Comparison of the Superagonist Complex, ALT-803, to IL15 as Cancer Immunotherapeutics in Animal Models

Continuous treatment with IL-15 exhausts human NK cells via a metabolic defect

NK cell-based immunotherapies have been gaining traction in the clinic for treatment of cancer. IL-15 is currently being used in number of clinical trials to improve NK cell expansion and function. The objective of this study is to evaluate the effect of repetitive IL-15 exposure on NK cells. An in vitro model in which human NK cells are continuously (on on on) or intermittently (on off on) treated with IL-15 was used to explore this question. After treatment, cells were evaluated for proliferation, survival, cell cycle gene expression, function, and metabolic processes. Our data indicate that continuous treatment of NK cells with IL-15 resulted in decreased viability and a cell cycle arrest gene expression pattern. This was associated with diminished signaling, decreased function both in vitro and in vivo, and reduced tumor control. NK cells continuously treated with IL-15 also displayed a reduced mitochondrial respiration profile when compared with NK cells treated intermittently with IL-15. This profile was characterized by a decrease in the spare respiratory capacity that was dependent on fatty acid oxidation (FAO). Limiting the strength of IL-15 signaling via utilization of an mTOR inhibitor rescued NK cell functionality in the group continuously treated with IL-15. The findings presented here show that human NK cells continuously treated with IL-15 undergo a process consistent with exhaustion that is accompanied by a reduction in FAO. These findings should inform IL-15-dosing strategies in NK cell cancer immunotherapeutic settings.

Immunotherapy for Dogs: Running Behind Humans

A number of excellent reviews on the potential of canine cancer immunotherapy are available, but many extrapolate from observations in humans when in fact only very few immunotherapies have been developed for canines that have shown efficacy in well-designed studies. Pharmaceutical and biotech companies are aware that the market for more expensive immunotherapies in canines is limited resulting in limited funding for clinical trials. However, dogs and other pets deserve access to this new form of cancer therapy. The purpose of this brief review is to summarize the current status of available immunotherapies for dogs and their near-term prospects, provided we can effectively translate discoveries and progress in humans to canines.

An IL-15 superagonist/IL-15Rα fusion complex protects and rescues NK cell-cytotoxic function from TGF-β1-mediated immunosuppression

Natural killer (NK) cells are innate cytotoxic lymphocytes that play a fundamental role in the immunosurveillance of cancers. NK cells of cancer patients exhibit impaired function mediated by immunosuppressive factors released from the tumor microenvironment (TME), such as transforming growth factor (TGF)-β1. An interleukin (IL)-15 superagonist/IL-15 receptor α fusion complex (IL-15SA/IL-15RA; ALT-803) activates the IL-15 receptor on CD8 T cells and NK cells, and has shown significant anti-tumor activity in several in vivo studies. This in vitro study investigated the efficacy of IL-15SA/IL-15RA on TGF-β1-induced suppression of NK cell-cytotoxic function. IL-15SA/IL-15RA inhibited TGF-β1 from decreasing NK cell lysis of four of four tumor cell lines (H460, LNCap, MCF7, MDA-MB-231). IL-15SA/IL-15RA rescued healthy donor and cancer patient NK cell-cytotoxicity, which had previously been suppressed by culture with TGF-β1. TGF-β1 downregulated expression of NK cell-activating markers and cytotoxic granules, such as CD226, NKG2D, NKp30, granzyme B, and perforin. Smad2/3 signaling was responsible for this TGF-β1-induced downregulation of NK cell-activating markers and cytotoxic granules. IL-15SA/IL-15RA blocked Smad2/3-induced transcription, resulting in the rescue of NK cell-cytotoxic function from TGF-β1-induced suppression. These findings suggest that in addition to increasing NK cell function via promoting the IL-15 signaling pathway, IL-15SA/IL-15RA can function as an inhibitor of TGF-β1 signaling, providing a potential remedy for NK cell dysfunction in the immunosuppressive tumor microenvironment.

IL-2 and Beyond in Cancer Immunotherapy

The development of the T- and natural killer (NK) cell growth factor IL-2 has been a sentinel force ushering in the era of immunotherapy in cancer. With the advent of clinical grade recombinant IL-2 in the mid-1980s, oncologists could for the first time directly manipulate lymphocyte populations with systemic therapy. By itself, recombinant IL-2 can induce clinical responses in up to 15% of patients with metastatic cancer or renal cell carcinoma. When administered with adoptively transferred tumor-reactive lymphocytes, IL-2 promotes T cell engraftment and response rates of up to 50% in metastatic melanoma patients. Importantly, these IL-2-driven responses can yield complete and durable responses in a subset of patients. However, the use of IL-2 is limited by toxicity and concern of the expansion of T regulatory cells. To overcome these limitations and improve response rates, other T cell growth factors, including IL-15 and modified forms of IL-2, are in clinical development. Administering T cell growth factors in combination with other agents, such as immune checkpoint pathway inhibitors, may also improve efficacy. In this study, we review the development of T- and NK cell growth factors and highlight current combinatorial approaches based on these reagents.

