Disruption of CD47-SIRPα signaling restores inflammatory function in tumor-associated myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous immune population with diverse immunosuppressive functions in solid tumors. Here, we explored the role of the tumor microenvironment in regulating MDSC differentiation and immunosuppressive properties via signal-regulatory protein alpha (SIRPα)/CD47 signaling. In a murine melanoma model, we observed progressive increases in monocytic MDSCs and monocyte-derived dendritic cells that exhibited potent T cell-suppressive capabilities. These adaptations could be recapitulated in vitro by exposing hematopoietic stem cells to tumor-derived factors. Engagement of CD47 with SIRPα on myeloid cells reduced their phagocytic capability, enhanced expression of immune checkpoints, increased reactive oxygen species production, and suppressed T cell proliferation. Perturbation of SIRPα signaling restored phagocytosis and antigen presentation by MDSCs, which was accompanied by renewed T cell activity and delayed tumor growth in multiple solid cancers. These data highlight that therapeutically targeting myeloid functions in combination with immune checkpoint inhibitors could enhance anti-tumor immunity.

Generation of Fcabs targeting human and murine LAG-3 as building blocks for novel bispecific antibody therapeutics

The immunoglobulin superfamily protein lymphocyte-activation gene 3 (LAG-3) participates in immune suppression and has been identified as a suitable target for cancer therapies. In order to generate bispecific antibodies targeting LAG-3, Fcabs (Fc-region with antigen binding) targeting human and murine LAG-3 were generated from phage libraries. These Fcabs bind to LAG-3, inhibiting its interaction with MHC class II, and induce IL-2 production in a T cell assay. Bispecific antibodies, known as mAb², were produced by replacing the Fc region of a monoclonal antibody with Fcab sequences in the CH3 domain. mAb² containing anti-LAG-3 Fcabs have mAb-like biophysical characteristics and retain LAG-3 binding and functional activity. mAb² can thus be generated using multiple Fabs to investigate bispecific parings and develop novel therapeutics.

Abstract 2719: Dual blockade of PD-L1 and LAG-3 with FS118, a unique bispecific antibody, induces CD8+ T-cell activation and modulates the tumor microenvironment to promote antitumor immune responses

Background

Despite advances with therapies targeting the PD-1/PD-L1 pathway, many patients are refractory or relapse following treatment. LAG-3 expression on exhausted T cells and T-regulatory cells (Tregs) in the tumor may be responsible for this resistance and provides a rationale for co-treatment with antibodies targeting LAG-3 and PD-L1. An alternative approach is the development of a bispecific antibody encompassing binding sites for two antigens. FS118 is a bispecific antibody targeting LAG-3 and PD-L1 that provides dual pathway blockade with the potential to drive unique biology via co-binding of PD-L1 and LAG-3.

Methods

FS118 was evaluated in vitro for antigen binding and de-repression of LAG-3 and PD-L1 function in both a D011.10 T-cell activation system and a super-antigen stimulated peripheral blood mononuclear cells (PBMC) assay. FS118 was also assessed in a human CD8 specific MHC I restricted antigen recall assay. Anti-tumor activity of a murine-specific molecule, mLAG-3/PD-L1 mAb2, was evaluated in vivo in the MC38 mouse tumor model and associated immunophenotypic changes were evaluated using flow cytometry.

Results

In murine in vitro assay systems, mLAG3/PD-L1 mAb2 recapitulates the function of FS118 in human systems. Furthermore, FS118 was shown to provide increased activation of human CD8+ T-cells compared to a PD-L1 mAb alone in response to stimulation with MHC Class I restricted peptides. In vivo, studies performed in MC38 tumor-bearing mice studies indicated that mLAG-3/PD-L1 could result in significant anti-tumor activity equivalent to a combination of antibodies targeting LAG-3 and PD-L1. Pharmacodynamic assessment demonstrated changes in the immunophenotype of tumor-infiltrating lymphocytes in the tumor of mLAG3/PD-L1 mAb2 treated mice. These changes were observed in cohorts which received the anti-mouse LAG-3/PD-L1 mAb2 and revealed a both a loss of LAG-3 surface expression on CD4+ and CD8+ T cells, as well as an increase in the CD8:Treg ratio.

Conclusions

Dual blockade of LAG-3 and PD-L1 with a bispecific antibody results in T-cell activation at least comparable to a combination of antibodies targeting LAG-3 and PD-L1 in primary T-cell assays and murine tumor models. Taken together, the human PBMC based assays and mouse tumor model data demonstrate that a LAG-3/PD-L1 mAb2 can not only potently suppress the checkpoint inhibitor LAG-3 at the tumor site, but does this in part through stimulating a CD8+ T cell mediated response. These data provide evidence to support the rationale for clinical development of FS118, a LAG-3/PD-L1 mAb2, for the treatment of human cancers.

Citation Format: Matthew Kraman, Natalie Fosh, Katarzyna Kmiecik, Katy Everett, Carlo Zimarino, Mustapha Faroudi, Mateusz Wydro, Alexander Koers, Lesley Young, Daniel Gliddon, Michelle Morrow, Jacqueline Doody, Mihriban Tuna, Neil Brewis. Dual blockade of PD-L1 and LAG-3 with FS118, a unique bispecific antibody, induces CD8+ T-cell activation and modulates the tumor microenvironment to promote antitumor immune responses [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 2719.

