PD-L1 immunohistochemistry (IHC) is the primary method for selecting patients who may benefit from immune checkpoint inhibitors. However, four different FDA-approved PD-L1 IHC assays exist, each using a different antibody clone and a different scoring system. Published concordance studies have shown that these clones are not interchangeable — and choosing the wrong clone for your research context can lead to conflicting results.
This article summarizes published data on PD-L1 clone concordance and outlines the practical differences researchers should consider. Product data at the end of the article references abinScience catalog products, all for Research Use Only (RUO).
Why Clone Choice Matters: The Blueprint Project
The Blueprint PD-L1 IHC Assay Comparison Project was a multicenter study designed to test whether the four FDA-approved PD-L1 assays produce concordant results on the same tumor samples. Phase 1 evaluated 39 NSCLC tumors; Phase 2 expanded to 81 NSCLC specimens scored by 25 pathologists from 15 countries.
The key findings, published in the Journal of Thoracic Oncology (2017, 2018):
Finding 1: Three clones — 22C3, 28-8, and SP263 — showed highly comparable tumor cell (TC) staining, with similar analytical performance.
Finding 2: SP142 consistently detected fewer PD-L1-positive tumor cells than the other three assays, showing significantly lower sensitivity.
Finding 3: Immune cell (IC) scoring showed much higher variability across all four assays compared to TC scoring.
References: Hirsch FR et al. J Thorac Oncol. 2017;12(2):208-222 (Blueprint Phase 1). Tsao MS et al. J Thorac Oncol. 2018;13(9):1302-1311 (Blueprint Phase 2).
Clone-by-Clone: Clinical Context and Scoring Systems
22C3 — Pembrolizumab (Keytruda®)
Used in the Dako PD-L1 IHC 22C3 pharmDx assay. Scores PD-L1 by Tumor Proportion Score (TPS) in NSCLC (≥50% for first-line monotherapy, ≥1% for second-line) and by Combined Positive Score (CPS) in gastric, cervical, HNSCC, urothelial, TNBC, and other indications. The most broadly applied PD-L1 scoring clone across cancer types.
SP142 — Atezolizumab (Tecentriq®)
Used in the Ventana PD-L1 (SP142) assay. Uniquely scores PD-L1 on tumor-infiltrating immune cells (IC scoring) rather than (or in addition to) tumor cells. Published data consistently show SP142 detects fewer PD-L1-positive TCs than 22C3, SP263, or 28-8. This clone may underestimate PD-L1 on tumor cells if used as a substitute for 22C3 or SP263.
SP263 — Durvalumab (Imfinzi®)
Used in the Ventana PD-L1 (SP263) assay. Approved as a complementary diagnostic for durvalumab. Blueprint Phase 2 and meta-analysis data suggest SP263 may have slightly higher analytical sensitivity than 22C3 on tumor cells, though the two are generally considered interchangeable at standard cutoffs (≥1%, ≥25%).
28-8 — Nivolumab (Opdivo®)
Used in the Dako PD-L1 IHC 28-8 pharmDx assay. Shows comparable analytical performance to 22C3 and SP263 on tumor cells. Note: abinScience does not currently carry clone 28-8 in our catalog.
Concordance Summary Across Tumor Types
| Clone Pair |
TC Concordance |
IC Concordance |
Evidence |
| 22C3 vs SP263 |
High (OPA >90%) |
Moderate |
Blueprint Phase 1&2, UC study (N=335) |
| 22C3 vs SP142 |
Low — SP142 detects fewer TCs |
Low |
Blueprint Phase 1&2, Sci Rep 2017, meta-analysis |
| SP263 vs SP142 |
Low (~76% concordance) |
Variable |
NSCLC validation study (N=80) |
| 22C3 vs SP263 (ESCC) |
High (OPA 0.896) |
Moderate |
ESCC concordance study (N=50, 68 pathologists) |
Sources: Hirsch et al. J Thorac Oncol 2017; Tsao et al. J Thorac Oncol 2018; Zajac et al. Sci Rep 2017; Ratcliffe et al. JCO 2017; Concordance study in UC: Diag Pathol 2019; ESCC concordance: J Cancer Res Clin Oncol 2024.
Practical Implications for Researchers
1. Match clone to drug program. If your study references pembrolizumab data, use 22C3. If referencing atezolizumab, use SP142. Using the wrong clone may produce discordant results that cannot be compared to published clinical trial data.
2. SP142 is not interchangeable with 22C3/SP263. Multiple studies confirm SP142 detects fewer PD-L1-positive tumor cells. Do not substitute SP142 for 22C3 or SP263 in TPS-based studies.
3. 22C3 and SP263 are largely interchangeable for TC scoring. Blueprint Phase 2 and meta-analyses support this at standard cutoffs (≥1%, ≥25%, ≥50%). However, borderline cases near cutoff thresholds may still be discordant.
