Background: A high quality PD-L1 companion diagnostic may help predict which patients are more likely to respond to PD-1/PD-L1 antibody-based therapy. Here we describe a PD-L1 immunohistochemical (IHC) diagnostic test developed by Ventana Medical Systems for use with durvalumab.

Methods: An anti-human PD-L1 rabbit monoclonal antibody (SP263) was optimized for use with Ventana OptiView DAB IHC Detection Kit on the automated BenchMark ULTRA platform. The PD-L1 IHC assay was validated for use in formalin-fixed, paraffin-embedded samples of NSCLC in a series of studies addressing sensitivity, specificity, robustness, and precision. Durvalumab is a human IgG1 mAb that blocks PD-L1 binding to PD-1 and CD80 with high affinity and selectivity. A subset of clinical trial samples from a Phase 1/2 study of durvalumab (NCT01693562) was analyzed to determine optimal cut-off for enriching response to durvalumab. Inter-reader precision was established by 3 pathologists who evaluated 81 NSCLC samples across the range of expression levels.

Results: The Ventana PD-L1 IHC (SP263) assay met all pre-defined acceptance criteria. The scoring algorithm was defined using statistical analysis of clinical response data and PD-L1 staining parameters observed in a set of NCT01693562 clinical trial samples. Samples of both cancer types are considered test positive when the membrane of ≥ 25% of tumor cells stain for PD-L1 at any intensity. Inter-reader precision in determining PD-L1 status resulted in an overall percentage agreement of 97% for NSCLC. PD-L1+ patients identified by the scoring algorithm had a higher response rate than PD-L1- patients. Interlaboratory testing was performed at 3 external laboratories and demonstrated an overall agreement rate of 86.4%.

Conclusions: These results highlight the robustness and reproducibility of the PD-L1 IHC (SP263) assay in a clinical setting. In NSCLC patients treated with durvalumab, PD-L1+ patients identified by the scoring algorithm had a higher response rate than PD-L1- patients. The clinical utility of the PD-L1 diagnostic assay will be further validated in a prospective manner using additional patients in this study and in other durvalumab studies.

Citation Format: Marlon C. Rebelatto, Amita Mistry, Constantine Sabalos, Nicole Schechter, Jill Walker, Anita Midha, Keith E. Steele, Paul B. Robbins, Xia Li, Li Shi, John A. Blake-Haskins, Ramy A. Ibrahim, Laura Richman. An immunohistochemical PD-L1 companion diagnostic assay for treatment with durvalumab (MEDI4736) in NSCLC patients. [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 B005.