Abstract 4871: Two novel anti-PD-1 antibodies, 244C8 and 388D4, elicit in vivo antitumor efficacy in a lung PDX tumorgraft in immuno-humanized NSG mice
Authors: Scheuplein Felix , Ranganath Sheila , Feng Bin , McQuade Thomas , Wang Lei , Spaulding Vikki , Vadde Sri , Mehta Shanu , Chiu Maria Isabel , Nguyen Cokey 
Published: July 2016

Abstract
We have previously described the identification of more than 300 anti-PD-1 monoclonal antibody candidates using Enumeral's proprietary single cell immune-profiling technology, on which our antibody discovery platform is based. Bioinformatics analysis of heavy chain CDR3 sequences show they comprise diverse families, encompassing 26 phylogenetic clades. Functional studies from cell-based, ex vivo human assays led to the discovery of two distinct lead candidates, 244C8 and 388D4. The former represents a novel class of anti-PD-1 antibodies with a potentially differentiated mechanism of action, as they appear not to compete with currently marketed antibodies for PD-1 nor do they compete with PD-L1 for PD-1 binding. Further, antibodies from the 244C8 family elicit both a higher T cell activation and an increased expression of the high affinity IL-2 receptor CD25 than currently marketed anti-PD-1 antibodies in ex vivo human cell based assays. Lead antibodies from both anti-PD-1 classes, 244C8 and 388D4, have been humanized for preclinical testing in preparation for Phase 1 clinical studies. Here we describe the in vivo efficacy testing of these two antibodies in a human PDX tumorgraft model derived from a core needle biopsy of a patient with metastatic non-small cell lung carcinoma (LG1306). Direct testing of the anti-human PD-1 antibodies was made possible by the use of immune-humanized NSG mice. Pembrolizumab, a currently marketed anti-PD-1 antibody, served as control, along with vehicle alone. Treatment with each of the humanized lead PD-1 antibodies, 388D4 and 244C8, was well tolerated at 5 mg/kg and led to significant tumor growth inhibition over a 28-day study period. Both showed equivalent efficacy to pembrolizumab with tumor growth inhibition (%TGI) at 40% and 38% respectively compared to 37% for pembrolizumab. All three treatment agents showed significant tumor growth inhibition relative to vehicle, with Student T-test p values &lt; 0.003 at end of study assessment. These results show that, contrary to expectation, competition for binding to PD-L1 ligand by an anti-PD-1 antibody is not a pre-requisite for functional efficacy in vivo, as we observed with 244C8. In addition to the in vivo efficacy studies, we will report on post-treatment analyses of all treatment cohorts by immunohistochemistry and RNAseq of the tumor samples, immunoprofiling analysis of tumor infiltrating lymphocytes (TILs) from all treatment cohorts, as well as donor-specific differences that influence response to treatment.
Citation Format: Felix Scheuplein, Sheila Ranganath, Bin Feng, Thomas McQuade, Lei Wang, Vikki Spaulding, Sri Vadde, Shanu Mehta, Maria Isabel Chiu, Cokey Nguyen. Two novel anti-PD-1 antibodies, 244C8 and 388D4, elicit in vivo antitumor efficacy in a lung PDX tumorgraft in immuno-humanized NSG mice. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4871.