Treatment with native heterodimeric IL-15 increases cytotoxic lymphocytes and reduces SHIV RNA in lymph nodes

B cell follicles in secondary lymphoid tissues represent an immune privileged sanctuary for AIDS viruses, in part because cytotoxic CD8+ T cells are mostly excluded from entering the follicles that harbor infected T follicular helper (TFH) cells. We studied the effects of native heterodimeric IL-15 (hetIL-15) treatment on uninfected rhesus macaques and on macaques that had spontaneously controlled SHIV infection to low levels of chronic viremia. hetIL-15 increased effector CD8+ T lymphocytes with high granzyme B content in blood, mucosal sites and lymph nodes, including virus-specific MHC-peptide tetramer+ CD8+ cells in LN. Following hetIL-15 treatment, multiplexed quantitative image analysis (histo-cytometry) of LN revealed increased numbers of granzyme B+ T cells in B cell follicles and SHIV RNA was decreased in plasma and in LN. Based on these properties, hetIL-15 shows promise as a potential component in combination immunotherapy regimens to target AIDS virus sanctuaries and reduce long-term viral reservoirs in HIV-1 infected individuals.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02452268.

The human IL-15 superagonist ALT-803 directs SIV-specific CD8+ T cells into B-cell follicles

Sequestering of latent HIV in follicular helper T cells within B-cell follicles that largely exclude cytotoxic T cells is a major barrier to cellular immune-based approaches to eradicate HIV. Here, we show that the clinical-grade human interleukin-15 (IL-15) superagonist ALT-803 activates and redirects simian immunodeficiency virus (SIV)-specific CD8+ T cells from the peripheral blood into B-cell follicles. In agreement with the increased trafficking of SIV-specific cytotoxic T cells to sites of cryptic viral replication, lymph nodes of elite controlling macaques contained fewer cells expressing SIV RNA or harboring SIV DNA post-ALT-803 treatment. These data establish ALT-803 as an immunotherapeutic for HIV and other chronic viral pathogens that evade host immunity by persisting in B-cell follicles.

ALT-803 Transiently Reduces Simian Immunodeficiency Virus Replication in the Absence of Antiretroviral Treatment

Developing biological interventions to control human immunodeficiency virus (HIV) replication in the absence of antiretroviral therapy (ART) could contribute to the development of a functional cure. As a potential alternative to ART, the interleukin-15 (IL-15) superagonist ALT-803 has been shown to boost the number and function of HIV-specific CD8⁺ T and NK cell populations in vitro Four simian immunodeficiency virus (SIV)-positive rhesus macaques, three of whom possessed major histocompatibility complex alleles associated with control of SIV and all of whom had received SIV vaccine vectors that had the potential to elicit CD8⁺ T cell responses, were given ALT-803 in three treatment cycles. The first and second cycles of treatment were separated by 2 weeks, while the third cycle was administered after a 29-week break. ALT-803 transiently elevated the total CD8⁺ effector and central memory T cell and NK cell populations in peripheral blood, while viral loads transiently decreased by ∼2 logs in all animals. Virus suppression was not sustained as T cells became less responsive to ALT-803 and waned in numbers. No effect on viral loads was observed in the second cycle of ALT-803, concurrent with downregulation of the IL-2/15 common γC and β chain receptors on both CD8⁺ T cells and NK cells. Furthermore, populations of immunosuppressive T cells increased during the second cycle of ALT-803 treatment. During the third treatment cycle, responsiveness to ALT-803 was restored. CD8⁺ T cells and NK cells increased again 3- to 5-fold, and viral loads transiently decreased again by 1 to 2 logs.IMPORTANCE Overall, our data show that ALT-803 has the potential to be used as an immunomodulatory agent to elicit effective immune control of HIV/SIV replication. We identify mechanisms to explain why virus control is transient, so that this model can be used to define a clinically appropriate treatment regimen.

