Immunotherapeutic approach to reduce senescent cells and alleviate senescence-associated secretory phenotype in mice

Accumulation of senescent cells (SNCs) with a senescence-associated secretory phenotype (SASP) has been implicated as a major source of chronic sterile inflammation leading to many age-related pathologies. Herein, we provide evidence that a bifunctional immunotherapeutic, HCW9218, with capabilities of neutralizing TGF-β and stimulating immune cells, can be safely administered systemically to reduce SNCs and alleviate SASP in mice. In the diabetic db/db mouse model, subcutaneous administration of HCW9218 reduced senescent islet β cells and SASP resulting in improved glucose tolerance, insulin resistance, and aging index. In naturally aged mice, subcutaneous administration of HCW9218 durably reduced the level of SNCs and SASP, leading to lower expression of pro-inflammatory genes in peripheral organs. HCW9218 treatment also reverted the pattern of key regulatory circadian gene expression in aged mice to levels observed in young mice and impacted genes associated with metabolism and fibrosis in the liver. Single-nucleus RNA Sequencing analysis further revealed that HCW9218 treatment differentially changed the transcriptomic landscape of hepatocyte subtypes involving metabolic, signaling, cell-cycle, and senescence-associated pathways in naturally aged mice. Long-term survival studies also showed that HCW9218 treatment improved physical performance without compromising the health span of naturally aged mice. Thus, HCW9218 represents a novel immunotherapeutic approach and a clinically promising new class of senotherapeutic agents targeting cellular senescence-associated diseases.

A novel interleukin-2-based fusion molecule, HCW9302, differentially promotes regulatory T cell expansion to treat atherosclerosis in mice

Atherosclerosis is a chronic inflammatory disease caused by deposition of oxidative low-density lipoprotein (LDL) in the arterial intima which triggers the innate immune response through myeloid cells such as macrophages. Regulatory T cells (Tregs) play an important role in controlling the progression or regression of atherosclerosis by resolving macrophage-mediated inflammatory functions. Interleukin-2 (IL-2) signaling is essential for homeostasis of Tregs. Since recombinant IL-2 has an unfavorable pharmacokinetic profile limiting its therapeutic use, we constructed a fusion protein, designated HCW9302, containing two IL-2 domains linked by an extracellular tissue factor domain. We found that HCW9302 exhibited a longer serum half-life with an approximately 1000-fold higher affinity for the IL-2Rα than IL-2. HCW9302 could be administered to mice at a dosing range that expanded and activated Tregs but not CD4⁺ effector T cells. In an ApoE^-/- mouse model, HCW9302 treatment curtailed the progression of atherosclerosis through Treg activation and expansion, M2 macrophage polarization and myeloid-derived suppressor cell induction. HCW9302 treatment also lessened inflammatory responses in the aorta. Thus, HCW9302 is a potential therapeutic agent to expand and activate Tregs for treatment of inflammatory and autoimmune diseases.

Robust human regulatory T cell expansion with fusion proteins HCW9302 and HCW9213 circumvents need for magnetic-bead or feeder cell approaches for adoptive cell therapy

Regulatory T cells (CD4+CD25+FoxP3+) (Tregs) are a subset of CD4 T cells that suppress the activities of other immune cells and have applications in the treatment of autoimmune and inflammatory diseases. Their use as an adoptive cell therapy has been limited by the practicality of expanding and purifying clinically sufficient numbers of cells. HCW9213 and HCW9302 are fusion proteins based on HCW Biologics’ TOBI™ technology platform, consisting of anti-CD3/anti-CD28 antibody domains and IL-2 domains, respectively. When used in combination, these fusion proteins were capable of expanding human Treg cells in vitro without the use of anti-CD3/CD28 magnetic beads and/or feeder cells, improving the overall yield, process efficiency and overcoming regulatory hurdles in manufacturing. Tregs generated with these molecules displayed similar phenotypes and suppressive cytokine production as Tregs expanded with recombinant human IL-2. Using a proprietary anti-CD39 antibody to isolate CD39+ Tregs, we have also been able to generate a Treg population with twice the suppressive activity against CD4+ T responder cells as traditional CD4+CD25+CD127lo Tregs. Thus, using its novel fusion proteins, HCW Biologics has been able to develop a superior Treg cell product ideal for the use in adoptive cell transfer. Additionally, this Treg platform can potentially be further optimized with addition of disease-targeted chimeric antigen receptors (CAR).

A feeder cell-free activation and expansion strategy to generate memory-like NK cells sufficient for off-the-shelf multi-dose adoptive cell therapy

Adoptive cell therapy (ACT) using NK cells is a promising armament in the fight against cancer. Cytokine induced memory like (CIML) NK cells have been shown in clinical studies to have potent antitumor activity with superior in vivo persistence. Currently, the expansion of NK cells for clinical development is mainly based on feeder cells, which imposes significant regulatory hurdles and increases the costs for manufacturing. We have developed fusion proteins, HCW9201 and HCW9206 comprising of IL-15/IL-18/IL-12 and IL15/IL-7/IL-21, respectively, capable of priming memory-like differentiation and expanding CIML NK cell products without using feeder cells. This “Kick and Expand” strategy allows greater than 100x expansion of CIML NK cells from donor PBMCs in as little as 14 days without the use of exogenous feeder cells. Continued expansion can yield sufficient CIML NK cells for cryopreservation and multiple ACT infusions. The NK cells generated have bona fide memory-like properties: enhanced antitumor activity across multiple cancer cell lines, higher metabolic capacity, stable epigenetic demethylation of the IFN-γ promoter and increased persistence in NSG mice, when compared to conventional NK cells. In conclusion, this “Kick and Expand” process supports generation of abundant CIML NK cells for multiple ACT infusions and provides simpler, more regulatory friendly, off-the-shelf platform for generating NK cell products, including those with chimeric antigen receptor (CAR) constructs.

Immunotherapeutic HCW9218 augments anti-tumor activity of chemotherapy via NK cell-mediated reduction of therapy-induced senescent cells

Therapy induced senescence (TIS) in tumors and TIS cancer cells secrete proinflammatory senescence-associated secretory phenotype (SASP) factors. SASP factors promote TIS cancer cells to re-enter the growth cycle with stemness characteristics, resulting in chemo-resistance and disease relapse. Herein, we show that the immunotherapeutic HCW9218, comprising transforming growth factor-β (TGF-β) receptor II and interleukin (IL)-15/IL-15 receptor α domains, enhances metabolic and cytotoxic activities of immune cells and reduces TIS tumor cells in vivo to improve the efficacy of docetaxel and gemcitabine plus nab-paclitaxel against B16F10 melanoma and SW1990 pancreatic tumors, respectively. Mechanistically, HCW9218 treatment reduces the immunosuppressive tumor microenvironment and enhances immune cell infiltration and cytotoxicity in the tumors to eliminate TIS cancer cells. Immuno-depletion analysis suggests that HCW9218-activated natural killer cells play a pivotal role in TIS cancer cell removal. HCW9218 treatment following docetaxel chemotherapy further enhances efficacy of tumor antigen-specific and anti-programmed death-ligand 1 (PD-L1) antibodies in B16F10 tumor-bearing mice. We also show that HCW9218 treatment decreases TIS cells and lowers SASP factors in off-target tissues caused by chemotherapy of tumor-bearing mice. Collectively, HCW9218 has the potential to significantly enhance anti-tumor efficacy of chemotherapy, therapeutic antibodies, and checkpoint blockade by eliminating TIS cancer cells while reducing TIS-mediated proinflammatory side effects in normal tissues.

