Hirdler, Jake

Abstract Description Therapies targeting the PD-1/PD-L1 axis are among the leading treatments of cancer, but only a minority of patients benefit. Many therapies focus on preventing PD-L1 from binding to its receptor, PD-1, but do not address PD-L1’s ability to be recycled to the cell surface and any intrinsic functions it may possess. Our lab has developed an antibody (H1A) that binds to PD-L1 and prevents its association with a stabilizing protein, CMTM6, therefore targeting it for lysosomal degradation. Consequently, H1A limits any PD-L1 intrinsic function while also decreasing interactions with PD-1. Here, we use human-derived immune cells to test H1A’s effect on immune responses through flow cytometry, multiplex screening, and cytotoxicity assays. Additionally, we have developed a humanized PD-1/PD-L1 mouse model that allows us to test H1A’s effect on tumor growth inhibition in an immunocompetent host. Our results show that H1A specifically targets human myeloid cells, resulting in increased co-stimulation, antigen presentation, and cytokine secretion. H1A demonstrated enhanced T cell cytotoxicity in a whole PBMC culture. Finally, H1A resulted in greater tumor growth inhibition and survival in our in vivo tumor models. This work highlights the importance of targeting beyond PD-1/PD-L1 ligation and that myeloid cells are instrumental to enhancing the immune response against cancer. H1A is emerging as a new immunotherapy tool to target PD-L1 and CMTM6 in myeloid cells for treatment of cancers. Funding Sources NIH R01 92389022; NIH T32 AI170478; Mayo Clinic Graduate School of Biomedical Sciences Topic Categories Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)

Abstract Background: Although targeting myeloid cells has become one of the next generation targets for cancer immunotherapy, there is a lack of therapeutic tools to specifically target these cells. Our group has developed a novel humanized PD-L1-targeting antibody, H1A, that induces PD-L1 degradation via blockade of PD-L1 and CMTM6, therefore limiting PD-L1 intrinsic signaling while also preventing interactions with PD-1. In the immune cell compartment, CMTM6 expression is restricted to myeloid cells, making these cells the primary target of H1A. Recently, we unexpectedly found that targeting intrinsic PD-L1 in myeloid cells via H1A resulted in increased release of CCL2 from myeloid cells. In this study, we examined the role of CCL2/CCR2 signaling in CD8 T cell function using human peripheral blood-derived immune cells and evaluated the therapeutic potential of H1A antibody using our humanized PD-L1/PD-1 mouse model. Methods: Human PBMCs derived from healthy donors were treated with H1A or Atezolizumab, a blocking PD-L1 antibody, followed by mass cytometry and flow cytometry to evaluate immune cell phenotype and functional states. PD-L1 expressing myeloid cells isolated from human PBMCs were treated with H1A or Atezolizumab and assessed for CCL2 secretion using multiplex immunoassays. CCL2 production and transcription were confirmed by flow cytometry and single-cell RNA-sequencing. CCR2 blockade was used on human PBMCs to evaluate the effects of CCL2/CCR2 signaling on T cell function alongside H1A treatment. Finally, in vivo antitumor activity of H1A and Atezolizumab were compared in two humanized PD-L1 tumor models. Results: H1A reduced the frequency of regulatory T cells and increased effector T cells, in whole PBMCs upon global T cell activation with anti-CD3/CD28. H1A enhanced the secretion and production of CCL2 from myeloid cells, which was confirmed at a transcript level. CCR2 blockade diminished CD8 T cells’ ability to differentiate into effector cells in H1A treated PBMCs. H1A demonstrated comparable therapeutic effects with Atezolizumab in treatment of immunogenic and ICI-responsive mouse tumor MC38, which is CD8 T cell-dependent, but showed superior therapeutic effects in treatment of ICI-insensitive mouse tumor E0771 compared to Atezolizumab. Both treatments elicited durable memory specific immune responses upon E0771 tumor rechallenge. Conclusion: H1A demonstrated a superior antitumor activity compared to Atezolizumab in our preclinical models via a new mechanism by which H1A caused degradation of intrinsic PD-L1 in myeloid cells. This causes more release of CCL2 to improve T cell function via CCR2 upon T cell activation. Thus, H1A is emerging as a new immunotherapy tool to target PD-L1/CMTM6 in myeloid cells for treatment of cancers that are refractory to current immune checkpoint inhibitor therapy. Citation Format: Michelle Alexandria Hsu, Xin Liu, Ying Li, Whitney Barham, Kevin Pavelko, Jake Hirdler, Fabrice Lucien, Haidong Dong. Targeting PD-L1/CMTM6 in myeloid cells results in elevated release of CCL2 to improve CD8 T cell-mediated antitumor response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2664.