Newcastle disease virus co-expressing interleukin 7 and interleukin 15 modified tumor cells as a vaccine for cancer immunotherapy

Interleukin 15 (IL15) and IL7 are two cytokines essential for T cell development and homeostasis. In order to improve the antitumor activity by Newcastle disease virus (NDV)-modified tumor vaccine, we generated a recombinant NDV co-expressing IL15 and IL7 (LX/IL(15+7)) through incorporation of a 2A self-processing peptide into IL15 and IL7 using reverse genetics. B16 cells infected with LX/IL(15+7) expressed both IL15 and IL7 stably. The cytotoxicity assay showed that murine melanoma cells modified with LX/IL(15+7) could significantly enhance the antitumor immune response in vitro. Then, the antitumor effects of tumor vaccine modified with recombinant virus were tested in the murine tumor models. We observed strong antitumor responses induced by LX/IL(15+7)-modified tumor cells both in prophylaxis and therapeutic models. Although the tumor-infiltrating CD4⁺ T cells and CD8⁺ T cells were both increased, the antitumor activity of the tumor vaccine modified with LX/IL(15+7) was dependent on CD8⁺ T cells. Taken together, our data strongly indicated that tumor vaccine modified with NDV strain LX/IL(15+7) is a promising agent for cancer immunotherapy.

Preclinical Characterization of a Novel Monoclonal Antibody NEO-201 for the Treatment of Human Carcinomas

NEO-201 is a novel humanized IgG1 monoclonal antibody that was derived from an immunogenic preparation of tumor-associated antigens from pooled allogeneic colon tumor tissue extracts. It was found to react against a variety of cultured human carcinoma cell lines and was highly reactive against the majority of tumor tissues from many different carcinomas, including colon, pancreatic, stomach, lung, and breast cancers. NEO-201 also exhibited tumor specificity, as the majority of normal tissues were not recognized by this antibody. Functional assays revealed that treatment with NEO-201 is capable of mediating both antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against tumor cells. Furthermore, the growth of human pancreatic xenograft tumors in vivo was largely attenuated by treatment with NEO-201 both alone and in combination with human peripheral blood mononuclear cells as an effector cell source for ADCC. In vivo biodistribution studies in human tumor xenograft-bearing mice revealed that NEO-201 preferentially accumulates in the tumor but not organ tissue. Finally, a single-dose toxicity study in non-human primates demonstrated safety and tolerability of NEO-201, as a transient decrease in circulating neutrophils was the only related adverse effect observed. These findings indicate that NEO-201 warrants clinical testing as both a novel diagnostic and therapeutic agent for the treatment of a broad variety of carcinomas.

Enhanced protection of C57 BL/6 vs Balb/c mice to melanoma liver metastasis is mediated by NK cells

The B16F10 murine melanoma cell line displays a low expression of MHC class I molecules favoring immune evasion and metastases in immunocompetent C57 BL/6 wild-type mice. Here, we generated metastases to the liver, an organ that is skewed towards immune tolerance, by intrasplenic injection of B16F10 cells in syngeneic C57 BL/6 compared to allogeneic Balb/c mice. Surprisingly, Balb/c mice, which usually display a pronounced M2 macrophage and Th2 T cell polarization, were ∼3 times more susceptible to metastasis than C57 BL/6 mice, despite a much higher M1 and Th1 T cell immune response. The anti-metastatic advantage of C57 BL/6 mice could be attributed to a more potent NK-cell mediated cytotoxicity against B16F10 cells. Our findings highlight the role of NK cells in innate anti-tumor immunity in the context of the liver – particularly against highly aggressive MHC I-deficient cancer cells. Moreover, the B16F10 model of melanoma liver metastasis is suited for developing novel therapies targeting innate NK cell related immunity in liver metastases and liver cancer.

IL-15 superagonist/IL-15RαSushi-Fc fusion complex (IL-15SA/IL-15RαSu-Fc; ALT-803) markedly enhances specific subpopulations of NK and memory CD8+ T cells, and mediates potent anti-tumor activity against murine breast and colon carcinomas

