Immunohistochemical (IHC) detection of PD-L1 expression is a gatekeeper test in modern oncology. For clinics deciding which patients might respond to PD-L1/PD-1 blockade, the choice of antibody clone shapes the readout that drives treatment. The 28-8 clone, validated with nivolumab (Opdivo), provides a tumor proportion score (TPS) used to identify who is more likely to benefit. This article explains how 28-8 fits into population screening, compares its scoring with 22C3 and SP263, and notes what procurement teams should verify.
PD-L1 expression is heterogeneous across and within tumors. Rather than a binary result, the 28-8 assay reports the proportion of viable tumor cells showing partial or complete membrane staining. In non-small cell lung cancer (NSCLC), this TPS is stratified into categories—typically <1%, 1–49%, and ≥50%—which map to different expectations for checkpoint inhibitor benefit. Screening this way lets oncologists prioritize immunotherapy for higher-expression patients while reserving other lines for those with minimal PD-L1.
Three PD-L1 IHC clones dominate clinical use: 28-8, 22C3, and SP263. They were developed alongside different companion indications—22C3 with pembrolizumab, SP263 with durvalumab, and 28-8 with nivolumab. Although they target the same protein, their antibodies bind different epitopes and use different protocols, so the raw percentage can differ by a few points on the same slide. These differences rarely change decisions for most patients, but they matter at borderline cutoffs. Concordance studies show substantial agreement, yet laboratories must validate the platform and scoring protocol they adopt.
Regulatory agencies and professional societies recognize that the three clones produce broadly comparable results in NSCLC, and in many jurisdictions the assay need not match the original companion test. However, this "interchangeability" is a laboratory responsibility, not a given. A lab adopting 28-8 should run its own concordance check against a reference clone before routine reporting. For trial sites, a single well-validated clone reduces variability and makes population-level readouts more defensible.
When sourcing PD-L1 28-8 IHC kits, verify the clone certificate, platform compatibility (e.g., Dako Autostainer or Ventana), and whether a validated scoring algorithm is supplied. Ask about lot-to-lot consistency, since batch variation directly affects the TPS your pathologists report. Confirm whether a companion positive-control cell line is included, because a reliable control is essential.
Q: Is PD-L1 28-8 the same as 22C3? A: No. They are distinct antibody clones targeting different epitopes of the PD-L1 protein. They generally produce concordant results in NSCLC, but a laboratory should validate its own platform before treating them as interchangeable.
Q: What does a tumor proportion score (TPS) of 1–49% mean for treatment? A: It indicates intermediate PD-L1 expression. In many protocols it is not a strict exclusion criterion but is weighed alongside tumor histology, disease burden, and prior therapy when deciding on checkpoint inhibitor use.
Q: Can 28-8 be used for patients treated with pembrolizumab? A: In several regulatory settings the assay need not match the original companion clone, and 28-8 results are often accepted for PD-L1-guided decision making. Confirm the local requirements for your site.
Q: Why does lot-to-lot consistency matter for PD-L1 IHC? A: Antibody batch variation can shift staining intensity and, in turn, the percentage of positive cells. Consistent lots keep TPS scoring stable and reproducible, which is essential for reliable clinical decisions.
Immunohistochemical (IHC) detection of PD-L1 expression is a gatekeeper test in modern oncology. For clinics deciding which patients might respond to PD-L1/PD-1 blockade, the choice of antibody clone shapes the readout that drives treatment. The 28-8 clone, validated with nivolumab (Opdivo), provides a tumor proportion score (TPS) used to identify who is more likely to benefit. This article explains how 28-8 fits into population screening, compares its scoring with 22C3 and SP263, and notes what procurement teams should verify.
PD-L1 expression is heterogeneous across and within tumors. Rather than a binary result, the 28-8 assay reports the proportion of viable tumor cells showing partial or complete membrane staining. In non-small cell lung cancer (NSCLC), this TPS is stratified into categories—typically <1%, 1–49%, and ≥50%—which map to different expectations for checkpoint inhibitor benefit. Screening this way lets oncologists prioritize immunotherapy for higher-expression patients while reserving other lines for those with minimal PD-L1.
Three PD-L1 IHC clones dominate clinical use: 28-8, 22C3, and SP263. They were developed alongside different companion indications—22C3 with pembrolizumab, SP263 with durvalumab, and 28-8 with nivolumab. Although they target the same protein, their antibodies bind different epitopes and use different protocols, so the raw percentage can differ by a few points on the same slide. These differences rarely change decisions for most patients, but they matter at borderline cutoffs. Concordance studies show substantial agreement, yet laboratories must validate the platform and scoring protocol they adopt.
Regulatory agencies and professional societies recognize that the three clones produce broadly comparable results in NSCLC, and in many jurisdictions the assay need not match the original companion test. However, this "interchangeability" is a laboratory responsibility, not a given. A lab adopting 28-8 should run its own concordance check against a reference clone before routine reporting. For trial sites, a single well-validated clone reduces variability and makes population-level readouts more defensible.
When sourcing PD-L1 28-8 IHC kits, verify the clone certificate, platform compatibility (e.g., Dako Autostainer or Ventana), and whether a validated scoring algorithm is supplied. Ask about lot-to-lot consistency, since batch variation directly affects the TPS your pathologists report. Confirm whether a companion positive-control cell line is included, because a reliable control is essential.
Q: Is PD-L1 28-8 the same as 22C3? A: No. They are distinct antibody clones targeting different epitopes of the PD-L1 protein. They generally produce concordant results in NSCLC, but a laboratory should validate its own platform before treating them as interchangeable.
Q: What does a tumor proportion score (TPS) of 1–49% mean for treatment? A: It indicates intermediate PD-L1 expression. In many protocols it is not a strict exclusion criterion but is weighed alongside tumor histology, disease burden, and prior therapy when deciding on checkpoint inhibitor use.
Q: Can 28-8 be used for patients treated with pembrolizumab? A: In several regulatory settings the assay need not match the original companion clone, and 28-8 results are often accepted for PD-L1-guided decision making. Confirm the local requirements for your site.
Q: Why does lot-to-lot consistency matter for PD-L1 IHC? A: Antibody batch variation can shift staining intensity and, in turn, the percentage of positive cells. Consistent lots keep TPS scoring stable and reproducible, which is essential for reliable clinical decisions.
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