Abstract 5651: A LAG-3/PD-L1 bispecific antibody inhibits tumor growth in two syngeneic colon carcinoma models

Combining immunotherapeutic antibodies in cancer treatment has shown benefits over single agents. An alternative to combining two antibodies is the development of bispecific antibodies that not only bring two biologies together but may result in novel mechanisms of action that are impossible to attain with combinations. Lymphocyte Activation Gene-3 (LAG-3) is a member of the Ig superfamily expressed on activated T cells, NK cells, pDCs, B cells, γδ T cells and participates in immune suppression. Programmed Cell Death receptor (PD-1) binds to its ligand PD-L1, expressed not only on activated immune cells to inhibit cellular immune responses but also on tumor cells. Expression of both these surface molecules therefore leads to T cell exhaustion allowing the tumor to escape immune surveillance. A mAb² TM (bispecific antibody) was engineered which binds murine LAG-3 and PD-L1 simultaneously and with nanomolar affinities. The anti-LAG-3/PD-L1 mAb² inhibits LAG-3 binding to MHCII and PD-L1 binding to PD-1 and CD80, resulting in T cell activation in vitro. This translates into in vivo efficacy, where the mAb² decreased tumor burden in the MC38 colon carcinoma tumor model. At the end of the study tumor-free animals were more numerous in the LAG-3/PD-L1 bispecific group than in the group given a combination of individual anti-LAG-3 and PD-L1 antibodies. The results were recapitulated in the CT26 murine colon cancer model, where the mAb² showed an increase of antitumor activity as compared to the antibodies given in combination. Thus, the preclinical data supports developing an anti-human LAG-3/PD-L1 mAb² for the treatment of cancer patients.

Citation Format: Matthew Kraman, Katarzyna Kmiecik, Carlo Zimarino, Katy Everett, Mustapha Faroudi, Mateusz Wydro, Jacqueline Doody. A LAG-3/PD-L1 bispecific antibody inhibits tumor growth in two syngeneic colon carcinoma models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5651. doi:10.1158/1538-7445.AM2017-5651

Abstract PR06: A LAG-3/PD-L1 bispecific antibody inhibits tumour growth in two syngeneic colon carcinoma models

Combining immunotherapeutic antibodies for treatment of cancer patients has shown benefits over single agent treatment. For example, the addition of anti-PD-1 antibodies to anti-CTLA-4 treatment in advanced melanoma patients has increased objective response rates from 19% to 57.6% (Larkin,J et al. 2015. NEJM 373:23-34). An alternative to combining two antibodies is the development of bispecific antibodies that not only bring two biologies together but may result in novel mechanisms of action that are impossible to attain with combinations.

Lymphocyte Activation Gene-3 (LAG-3) is a member of the Ig superfamily expressed on activated T cells, NK cells, pDCs, B cells, γδ T cells and participates in immune suppression, particularly through persistent strong expression in a percentage of regulatory T cells (Tregs). Programmed Cell Death receptor (PD-1) binds to its ligand PD-L1, expressed not only on activated immune cells to inhibit cellular immune responses but also on tumour cells. Expression of LAG-3 and PD-1 leads to T cell exhaustion, allowing tumour escape from immune surveillance. Combining inhibitory antibodies to PD-1 and LAG-3 reactivates T cells leading to efficacy in murine models over single treatment (Woo,S-R et al. 2012. Cancer Res. 15: 917-27) which prompted interest in the development of a LAG-3 and PD-L1 bispecific antibody for inhibiting tumour growth.

A murine-specific anti-LAG-3 and PD-L1 mAb²TM (bispecific antibody) was engineered which binds both antigens simultaneously and with nanomolar affinities. The anti-LAG-3/PD-L1 mAb² inhibits LAG-3 binding to MHCII and PD-L1 binding to PD-1 and CD80, resulting in T cell activation in an in vitro assay. This potency translates into in vivo efficacy, where the anti-LAG-3/PD-L1 mAb² decreased tumour burden in the MC38 colon carcinoma tumour model, both in early-established or well-established tumours. At the end of the study tumour-free animals were more numerous in the LAG-3/PD-L1 bispecific group than in the group given a combination of individual anti-LAG-3 and PD-L1 antibodies. The results were recapitulated in the CT26 murine colon cancer model, where the LAG-3/PD-L1 mAb² showed an increase of anti-tumour activity as compared to the combination of anti-LAG-3 and anti-PD-L1 antibodies. Thus, the preclinical data supports developing an anti-human LAG-3/PD-L1 mAb² for the treatment of cancer patients.

This abstract is also being presented as Poster A27.

Citation Format: Katy Everett, Matthew Kraman, Katarzyna Kmiecik, Natalie Allen, Mustapha Faroudi, Carlo Zimarino, Mateusz Wydro, Jacqueline Doody. A LAG-3/PD-L1 bispecific antibody inhibits tumour growth in two syngeneic colon carcinoma models. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr PR06.