A Fusion Protein Complex that Combines IL-12, IL-15, and IL-18 Signaling to Induce Memory-Like NK Cells for Cancer Immunotherapy

Natural killer (NK) cells are a promising cellular therapy for cancer, with challenges in the field including persistence, functional activity, and tumor recognition. Briefly, priming blood NK cells with recombinant human (rh)IL-12, rhIL-15, and rhIL-18 (12/15/18) results in memory-like NK cell differentiation and enhanced responses against cancer. However, the lack of available, scalable Good Manufacturing Process (GMP)-grade reagents required to advance this approach beyond early-phase clinical trials is limiting. To address this challenge, we developed a novel platform centered upon an inert tissue factor scaffold for production of heteromeric fusion protein complexes (HFPC). The first use of this platform combined IL-12, IL-15, and IL-18 receptor engagement (HCW9201), and the second adds CD16 engagement (HCW9207). This unique HFPC expression platform was scalable with equivalent protein quality characteristics in small- and GMP-scale production. HCW9201 and HCW9207 stimulated activation and proliferation signals in NK cells, but HCW9207 had decreased IL-18 receptor signaling. RNA sequencing and multidimensional mass cytometry revealed parallels between HCW9201 and 12/15/18. HCW9201 stimulation improved NK cell metabolic fitness and resulted in the DNA methylation remodeling characteristic of memory-like differentiation. HCW9201 and 12/15/18 primed similar increases in short-term and memory-like NK cell cytotoxicity and IFNγ production against leukemia targets, as well as equivalent control of leukemia in NSG mice. Thus, HFPCs represent a protein engineering approach that solves many problems associated with multisignal receptor engagement on immune cells, and HCW9201-primed NK cells can be advanced as an ideal approach for clinical GMP-grade memory-like NK cell production for cancer therapy.

Bifunctional TGF-β trap/IL-15 Protein Complex Elicits Potent NK Cell and CD8+ T Cell Immunity Against Solid Tumors

Advances in immunostimulatory and anti-immunosuppressive therapeutics have revolutionized cancer treatment. However, novel immunotherapeutics with these dual functions are not frequently reported. Here we describe the creation of a heterodimeric bifunctional fusion molecule, HCW9218, constructed using our soluble tissue factor-based scaffold technology. This complex comprises extracellular domains of the human transforming growth factor-β (TGF-β) receptor II and a human interleukin (IL)-15/IL-15 receptor α complex. HCW9218 can be readily expressed in CHO cells and purified using antibody-based affinity chromatography in a large-scale manufacturing setting. HCW9218 potently activates mouse natural killer (NK) cells and CD8⁺ T cells in vitro and in vivo to enhance cell proliferation, metabolism and antitumor cytotoxic activities. Similarly, human immune cells become activated with increased cytotoxicity following incubation with HCW9218. This fusion complex also exhibits TGF-β neutralizing activity in vitro and sequesters plasma TGF-β in vivo. In a syngeneic B16F10 melanoma model, HCW9218 displayed strong antitumor activity mediated by NK cells and CD8⁺ T cells, and increased their infiltration into tumors. Repeat-dose subcutaneous administration of HCW9218 was well tolerated by mice, with a half-life sufficient to provide long lasting biological activity. Thus, HCW9218 may serve as a novel therapeutic to simultaneously provide immunostimulation and lessen immunosuppression associated with tumors.

Preliminary phase 2 clinical results of IL-15RαFc superagonist N-803 with BCG in BCG-unresponsive non-muscle invasive bladder cancer (NMIBC) patients

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Background: Patients with non-muscle-invasive bladder cancer (NMIBC) unresponsive to BCG therapy have limited treatment options. N-803 (also known as ALT-803) is an IL-15-based immunostimulatory protein complex (IL-15RαFc) that promotes proliferation and activation of natural killer (NK) cells and CD8+ T cells, but not regulatory T cells. Phase Ib data in BCG-naïve patients with NMIBC demonstrate that intravesical administration of N-803 with BCG induced complete response in all patients, without recurrences for the study duration of 24 months. Methods: An open-label, single-arm multicenter Phase 2 study of intravesical BCG plus N-803 in patients with BCG-unresponsive high-grade NMIBC (NCT03022825) was opened. The study has two cohorts: Cohort A, patients with BCG-unresponsive carcinoma in situ (CIS) [with or without Ta or T1 disease] and Cohort B, patients with BCG-unresponsive high-grade Ta/T1 disease. All treated patients receive intravesical N-803 plus BCG, similar to a standard induction and maintenance treatment schedule. The primary endpoint for Cohort A is incidence of complete response (CR) of CIS at any time, and the primary endpoint for Cohort B is disease-free rate at 12 months. Results: To date, forty-six patients have enrolled in this phase 2 trial (Cohort A (CIS), n = 23, Cohort B (Papillary), n = 23). Of eleven evaluable patients in Cohort A, nine patients (82%) have a reported CR. In addition, seven out of nine (78%) patients in Cohort A demonstrated CR at their 6-month response assessment. Of thirteen evaluable patients in Cohort B, ten patients (77%) showed no evidence of recurrence at their 3-month response assessment; of these, none (0/8) evaluated past 3 months have had disease recurrence. Three serious adverse events (AEs) have been reported (E coli infection, anemia, and bacteremia), with no immune-related AEs. Conclusions: Nine out of eleven (82%) patients with BCG-unresponsive CIS of the bladder demonstrated a complete response. Ten out of thirteen patients with BCG-unresponsive papillary NMIBC show no evidence of disease at first assessment. Intravesical N-803 plus BCG was well-tolerated and no patients experienced immune-related AEs. Clinical trial information: NCT03022825.

Phase I Trial of ALT-803, A Novel Recombinant IL15 Complex, in Patients with Advanced Solid Tumors

Purpose: IL15 induces the activation and proliferation of natural killer (NK) and memory CD8⁺ T cells and has preclinical antitumor activity. Given the superior activity and favorable kinetics of ALT-803 (IL15N72D:IL15RαSu/IgG1 Fc complex) over recombinant human IL15 (rhIL15) in animal models, we performed this first-in-human phase I trial of ALT-803 in patients with advanced solid tumors.Patients and Methods: Patients with incurable advanced melanoma, renal cell, non-small cell lung, and head and neck cancer were treated with ALT-803 0.3 to 6 μg/kg weekly intravenously or 6 to 20 μg/kg weekly subcutaneously for 4 consecutive weeks, every 6 weeks. Immune correlates included pharmacokinetics, immunogenicity, and lymphocyte expansion and function. Clinical endpoints were toxicity and antitumor activity.Results: Twenty-four patients were enrolled; 11 received intravenous and 13 received subcutaneous ALT-803. Of these patients, nine had melanoma, six renal, three head and neck, and six lung cancer. Although total lymphocyte and CD8⁺ T-cell expansion were modest, NK cell numbers rose significantly. Neither anti-ALT-803 antibodies nor clinical activity were observed. Overall, ALT-803 was well tolerated, with adverse effects including fatigue and nausea most commonly with intravenous administration, whereas painful injection site wheal was reported most commonly with subcutaneous ALT-803.Conclusions: Subcutaneous ALT-803 produced the expected NK cell expansion and was well tolerated with minimal cytokine toxicities and a strong local inflammatory reaction at injection sites in patients with advanced cancer. These data, together with compelling evidence of synergy in preclinical and clinical studies, provide the rationale for combining ALT-803 with other anticancer agents. Clin Cancer Res; 24(22); 5552-61. ©2018 AACR.

ALT-803, an IL-15 superagonist, in combination with nivolumab in patients with metastatic non-small cell lung cancer: a non-randomised, open-label, phase 1b trial

BACKGROUND

Immunotherapy with PD-1 or PD-L1 blockade fails to induce a response in about 80% of patients with unselected non-small cell lung cancer (NSCLC), and many of those who do initially respond then develop resistance to treatment. Agonists that target the shared interleukin-2 (IL-2) and IL-15Rβγ pathway have induced complete and durable responses in some cancers, but no studies have been done to assess the safety or efficacy of these agonists in combination with anti-PD-1 immunotherapy. We aimed to define the safety, tolerability, and activity of this drug combination in patients with NSCLC.

