Background: FcRn controls the serum persistence of antibodies. Results: A panel of novel Fc mutations reveals sites controlling pH dependence and FcRn affinity. Conclusion: FcRn affinity thresholds determine IgG recycling efficiency. Significance: Knowledge of the relationship between FcRn binding and serum persistence can aid in designing better therapeutic antibodies.

The clinical benefit of PD-1 blockade can be improved by combination with CTLA4 inhibition but is commensurate with significant immune-related adverse events suboptimally limiting the doses of anti-CTLA4 mAb that can be used. MEDI5752 is a monovalent bispecific antibody designed to suppress the PD-1 pathway and provide modulated CTLA4 inhibition favoring enhanced blockade on PD-1+ activated T cells. We show that MEDI5752 preferentially saturates CTLA4 on PD-1+ T cells versus PD-1− T cells, reducing the dose required to elicit IL2 secretion. Unlike conventional PD-1/CTLA4 mAbs, MEDI5752 leads to the rapid internalization and degradation of PD-1. Moreover, we show that MEDI5752 preferentially localizes and accumulates in tumors providing enhanced activity when compared with a combination of mAbs targeting PD-1 and CTLA4 in vivo. Following treatment with MEDI5752, robust partial responses were observed in two patients with advanced solid tumors. MEDI5752 represents a novel immunotherapy engineered to preferentially inhibit CTLA4 on PD-1+ T cells. Significance: The unique characteristics of MEDI5752 represent a novel immunotherapy engineered to direct CTLA4 inhibition to PD-1+ T cells with the potential for differentiated activity when compared with current conventional mAb combination strategies targeting PD-1 and CTLA4. This molecule therefore represents a step forward in the rational design of cancer immunotherapy. See related commentary by Burton and Tawbi, p. 1008. This article is highlighted in the In This Issue feature, p. 995

Bispecific antibody (bsAb) applications have exponentially expanded with the advent of molecular engineering strategies that have addressed many of the initial challenges, including improper light chain pairing, heterodimer purity, aggregation, and pharmacokinetics. However, the lack of high-throughput methods for the generation of monovalent bsAbs has resulted in a bottleneck that has hampered their therapeutic evaluation, as current technologies can be cost-prohibitive and impractical. To address this issue, we incorporated single-matched point mutations in the CH3 domain to recapitulate the physiological process of human IgG4 Fab-arm exchange to generate monovalent bsAbs. Furthermore, we utilized the substitutions H435R and Y436F in the CH3 domain of IgG1, which incorporates residues from human IgG3, thus ablating protein A binding. By exploiting this combination of mutations and optimizing the reduction and reoxidation conditions for Fab arm exchange, highly pure monovalent bsAbs can be rapidly purified directly from combined culture media using standard protein A purification. This methodology, reported herein for the first time, allows for the high-throughput generation of monovalent bsAbs, thus increasing the capacity for evaluating monovalent bsAb iterations for therapeutic potential.

Studies have demonstrated that the clinical benefit of PD-1 blockade can be further improved by combination with an αCTLA-4 mAb in some indications. However, this increased activity is commensurate with significant immune related adverse events (irAE's). Therefore, novel approaches are required to uncouple toxicity from anti-tumour efficacy and realise the full potential of this combination. MEDI5752 is a monovalent bispecific human IgG1 monoclonal antibody (mAb) with an engineered fragment crystallisable (Fc) domain to reduce Fc effector function, that specifically binds two clinically validated negative T cell regulators; PD-1 (programmed cell death 1) and CTLA-4 (cytotoxic T-lymphocyte-associated protein 4). MEDI5752 has been designed to suppress the PD-1 pathway and provide modulated CTLA-4 inhibition to uncouple CTLA-4 dependent peripheral toxicity from tumour efficacy. PD-1 expression is a defining feature of tumour infiltrating lymphocytes (TILs). We show that MEDI5752 can saturate CTLA-4 on PD-1+ cells at orders of magnitude lower concentrations than required to saturate CTLA-4 on PD-1- cells. Moreover, our data demonstrate that monovalent targeting of CTLA-4 with MEDI5752 is significantly less potent (15 fold) than bivalent targeting with a parental αCTLA-4 mAb in reporter assays. In contrast, the switch to monovalent targeting of PD-1 has limited effect on potency (within 3-fold compared to a parental αPD-1 mAb) in a PD-1/L1 reporter assay. Together these data demonstrate the potential for MEDI5752 to inhibit CTLA-4 on TILs whilst sparing peripheral T cell populations and reducing toxicity. Furthermore, profiling of MEDI5752 in a range of primary T cell activation assays reveals equivalent activity to a combination of parental PD-1 and CTLA-4 antibodies. MEDI5752 is rapidly internalised upon target binding with kinetics similar to the parental αCTLA-4 mAb reflecting the rapid recycling of this receptor. However, in contrast to an αCTLA-4 mAb (or an αPD-1 mAb), MEDI5752, by tethering CTLA-4 to PD-1, leads to the internalisation and subsequent degradation of PD-1. This novel mechanism of action further differentiates MEDI5752 from a combination of mAb's targeting PD-1 and CTLA-4. MEDI5752 is a novel monovalent bispecific which may provide an improved therapeutic index when compared to a combination of bivalent αPD-1 and αCTLA-4 mAb's, and could provide benefit in cancer indications. Citation Format: Simon J. Dovedi, Yariv Mazor, Matthew Elder, Sumati Hasani, Bo Wang, Suzanne Mosely, Desmond Jones, Anna Hansen, Chuning Yang, Yanli Wu, Ikbel Achour, Nick Durham, Gareth Browne, Thomas Murray, James Hair, Michelle Morrow, Godfrey Rainey, Maria Jure Kunkel, John Gooya, Daniel Freeman, Ronald Herbst, Robert Wilkinson. MEDI5752: A novel bispecific antibody that preferentially targets CTLA-4 on PD-1 expressing T-cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2776.

Avian beta-defensin 9 (AvBD9) is a small cationic peptide consisting of 41 amino acids that plays a crucial rule in innate immunity and acquired immunity in chickens. Owing to its wide antibacterial spectrum, lack of a residue, and failure to induce bacterial drug resistance, AvBD9 is expected to become a substitute for conventional antibiotics in the livestock and poultry industries. Using the preferred codon of Pichia pastoris, the mature AvBD9 peptide was designed and synthesized, based on the sequence from GenBank. The P. pastoris constitutive expression vector pGHKα was used to construct a pGHKα-AvBD9 recombinant plasmid. Restriction enzyme digestion was performed using SacI and BglII to remove the ampicillin resistance gene, and the plasmid was electrotransformed into P. pastoris GS115. High-expression strains with G418 resistance were screened, and the culture supernatant was analyzed by Tricine-SDS-PAGE and western blot assay to identify target bands of about 6 kDa. A concentrate of the supernatant containing AvBD9 was used for determination of antimicrobial activity. The supernatant concentrate was effective against Escherichia coli, Salmonella paratyphi, Salmonella pullorum, Pseudomonas aeruginosa, Enterococcus faecalis, and Enterobacter cloacae. The fermentation product of P. pastoris carrying the recombinant AvBD9 plasmid was adjusted to 1.0 × 10(8) CFU/ml and added to the drinking water of white feather broilers at different concentrations. The daily average weight gain and immune organ indices in broilers older than 7 days were significantly improved by the AvBD9 treatment.