading to higher numbers of tumorsphere-infiltrating NK cells in vitro (P = 0.002). In an orthotopic PDX model, animals receiving chemoimmunotherapy with an anti-GD2 antibody, GM-CSF, and a soluble IL15/IL15Rα complex had greater tumor regression than did those receiving chemotherapy alone (P = 0.012) or combined with anti-GD2 antibody and GM-CSF with (P = 0.016) or without IL2 (P = 0.035). This was most likely due to lower numbers of immature tumor-infiltrating NK cells (DX5⁺CD27⁺) after IL15/IL15Rα administration (P = 0.029) and transcriptional upregulation of Gzmd.

CONCLUSIONS

The substitution of IL15 for IL2 leads to significant tumor regression in vitro and in vivo and supports clinical testing of IL15 for immunotherapy in pediatric neuroblastoma.

An IL-15-based superagonist ALT-803 enhances the NK cell response to cetuximab-treated squamous cell carcinoma of the head and neck

Squamous cell carcinoma of the head and neck (SCCHN) is the sixth most common cancer worldwide and epidermal growth factor receptor (EGFR) is overexpressed in greater than 90% of patient tumors. Cetuximab is a monoclonal antibody that binds to EGFR and can activate immune cells, such as natural killer (NK) cells, that express receptors for the Fc (constant region) of immunoglobulin G. IL-15 (interleukin-15) is a critical factor for the development, proliferation and activation of effector NK cells. A novel IL-15 compound known as ALT-803 that consists of genetically modified IL-15 plus the IL-15 receptor alpha protein (IL15Rα) fused to the Fc portion of IgG1 has recently been developed. We hypothesized that treatment with ALT-803 would increase NK cell-mediated cytotoxicity of cetuximab-coated head and neck squamous cells. CD56+ NK cells from normal healthy donors were treated overnight with ALT-803 and tested for their ability to lyse cetuximab-coated tumor cells. Cytotoxicity was greater following NK cell ALT-803 activation, as compared to controls. ALT-803-treated NK cells secreted significantly higher levels of IFN-γ than control conditions. Additionally, NK cells showed increased levels of phospho-ERK and phospho-STAT5 when co-cultured with cetuximab-coated tumors and ALT-803. Administration of both cetuximab and ALT-803 to mice harboring Cal27 SCCHN tumors resulted in significantly decreased tumor volume when compared to controls and compared to single-agent treatment alone. Overall, the present data suggest that cetuximab treatment in combination with ALT-803 in patients with EGFR-positive SCCHN may result in significant NK cell activation and have important anti-tumor activity.

The Mechanism of Anti-PD-L1 Antibody Efficacy against PD-L1-Negative Tumors Identifies NK Cells Expressing PD-L1 as a Cytolytic Effector

Blockade of PD-L1 expression on tumor cells via anti-PD-L1 monoclonal antibody (mAb) has shown great promise for successful cancer treatment by overcoming T-cell exhaustion; however, the function of PD-L1 on natural killer (NK) cells and the effects of anti-PD-L1 mAb on PD-L1⁺ NK cells remain unknown. Moreover, patients with PD-L1 ^- tumors can respond favorably to anti-PD-L1 mAb therapy for unclear reasons. Here, we show that some tumors can induce PD-L1 on NK cells via AKT signaling, resulting in enhanced NK-cell function and preventing cell exhaustion. Anti-PD-L1 mAb directly acts on PD-L1⁺ NK cells against PD-L1 ^- tumors via a p38 pathway. Combination therapy with anti-PD-L1 mAb and NK cell-activating cytokines significantly improves the therapeutic efficacy of human NK cells against PD-L1 ^- human leukemia when compared with monotherapy. Our discovery of a PD-1-independent mechanism of antitumor efficacy via the activation of PD-L1⁺ NK cells with anti-PD-L1 mAb offers new insights into NK-cell activation and provides a potential explanation as to why some patients lacking PD-L1 expression on tumor cells still respond to anti-PD-L1 mAb therapy. SIGNIFICANCE: Targeting PD-L1 expressed on PD-L1⁺ tumors with anti-PD-L1 mAb successfully overcomes T-cell exhaustion to control cancer, yet patients with PD-L1 ^- tumors can respond to anti-PD-L1 mAb. Here, we show that anti-PD-L1 mAb activates PD-L1⁺ NK cells to control growth of PD-L1 ^- tumors in vivo, and does so independent of PD-1.This article is highlighted in the In This Issue feature, p. 1325.

