IgE antibodies are key mediators of antiparasitic immune responses, but their potential for cancer treatment via antibodydependent cell-mediated cytotoxicity (ADCC) has been little studied. Recently, tumor antigen-specific IgEs were reported to restrict cancer cell growth by engaging high-affinity Fc receptors on monocytes and macrophages; however, the underlying therapeutic mechanisms were undefined and in vivo proof of concept was limited. Here, an immunocompetent rat model was designed to recapitulate the human IgE-Fce receptor system for cancer studies. We also generated rat IgE and IgG mAbs specific for the folate receptor (FRa), which is expressed widely on human ovarian tumors, along with a syngeneic rat tumor model expressing human FRa. Compared with IgG, anti-FRa IgE reduced lung metastases. This effect was associated with increased intratumoral infiltration by TNFa þ and CD80

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Our findings indicate safety of MOv18 IgE, in conjunction with efficacy and immune activation, supporting the translation of this therapeutic approach to the clinical arena.

Background: All antibodies approved for the treatment of cancer are monoclonal IgGs, and no IgE therapy has yet been tested in humans. The biology of IgE, compared with IgG, offers potential for enhanced immune surveillance and superior effector cell potency against tumor cells. IgE antibodies in preclinical cancer models are not associated with allergic toxicity even in immunocompetent animals, and in vivo efficacy compares favorably with equivalent IgGs. Methods: We conducted a first-in-human first-in-class trial of MOv18, a chimeric monoclonal IgE, in patients with solid tumors expressing folate receptor-alpha, the antigen recognized by this antibody. Antigen expression was deemed positive in the presence of >5% membrane staining of any intensity using the mouse clone BN3.2. Intravenous treatment was administered weekly for 6 weeks, then two-weekly. The trial incorporated pre-treatment skin prick testing with MOv18 IgE, and an ex vivo basophil activation test (BAT) using patient whole blood, with the aim of predicting systemic allergic toxicity and excluding patients at potential risk. Safety, efficacy, markers of immune response, and pharmacokinetics have been evaluated in 24 patients to date, at total doses ranging from 0.07 to 3.0mg. Results: Treatment was well tolerated in almost all patients. The most common toxicity was readily manageable urticaria, without systemic symptoms, signs or tryptase elevation. One patient treated at the 0.5mg dose experienced anaphylaxis, with tryptase elevation, despite a negative pre-dose skin prick test. This was the only patient in the trial with baseline circulating basophils that could be activated by ex vivo exposure to MOv18 IgE. This BAT assay was subsequently used to ensure no further patient with reactive basophils was exposed. Maximum tolerated dose has not yet been reached. Dose-dependent increases in Cmax were observed, and plasma concentrations of 70-100ng/mL achieved at the 1.5mg dose are comparable to typical levels of endogenous IgE. No consistent anti-drug antibody response has been detected. Preliminary evidence of anti-tumor activity was seen in a patient with ovarian cancer at a total MOv18 IgE dose of 0.7mg. Shrinkage of peritoneal metastases was accompanied by a tumor marker reduction meeting Gynecologic Cancer InterGroup criteria for response. Conclusions: These results support for the first time the safety of IgE as a treatment for cancer, and provide preliminary evidence for anti-tumor efficacy of this new therapeutic class. The mechanism of cutaneous toxicity is being investigated. Clinical testing of class-switched IgE versions of approved IgG-based therapeutic antibodies is warranted. Citation Format: James Spicer, Bristi Basu, Ana Montes, Udai Banerji, Rebecca Kristeleit, Gareth J. Veal, Christopher Corrigan, Stephen Till, George Nintos, Timothy Brier, Ionut G. Funingana, Joo Ern Ang, Kam Zaki, Annie Griffin, Claire Barton, Paul Jones, Sarah Mellor, Susan Brook, Katie Stoddart, Christopher Selkirk, Simon Carroll, Heike Lentfer, Natalie Woodman, Amy Pope, Giulia Pellizzari, Mano Nakamura, Kristina M. Ilieva, Atousa Khiabany, Chara Stavraka, Hannah Gould, Jitesh Chauhan, Heather Bax, Sarah Pinder, Debra Josephs, Sophia Karagiannis. Phase 1 trial of MOv18, a first-in-class IgE antibody therapy for cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT141.

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