METHODS

In this non-randomised, open-label, phase 1b trial, we enrolled patients (aged ≥18 years) with previously treated histologically or cytologically confirmed stage IIIB or IV NSCLC from three academic hospitals in the USA. Key eligibility criteria included measurable disease, eligibility to receive anti-PD-1 immunotherapy, and an Eastern Cooperative Oncology Group performance status of 0 or 1. Patients received the anti-PD-1 monoclonal antibody nivolumab intravenously at 3 mg/kg (then 240 mg when US Food and Drug Administration [FDA]-approved dosing changed) every 14 days (either as new treatment or continued treatment at the time of disease progression) and the IL-15 superagonist ALT-803 subcutaneously once per week on weeks 1-5 of four 6-week cycles for 6 months. ALT-803 was administered at one of four escalating dose concentrations: 6, 10, 15, or 20 μg/kg. The primary endpoint was to define safety and tolerability and to establish a recommended phase 2 dose of ALT-803 in combination with nivolumab. Analyses were per-protocol and included any patients who received at least one dose of study treatment. This trial is registered with ClinicalTrials.gov, number NCT02523469; phase 2 enrolment of patients is ongoing.

FINDINGS

Between Jan 18, 2016, and June 28, 2017, 23 patients were enrolled and 21 were treated at four dose levels of ALT-803 in combination with nivolumab. Two patients did not receive treatment because of the development of inter-current illness during enrolment, one patient due to leucopenia and one patient due to pulmonary dysfunction. No dose-limiting toxicities were recorded and the maximum tolerated dose was not reached. The most common adverse events were injection-site reactions (in 19 [90%] of 21 patients) and flu-like symptoms (15 [71%]). The most common grade 3 adverse events, occurring in two patients each, were lymphocytopenia and fatigue. A grade 3 myocardial infarction occurred in one patient. No grade 4 or 5 adverse events were recorded. The recommended phase 2 dose of ALT-803 is 20 μg/kg given once per week subcutaneously in combination with 240 mg intravenous nivolumab every 2 weeks.

INTERPRETATION

ALT-803 in combination with nivolumab can be safely administered in an outpatient setting. The promising clinical activity observed with the addition of ALT-803 to the regimen of patients with PD-1 monoclonal antibody relapsed and refractory disease shows evidence of anti-tumour activity for a new class of agents in NSCLC.

FUNDING

Altor BioScience (a NantWorks company), National Institutes of Health, and Medical University of South Carolina Hollings Cancer Center.

Evaluation of the biological activities of the IL-15 superagonist complex, ALT-803, following intravenous versus subcutaneous administration in murine models

ALT-803 is a fusion protein complex consisting of an interleukin (IL)-15 superagonist and a dimeric IL-15 receptor alpha sushi domain IgG1 Fc fusion protein. When administered to mice, ALT-803 is capable of inducing natural killer (NK) and CD8⁺ T cell proliferation and activation, and effectively promoting potent anti-tumor responses. Currently, ALT-803 is in clinical trials for treatment of various solid tumors and hematological malignancies. In the initial phase of these clinical studies, intravenous (iv) injection was used according to the route used in pre-clinical efficacy studies. In order to evaluate the possible advantage of subcutaneous (sc) injection versus iv injection, this study compared the biological activity of the two treatment regimens of ALT-803 in pre-clinical in vivo models. The pharmacokinetics, immune stimulation, and anti-tumor efficacy of iv and sc injection routes of ALT-803 in C57BL/6 mice were compared. The half-life of ALT-803 was 7.5 h for iv versus 7.7 h for sc with the maximal detected serum concentration of ALT-803 to be 3926 ng/ml at 0.5 h time-point following iv injection versus 495 ng/ml at 16 h post sc injection. Biodistribution studies indicated that sc ALT-803, similarly to iv ALT-803 as previously reported, has a greater tissue distribution and longer residence time in lymphoid tissues compared to recombinant IL-15. Notably, ALT-803 when administered either iv or sc induced comparable proliferation and activation of CD8⁺ T and NK cells and resulted in similar reductions of tumor burden. A toxicity study of mice receiving multiple injections of ALT-803 for 4 weeks by iv or sc routes revealed equivalent immune-related changes. The gradual absorbance into the blood stream and lower maximal blood levels of ALT-803 in sc-injected mice, along with similar anti-tumor efficacy support the administration of ALT-803 by sc injection in patients with various malignancies and infectious diseases.

Therapeutic effects of 2B8T2M, a novel fusion of ALT-803, an IL-15 superagonist, with 4 single-chains of anti-CD20 antibody in combination with expanded natural killer cells against rituximab sensitive and resistant Burkitt lymphoma (BL)

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Background: Patients retreated with rituximab often relapse which limit patient treatment options (Goldman/Cairo, Leukemia, 2013). Our group has successfully expanded functional and active peripheral blood NK cells (exPBNK) to target BL (Chu/Cairo, et al, Can Imm Res, 2015). 2B8T2M was generated by fusing ALT-803, an IL-15 superagonist, to four single-chains of rituximab (Liu/Wong, et al, JBC, 2016). 2B8T2M displayed tri-specific CD20 binding activity, activated NK cells to enhance antibody-dependent cellular cytotoxicity, and induced apoptosis of B-lymphoma cells (Liu/Wong, et al, JBC, 2016). Methods: ALT-803 and 2B8T2M were generously provided by Altor BioScience Corporation. NK expansion, NK receptors expression and cytotoxicity were examined as we previous described (Chu/Cairo, et al, Can Imm Res 2015). IFNg and granzyme B levels were examined by ELISA assays. Equal doses of IgG, Rituximab, ALT-803, Rituximab+ALT-803, obinutuzumab (obinu, generously provided by Christian Klein, PhD from Roche) were used for comparison. Results: 2B8T2M significantly enhanced exPBNK cytotoxicity against rituximab-sensitive Raji cells compared to the controls IgG, Rituximab, ALT-803, Rituximab+ALT-803, obinu (p < 0.001, E:T = 1:1). 2B8T2M also significantly enhanced exPBNK cytotoxicity against rituximab-resistant Raji-2R cells (p < 0.001, E:T = 1:1) and resistant Raji-4RH cells (p < 0.001, E:T = 1:1). Furthermore, 2B8T2M significantly enhanced IFN-g and granzyme B production from exPBNK against Raji, Raji-2R and Raji-4RH compared to IgG (p < 0.001), rituximab (p < 0.001), ALT-803 (p < 0.001), Rituximab+ALT-803 (p < 0.001), and obinutuzumab (p < 0.001). Conclusions: 2B8T2M compared to rituximab, ALT-803 or obinutuzumab significantly enhanced exPBNK in vitro cytotoxicity against rituximab-sensitive and –resistant BL cells. The in vivo functions of 2B8T2M with exPBNK using humanized NSG models are under investigation.

Biological Activities of IL-15 superagonist - IL-15 Mutein:IL-15RaFc complex following Intravenous or Subcutaneous Administration

ALT-803 is a fusion protein complex consisting of IL-15N72D superagonist and a dimeric IL-15 receptor alpha (IL-15Rα) sushi domain IgG1 Fc fusion protein. When administered to mice, ALT-803 is capable of inducing NK and CD8+ T cell proliferation and activation, as well as potent antitumor responses. ALT-803 is currently in clinical studies using an intravenous (iv) route of administration. We were interested in exploring treatment regimens using subcutaneous (sc) administration of ALT-803 as an alternative to iv administration in order to lessen the adverse side effects that were observed. In this study, we compared the pharmacokinetics, immunostimulation, and anti-tumor efficacy of iv and sc administration of ALT-803 in C57BL/6 mice. We found the half-life of ALT-803 to be 7.5 hrs for iv administration vs. 7.7 hrs for sc. The maximal detected serum concentration of ALT-803 was 495 ng/ml at 16 hr time point following sc administration or 3926 ng/ml at 0.5 hr time point following iv administration. Similar bio-distribution of radio-labeled ALT-803 in mice was observed using quantitative PET-scan studies. We also demonstrated that ALT-803 administered iv or sc induced comparable proliferation of CD8+ T cells and NK cells and similarly activated immune cells which resulted in the reduction of tumor burden. A toxicity study of mice receiving multiple injections of ALT-803 for 4 weeks by iv or sc administration revealed that comparable immune system-related changes were observed and ALT-803 was well tolerated. The gradual absorbance into blood stream and lower maximal blood level of ALT-803 in sc injected mice, along with similar antitumor efficacy supports the use of ALT-803 by sc administration in patients with metastatic malignancies.