Strategies to Augment Natural Killer (NK) Cell Activity against Solid Tumors

The immune system plays a crucial role to prevent local growth and dissemination of cancer. Therapies based on activating the immune system can result in beneficial responses in patients with metastatic disease. Treatment with antibodies targeting the immunological checkpoint axis PD-1 / PD-L1 can result in the induction of anti-tumor T cell activation leading to meaningful long-lasting clinical responses. Still, many patients acquire resistance or develop dose-limiting toxicities to these therapies. Analysis of tumors from patients who progress on anti-PD-1 treatment reveal defective interferon-signaling and antigen presentation, resulting in immune escape from T cell-mediated attack. Natural killer (NK) cells are innate lymphocytes that can kill tumor cells without prior sensitization to antigens and can be activated to kill tumor cells that have an impaired antigen processing and presentation machinery. Thus, NK cells may serve as useful effectors against tumor cells that have become resistant to classical immune checkpoint therapy. Various approaches to activate NK cells are being increasingly explored in clinical trials against cancer. While clinical benefit has been demonstrated in patients with acute myeloid leukemia receiving haploidentical NK cells, responses in patients with solid tumors are so far less encouraging. Several hurdles need to be overcome to provide meaningful clinical responses in patients with solid tumors. Here we review the recent developments to augment NK cell responses against solid tumors with regards to cytokine therapy, adoptive infusion of NK cells, NK cell engagers, and NK cell immune checkpoints.

CD56 Homodimerization and Participation in Anti-Tumor Immune Effector Cell Functioning: A Role for Interleukin-15

A particularly interesting marker to identify anti-tumor immune cells is the neural cell adhesion molecule (NCAM), also known as cluster of differentiation (CD)56. Namely, hematopoietic expression of CD56 seems to be confined to powerful effector immune cells. Here, we sought to elucidate its role on various killer immune cells. First, we identified the high motility NCAM-120 molecule to be the main isoform expressed by immune cells. Next, through neutralization of surface CD56, we were able to (1) demonstrate the direct involvement of CD56 in tumor cell lysis exerted by CD56-expressing killer cells, such as natural killer cells, gamma delta (γδ) T cells, and interleukin (IL)-15-cultured dendritic cells (DCs), and (2) reveal a putative crosstalk mechanism between IL-15 DCs and CD8 T cells, suggesting CD56 as a co-stimulatory molecule in their cell-to-cell contact. Moreover, by means of a proximity ligation assay, we visualized the CD56 homophilic interaction among cancer cells and between immune cells and cancer cells. Finally, by blocking the mitogen-activated protein kinase (MAPK) pathway and the phosphoinositide 3-kinase (PI3K)-Akt pathway, we showed that IL-15 stimulation directly led to CD56 upregulation. In conclusion, these results underscore the previously neglected importance of CD56 expression on immune cells, benefiting current and future immune therapeutic options.

Γδ T Cell-Based Immunotherapy in Melanoma: State of the Art

Metastatic melanoma is still associated with a poor prognosis, and there is increasing interest in immunotherapy alone or in combination with other adjuvant therapies. Γδ T lymphocytes play a pivot role in the immune response against cancer, but while γδ-based immunotherapy is already a clinical reality for several solid tumors, data on melanoma are still limited and fragmented. This systematic review presents preclinical and clinical evidence for a role of γδ T lymphocytes in immunotherapeutic strategies for advanced melanoma and discusses research state of the art and future perspectives. Current strategies focus on in vivo stimulation, and ex vivo adoptive therapy and vaccination; results are promising, but further studies are needed to better investigate the interactions in tumoral microenvironment and to improve clinical efficacy of immunotherapeutic protocols.

