Upregulation of CD47, a “Do Not Eat Me” signal, is observed in nearly all solid and hematological malignancies. Engagement of CD47 on tumor cells with SIRPα on macrophages inhibits phagocytosis of tumor cells. Anti-CD47 antibodies block the CD47 - SIRPα engagement and reactivate phagocytosis of tumor cells by macrophages. Yet the ubiquitous expression of CD47 on normal cells, including red blood cells, presents a therapeutic challenge. Systemic targeting of CD47, by either anti-CD47 monoclonal antibodies or SIRPα-Fc fusion proteins, yielded only moderate clinical benefit due to severe adverse side effects, mainly anemia. QL401 is PD-L1 x CD47 bispecific antibody engineered to reduce binding to red blood cells while retaining potent phagocytic activation of macrophages in vitro and delayed tumor growth in vivo. QL401 comprises three functional components: a PD-L1 binding Fab arm, a CD47 binding scFv arm, and a human IgG4 backbone. The PD-L1 binding arm provides both tumor targeting and blocking of PD-1 for reactivating T cells. The CD47 arm blocks the binding of SIRPα, the “Do Not Eat Me” signal, while the IgG4 Fc retains Fc gamma receptor binding to provide a phagocytic “Eat Me” signal. Therefore, QL401 is multi-functional antibody that re-actives both the innate and adaptive immune response. In preclinical efficacy studies, QL401 potently blocked SIRPα to promote phagocytosis of tumor cells with sub-nanomolar potency. In vivo efficacy studies in mouse models of solid and hematological tumors showed QL401 to be comparable or superior to PD-L1 or CD47 monoclonal antibodies alone and in combination. In vitro safety evaluation of Q401 showed significantly reduced binding and phagocytosis of red blood cells, in contrast to CD47 monoclonal antibodies. In addition, Q401 did not induce hemagglutination. In non-human primates, QL401 was well tolerated up to 100 mg/kg without reduction of red blood cells below normal range. A phase 1 dose escalation and expansion study is expected to start Q1 2022 to evaluate the safety, tolerability, and early efficacy of QL401. Citation Format: Irene Tang, Lauren Schwimmer, Shenda Gu, Wei Wei Prior, Hieu V. Tran, Allan Chan, Anna McClain, Shihao Chen, Chuanzeng Cao, Chunyan Sun, Meimei Si, Guijiang Wang. QL401, a dual PD-L1/CD47 blocker effective against both solid and hematological malignancies with improved blood safety [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2894.

Cytokines are potent stimulators of the immune system and have long been investigated and used as therapeutics to treat cancer. However, free cytokines have short half-life and the lack of tumor targeting often results in systemic toxicity. IL-15 is a stimulatory cytokine that shares the common beta and gamma receptors with IL-2. In contrast to IL-2, IL-15 is more selective for NK and effector memory T cells, with less proliferative effect on Tregs, making it a more preferred therapeutic candidate for cancer. QL415 is an anti-PD-L1 x IL-15 fusion protein designed to enhance tumor accumulation and prolong blood circulation, thereby widening the therapeutic window. IL-15 and IL-15 receptor alpha sushi domain are covalently linked to the C-terminus of our proprietary PD-L1 antibody. Fc-mediated effector functions were ablated using mutations in the CH2 domain, to prevent depletion of effector immune cells. In vitro studies showed QL415 to be highly potent in promoting proliferation and pSTAT5 signaling of IL-15 -responding NK92 and M07e cells. QL415 selectively induced proliferation of NK and CD8+ T cells from human PBMC in vitro and mouse CD8+ and NK1.1 cells in vivo. In a MC38 mouse colon cancer model expressing human PD-L1, QL401 was highly effective in suppressing tumor growth, in contrast to PD-L1 monoclonal antibody or a non-targeted IL-15 control. Follow up tumor rechallenge study showed protective memory against cognate MC38 but not B16F10. In a separate MC38 tumor model using a mouse surrogate molecule of QL415, immunophenotyping of antigen presenting cells offered preliminary evidence of enrichment of conventional dendritic cells 1 in the tumor draining lymph nodes. Therefore, QL415 not only directly stimulates effector immune cells, but also indirectly through antigen presenting cells, promotes robust anti-tumor response. In non-human primates, Q415 was tolerated up to 1.5 mg/kg, well above the effective therapeutic dose. In light of these favorable preclinical efficacy and safety results, a phase 1 dose escalation and expansion study has been initiated to evaluate the safety, tolerability, and early efficacy of QL415. Citation Format: Irene Tang, Lauren Schwimmer, Monica Jin, Shenda Gu, Wei Wei Prior, Arianne Capacio, Hieu V. Tran, Allan Chan, Anna McClain, Shihao Chen, Chuanzeng Cao, Xiaoran Wu, Yanling Xu, Dongmei Guan, Xi Chen, Xianli Su. QL415, a tumor targeted IL-15 fusion protein stimulating both lymphoid and myeloid immune cells for optimal anti-tumor immune response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3504.

Cell surface molecules PD-L1 and CD47 are potent inhibitors of adaptive and innate anti-cancer immunity. We sought to generate a safe, therapeutic, bispecific antibody specifically targeting, and blocking both PD-L1 and CD47 inhibitory activity. Novel anti-PDL-1 and anti-CD47 antibodies with favorable inhibitory activity, were humanized and constructed into a unique bi-specific antibody intended for clinical use. Previous pre-clinical and clinical studies using anti-CD47 antibodies indicated anemia and thrombocytopenia as potential risks. QL401 is a PD-L1 x CD47 bispecific antibody engineered to reduce effect on red blood cells while retaining potent phagocytic activation of macrophages in vitro and delayed tumor growth in vivo. QL401 comprises three functional components: a PD-L1 binding Fab arm, a CD47 binding scFv arm, and a human IgG4 backbone. The PD-L1 binding arm provides both tumor targeting and blocking of PD-1 for reactivating T cells. The CD47 arm blocks the binding of SIRPα, while the IgG4 Fc retains Fc gamma receptor binding to provide a phagocytic signal. In preclinical efficacy studies, QL401 potently blocked SIRPα to promote phagocytosis of tumor cells with sub-nanomolar potency. In vivo efficacy studies in mouse xenograft tumor models showed QL401 to be comparable or superior to PD-L1 or CD47 monoclonal antibodies alone or in combination. In vitro safety evaluation of QL401 showed significantly reduced binding and phagocytosis of red blood cells, in contrast to CD47 monoclonal antibodies. In addition, QL401 did not induce hemagglutination. In non-human primates, QL401 was well tolerated up to 100 mg/kg without reduction of red blood cells or platelets below the normal range. QL401 is presently in a human phase I safety study.