Abstract 2827: Anti-PD-L1/IL-15 fusion protein demonstrated efficient T-cell redirected killing of PD-L1 expressing target cells and in vivo efficacy that correlated to its retention in tumors
Authors: Martomo Stella , Lu Dan , Polonskaya Zhanna , Zhang Zhikai , Luna Xenia , Almstead Danielle , Lumban-Tobing Radovan , Feldstein Samuel , Patel Jeegar 
Published: September 2020

Abstract
Background: Administration of immune checkpoint inhibitors anti-PD-1/PD-L1 have led to durable responses in some patients in select cancers. However, the majority of patients still fail to respond or become resistant to these therapies. We have generated a therapeutic fusion protein by combining a proprietary high affinity monoclonal antibody recognizing only human PD-L1 (KD033) and its surrogate antibody recognizing human and mouse PD-L1 (srKD033), both fused to human IL-15. KD033 and srKD033 similarly and significantly increased CD8+ T, NK and NKT-like cells in vitro and in peripheral blood from monkeys and mice respectively. Single dose monotherapy of srKD033 in syngeneic mouse models of colon carcinoma resulted in tumor clearance, memory responses and epitope spreading in twenty percent of treated mice. Tumors obtained from these responding mice showed evidence of robust cytotoxic immune gene signatures with broad activation of innate and adaptive immune responses. In this study, we evaluated anti-PD-L1/IL-15 retention in tumors and its correlation to immune cell activation in the tumor microenvironment (TME).
Methods: Syngeneic cancer cells were grown subcutaneously in mice prior to treatments with fusion proteins. To evaluate immune cells populations in TME, tumors were isolated 7 days after treatments for gene expression analysis and immunohistochemistry. In vitro cytolytic and internalization assays were done using IncuCyte technology. To understand the value of targeting PD-L1, we have generated monoclonal antibodies against some relevant tumor-associated targets (anti-TAT) and fused them to human IL-15 (anti-TAT/IL-15).
Results: srKD033 treatment induced increased cytotoxic lymphocyte infiltrations in tumors and in TME. The cytolytic activity of anti-PD-L1/IL-15 was compared to different anti-TAT/IL-15 on select immune cell populations. In vitro, anti-PD-L1/IL-15 exhibited better cytolytic activity to target cancer cells compared to other anti-TAT/IL-15. In vivo, srKD033 surrogate retention in tumors increased tumor infiltrating cells with new and expanded T-cell receptors and B-cell receptors.
Conclusions: srKD033 inhibited tumor growth inhibition and demonstrated evidence of epitope spreading. Broad activation of innate and adaptive immune responses in tumors was observed. These observations strongly support KD033 clinical development. A Phase 1 clinical trial of KD033 is planned in 2H 2019.
Citation Format: Stella Martomo, Dan Lu, Zhanna Polonskaya, Zhikai Zhang, Xenia Luna, Danielle Almstead, Radovan Lumban-Tobing, Samuel Feldstein, Jeegar Patel. Anti-PD-L1/IL-15 fusion protein demonstrated efficient T-cell redirected killing of PD-L1 expressing target cells and in vivo efficacy that correlated to its retention in tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2827.