Interleukin (IL)-15-N72D superagonist-complexed with IL-15RαSushi-Fc fusion protein (IL-15SA/IL-15RαSu-Fc; ALT-803) has been reported to exhibit significant anti-tumor activity in murine myeloma, rat bladder cancer, and murine glioblastoma models. In this study, we examined the immunomodulatory and anti-tumor effects of IL-15SA/IL-15RαSu-Fc in tumor-free and highly metastatic tumor-bearing mice. Here, IL-15SA/IL-15RαSu-Fc significantly expanded natural killer (NK) and CD8⁺ T cells. In examining NK cell subsets, the greatest significant increase was in highly cytotoxic and migrating (CD11b⁺, CD27^hi; high effector) NK cells, leading to enhanced function on a per-cell basis. CD8⁺ T cell subset analysis determined that IL-15SA/IL-15RαSu-Fc significantly increased IL-15 responding memory (CD122⁺, CD44⁺) CD8⁺ T cells, in particular those having the innate (NKG2D⁺, PD1⁻) phenotype. In 4T1 breast tumor–bearing mice, IL-15SA/IL-15RαSu-Fc induced significant anti-tumor activity against spontaneous pulmonary metastases, depending on CD8⁺ T and NK cells, and resulting in prolonged survival. Similar anti-tumor activity was seen in the experimental pulmonary metastasis model of CT26 colon carcinoma cells, particularly when IL-15SA/IL-15RαSu-Fc was combined with a cocktail of checkpoint inhibitors, anti-CTLA-4 and anti-PD-L1. Altogether, these studies showed for the first time that IL-15SA/IL-15RαSu-Fc (1) promoted the development of high effector NK cells and CD8⁺ T cell responders of the innate phenotype, (2) enhanced function of NK cells, and (3) played a vital role in reducing tumor metastasis and ultimately survival, especially in combination with checkpoint inhibitors.

Decitabine enhances targeting of AML cells by CD34+ progenitor-derived NK cells in NOD/SCID/IL2Rgnull mice

Combining natural killer (NK) cell adoptive transfer with hypomethylating agents (HMAs) is an attractive therapeutic approach for patients with acute myeloid leukemia (AML). However, data regarding the impact of HMAs on NK cell functionality are mostly derived from in vitro studies with high nonclinical relevant drug concentrations. In the present study, we report a comparative study of azacitidine (AZA) and decitabine (DAC) in combination with allogeneic NK cells generated from CD34⁺ hematopoietic stem and progenitor cells (HSPC-NK cells) in in vitro and in vivo AML models. In vitro, low-dose HMAs did not impair viability of HSPC-NK cells. Furthermore, low-dose DAC preserved HSPC-NK killing, proliferation, and interferon gamma production capacity, whereas AZA diminished their proliferation and reactivity. Importantly, we showed HMAs and HSPC-NK cells could potently work together to target AML cell lines and patient AML blasts. In vivo, both agents exerted a significant delay in AML progression in NOD/SCID/IL2Rg^null mice, but the persistence of adoptively transferred HSPC-NK cells was not affected. Infused NK cells showed sustained expression of most activating receptors, upregulated NKp44 expression, and remarkable killer cell immunoglobulin-like receptor acquisition. Most importantly, only DAC potentiated HSPC-NK cell anti-leukemic activity in vivo. Besides upregulation of NKG2D- and DNAM-1-activating ligands on AML cells, DAC enhanced messenger RNA expression of inflammatory cytokines, perforin, and TRAIL by HSPC-NK cells. In addition, treatment resulted in increased numbers of HSPC-NK cells in the bone marrow compartment, suggesting that DAC could positively modulate NK cell activity, trafficking, and tumor targeting. These data provide a rationale to explore combination therapy of adoptive HSPC-NK cells and DAC in patients with AML.

Allogeneic stem cell transplantation in fully MHC-matched Mauritian cynomolgus macaques recapitulates diverse human clinical outcomes

Allogeneic hematopoietic stem cell transplantation (HSCT) is a critically important therapy for hematological malignancies, inborn errors of metabolism, and immunodeficiency disorders, yet complications such as graft-vs.-host disease (GvHD) limit survival. Development of anti-GvHD therapies that do not adversely affect susceptibility to infection or graft-vs.-tumor immunity are hampered by the lack of a physiologically relevant, preclinical model of allogeneic HSCT. Here we show a spectrum of diverse clinical HSCT outcomes including primary and secondary graft failure, lethal GvHD, and stable, disease-free full donor engraftment using reduced intensity conditioning and mobilized peripheral blood HSCT in unrelated, fully MHC-matched Mauritian-origin cynomolgus macaques. Anti-GvHD prophylaxis of tacrolimus, post-transplant cyclophosphamide, and CD28 blockade induces multi-lineage, full donor chimerism and recipient-specific tolerance while maintaining pathogen-specific immunity. These results establish a new preclinical allogeneic HSCT model for evaluation of GvHD prophylaxis and next-generation HSCT-mediated therapies for solid organ tolerance, cure of non-malignant hematological disease, and HIV reservoir clearance.

