Author: Harrabi, Ons ; Doyle, Laura V ; Fu, Yang-Xin ; Pons, Jaume ; Chen, Amy ; Han, Bora ; Sangalang, Emma ; Sockolosky, Jonathan T ; Bollini, Sangeetha ; Zhang, Anli ; Kauder, Steven E ; Kuo, Tracy C ; Wan, Hong I ; Fontaine, Danielle ; Sim, Janet

AbstractBackgroundSignal regulatory protein α (SIRPα) is a myeloid-lineage inhibitory receptor that restricts innate immunity through engagement of its cell surface ligand CD47. Blockade of the CD47–SIRPα interaction synergizes with tumor-specific antibodies and T-cell checkpoint inhibitors by promoting myeloid-mediated antitumor functions leading to the induction of adaptive immunity. Inhibition of the CD47–SIRPα interaction has focused predominantly on targeting CD47, which is expressed ubiquitously and contributes to the accelerated blood clearance of anti-CD47 therapeutics. Targeting SIRPα, which is myeloid-restricted, may provide a differential pharmacokinetic, safety, and efficacy profile; however, SIRPα polymorphisms and lack of pan-allelic and species cross-reactive agents have limited the clinical translation of antibodies against SIRPα. Here, we report the development of humanized AB21 (hAB21), a pan-allelic anti-SIRPα antibody that binds human, cynomolgus monkey, and mouse SIRPα alleles with high affinity and blocks the interaction with CD47.MethodsHuman macrophages derived from donors with various SIRPα v1 and v2 allelic status were used to assess the ability of hAB21 to enhance phagocytosis. HAB21_IgG subclasses were evaluated for targeted depletion of peripheral blood mononuclear cells, phagocytosis and in vivo efficacy in xenograft models. Combination therapy with anti-PD1/anti-PD-L1 in several syngeneic models was performed. Immunophenotyping of tissues from MC38 tumor-bearing mice treated with AB21 and anti-PD-1 was evaluated. PK, PD and tolerability of hAB21 were evaluated in cynomolgus monkeys.ResultsSIRPα blockade with hAB21 promoted macrophage-mediated antibody-dependent phagocytosis of tumor cells in vitro and improved responses to rituximab in the Raji human tumor xenograft mouse model. Combined with PD-1/PD-L1 blockade, AB21 improved response rates by facilitating monocyte activation, dendritic cell activation, and T cell effector functions resulting in long term, durable antitumor immunity. In cynomolgus monkeys, hAB21 has a half-life of 5.3 days at 10 mg/kg and complete target occupancy with no hematological toxicity or adverse findings at doses up to 30 mg/kg.ConclusionsThe in vitro and in vivo antitumor activity of hAB21 broadly recapitulates that of CD47 targeted therapies despite differences in ligand expression, binding partners, and function, validating the CD47–SIRPα axis as a fundamental myeloid checkpoint pathway and its blockade as promising therapeutic intervention for treatment of human malignancies.

01 Jun 2014·Antiviral ResearchQ2 · MEDICINE

A novel neutralizing antibody against diverse clades of H5N1 influenza virus and its mutants capable of airborne transmission

Q2 · MEDICINE

Article

Author: Cao, Zhiliang ; Wu, Ruiping ; He, Yuxian ; Qiu, Zonglin ; Zheng, Bo-Jian ; Leung, Ho-Chuen ; Li, Xingxing ; Zhou, Yusen

Highly pathogenic avian influenza A virus H5N1 continues to spread among poultry and has frequently broken the species barrier to humans. Recent studies have shown that a laboratory-mutated or reassortant H5N1 virus bearing hemagglutinin (HA) with as few as four or five mutations was capable of transmitting more efficiently via respiratory droplets between ferrets, posing a serious threat to public health and underscoring the priority of effective vaccines and therapeutics. In this study, we identified a novel monoclonal antibody (mAb) named HAb21, that has a broadly neutralizing activity against all tested strains of H5N1 covering clades 0, 1, 2.2, 2.3.4, and 2.3.2.1. Importantly, HAb21 efficiently neutralized diverse H5N1 variants with single or combination forms of mutations capable of airborne transmission. We demonstrated that HAb21 blocked viral entry during the receptor-binding step by targeting a previously uncharacterized epitope at the tip of the HA head. This novel epitope closely neighbors the receptor-binding site (RBS) and the interface of HA trimer and is highly conserved among divergent H5N1 strains. Our studies provide a new tool for use either for therapeutic purposes or as a basis of vaccine development.

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Neoplasms	Preclinical	US	ALX Oncology, Inc.	30 Nov 2020

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