Novel antitumor complexes of bispecific antibodies using ALT-803 as a scaffold demonstrate Tetra-specific binding activities

IL-15 and its receptor α (IL-15Ra) are co-expressed in antigen presenting cells allowing trans-presentation of IL-15 to immune cells bearing IL-2Rβγc and stimulation of effector immune responses. We have demonstrated that an IL-15 superagonist:IL-15Rα-Fc complex (ALT-803) is capable of stimulating T cell and NK cell responses. We have reported that ALT-803 could be exploited to create a functional scaffold for the design of multivalent disease-targeted complexes (Liu et al, J. Biol. Chem. 2016 291: 23869). The lead molecule based on anti-CD20 rituximab is currently in pre-clinical development. In this study, this approach was further optimized by generating an IL-15 superagonist:IL-15Rα-Fc complex (2B8T3M) comprising two anti-human CD20 scFv domains and two anti-human CD3 scFv domains. 2B8T3M molecules exhibit CD3, CD20, Fc-receptor and IL-15Rbgc tetra-specific binding activities and IL-15 bioactivity. In contrast to 2B8T2M which redirects NK cells to lyse CD20+ B-lymphoma cells (ADCC), 2B8T3M was capable of redirecting both CD8+ T cells via the anti-CD3 scFv domains and NK cells via the Fc domain against CD20+ Daudi cells. In order to investigate antitumor activities in vivo of the tetra-specific molecules in immunocompetent mouse, we have also constructed and generated mouse CD3/CD19-binding T3M complexes. Antitumor efficacy of these molecules is being assessed in mouse A20 B cell lymphoma model. These findings suggest that tetra-specific T3M complexes may serve as novel, T-cell based targeted immunotherapeutics for treating cancer.

Novel antibody-like single-chain TCR antibody Fc fusion protein

We have previously reported the construction of a fusion protein composed of a soluble single-chain T cell receptor genetically linked to the constant domain of the human IgG1 heavy chain (TCR-Ig). The antigen recognition portion of the protein binds to an unmutated peptide derived from human p53 (amino acids 264–272) presented in the context of HLA-A2.1, whereas the IgG1 Fc provides effector functions. The protein is capable of forming dimers, specifically staining tumor cells, and promoting target and effector cell conjugation. The protein also has potent antitumor effects against p53+/HLA-A2.1+ human tumor xenografts in athymic nude mice and can mediate cell killing by antibody-dependent cellular cytotoxicity. Therefore, TCR-Ig behaves like an antibody, but possesses the ability to recognize antigens derived from intracellular targets. To test TCR-Ig in fully immunocompetent models, we have generated murine tumor cells stably expressing the human p53 epitope by constructing a single chain trimer composed of the human p53 peptide genetically linked to murine beta 2 microglobulin genetically linked to HLA-A2.1, with the inclusion of a disulfide trap to enhance stability. Utilizing haNK (NK-92 cells stably expressing high affinity Fc receptor and IL-2) as effector cells in the presence of TCR-Ig we demonstrated specific killing of murine single chain trimer expressing tumor cells. We are currently evaluating the antitumor activities and vaccinal effects of TCR-Ig in an HLA-A2.1 transgenic mouse model. TCR-Ig may represent a novel group of immunotherapeutics that has the potential to expand the range of tumors available for targeted therapies beyond those currently addressed by conventional antibody-based approaches.

Enhancement of Anti-Tumor Activities of Daratumumab Using ALT-803, an IL-15 Superagonist, in an Experimental Model and Against Primary Human Lymphoma Cells

Daratumumab has recently been approved by FDA for treatment of patients with relapsed or refractory multiple myeloma. Daratumumab has been shown to reduce the tumor burden by targeting CD38 expressing tumor cells. In this study, we examined the in vitro as well as in vivo ability of ALT-803, a novel IL-15 superagonist-complex, to enhance the tumor targeting antibody dependent cellular cytotoxicity (ADCC) of daratumumab in combination therapy. Using freshly isolated PBMCs, we demonstrated that ALT-803 significantly enhanced the ADCC activity of Daratumumab against Daudi, human B lymphoma, cells. We also observed that purified human NK cells, which were activated by ALT-803, enhanced daratumumab-mediated ADCC activity against primary human B-lymphoma cells. We also assessed the in vivo effects of ALT-803 on daratumumab-mediated antitumor activity against Daudi cells in the SCID xenograft model. We observed that both ALT-803 and daratumumab alone were capable of reducing Daudi tumor burden in tumor-bearing mice. However, the combination of ALT-803 with daratumumab increased antitumor activity which significantly reduced Daudi cells in the bone marrow. These observations indicate that the addition of ALT-803 to daratumumab treatment enhances the antitumor efficacy of Daratumumab compared to daratumumab alone. In addition, we have evidence that ALT-803 also augment the Antibody Dependent Cytotoxicity of Phagocytosis of Daratumumab against tumor cells. In a current clinical study, our correlative studies also show that ALT-803 augment the ADCC activity of Daratumumab against Daudi cells. This also demonstrates that ALT-803 possesses synergistic antitumor activities with tumor-specific antibodies in vivo.

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.

Phase Ib trial of ALT-803, an IL-15 superagonist, plus Bacillus Calmette Guerin (BCG) for the treatment of patients with BCG-naïve non-muscle-invasive bladder cancer (NMIBC)

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Background: Novel agents are necessary to treat NMIBC to avoid recurrence and progression. This phase Ib clinical trial evaluated the safety and toleraibility of ALT-803, an IL-15 superagonist, plus BCG in patients with BCG-naïve NMIBC. Methods: This is a Phase Ib trial using the 3+3 design to evaluate intravesical ALT-803 plus BCG 50 mg in BCG-naïve NMIBC patients, who would normally be eligible for intravesical BCG alone. The initial dose of ALT-803 was 100 μg/instillation with 2 dose-escalations allowed (200 μg/instillation and 400 μg/instillation) if dose limiting toxicities (DLTs) were not evident. Patients received intravesical ALT-803 in conjunction with BCG weekly for 6 consecutive weeks (Induction Phase). Patients then had routine follow-up with cystoscopy and voided urinary cytology (VUC) every 3 months for 2 years equating to confirmatory response assessment. Negative cystoscopy, VUC and/or biopsy yielded a complete response (CR). When appropriate for high-risk patients, physicians and patients were encouraged to receive maintenance BCG alone as per common practice patterns. Results: No patient in 100 μg/instillation of ALT-803/BCG and 200 μg/instillation of ALT-803/BCG reported an AE. One patient in 400 μg/instillation/BCG cohort developed a urinary tract infection requiring delay of intravesical treatment by 1 week. No grade 3/4 toxicities were noted. All patients have completed therapy without DLTs. To date, 4 patients have 12 month follow-up and are CR. The remaining 5 patients have no evidence of disease. However, follow-ups are currently approximately 3 months. Corollary immune studies are still pending. Conclusions: Intravesical ALT-803 plus BCG was safe and tolerable in patients with BCG-naive NMIBC. Further evaluation in expansion cohorts in a phase II trial is currently underway. Clinical trial information: NCT02138734.