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

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

Analyses of functions of an anti-PD-L1/TGFβR2 bispecific fusion protein (M7824)

M7824 (MSB0011359C) is a novel first-in-class bifunctional fusion protein consisting of a fully human IgG1 anti-PD-L1 monoclonal antibody (with structural similarities to avelumab) linked to the extracellular domain of two TGFβ receptor 2 (TGFβR2) molecules serving as a TGFβ Trap. Avelumab has demonstrated clinical activity in a range of human cancers and has been approved by the Food and Drug Administration for the therapy of Merkel cell and bladder carcinomas. Preclinical studies have shown this anti-PD-L1 is capable of mediating antibody-dependent cell-mediated cytotoxicity (ADCC). In the studies reported here, it is shown that M7824 is also capable of mediating ADCC of a wide range of human carcinoma cells in vitro, employing natural killer (NK) cells as effectors, albeit not as potent as anti-PD-L1 employing some tumor cells as targets. The addition of the IL-15 superagonist fusion protein complex ALT-803 enhanced the ADCC capacity of both anti-PD-L1 and M7824, and to levels that both agents now demonstrated similar levels of ADCC of tumor cells. TGFβ is a known immunosuppressive entity. Studies reported here show TGFβ1 induced reduction of several NK activation markers as well as reduction of endogenous NK lytic activity and NK-mediated ADCC of tumor cells. These phenomena could be reduced or mitigated, however, by M7824, but not by anti-PD-L1. M7824, but not anti-PD-L1, was also shown to reduce the immunosuppressive activity of regulatory T cells on human CD4+ T-cell proliferation. These studies thus demonstrate the dual functionalities of M7824 and provide the rationale for its further clinical development.

Recombinant Antibodies to Arm Cytotoxic Lymphocytes in Cancer Immunotherapy

Immunotherapy has the potential to support and expand the body's own armamentarium of immune effector functions, which have been circumvented during malignant transformation and establishment of cancer and is presently considered to be the most promising treatment option for cancer patients. Recombinant antibody technologies have led to a multitude of novel antibody formats, which are in clinical development and hold great promise for future therapies. Among these formats, bispecific antibodies are extremely versatile due to their high efficacy to recruit and activate anti-tumoral immune effector cells, their excellent safety profile, and the opportunity for use in combination with cellular therapies. This review article summarizes the latest developments in cancer immunotherapy using immuno-engagers for recruiting T cells and NK cells to the tumor site. In addition to antibody formats, malignant cell targets, and immune cell targets, opportunities for combination therapies, including check point inhibitors, cytokines and adoptive transfer of immune cells, will be summarized and discussed.

The potential and promise of IL-15 in immuno-oncogenic therapies

This review provides an in-depth description of the preclinical and clinical studies demonstrating the effectiveness and limitations of IL-15 and IL-15 analogs given as an exogenous immuno-oncology agent. IL-15 is a cytokine that primarily stimulates the proliferation and cytotoxic functions of CD8T cells and NK cells leading to enhanced anti-tumor responses. While initially showing promise as a cancer therapeutic, the efficacy of IL-15 was limited by its short in vivo half-life. More recently, various approaches have been developed to improve the in vivo half-life and efficacy of IL-15, largely by generating IL-15/IL-15Rα conjugates. These new IL-15 based agents renew the prospect of IL-15 as a cancer immunotherapeutic agent. While having some efficacy in inducing tumor regression as a monotherapy, IL-15 agents also show great potential in being used in combination with other immuno-oncological therapies. Indeed, IL-15 used in combination therapy yields even better anti-tumor responses and prolongs survival than IL-15 treatment alone in numerous murine cancer models. The promising results from these preclinical studies have led to the implementation of several clinical trials to test the safety and efficacy of IL-15-based agents as a stand-alone treatment or in conjunction with other therapies to treat both advanced solid tumors and hematological malignancies.

CAR T Cells Administered in Combination with Lymphodepletion and PD-1 Inhibition to Patients with Neuroblastoma

Targeting disialoganglioside (GD2) on neuroblastoma (NB) with T cells expressing a first-generation chimeric antigen receptor (CAR) was safe, but the cells had poor expansion and long-term persistence. We developed a third-generation GD2-CAR (GD2-CAR3) and hypothesized that GD2-CAR3 T cells (CARTs) would be safe and effective. This phase 1 study enrolled relapsed or refractory NB patients in three cohorts. Cohort 1 received CART alone, cohort 2 received CARTs plus cyclophosphamide and fludarabine (Cy/Flu), and cohort 3 was treated with CARTs, Cy/Flu, and a programmed death-1 (PD-1) inhibitor. Eleven patients were treated with CARTs. The infusions were safe, and no dose-limiting toxicities occurred. CARTs were detectable in cohort 1, but the lymphodepletion induced by Cy/Flu increased circulating levels of the homeostatic cytokine interleukin (IL)-15 (p = 0.003) and increased CART expansion by up to 3 logs (p = 0.03). PD-1 inhibition did not further enhance expansion or persistence. Antitumor responses at 6 weeks were modest. We observed a striking expansion of CD45/CD33/CD11b/CD163⁺ myeloid cells (change from baseline, p = 0.0126) in all patients, which may have contributed to the modest early antitumor responses; the effect of these cells merits further study. Thus, CARTs are safe, and Cy/Flu can further increase their expansion.

