Abstract 1874: Preclinical characterization of MBS307, a CD40/PD-L1 trispecific antibody with increased therapeutic window and efficacy
Authors: Li Feng , Li Jiangmei , Zhou Xuechen , Lin Guangzhong , Hu Wenqi , Liu Huifang 
Published: April 2023

Abstract
Immunotherapies that target PD1/PDL1 pathway have relatively low response rate in “cold tumor”, combined with suitable immune co-stimulatory signal could be a potentially powerful approach for activation of the immune response to suppress tumors. However, the clinical application of stimulatory immune checkpoints has been substantially restricted due to their toxicities. MBS307 is a novel first in class PD-L1/PD-L1/CD40 tri-specific antibody that can promote CD40 agonist signaling in a PD-L1 dependent manner and simultaneously block PD-1/PD-L1 interaction. We developed eight multi-specific antibody formats to analyze its structure-activity relationship, and selected an optimal format of CD40/PD-L1 multi-specific antibody contains bivalent anti-CD40 binding one unique epitope and two distal anti-PD-L1 binding to distinct uncompetitive epitopes. These two uncompetitive PD-L1 binding epitopes can: i) reduce the dissociation rate of MBS307 from PD-L1 positive cells ; ii) enhance PD-L1/PD-1 blockade efficacy; iii) offer a super cross-linking effect for CD40 agonist signaling. This format advantage allows MBS307 to be enriched in PD-L1 positive tumor tissue with conditionally activation of CD40+ cells in tumor microenvironment. We also conducted Fc engineering to abolish the interaction of Fc and FcRs, including FcRIIb, to avoid agonist associated liver toxicity. Our in vitro study indicated that, CD40 mAB has significant effect on macrophage, such as decreasing CD24 antibody induced ADCP efficacy and increasing TNF-α secretion. However, MBS307 has almost none effect on macrophage. Meanwhile, MBS307 has agonist activity to DCs. We suspected that this different immunocyte activation pattern may relate with the different expression level of PD-L1 on macrophages and DCs. Co-incubation DCs with PD-L1 positive cancer cells can significantly enhance MBS307 agonist activity to DCs, indicating its predominant activity in PD-L1 positive tumor microenvironment. In vivo study results show that MBS307 demonstrate the most superior anti-tumor efficacy compared to single or combination mAbs against MC38-hPD-L1 tumors in PD-L1/PD1/CD40 triple humanized mice (B-hPD-L1/hPD1/hCD40). Furthermore, unlike single CD40 mAB treatment at 10 mg/kg, MBS307 at high dose 15 mg/kg did not elevate liver enzymes and decrease mouse body weight, indicating its improved safety profile. In summary, our data show MBS307 is a functional base designed tri-specific antibody with promising anti-tumor efficacy and safety profile by simultaneously blocking PD-1 and stimulating CD40 pathways.
Citation Format: Feng Li, Jiangmei Li, Xuechen Zhou, Guangzhong Lin, Wenqi Hu, Huifang Liu. Preclinical characterization of MBS307, a CD40/PD-L1 trispecific antibody with increased therapeutic window and efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1874.