Discovery of high affinity, pan-allelic, and pan-mammalian reactive antibodies against the myeloid checkpoint receptor SIRP?.

ABSTRACT: Targeting the CD47-signal-regulatory protein ? (SIRP?) pathway represents a novel therapeutic approach to enhance anti-cancer immunity by promoting both innate and adaptive immune responses. Unlike CD47, which is expressed ubiquitously, SIRP? expression is mainly restricted to myeloid cells and neurons. Therefore, compared to CD47-targeted therapies, targeting SIRP? may result in differential safety and efficacy profiles, potentially enabling lower effective doses and improved pharmacokinetics and pharmacodynamics. The development of effective SIRP? antagonists is restricted by polymorphisms within the CD47-binding domain of SIRP?, necessitating pan-allele reactive anti-SIRP? antibodies for therapeutic intervention in diverse patient populations. We immunized wild-type and human antibody transgenic chickens with a multi-allele and multi-species SIRP? regimen in order to discover pan-allelic and pan-mammalian reactive anti-SIRP? antibodies suitable for clinical translation. A total of 200 antibodies were isolated and screened for SIRP? reactivity from which approximately 70 antibodies with diverse SIRP? binding profiles, sequence families, and epitopes were selected for further characterization. A subset of anti-SIRP? antibodies bound to both human SIRP? v1 and v2 alleles with high affinity ranging from low nanomolar to picomolar, potently antagonized the CD47/SIRP? interaction, and potentiated macrophage-mediated antibody-dependent cellular phagocytosis in vitro. X-ray crystal structures of five anti-SIRP? antigen-binding fragments, each with unique epitopes, in complex with SIRP? (PDB codes 6NMV, 6NMU, 6NMT, 6NMS, and 6NMR) are reported. Furthermore, some of the anti-SIRP? antibodies cross-react with cynomolgus SIRP? and various mouse SIRP? alleles (BALB/c, NOD, BL/6), which can facilitate preclinical to clinical development. These properties provide an attractive rationale to advance the development of these anti-SIRP? antibodies as a novel therapy for advanced malignancies. Abbreviations: ADCC: antibody-dependent cellular cytotoxicity; ADCP: antibody-dependent cellular phagocytosis; CFSE: carboxyfluorescein succinimidyl ester; Fab: fragment antigen binding; Fc: fragment crystallizable; Fc?R: Fc? receptor; Ig: immunoglobulin; IND: investigational new drug; MDM?: monocyte-derived macrophage; NOD: non-obese diabetic; scFv: single chain fragment variable; SCID: severe combined immunodeficiency; SIRP: signal-regulatory protein.

SUBMITTER: Sim J 

PROVIDER: S-EPMC6748616 | biostudies-literature | 2019 Aug/Sep

REPOSITORIES: biostudies-literature