Intravesical ALT-803 for BCG-unresponsive Bladder Cancer - A Case Report

The administration of intravesical chemotherapy or BCG often can prolong the progression-free interval after initial transurethral resection in select bladder cancer (BCa) patients. However, 60% of these patients will recur and up to 30% of patients with recurrent BCa will progress and succumb to their disease over a 15 year period, while another 50% will cystectomy in an attempt to control their disease. Thus better therapeutic strategies are needed for patients who have failed intravesical therapy. In this article, we report the treatment of a 91-year-old man with NMIBC with high-risk features that had failed multiple intravesical therapies.

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

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

Successful Transfer of Umbilical Cord Blood CD34+ Hematopoietic Stem and Progenitor-derived NK Cells in Older Acute Myeloid Leukemia Patients

Purpose: Older acute myeloid leukemia (AML) patients have a poor prognosis; therefore, novel therapies are needed. Allogeneic natural killer (NK) cells have been adoptively transferred with promising clinical results. Here, we report the first-in-human study exploiting a unique scalable NK-cell product generated ex vivo from CD34⁺ hematopoietic stem and progenitor cells (HSPC) from partially HLA-matched umbilical cord blood units.Experimental Design: Ten older AML patients in morphologic complete remission received an escalating HSPC-NK cell dose (between 3 and 30 × 10⁶/kg body weight) after lymphodepleting chemotherapy without cytokine boosting.Results: HSPC-NK cell products contained a median of 75% highly activated NK cells, with <1 × 10⁴ T cells/kg and <3 × 10⁵ B cells/kg body weight. HSPC-NK cells were well tolerated, and neither graft-versus-host disease nor toxicity was observed. Despite no cytokine boosting being given, transient HSPC-NK cell persistence was clearly found in peripheral blood up to 21% until day 8, which was accompanied by augmented IL15 plasma levels. Moreover, donor chimerism up to 3.5% was found in bone marrow. Interestingly, in vivo HSPC-NK cell maturation was observed, indicated by the rapid acquisition of CD16 and KIR expression, while expression of most activating receptors was sustained. Notably, 2 of 4 patients with minimal residual disease (MRD) in bone marrow before infusion became MRD negative (<0.1%), which lasted for 6 months.Conclusions: These findings indicate that HSPC-NK cell adoptive transfer is a promising, potential "off-the-shelf" translational immunotherapy approach in AML. Clin Cancer Res; 23(15); 4107-18. ©2017 AACR.

Tumor-infiltrating lymphocytes are dynamically desensitized to antigen but are maintained by homeostatic cytokine

T cells that enter tumors are largely tolerized, but how that process is choreographed and how the ensuing "dysfunctional" tumor-infiltrating lymphocytes (TILs) are maintained are poorly understood and are difficult to assess in spontaneous disease. We exploited an autochthonous model of breast cancer for high-resolution imaging of the early and later stages of tumor residence to understand the relationships between cellular behaviors and cellular phenotypes. "Dysfunctional" differentiation began within the first days of tumor residence with an initial phase in which T cells arrest, largely on tumor-associated macrophages. Within 10 days, cellular motility increased and resembled a random walk, suggesting a relative absence of TCR signaling. We then studied the concurrent and apparently contradictory phenomenon that many of these cells express molecular markers of activation and were visualized undergoing active cell division. We found that whereas proliferation did not require ongoing TCR/ZAP70 signaling, instead this is driven in part by intratumoral IL-15 cytokine. Thus, TILs undergo sequential reprogramming by the tumor microenvironment and are actively retained, even while being antigen insensitive. We conclude that this program effectively fills the niche with ineffective yet cytokine-dependent TILs, and we propose that these might compete with new clones, when they arise.

