PD-L1 quantification across tumor types using the reverse phase protein microarray: implications for precision medicine.

Anti-programmed cell death protein 1 and programmed cell death ligand 1 (PD-L1) agents are broadly used in first-line and second-line treatment across different tumor types. While immunohistochemistry-based assays are routinely used to assess PD-L1 expression, their clinical utility remains controversial due to the partial predictive value and lack of standardized cut-offs across antibody clones. Using a high throughput immunoassay, the reverse phase protein microarray (RPPA), coupled with a fluorescence-based detection system, this study compared the performance of six anti-PD-L1 antibody clones on 666 tumor samples.

PD-L1 expression was measured using five antibody clones (22C3, 28-8, CAL10, E1L3N and SP142) and the therapeutic antibody atezolizumab on 222 lung, 71 ovarian, 52 prostate and 267 breast cancers, and 54 metastatic lesions. To capture clinically relevant variables, our cohort included frozen and formalin-fixed paraffin-embedded samples, surgical specimens and core needle biopsies. Pure tumor epithelia were isolated using laser capture microdissection from 602 samples. Correlation coefficients were calculated to assess concordance between antibody clones. For two independent cohorts of patients with lung cancer treated with nivolumab, RPPA-based PD-L1 measurements were examined along with response to treatment.

Median-center PD-L1 dynamic ranged from 0.01 to 39.37 across antibody clones. Correlation coefficients between the six antibody clones were heterogeneous (range: -0.48 to 0.95) and below 0.50 in 61% of the comparisons. In nivolumab-treated patients, RPPA-based measurement identified a subgroup of tumors, where low PD-L1 expression equated to lack of response.

Continuous RPPA-based measurements capture a broad dynamic range of PD-L1 expression in human specimens and heterogeneous concordance levels between antibody clones. This high throughput immunoassay can potentially identify subgroups of tumors in which low expression of PD-L1 equates to lack of response to treatment.

Journal for immunotherapy of cancer. 2021 Oct [Epub]

Elisa Baldelli, K Alex Hodge, Guido Bellezza, Neil J Shah, Guido Gambara, Angelo Sidoni, Martina Mandarano, Chamodya Ruhunusiri, Bryant Dunetz, Maysa Abu-Khalaf, Julia Wulfkuhle, Rosa I Gallagher, Lance Liotta, Johann de Bono, Niven Mehra, Ruth Riisnaes, Antonella Ravaggi, Franco Odicino, Maria Isabella Sereni, Matthew Blackburn, Angela Zupa, Giuseppina Improta, Perry Demsko, Lucio Crino', Vienna Ludovini, Giuseppe Giaccone, Emanuel F Petricoin, Mariaelena Pierobon

Center for Applied Proteomics and Molecular Medicine, George Mason University, Manassas, Virginia, USA., Department of Experimental Medicine, Section of Anatomic Pathology and Histology, University of Perugia, Perugia, Italy., Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, District of Columbia, USA., Side Out Foundation, Fairfax, Virginia, USA., Department of Medical Oncology, Sidney Kimmel Cancer Center at Jefferson Health, Thomas Jefferson University, Philadelphia, Pennsylvania, USA., The Institute of Cancer Research, London, UK., Angelo Nocivelli Institute of Molecular Medicine, Division of Gynecologic Oncology, University of Brescia and ASST Spedali Civili di Brescia, Brescia, Italy., Department of Medical Oncology, Istituto Scientifico Romagnolo per lo Studio e la Cura dei Tumori (IRST) IRCCS, Meldola, Italy., Division of Medical Oncology, S. Maria della Misericordia Hospital, Perugia, Italy., Center for Applied Proteomics and Molecular Medicine, George Mason University, Manassas, Virginia, USA .