Overview

PD-L1 expression measured by the 22C3 clone is one of the few biomarker assays tied to labelled immune-oncology indications, so its regulatory standing matters as much as its biology. For labs and distributors, offering a 22C3 IHC service means meeting the validation and reporting rules that payers and regulators expect before a result can guide therapy. Procurement teams should therefore ask for the validation dossier and the threshold table up front, because a result without a named assay and score is not clinically actionable.

How It Works

The 22C3 mouse monoclonal antibody binds the PD-L1 protein on formalin-fixed sections. After antigen retrieval and staining, a pathologist scores the percentage of tumor cells with membrane staining, expressed as the tumor proportion score (TPS). A validated external control and an automated platform keep staining intensity consistent across sites, which is the foundation of reproducible regulatory-grade reporting. Slide scanning and digital review further reduce reader drift between pathologists working in different locations.

Clinical Indications

22C3 TPS is used across multiple tumor types to support immune checkpoint inhibitor selection, with threshold values defined per indication. It is requested when a prescriber needs a labelled, audit-ready PD-L1 result rather than a research-grade estimate. Some programs also archive the scored slide so the same block can be re-read if a new indication threshold is approved later.

Specimen & Turnaround

A four to five micron FFPE section is required, with a matched H&E for review. Scoring follows the clone-specific algorithm, and equivocal cases are confirmed by a second reader. The signed report states the TPS value and the scoring assay used. Turnaround is tracked against a service-level window so treating teams can plan the immune-therapy discussion without uncertainty.

Storage & Logistics

Slides are shipped ambient in a rigid mailer; prolonged heat is avoided to protect antigenicity. Service labs maintain a validated reagent lot and calibration slides so overseas partners receive results comparable to the originating site. Batch-level quality metrics are retained for audit, which is what regulators expect from a companion diagnostic workflow.

FAQ

Q: Why is 22C3 treated as a companion diagnostic? A: It carries indication-specific thresholds, so scoring must follow the validated algorithm and be audit-ready. The named assay and score are part of the regulatory label.

Q: Can 22C3 and 28-8 results be compared directly? A: No. Different clones use different thresholds and antibodies, so they are not interchangeable. Each must be interpreted with its own scoring rule.

Q: What sample protects score reliability? A: A four to five micron FFPE section with a matched H&E, shipped ambient in a rigid mailer. Avoid heat and humidity that could weaken the antigen signal before staining.