Abstract B001: Development of a PD-L1 companion diagnostic IHC assay (SP142) for atezolizumab

Background: Understanding of immune tolerance mechanisms of cancer has prompted the development of cancer immunotherapies such as atezolizumab (anti-PD-L1, MPDL3280A). Robust, durable responses have been observed, leading to Breakthrough status designation by the FDA for atezolizumab for previously treated NSCLC and bladder cancer (UBC) patients. Roche/Ventana have developed a companion diagnostic (CDx) for atezoliziumab using a robust immunohistochemistry (IHC) assay and antibody clone (SP142), optimized to detect PD-L1 expression in both tumor cells (TC) and tumor-infiltrating immune cells (IC). Here we describe the characteristics of the SP142 assay, PD-L1 expression patterns observed by immunohistochemistry in TC and IC compartments, and their association with clinical efficacy for NSCLC and UBC patients. Methods: The anti-human PD-L1 rabbit monoclonal antibody SP142 was optimized for detection of both TC and IC expression of PD-L1 with the Ventana OptiView DAB IHC Detection Kit on the automated BenchMark ULTRA platform. The VENTANA PD-L1 (SP142) CDx assay was validated for use in formalin-fixed, paraffin-embedded samples of NSCLC and UBC in a series of studies addressing sensitivity, specificity, robustness, and precision. Formalin fixed, paraffin embedded tumor specimens were obtained from patients prescreened and/or enrolled into Genentech Ph I study PCD4989g, and PD-L1 expression was measured using the SP142 assay and PCR gene expression assays. Results: The SP142 assay met pre-defined acceptance criteria for TC and IC assessment of PD-L1 expression in NSCLC and UBC tumors, including u003e90% inter-reader concordance between pathologist readers. Rapid and durable responses were observed in the Ph I study (PCD4989g), and correlated with PD-L1 expression patterns observed by immunohistochemistry in TC and IC. In the same Ph I study (PCD4989g), PD-L1 expression as measured by PCR did not demonstrate the same predictive value as observed for IHC. Conclusions: The PD-L1 IHC (SP142) CDx is a robust assay to measure PD-L1 expression in both IC and TC. Further, the high reproducibility of results between pathologists shows that the scoring algorithms in UBC and NSCLC are precise, reproducible, and practical in the diagnostic setting. The results indicate that favorable atezolizumab efficacy for UBC is strongly associated with higher IC levels as assessed by the sensitive and specific PD-L1 IHC (SP142) CDx assay. In NSCLC, favorable atezolizumab efficacy is associated with tumors expressing either high TC or high IC levels by the PD-L1 IHC (SP142) CDx assay. These data support the predictive value of tumor PD-L1 levels by IHC for NSCLC and UBC patients receiving atezoliziumab. Citation Format: Zachary S. Boyd, Dustin Smith, Brian Baker, Bharathi Vennapusa, Hartmut Koeppen, Marcin Kowanetz, Sanjeev Mariathasan, Jean-Marie Bruey, Howard Mackey, Gregg Fine, Simonetta Mocci, Priti Hegde, J. Andrew Williams, Ian McCaffery. Development of a PD-L1 companion diagnostic IHC assay (SP142) for atezolizumab. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B001.