Targeting Tumors with IL-10 Prevents Dendritic Cell-Mediated CD8+ T Cell Apoptosis

Increasing evidence demonstrates that interleukin-10 (IL-10), known as an immunosuppressive cytokine, induces antitumor effects depending on CD8⁺ T cells. However, it remains elusive how immunosuppressive effects of IL-10 contribute to CD8⁺ T cell-mediated antitumor immunity. We generated Cetuximab-based IL-10 fusion protein (CmAb-(IL10)₂) to prolong its half-life and allow tumor-targeted delivery of IL-10. Our results demonstrated potent antitumor effects of CmAb-(IL10)₂ with reduced toxicity. Moreover, we revealed a mechanism of CmAb-(IL10)₂ preventing dendritic cell (DC)-mediated CD8⁺ tumor-infiltrating lymphocyte apoptosis through regulating IFN-γ production. When combined with immune checkpoint blockade, CmAb-(IL10)₂ significantly improves antitumor effects in mice with advanced tumors. Our findings reveal a DC-regulating role of IL-10 to potentiate CD8⁺ T cell-mediated antitumor immunity and provide a potential strategy to improve cancer immunotherapy.

Cancer Immunotherapy Based on Natural Killer Cells: Current Progress and New Opportunities

Cancer immunotherapy has been firmly established as a new milestone for cancer therapy, with the development of multiple immune cells as therapeutic tools. Natural killer (NK) cells are innate immune cells endowed with potent cytolytic activity against tumors, and meanwhile act as regulatory cells for the immune system. The efficacy of NK cell-mediated immunotherapy can be enhanced by immune stimulants such as cytokines and antibodies, and adoptive transfer of activated NK cells expanded ex vivo. In addition, NK cells can arm themselves with chimeric antigen receptors (CARs), which may greatly enhance their anti-tumor activity. Most recently, extracellular vesicles (EVs) derived from NK cells show promising anti-tumor effects in preclinical studies. Herein, we carefully review the current progress in these NK cell-based immunotherapeutic strategies (NK cells combined with stimulants, adoptive transfer of NK cells, CAR-NK cells, and NK EVs) for the treatment of cancers, and discussed the challenges and opportunities for opening a new horizon for cancer immunotherapy.

IL15 by Continuous Intravenous Infusion to Adult Patients with Solid Tumors in a Phase I Trial Induced Dramatic NK-Cell Subset Expansion

PURPOSE

The first-in-human clinical trial with human bolus intravenous infusion IL15 (rhIL15) was limited by treatment-associated toxicity. Here, we report toxicity, immunomodulation, and clinical activity of rhIL15 administered as a 10-day continuous intravenous infusion (CIV) to patients with cancers in a phase I trial.

PATIENTS AND METHODS

Patients received treatment for 10 days with CIV rhIL15 in doses of 0.125, 0.25, 0.5, 1, 2, or 4 μg/kg/day. Correlative laboratory tests included IL15 pharmacokinetic (PK) analyses, and assessment of changes in lymphocyte subset numbers.

RESULTS

Twenty-seven patients were treated with rhIL15; 2 μg/kg/day was identified as the MTD. There were eight serious adverse events including two bleeding events, papilledema, uveitis, pneumonitis, duodenal erosions, and two deaths (one due to likely drug-related gastrointestinal ischemia). Evidence of antitumor effects was observed in several patients, but stable disease was the best response noted. Patients in the 2 μg/kg/day group had a 5.8-fold increase in number of circulating CD8⁺ T cells, 38-fold increase in total NK cells, and 358-fold increase in CD56^bright NK cells. Serum IL15 concentrations were markedly lower during the last 3 days of infusion.

CONCLUSIONS

This phase I trial identified the MTD for CIV rhIL15 and defined a treatment regimen that produced significant expansions of CD8⁺ T and NK effector cells in circulation and tumor deposits. This regimen has identified several biological features, including dramatic increases in numbers of NK cells, supporting trials of IL15 with anticancer mAbs to increase antibody-dependent cell-mediated cytotoxicity and anticancer efficacy.