Tethered IL-15 augments antitumor activity and promotes a stem-cell memory subset in tumor-specific T cells

Adoptive immunotherapy retargeting T cells to CD19 via a chimeric antigen receptor (CAR) is an investigational treatment capable of inducing complete tumor regression of B-cell malignancies when there is sustained survival of infused cells. T-memory stem cells (T_SCM) retain superior potential for long-lived persistence, but challenges exist in manufacturing this T-cell subset because they are rare among circulating lymphocytes. We report a clinically relevant approach to generating CAR⁺ T cells with preserved T_SCM potential using the Sleeping Beauty platform. Because IL-15 is fundamental to T-cell memory, we incorporated its costimulatory properties by coexpressing CAR with a membrane-bound chimeric IL-15 (mbIL15). The mbIL15-CAR T cells signaled through signal transducer and activator of transcription 5 to yield improved T-cell persistence independent of CAR signaling, without apparent autonomous growth or transformation, and achieved potent rejection of CD19⁺ leukemia. Long-lived T cells were CD45RO^negCCR7⁺CD95⁺, phenotypically most similar to T_SCM, and possessed a memory-like transcriptional profile. Overall, these results demonstrate that CAR⁺ T cells can develop long-term persistence with a memory stem-cell phenotype sustained by signaling through mbIL15. This observation warrants evaluation in clinical trials.

IL-15 signaling in NK cell cancer immunotherapy

While cancer has been traditionally treated by chemotherapy, radiation, targeted therapies and surgery, a fifth pillar of cancer treatment, immunotherapy, has emerged over the past 10 years and revolutionized our war on cancer. The benchmark for drugs in this category has been set by the development of CD8 T cell checkpoint (CTLA-4 and PD-1/PD-L1) inhibitors. These therapies effectively expand and reactivate the pool of tumor-specific T cells leading to objective response rates of up to 50% in patients with certain cancers. However, the significant number of patients and cancer types that altogether fail or acquire resistance to these therapies highlights the need for novel immunotherapies that target alternate pathways and effector cells. Thus, there is renewed interest in harnessing the tumor-killing abilities of Natural Killer (NK) cells, though it has proven difficult to efficiently and specifically target these cells cancer patients. The commercial success of T cell checkpoint inhibitors has seen a swam of new biotech companies emerge with innovative or revised strategies that aim to harness the innate non-antigen dependent tumor lysis potential of NK cells. This review will focus on IL-15 biology in NK cells and proposes the development novel therapies aimed at this pathway in humans.

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

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

IL-15 receptor alpha as the magic wand to boost the success of IL-15 antitumor therapies: The upswing of IL-15 transpresentation

Interleukin (IL)-15 as a stand-alone therapy can activate the antitumor functions of immune effector cells resulting in significant tumor regression. Interestingly, combining IL-15 with the α-moiety of its receptor (IL-15Rα), also called IL-15 transpresentation, increases the in vivo half-life of IL-15 and enhances binding of IL-15 with cells expressing the IL-15Rβγ, such as NK cells and CD8⁺ T cells. These features enlarge the signal transmission of IL-15, resulting in improved proliferation and antitumor activities of both NK cells and CD8⁺ T cells, eventually leading to enhanced killing of tumor cells. In this review, we discuss the antitumor strategies in which this IL-15 transpresentation mechanism is implemented, that are currently under preclinical investigation. Furthermore, we give an overview of the studies in which the IL-15/IL-15Rα complexes are combined with other antitumor therapies. The promising results in these preclinical studies have incited several clinical trials to test the safety and efficacy of IL-15 transpresentation strategies to treat both hematological and advanced solid tumors.

A Novel Fusion of ALT-803 (Interleukin (IL)-15 Superagonist) with an Antibody Demonstrates Antigen-specific Antitumor Responses

IL-15 and its receptor α (IL-15Rα) are co-expressed on antigen-presenting cells, allowing transpresentation of IL-15 to immune cells bearing IL-2Rβγ_C and stimulation of effector immune responses. We reported previously that the high-affinity interactions between an IL-15 superagonist (IL-15N72D) and the extracellular IL-15Rα sushi domain (IL-15RαSu) could be exploited to create a functional scaffold for the design of multivalent disease-targeted complexes. The IL-15N72D·IL-15RαSuFc complex, also known as ALT-803, is a multimeric complex constructed by fusing IL-15N72D·IL-15RαSu to the Fc domain of IgG1. ALT-803 is an IL-15 superagonist complex that has been developed as a potent antitumor immunotherapeutic agent and is in clinical trials. Here we describe the creation of a novel fusion molecule, 2B8T2M, using the ALT-803 scaffold fused to four single chains of the tumor-targeting monoclonal antibody rituximab. This molecule displays trispecific binding activity through its recognition of the CD20 molecule on tumor cells, stimulation via IL-2Rβγ_C displayed on immune effector cells, and binding to Fcγ receptors on natural killer cells and macrophages. 2B8T2M activates natural killer cells to enhance antibody-dependent cellular cytotoxicity, mediates complement-dependent cytotoxicity, and induces apoptosis of B-lymphoma cells. Compared with rituximab, 2B8T2M exhibits significantly stronger antitumor activity in a xenograft SCID mouse model and depletes B cells in cynomolgus monkeys more efficiently. Thus, ALT-803 can be modified as a functional scaffold for creating multispecific, targeted IL-15-based immunotherapeutic agents and may serve as a novel platform to improve the antitumor activity and clinical efficacy of therapeutic antibodies.

