Sym021, a promising anti-PD1 clinical candidate antibody derived from a new chicken antibody discovery platform

Abstract

Discovery of therapeutic antibodies is a field of intense development, where immunization of rodents remains a major source of antibody candidates. However, high orthologue protein sequence homology between human and rodent species disfavors generation of antibodies against functionally conserved binding epitopes. Chickens are phylogenetically distant from mammals. Since chickens generate antibodies from a restricted set of germline genes, the possibility of adapting the Symplex antibody discovery platform to chicken immunoglobulin genes and combining it with high-throughput humanization of antibody frameworks by "mass complementarity-determining region grafting" was explored. Hence, wild type chickens were immunized with an immune checkpoint inhibitor programmed cell death 1 (PD1) antigen, and a repertoire of 144 antibodies was generated. The PD1 antibody repertoire was successfully humanized, and we found that most humanized antibodies retained affinity largely similar to that of the parental chicken antibodies. The lead antibody Sym021 blocked PD-L1 and PD-L2 ligand binding, resulting in elevated T-cell cytokine production in vitro. Detailed epitope mapping showed that the epitope recognized by Sym021 was unique compared to the clinically approved PD1 antibodies pembrolizumab and nivolumab. Moreover, Sym021 bound human PD1 with a stronger affinity (30 pM) compared to nivolumab and pembrolizumab, while also cross-reacting with cynomolgus and mouse PD1. This enabled direct testing of Sym021 in the syngeneic mouse in vivo cancer models and evaluation of preclinical toxicology in cynomolgus monkeys. Preclinical in vivo evaluation in various murine and human tumor models demonstrated a pronounced anti-tumor effect of Sym021, supporting its current evaluation in a Phase 1 clinical trial.

Landscape of Non-canonical Cysteines in Human VH Repertoire Revealed by Immunogenetic Analysis

“…Although comparatively rare in humans, the presence of high cysteine numbers and motifs in CDR-H3s, as consistently observed in multiple individuals, is reminiscent of that found in chicken, camel, llama, shark, and cow. Knowledge of noncanonical cysteines and better understanding of their roles in creating genetic diversity and distinct paratope surfaces of these non-human species have led to the development of several promising antibody-discovery platform technologies (Feng et al, 2019;Gjetting et al, 2019;Kö nitzer et al, 2017;Muyldermans, 2013;Muyldermans and Smider, 2016). In contrast, for human, it was generally held that such genetic and structural diversity did not exist.…”

Assessing the binding properties of the anti-PD-1 antibody landscape using label-free biosensors

“…[16,17] In contrast, a recent publication reported the affinity for pembro to human PD-1 at 3.4 nM. [18] Discrepancies like this populate the biosensor literature, and make it difficult to compare published data, especially data where sensorgrams with fits are not shown. Since samples based on these and other INN-registered mAbs are often used as positive controls, we used these studies as an opportunity to thoroughly characterize their binding properties.…”

In vitro Interactions of Chicken Programmed Cell Death 1 (PD-1) and PD-1 Ligand-1 (PD-L1)

“…The PD-1 and PD-L1 sequence homologies were lower in chPD-1 and chPD-L1 sequences compared with those of the mammalian species (Jeon et al, 2007;Gjetting et al, 2019). The conservation of the ITIM and ITSM motifs in the C-terminal, and highly conserved TEYATIVF indicated that the immune signal regulation associated with PD-1 is highly conserved among species (Okazaki et al, 2001).…”