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

IL15, a potent stimulant of CD8(+) T cells and natural killer (NK) cells, is a promising cancer immunotherapeutic. ALT-803 is a complex of an IL15 superagonist mutant and a dimeric IL15 receptor αSu/Fc fusion protein that was found to exhibit enhanced biologic activity in vivo, with a substantially longer serum half-life than recombinant IL15. A single intravenous dose of ALT-803, but not IL15, eliminated well-established tumors and prolonged survival of mice bearing multiple myeloma. In this study, we extended these findings to demonstrate the superior antitumor activity of ALT-803 over IL15 in mice bearing subcutaneous B16F10 melanoma tumors and CT26 colon carcinoma metastases. Tissue biodistribution studies in mice also showed much greater retention of ALT-803 in the lymphoid organs compared with IL15, consistent with its highly potent immunostimulatory and antitumor activities in vivo. Weekly dosing with 1 mg/kg ALT-803 in C57BL/6 mice was well tolerated, yet capable of increasing peripheral blood lymphocyte, neutrophil, and monocyte counts by >8-fold. ALT-803 dose-dependent stimulation of immune cell infiltration into the lymphoid organs was also observed. Similarly, cynomolgus monkeys treated weekly with ALT-803 showed dose-dependent increases of peripheral blood lymphocyte counts, including NK, CD4(+), and CD8(+) memory T-cell subsets. In vitro studies demonstrated ALT-803-mediated stimulation of mouse and human immune cell proliferation and IFNγ production without inducing a broad-based release of other proinflammatory cytokines (i.e., cytokine storm). Based on these results, a weekly dosing regimen of ALT-803 has been implemented in multiple clinical studies to evaluate the dose required for effective immune cell stimulation in humans.

The IL-15-Based ALT-803 Complex Enhances FcγRIIIa-Triggered NK Cell Responses and In Vivo Clearance of B Cell Lymphomas

PURPOSE

Anti-CD20 monoclonal antibodies (mAb) are an important immunotherapy for B-cell lymphoma, and provide evidence that the immune system may be harnessed as an effective lymphoma treatment approach. ALT-803 is a superagonist IL-15 mutant and IL-15Rα-Fc fusion complex that activates the IL-15 receptor constitutively expressed on natural killer (NK) cells. We hypothesized that ALT-803 would enhance anti-CD20 mAb-directed NK-cell responses and antibody-dependent cellular cytotoxicity (ADCC).

EXPERIMENTAL DESIGN

We tested this hypothesis by adding ALT-803 immunostimulation to anti-CD20 mAb triggering of NK cells in vitro and in vivo. Cell lines and primary human lymphoma cells were utilized as targets for primary human NK cells. Two complementary in vivo mouse models were used, which included human NK-cell xenografts in NOD/SCID-γc (-/-) mice.

RESULTS

We demonstrate that short-term ALT-803 stimulation significantly increased degranulation, IFNγ production, and ADCC by human NK cells against B-cell lymphoma cell lines or primary follicular lymphoma cells. ALT-803 augmented cytotoxicity and the expression of granzyme B and perforin, providing one potential mechanism for this enhanced functionality. Moreover, in two distinct in vivo B-cell lymphoma models, the addition of ALT-803 to anti-CD20 mAb therapy resulted in significantly reduced tumor cell burden and increased survival. Long-term ALT-803 stimulation of human NK cells induced proliferation and NK-cell subset changes with preserved ADCC.

CONCLUSIONS

ALT-803 represents a novel immunostimulatory drug that enhances NK-cell antilymphoma responses in vitro and in vivo, thereby supporting the clinical investigation of ALT-803 plus anti-CD20 mAbs in patients with indolent B-cell lymphoma.

Therapeutic administration of IL-15 superagonist complex ALT-803 leads to long-term survival and durable antitumor immune response in a murine glioblastoma model

Glioblastoma is the most aggressive primary central nervous system malignancy with a poor prognosis in patients. Despite the need for better treatments against glioblastoma, very little progress has been made in discovering new therapies that exhibit superior survival benefit than the standard of care. Immunotherapy has been shown to be a promising treatment modality that could help improve clinical outcomes of glioblastoma patients by assisting the immune system to overcome the immunosuppressive tumor environment. Interleukin-15 (IL-15), a cytokine shown to activate several effector components of the immune system, may serve as an excellent immunotherapeutic candidate for the treatment of glioblastoma. Thus, we evaluated the efficacy of an IL-15 superagonist complex (IL-15N72D:IL-15RαSu-Fc; also known as ALT-803) in a murine GL261-luc glioblastoma model. We show that ALT-803, as a single treatment as well as in combination with anti-PD-1 antibody or stereotactic radiosurgery, exhibits a robust antitumor immune response resulting in a prolonged survival including complete remission in tumor bearing mice. In addition, ALT-803 treatment results in long-term immune memory against glioblastoma tumor rechallenge. Flow cytometric analysis of tumor infiltrating immune cells shows that ALT-803 leads to increased percentage of CD8+-cell infiltration, but not the NK cells, and IFN-γ production into the tumor microenvironment. Cell depletion studies, in accordance with the flow cytometric results, show that the ALT-803 therapeutic effect is dependent on CD4+ and CD8+ cells. These results provide a rationale for evaluating the therapeutic activity of ALT-803 against glioblastoma in the clinical setting.

Intravesical ALT-803 and BCG treatment reduces tumor burden in a carcinogen induced bladder cancer rat model; a role for cytokine production and NK cell expansion

Intravesical Bacillus Calmette-Guérin (BCG) has been shown to induce a specific immunologic response (i.e., activation of IL-2 and effector T-cells), while preclinical studies using ALT-803 (mutated IL-15 analogue combined with IL-15Rα-Fc fusion) have shown promising results by prolonging the agent's half-life and stimulating CD8+ T-cells. Based on these results, we hypothesized that the intravesical administration of ALT-803 along with BCG will generate an immunologic response leading to significant bladder tumor burden reduction. Using a well-established carcinogen induced rat non-muscle invasive bladder cancer (NMIBC) model, we studied the effects of intravesical ALT-803 with and without BCG. Rat tissues were evaluated to document treatment response. Intravesical ALT-803 was safe and well tolerated alone and in combination with BCG. As a single treatment agent, ALT-803 reduced tumor burden by 35% compared to control whereas BCG alone only reduced tumor burden by 15%. However, the combination of ALT-803 plus BCG reduced tumor burden by 46% compared to control. Immune monitoring suggested that the antitumor response was linked to the production and secretion of IL-1α, IL-1β and RANTES, which in turn, induced the proliferation and activation of NK cells. Lastly, tumoral responses of the combinational treatment were associated with 76% reduction in angiogenesis, which is significantly higher than when assessed with either agent alone. The enhanced therapeutic index seen with this duplet provides justification for the development of this regimen for future clinical trials.

The IL-15-based superagonist ALT-803 promotes the antigen-independent conversion of memory CD8+ T cells into innate-like effector cells with antitumor activity

ALT-803, an interleukin-15-based superagonist, induces memory CD8⁺ T cells to proliferate, upregulate receptors involved in innate immunity, secrete interferon γ and acquire the ability to kill malignant cells in the absence of antigenic stimulation. Thus, ALT-803 can promote the expansion and activation of memory CD8⁺ T cells while converting them into innate immune effector cells that exhibit robust antineoplastic activity.

Efficacy and mechanism-of-action of a novel superagonist interleukin-15: interleukin-15 receptor αSu/Fc fusion complex in syngeneic murine models of multiple myeloma

ALT-803, a complex of an interleukin (IL)-15 superagonist mutant and a dimeric IL-15 receptor αSu/Fc fusion protein, was found to exhibit significantly stronger in vivo biologic activity on NK and T cells than IL-15. In this study, we show that a single dose of ALT-803, but not IL-15 alone, eliminated well-established 5T33P and MOPC-315P myeloma cells in the bone marrow of tumor-bearing mice. ALT-803 treatment also significantly prolonged survival of myeloma-bearing mice and provided resistance to rechallenge with the same tumor cells through a CD8(+) T-cell-dependent mechanism. ALT-803 treatment stimulated CD8(+) T cells to secrete large amounts of IFN-γ and promoted rapid expansion of CD8(+)CD44(high) memory T cells in vivo. These memory CD8(+) T cells exhibited ALT-803-mediated upregulation of NKG2D (KLRK1) but not PD-1 (PDCD1) or CD25 (IL2RA) on their cell surfaces. ALT-803-activated CD8(+) memory T cells also exhibited nonspecific cytotoxicity against myeloma and other tumor cells in vitro, whereas IFN-γ had no direct effect on myeloma cell growth. ALT-803 lost its antimyeloma activity in tumor-bearing IFN-γ knockout mice but retained the ability to promote CD8(+)CD44(high) memory T-cell proliferation, indicating that ALT-803-mediated stimulation of CD8(+)CD44(high) memory T cells is IFN-γ-independent. Thus, besides well-known IL-15 biologic functions in host immunity, this study shows that IL-15-based ALT-803 could activate CD8(+)CD44(high) memory T cells to acquire a unique innate-like phenotype and secrete IFN-γ for nonspecific tumor cell killing. This unique immunomodulatory property of ALT-803 strongly supports its clinical development as a novel immunotherapeutic agent against cancer and viral infections.

