Clinical Utility of the Combined Positive Score for Programmed Death Ligand-1 Expression and the Approval of Pembrolizumab for Treatment of Gastric Cancer.

CONTEXT.­: Regulatory approval of pembrolizumab for treatment of gastric and gastroesophageal junction (G/GEJ) adenocarcinoma required a reproducible scoring method for use of programmed death ligand-1 (PD-L1) protein expression as a companion diagnostic to identify likely responders to therapy. OBJECTIVE.­: To develop an immunohistochemical scoring algorithm that includes PD-L1 expression for tumor and immune cells, that is, the combined positive score. DESIGN.­: Four previously treated tumor types in the KEYNOTE-012 and KEYNOTE-028 studies were analyzed descriptively with a version of the PD-L1 immunohistochemical 22C3 pharmDx assay labeled for investigational use only to determine the relative importance of PD-L1 expression in tumor versus immune cells as a biomarker for pembrolizumab response. A combined positive score was developed as a novel scoring method and was compared with the tumor proportion score in cohort 1 from the KEYNOTE-059 study (G/GEJ cancer). External reproducibility was assessed. RESULTS.­: Per combined positive score cutoff of 1 or more, the prevalence of PD-L1 expression in patients with G/GEJ cancer was 57.6% (148 of 257 patients), with reasonable enrichment of responses (odds ratio, 2.8). Per tumor proportion score cutoff of 1% or more, prevalence was 12.5% (32 of 257 patients), with minimal enrichment (odds ratio, 1.4). External reproducibility assessments demonstrated interpathologist overall agreement of 96.6% (591 of 612; 95% CI, 94.0%-98.7%) and intrapathologist overall agreement of 97.2% (595 of 612; 95% CI, 95.3%-98.9%). CONCLUSIONS.­: Combined positive score is a robust, reproducible PD-L1 scoring method that predicts response to pembrolizumab in patients with G/GEJ cancer. This novel scoring method supported US Food and Drug Administration approval of pembrolizumab as third-line therapy for G/GEJ cancer and has facilitated investigation in other indications.

Influenza and respiratory syncytial virus detection in clinical specimens without nucleic acid extraction using FOCUS direct disc assay is substantially equivalent to the traditional methods and the FOCUS nucleic acid extraction-dependent RT-PCR assay.

In this study, we evaluated FOCUS diagnostic's Flu A/B & RSV direct kit (Direct Disc assay), designed to detect influenza (FLU) and respiratory syncytial viruses (RSV) directly in clinical specimens without nucleic acid extraction. This novel 'sample-to-answer', nucleic acid extraction-independent assay uses a unique disc to process, amplify, and detect viral targets in up to 8 specimens at a time. The performance of this assay for detecting FLU and RSV viruses was compared to the traditional methods (culture and/or direct florescent antibody testing) using 945 nasopharyngeal swab specimens. In addition, a total of 150 consecutive clinical specimens positive for FLU (FLU A=50, FLU B=50) or RSV (n=50) were tested in parallel using the novel Direct Disc assay and FOCUS diagnostic's nucleic acid extraction-dependent assay to assess their relative performance. Compared to the traditional methods, the overall (prospective+retrospective) positive/negative percent agreement was determined to be 96.6%/98.1% for FLU A, 98.4%/99.9% for FLU B, and 99.3%/98.8% for RSV. Compared to the nucleic acid extraction-dependent assay, the positive percent agreement was 90% (n=45/50) for FLU A, 92% (n=46/50) for FLU B, and 98% (n=49/50) for RSV. Overall, the Direct Disc assay showed good agreement with both traditional methods and nucleic acid extraction-dependent assay. Although we encountered some failures compared to the nucleic acid extraction-dependent assay, these limitations must be balanced against the substantial advantages of the extraction-free nature of this assay and rapid turnaround time.

A second-generation ELISA (STRATIFY JCV™ DxSelect™) for detection of JC virus antibodies in human serum and plasma to support progressive multifocal leukoencephalopathy risk stratification.

BACKGROUND: JC virus (JCV) infection is a prerequisite for development of progressive multifocal leukoencephalopathy (PML). The development and validation of a two-step enzyme-linked immunosorbent assay (ELISA) that detects JCV antibodies in human serum or plasma and its clinical utility for stratification of PML risk have been described. OBJECTIVE: To develop a second-generation JCV antibody ELISA kit with improved assay performance characteristics. STUDY DESIGN: The assay design was optimized by pre-coating the JC virus-like particles (VLP) on microtiter plates. Assay cut-points were statistically established using sera from >1300 multiple sclerosis patients from natalizumab clinical studies. The assay was analytically validated and then used to determine the presence of JCV antibodies in both treatment-naïve and natalizumab-treated MS patients, as well as in natalizumab-treated PML patients. RESULTS: An improved assay for detection of JCV antibodies in human serum and plasma was developed. Key enhancements included improved delineation and reproducibility of low JCV antibody responses and assay ease of use. The assay was validated, demonstrating good agreement with the original two-step JCV antibody ELISA, and similar seroprevalence of 50%-60%. Samples from 63 natalizumab-treated PML patients collected 6-180 months prior to PML diagnosis tested JCV antibody positive. One patient tested JCV antibody negative 15 months prior to PML diagnosis but JCV antibody positive 2 months prior to PML diagnosis. CONCLUSIONS: The validated second-generation JCV antibody ELISA offers improved assay design as a kit and enhanced performance characteristics that advance routine clinical use of the assay as a PML risk stratification tool.