4. IC scoring remains poorly concordant across all clones. If your study focuses on immune cell PD-L1 expression, expect higher inter-assay and inter-observer variability regardless of clone choice.
abinScience PD-L1 Product Portfolio
abinScience carries research-grade versions of the three companion diagnostic-related clones (22C3, SP142, SP263) as well as proprietary detection clones and functional/blocking antibodies. All products below are from our product catalog with validated applications from our datasheets.
IHC-Validated Detection Clones (Human PD-L1)
| Clone |
Host |
Validated Apps |
Conjugates |
Catalog # |
| 22C3 |
Mouse |
ELISA, IHC, WB (HV974103); FCM (HV974207) |
Unconj, FITC, PE, APC, PerCP |
HV974103, HV974207 |
| SP142 |
Mouse |
IHC, WB (HV974073); ELISA, IHC, WB (HV974113) |
Unconjugated |
HV974073, HV974113 |
| SP263 |
Mouse |
IHC |
Unconjugated |
HV974083 |
| 1A058–1A061 |
Mouse |
ELISA, IHC, WB |
Unconjugated |
HV974055, HV974065, HV974075, HV974085 |
| Polyclonal |
Rabbit |
ELISA, IHC, WB |
Unconjugated |
HV974014 |
Flow Cytometry Clones (Pre-Conjugated)
| Clone |
Host |
Reactivity |
Conjugates |
Catalog # |
| 22C3 |
Mouse |
Human |
FITC, PE, APC, PerCP |
HV974217, HV974227, HV974237, HV974247 |
| SAA0088 |
Human |
Human |
FITC, PE, APC, PerCP |
HV974117, HV974127, HV974137, HV974147 |
| SAA0268 |
Rat |
Mouse |
FITC, PE, APC, PerCP |
MV974117, MV974127, MV974137, MV974147 |
| SAA0359 |
Mouse |
Mouse |
FITC, PE, APC, PerCP |
MV974217, MV974227, MV974237, MV974247 |
Blocking & In Vivo Clones
| Clone |
Host |
Reactivity |
Validated Apps |
Catalog # |
| 2.7A4 |
Mouse |
Human |
Blocking, ELISA, FC |
HV974023 |
| SAA0142 |
Mouse |
Mouse |
Blocking, ELISA, FC |
MV974013 |
| 10F.9G2 |
Rat |
Mouse |
FC, IF, IHC (frozen), WB, In Vitro & In Vivo PD-L1 Blockade |
MV974020 |
Research-Grade Biosimilar Proteins
We also offer 59 research-grade PD-L1 biosimilar proteins — including research-grade versions of atezolizumab, durvalumab, avelumab, and other anti-PD-L1 therapeutic antibodies — with ELISA and FACS validation, produced in mammalian expression systems. These are suitable for binding comparability, cell-based functional assays, and pharmacokinetic reference studies.
References
1. Hirsch FR, et al. PD-L1 Immunohistochemistry Assays for Lung Cancer: Results from Phase 1 of the Blueprint PD-L1 IHC Assay Comparison Project. J Thorac Oncol. 2017;12(2):208-222.
2. Tsao MS, et al. PD-L1 Immunohistochemistry Comparability Study in Real-Life Clinical Samples: Results of Blueprint Phase 2 Project. J Thorac Oncol. 2018;13(9):1302-1311.
3. Xu H, Lin G, Huang C, et al. Assessment of Concordance between 22C3 and SP142 Immunohistochemistry Assays regarding PD-L1 Expression in Non-Small Cell Lung Cancer. Sci Rep. 2017;7:17066. doi:10.1038/s41598-017-17034-5.
4. Ratcliffe MJ, et al. Concordance of TC and IC staining with Ventana SP142, SP263, Dako 28-8 and 22C3 PD-L1 IHC tests in NSCLC. J Clin Oncol. 2017;35(15_suppl):e14503.
5. Concordance among four commercially available, validated programmed cell death ligand-1 assays in urothelial carcinoma. Diagn Pathol. 2019;14:99. doi:10.1186/s13000-019-0873-6.
6. Concordance of assessments of four PD-L1 immunohistochemical assays in esophageal squamous cell carcinoma (ESCC). J Cancer Res Clin Oncol. 2024. doi:10.1007/s00432-023-05595-0.
7. Torlakovic E, Lim H, Adam J, et al. "Interchangeability" of PD-L1 immunohistochemistry assays: a meta-analysis of diagnostic accuracy. Mod Pathol. 2020;33(1):4-17. doi:10.1038/s41379-019-0327-4.
All abinScience products are for Research Use Only (RUO). They are not FDA-approved diagnostic devices. Clone names (22C3, SP142, SP263) refer to antibody clone specificities produced by abinScience and do not imply equivalence to proprietary FDA-approved companion diagnostic assays. Keytruda® (Merck), Tecentriq® (Genentech/Roche), Imfinzi® (AstraZeneca), Opdivo® (Bristol-Myers Squibb) are registered trademarks of their respective owners. Product validation data from abinScience datasheets.
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