A phase I study evaluating the pharmacokinetics, safety and tolerability of an antibody-based tissue factor antagonist in subjects with acute lung injury or acute respiratory distress syndrome

Background

The tissue factor (TF)-dependent extrinsic pathway has been suggested to be a central mechanism by which the coagulation cascade is locally activated in the lungs of patients with acute lung injury and acute respiratory distress syndrome (ALI/ARDS) and thus represents an attractive target for therapeutic intervention. This study was designed to determine the pharmacokinetic and safety profiles of ALT-836, an anti-TF antibody, in patients with ALI/ARDS.

Methods

This was a prospective, randomized, placebo-controlled, dose-escalation Phase I clinical trial in adult patients who had suspected or proven infection, were receiving mechanical ventilation and had ALI/ARDS (PaO₂/FiO₂ ≤ 300 mm). Eighteen patients (6 per cohort) were randomized in a 5:1 ratio to receive ALT-836 or placebo, and were treated within 48 hours after meeting screening criteria. Cohorts of patients were administered a single intravenously dose of 0.06, 0.08 or 0.1 mg/kg ALT-836 or placebo. Blood samples were taken for pharmacokinetic and immunogenicity measurements. Safety was assessed by adverse events, vital signs, ECGs, laboratory, coagulation and pulmonary function parameters.

Results

Pharmacokinetic analysis showed a dose dependent exposure to ALT-836 across the infusion range of 0.06 to 0.1 mg/kg. No anti-ALT-836 antibody response was observed in the study population during the trial. No major bleeding episodes were reported in the ALT-836 treated patients. The most frequent adverse events were anemia, observed in both placebo and ALT-836 treated patients, and ALT-836 dose dependent, self-resolved hematuria, which suggested 0.08 mg/kg as an acceptable dose level of ALT-836 in this patient population.

Conclusions

Overall, this study showed that ALT-836 could be safely administered to patients with sepsis-induced ALI/ARDS.

Trial registration

ClinicalTrials.gov: NCT01438853

IL-15:IL-15 receptor alpha superagonist complex: high-level co-expression in recombinant mammalian cells, purification and characterization

IL-15, a promising cytokine for treating cancer and viral diseases, is presented in trans by the IL-15 receptor (IL-15R) alpha-chain to the IL-15Rβγc complex displayed on the surface of T cells and natural killer (NK) cells. We previously reported that an asparagine to aspartic acid substitution at amino acid 72 (N72D) of IL-15 provides a 4-5-fold increase in biological activity compared to the native molecule. In this report, we describe Chinese hamster ovary (CHO) cell expression of a soluble complex (IL-15 N72D:IL-15RαSu/Fc) consisting of the IL-15 N72D superagonist and a dimeric IL-15Rα sushi domain-IgG1 Fc fusion protein. A simple but readily scalable affinity and ion exchange chromatography method was developed to highly purify the complex having both IL-15 binding sites fully occupied. The immunostimulatory effects of this complex were confirmed using cell proliferation assays. Treatment of mice with a single intravenous dose of IL-15N72D:IL-15RαSu/Fc resulted in a significant increase in CD8+ T cells and NK cells that was not observed following IL-15 treatment. Pharmacokinetic analysis indicated that the complex has a 25-h half-life in mice which is considerably longer than <40-min half-life of IL-15. Thus, the enhanced activity of the IL-15N72D:IL-15RαSu/Fc complex is likely the result of the increased binding activity of IL-15N72D to IL-15Rβγc, optimized cytokine trans-presentation by the IL-15RαSu domain, the dimeric nature of the cytokine domain and its increased in vivo half-life compared to IL-15. These findings indicate that this IL-15 superagonist complex could serve as a superior immunostimulatory therapeutic agent.

Phase I trial of ALT-801, an interleukin-2/T-cell receptor fusion protein targeting p53 (aa264-272)/HLA-A*0201 complex, in patients with advanced malignancies

PURPOSE

ALT-801 is a bifunctional fusion protein comprising interleukin-2 (IL-2) linked to a soluble, single-chain T-cell receptor domain that recognizes a peptide epitope (aa264-272) of the human p53 antigen displayed on cancer cells in the context of HLA-A*0201 (p53+/HLA-A*0201). We evaluated the safety, pharmacokinetics, and pharmacodynamics of ALT-801 in p53+/HLA-A*0201 patients with metastatic malignancies.

EXPERIMENTAL DESIGN

p53+/HLA-A*0201 patients were treated with ALT-801 on a schedule of four daily 15-minute intravenous infusions, then 10 days rest and four more daily infusions. Cohorts of patients were treated at 0.015, 0.040, and 0.080 mg/kg/dose.

RESULTS

Four, 16, and 6 patients were treated at the 0.015, 0.04, and 0.08 mg/kg cohorts, respectively. Two dose-limiting toxicities (a grade 4 transient thrombocytopenia and a myocardial infarction) in the 0.08 mg/kg cohort established the maximum tolerated dose (MTD) at 0.04 mg/kg. Patients treated at the MTD experienced toxicities similar to those associated with high-dose IL-2 but of lesser severity. The serum half-life of ALT-801 was 4 hours and ALT-801 serum recovery was as expected based on the dose administered. ALT-801 treatment induced an increase of serum IFN-γ but not TNF-α. Response assessment showed 10 subjects with stable disease at at least 11 weeks, and in one who had melanoma metastasis, there is an ongoing complete absence of identifiable disease after resection of radiographically identified lesions.

CONCLUSION

This first-in-man study defines an ALT-801 regimen that can be administered safely and is associated with immunologic changes of potential antitumor relevance.

Interleukin-15:Interleukin-15 receptor α scaffold for creation of multivalent targeted immune molecules

Human interleukin-15 (hIL-15) and its receptor α (hIL-15Rα) are co-expressed in antigen presenting cells allowing trans-presentation of the cytokine to immune effector cells. We exploited the high-affinity interactions between hIL-15 and the extracellular hIL-15Rα sushi domain (hIL-15RαSu) to create a functional scaffold for the design of multispecific fusion protein complexes. Using single-chain T cell receptors (scTCRs) as recognition domains linked to the IL-15:IL-15Rα scaffold, we generated both bivalent and bispecific complexes. In these fusions, the scTCR domains retain the antigen-binding activity and the hIL-15 domain exhibits receptor binding and biological activity. As expected, bivalent scTCR fusions exhibited improved antigen binding due to increased avidity, whereas fusions comprising two different scTCR domains were capable of binding two cognate peptide/MHC complexes. Bispecific molecules containing scTCR and scCD8αβ domains also exhibit enhanced binding to peptide/MHC complexes, demonstrating that the IL-15:IL-15Rα scaffold displays flexibility necessary to support multi-domain interactions with a given target. Surprisingly, functional heterodimeric molecules could be formed by co-expressing the TCR α and β chains separately as fusions to the hIL-15 and hIL-15RαSu domains. Together, these properties indicate that the hIL-15 and hIL-15RαSu domains can be used as versatile, functional scaffold for generating novel targeted immune molecules.