Stimulation of Natural Killer Cell-Mediated Tumor Immunity by an IL15/TGFβ-Neutralizing Fusion Protein

The clinical efficacy of immune cytokines used for cancer therapy is hampered by elements of the immunosuppressive tumor microenvironment such as TGFβ. Here we demonstrate that FIST15, a recombinant chimeric protein composed of the T-cell-stimulatory cytokine IL15, the sushi domain of IL15Rα and a TGFβ ligand trap, can overcome immunosuppressive TGFβ to effectively stimulate the proliferation and activation of natural killer (NK) and CD8⁺ T cells with potent antitumor properties. FIST15-treated NK and CD8⁺ T cells produced more IFNγ and TNFα compared with treatment with IL15 and a commercially available TGFβ receptor-Fc fusion protein (sTβRII) in the presence of TGFβ. Murine B16 melanoma cells, which overproduce TGFβ, were lysed by FIST15-treated NK cells in vitro at doses approximately 10-fold lower than NK cells treated with IL15 and sTβRII. Melanoma cells transduced to express FIST15 failed to establish tumors in vivo in immunocompetent murine hosts and could only form tumors in beige mice lacking NK cells. Mice injected with the same cells were also protected from subsequent challenge by unmodified B16 melanoma cells. Finally, mice with pre-established B16 melanoma tumors responded to FIST15 treatment more strongly compared with tumors treated with control cytokines. Taken together, our results offer a preclinical proof of concept for the use of FIST15 as a new class of biological therapeutics that can coordinately neutralize the effects of immunosuppressive TGFβ in the tumor microenvironment while empowering tumor immunity. Cancer Res; 76(19); 5683-95. ©2016 AACR.

IL15 Agonists Overcome the Immunosuppressive Effects of MEK Inhibitors

Many signal transduction inhibitors are being developed for cancer therapy target pathways that are also important for the proper function of antitumor lymphocytes, possibly weakening their therapeutic effects. Here we show that most inhibitors targeting multiple signaling pathways have especially strong negative effects on T-cell activation at their active doses on cancer cells. In particular, we found that recently approved MEK inhibitors displayed potent suppressive effects on T cells in vitro However, these effects could be attenuated by certain cytokines that can be administered to cancer patients. Among them, clinically available IL15 superagonists, which can activate PI3K selectively in T lymphocytes, synergized with MEK inhibitors in vivo to elicit potent and durable antitumor responses, including by a vaccine-like effect that generated resistance to tumor rechallenge. Our work identifies a clinically actionable approach to overcome the T-cell-suppressive effects of MEK inhibitors and illustrates how to reconcile the deficiencies of signal transduction inhibitors, which impede desired immunologic effects in vivo Cancer Res; 76(9); 2561-72. ©2016 AACR.

Elevation and persistence of CD8 T-cells in HIV infection: the Achilles heel in the ART era

Introduction

HIV infection leads to a disturbed T-cell homeostasis, featured by a depletion of CD4 T-cells and a persistent elevation of CD8 T-cells over disease progression. Most effort of managing HIV infection has been focused on CD4 T-cell recovery, while changes in the CD8 compartment were relatively underappreciated in the past.

Methods

A comprehensive literature review of publications in English language was conducted using major electronic databases. Our search was focused on factors contributing to CD8 T-cell dynamics in HIV infection and following antiretroviral therapy (ART).

Discussion

Normalization of CD8 counts is seldom observed even with optimal CD4 recovery following long-term treatment. Initiation of ART in primary HIV infection leads to enhanced normalization of CD8 count compared with long-term ART initiated in chronic infection. Importantly, such CD8 elevation in treated HIV infection is associated with an increased risk of inflammatory non-AIDS-related clinical events independent of CD4 T-cell recovery. The mechanisms underlying CD8 persistence remain largely unknown, which may include bystander activation, exhaustion and immunosenescence of CD8 T-cells. The information provided herein will lead to a better understanding of factors associated with CD8 persistence and contribute to the development of strategies aiming at CD8 normalization.

Conclusions

Persistence of CD8 T-cell elevation in treated HIV-infected patients is associated with an increased risk of non-AIDS-related events. Now that advances in ART have led to decreased AIDS-related opportunistic diseases, more attention has been focused on reducing non-AIDS events and normalizing persistent CD8 T-cell elevation.