Inhibition of acute vascular thrombosis in chimpanzees by an anti-human tissue factor antibody targeting the factor X binding site

Tissue factor (TF) antagonists targeting the factor VII (FVII) binding domain have been shown to interrupt acute vascular thrombus formation without impairing haemostasis in non-human primates. In this study, we evaluate whether a human/mouse chimeric monoclonal antibody (ALT-836, formerly known as Sunol-cH36) blocking the factor X/factor IX (FX/FIX) binding site of tissue factor could achieve similar clinical benefits in an arterial thrombosis model induced by surgical endarterectomy in chimpanzees. In this model, sequential surgical endarterectomies on right and left superficial femoral arteries were performed 30 days apart in five chimpanzees. A bolus (1 mg/kg) of ALT-836 was injected intravenously immediately preceding the restoration of flow in the endarterectomised femoral artery. Pre-surgical labelling of autologous platelets using (111)In-Oxine and post-surgical gamma camera imaging of (111)In-platelet deposition at endarterectomy sites was performed. The manipulated arterial segments were harvested for patency analysis 30 days following surgery. The results indicate that ALT-836 was highly effective at reducing acute vascular thrombosis, with no significant variations in surgical blood loss and template-bleeding time in the treated group compared to the control animals. These data suggest that ALT-836 is an effective and safe antithrombotic agent in preventing TF-initiated vascular thrombogenesis without compromising haemostasis.

Novel human interleukin-15 agonists

IL-15 is an immunostimulatory cytokine trans-presented with the IL-15 receptor alpha-chain to the shared IL-2/IL-15Rbeta and common gamma-chains displayed on the surface of T cells and NK cells. To further define the functionally important regions of this cytokine, activity and binding studies were conducted on human IL-15 muteins generated by site-directed mutagenesis. Amino acid substitutions of the asparagine residue at position 72, which is located at the end of helix C, were found to provide both partial agonist and superagonist activity, with various nonconservative substitutions providing enhanced activity. Particularly, the N72D substitution provided a 4-5-fold increase in biological activity of the IL-15 mutein compared with the native molecule based on proliferation assays with cells bearing human IL-15Rbeta and common gamma-chains. The IL-15N72D mutein exhibited superagonist activity through improved binding ability to the human IL-15Rbeta-chain. However, the enhanced potency of IL-15N72D was not observed with cells expressing the mouse IL-15Ralpha-IL-15Rbeta-gamma(c) complex, suggesting that this effect is specific to the human IL-15 receptor. The enhanced biological activity of IL-15N72D was associated with more intense phosphorylation of Jak1 and Stat5 and better anti-apoptotic activity compared with the wild-type IL-15. IL-15N72D superagonist activity was also preserved when linked to a single-chain TCR domain to generate a tumor-specific fusion protein. Thus, the human IL-15 superagonist muteins and fusions may create opportunities to construct more efficacious immunotherapeutic agents with clinical utility.

Targeting activity of a TCR/IL-2 fusion protein against established tumors

We have previously reported that a single-chain T cell receptor/IL-2 fusion protein (scTCR-IL2) exhibits potent targeted antitumor activity in nude mice bearing human tumor xenografts that display cognate peptide/HLA complexes. In this study, we further explore the mechanism of action of this molecule. We compared the biological activities of c264scTCR-IL2, a scTCR-IL2 protein recognizing the aa264-272 peptide of human p53, with that of MART-1scTCR-IL2, which recognizes the MART-1 melanoma antigen (aa27-35). In vitro studies showed that c264scTCR-IL2 and MART-1scTCR-IL2 were equivalent in their ability to bind cell-surface IL-2 receptors and stimulate NK cell responses. In mice, MART-1scTCR-IL2 was found to have a twofold longer serum half-life than c264scTCR-IL2. However, despite its shorter serum half-life, c264scTCR-IL2 showed significantly better antitumor activity than MART-1scTCR-IL2 against p53(+)/HLA-A2(+) tumor xenografts. The more potent antitumor activity of c264scTCR-IL2 correlated with an enhanced capacity to promote NK cell infiltration into tumors. Similar differences in antigen-dependent tumor infiltration were observed with activated splenocytes pre-treated in vitro with c264scTCR-IL2 or MART-1scTCR-IL2 and then transferred into p53(+)/HLA-A2(+) tumor bearing recipients. The data support a model where c264scTCR-IL2 activates immune cells to express IL-2 receptors. Following stable interactions with cell-surface IL-2 receptors, c264scTCR-IL2 fusion molecule enhances the trafficking of immune cells to tumors displaying target peptide/HLA complexes where the immune cells mediate antitumor effects. Thus, this type of fusion molecule could be used directly as a targeted immunotherapeutic or in adoptive cell transfer approaches to activate and improve the anti-cancer activities of immune cells by providing them with pre-selected antigen recognition capability.

Recognition of Melanoma-Associated Antigens gp100 or Mart1/Melan-A in the Context of HLA-A2 by Soluble Single Chain T-Cell Receptor Multimers (93.15)

Melanoma-associated antigens gp100 and Mart1/Melan-A are specifically recognized by HLA-A2-restricted CD8+ CTLs derived from melanoma patients and are currently being evaluated in antigen-based vaccines for the treatment of melanoma patients. In this study, TCR genes isolated from the CTL clones recognizing gp100209-217/HLA-A2 and Mart126-35/HLA-A2 were used to generate soluble single chain TCR multimeric reagents, referred to as gp100scTCR and Mart1scTCR multimers. Like original CTL clones, both gp100scTCR and Mart1scTCR multimers recognize T2 cells pulsed with either native or analogue peptides. Gp100scTCR multimer recognize T2 cells pulsed with up to 50 nM of gp100209-217 or gp100209-217T210M and Mart1scTCR multimers recognize T2 cells pulsed with as low as 10 nM of Mart126-35 or Mart126-35A27L. Moreover, gp100scTCR multimer recognizes native peptide/HLA-A2 displayed on the surface of gp100+/HLA-A2+ melanoma cell lines 526 Mel and 624 Mel but not gp100+/HLA-A2− melanoma cell lines 888 Mel and 938 Mel. Thus, these tumor antigen-specific TCR multimers have potential uses as quality control reagents of dendritic cell-based vaccines and a variety of other research applications.

Potent antitumor activity of a tumor-specific soluble TCR/IL-2 fusion protein

We previously have generated a single-chain T cell receptor-cytokine fusion protein (264scTCR/IL-2) comprising interleukin-2 genetically linked to a soluble HLA-A2.1-restricted TCR recognizing a peptide of human p53 protein. In this report, we show that 264scTCR/IL-2 inhibits the growth of primary tumors derived from the A375 (p53+/HLA-A2.1+) human melanoma and exhibits significantly better antitumor activity than recombinant human IL-2 alone. Moreover, treatment with 264scTCR/IL-2 results in tumor growth retardation in mice bearing large A375 tumors and other p53+/HLA-A2.1+ human tumors but does not affect tumor outgrowth of HLA-A2.1-negative tumors. This suggests that antigen targeting plays a substantial role in the efficacy of 264scTCR/IL-2 against p53+/HLA-A2+ tumors. Further, the antitumor activity of 264scTCR/IL-2 was found to be likely mediated by NK cell activation and tumor infiltration. A biologically active chimeric version of the molecule (c264scTCR/IL-2) also exhibits favorable pharmacokinetic properties required of a clinical candidate for this novel class of potent antitumor activities and targeted anticancer immunotherapeutics.

Visualization of p53(264-272)/HLA-A*0201 complexes naturally presented on tumor cell surface by a multimeric soluble single-chain T cell receptor

Intracellular Ags are processed into small peptides that are presented on cell surfaces in the context of HLA class I molecules. These peptides are recognized by TCRs displayed by CD8+ T lymphocytes (T cells). To date, direct identification and quantitation of these peptides has relied primarily on mass spectrometry analysis, which is expensive and requires large quantities of diseased tissues to obtain useful results. Here we demonstrate that multimerization of a soluble single-chain TCR (scTCR), recognizing a peptide from p53 presented in the context of HLA-A2.1, could be used to directly visualize and quantitate peptide/MHC complexes on unmanipulated human tumor cells. Tumor cells displaying as few as 500 peptide/MHC complexes were readily detectable by flow cytometry. The scTCR/multimers exhibited exquisite recognition capability and could distinguish peptides differing in as little as a single amino acid. We also demonstrate that scTCR/multimers could specifically stain human tumors generated in mice, as well as tumors obtained from patient biopsies. Thus, scTCR/multimers represent a novel class of immunostaining reagents that could be used to validate, quantitate, or monitor epitope presentation by cancer cells.

Molecular cloning and characterization of the Saccharomyces cerevisiae SAB1 gene that suppresses a temperature-sensitive phenotype of the ARS-binding factor 1 mutant

A high-copy number suppressor gene of the yeast temperature-sensitive lethal abf1 mutant was isolated and named SAB1 (suppressor of ABF1). Chromoblot hybridization and grid-filter hybridization analyses showed that the SAB1 gene was located on chromosome IV. Deletion analyses of the SAB1 plasmid revealed that the suppressor activity was contained in a 1.1 kb DNA region. The nucleotide sequence of the 1.1 kb DNA fragment was determined and turned out to be identical to that of the yeast phosphoribosylanthranilate isomerase gene (TRP1). A binding site for ARS-Binding Factor 1 was located in the coding sequence of the TRP1 gene, which has been known to be a part of the B domain of yeast autonomously replicating sequence 1 (ARS1). Our results suggest that ABF1 might be important for the transcription of the yeast TRP1 gene in addition to having important roles in the stimulation of replication at the ARS1 locus.

Single-chain MHC class II molecules induce T cell activation and apoptosis

MHC class II/peptide complexes displayed on the surface of APCs play a pivotal role in initiating specific T cell responses. Evidence is presented here that components of this heterotrimeric complex can be genetically linked into a single polypeptide chain. Soluble single-chain (sc) murine class II IA(d) molecules with and without covalently attached peptides were produced in a recombinant baculovirus-insect cell expression system. Correct conformation of these molecules was verified based on 1) reactivity to Abs directed against conformational epitopes in IA(d) and 2) peptide-specific recognition of the IA(d)/peptide complexes by T cells. Both sc class II molecules loaded the appropriate peptides and sc class II/peptide fusions were effective in stimulating T cell responses, including cytokine release and apoptosis. Mammalian cells were also found to be capable of expressing functional sc class II molecules on their cell surfaces. The findings reported here open up the possibility of producing large amounts of stable sc class II/peptide fusion molecules for structural characterization and immunotherapeutic applications.

Single-chain MHC class II molecules induce T cell activation and apoptosis

MHC class II/peptide complexes displayed on the surface of APCs play a pivotal role in initiating specific T cell responses. Evidence is presented here that components of this heterotrimeric complex can be genetically linked into a single polypeptide chain. Soluble single-chain (sc) murine class II IA(d) molecules with and without covalently attached peptides were produced in a recombinant baculovirus-insect cell expression system. Correct conformation of these molecules was verified based on 1) reactivity to Abs directed against conformational epitopes in IA(d) and 2) peptide-specific recognition of the IA(d)/peptide complexes by T cells. Both sc class II molecules loaded the appropriate peptides and sc class II/peptide fusions were effective in stimulating T cell responses, including cytokine release and apoptosis. Mammalian cells were also found to be capable of expressing functional sc class II molecules on their cell surfaces. The findings reported here open up the possibility of producing large amounts of stable sc class II/peptide fusion molecules for structural characterization and immunotherapeutic applications.

Isolation and characterization of Saccharomyces cerevisiae SAB2, a suppressor gene for temperature-sensitive phenotype of ARS-binding factor 1 mutant

A high-copy number suppressor of yeast abf1-5 mutant, a temperature-sensitive lethal mutant, was isolated and named SAB2 (suppressor of ABF1). Hybridization to a yeast chromoblot and to prime clone grid filters revealed that the SAB2 gene was located near the yeast SUP3 on chromosome XV. The suppressor activity was contained in a 2.5 Kbp DNA region of the SAB2 plasmid. The nucleotide sequence of the DNA region contained a long open reading frame, which turned out to encode for yeast tryptophan permease. Four putative ABF1 binding sites were found in the promoter and the structural regions of the tryptophan permease gene. Binding of ABF1 to two of the sites tested in this study was detected. Our results indicate that ABF1 may be involved in the transcriptional control of the yeast tryptophan permease gene.

ABF1 is a phosphoprotein and plays a role in carbon source control of COX6 transcription in Saccharomyces cerevisiae

Previously, we have shown that the Saccharomyces cerevisiae DNA-binding protein ABF1 exists in at least two different electrophoretic forms (K. S. Sweder, P. R. Rhode, and J. L. Campbell, J. Biol. Chem. 263: 17270-17277, 1988). In this report, we show that these forms represent different states of phosphorylation of ABF1 and that at least four different phosphorylation states can be resolved electrophoretically. The ratios of these states to one another differ according to growth conditions and carbon source. Phosphorylation of ABF1 is therefore a regulated process. In nitrogen-starved cells or in cells grown on nonfermentable carbon sources (e.g., lactate), phosphorylated forms predominate, while in cells grown on fermentable carbon sources (e.g., glucose), dephosphorylated forms are enriched. The phosphorylation pattern is affected by mutations in the SNF1-SSN6 pathway, which is involved in glucose repression-depression. Whereas a functional SNF1 gene, which encodes a protein kinase, is not required for the phosphorylation of ABF1, a functional SSN6 gene is required for itsd ephosphorylation. The phosphorylation patterns that we have observed correlate with the regulation of a specific target gene, COX6, which encodes subunit VI of cytochrome c oxidase. Transcription of COX6 is repressed by growth in medium containing a fermentable carbon source and is derepressed by growth in medium containing a nonfermentable carbon source. COX6 repression-derepression is under the control of the SNF1-SSN6 pathway. This carbon source regulation is exerted through domain 1, a region of the upstream activation sequence UAS6 that binds ABF1 (J. D. Trawick, N. Kraut, F. Simon, and R. O. Poyton, Mol. Cell Biol. 12:2302-2314, 1992). We show that the greater the phosphorylation of ABF1, the greater the transcription of COX6. Furthermore, the ABF1-containing protein-DNA complexes formed at domain 1 differ according to the phosphorylation state of ABF1 and the carbon source on which the cells were grown. From these findings, we propose that the phosphorylation of ABF1 is involved in glucose repression-derepression of COX6 transcription.

Role of multifunctional autonomously replicating sequence binding factor 1 in the initiation of DNA replication and transcriptional control in Saccharomyces cerevisiae

Autonomously replicating sequence (ARS) binding factor 1 (ABF1) is an abundant DNA-binding protein that specifically recognizes the motif RTCRYN5ACG at many sites in the yeast genome, including promoter elements, mating-type silencers, and ARSs. Mutational analysis of these sites suggests that ABF1 is involved in constitutive and carbon source-regulated transcriptional activation, transcriptional silencing, and ARS activity. To better assess the role of ABF1 in DNA replication and transcriptional control, temperature-sensitive lethal mutations in the ABF1 gene were isolated. Several of the abf1(Ts) strains show rapid growth arrest at the nonpermissive temperature. At the semipermissive temperature, these strains show an ARS-specific defect in the mitotic stability of ARS-CEN plasmids, such that the abf1 mutants show defects in ARS function identical to those of mutants bearing the mutations in the cis-acting ABF1 binding sites analyzed previously by numerous investigators. Flow cytometric analysis and in vivo DNA labeling experiments on an alpha-factor synchronized abf1(Ts) strain showed that at the nonpermissive temperature, these cells fail to progress efficiently from G1 through S phase and synthesize DNA at 25% of the level seen in the isogenic ABF1 strain. RNA synthesis is also reduced in the abf1(Ts) strains. In addition, transcriptional activation by an ABF1 binding site upstream activation sequence is completely defective in an abf1(Ts) strain at the semipermissive temperature. These phenotypes provide evidence that the same protein, ABF1, functions in the initiation of DNA replication and transcriptional activation.