Target: GPC3 (Glypican-3)

Indication: Hepatocellular carcinoma (LIHC)

1) Surface Eligibility (Hard Requirement)

Localization evidence (UniProt):
- Subcellular localization: Cell membrane
- Topology: GPI-anchor
- Transmembrane domains: 0
- Note: “Oncofetal; near-absent in adult normal tissue -> excellent specificity.”

Interpretation:
GPC3 is a GPI-anchored cell-surface protein, meaning it is tethered to the extracellular leaflet of the plasma membrane. The protein is fully extracellular except for the GPI anchor, making it accessible to antibodies, CAR-T cells, ADCs, and bispecific T-cell engagers.

✅ Surface eligibility: ELIGIBLE

2) On-Tumor Signal (TCGA)

Tumor median expression (TPM):

• LIHC (hepatocellular carcinoma): 80.0 TPM

Comparator cohorts (selected):
- LUSC: 8.0
- LUAD: 5.0
- STAD: 3.0
- BRCA: 2.0
- COAD: 1.0
- DLBC: 0.5

Interpretation:
GPC3 expression in LIHC (80.0 TPM) is dramatically higher than in all other tumor cohorts (≤8.0 TPM). This indicates:

• Strong lineage enrichment in HCC
• High antigen density potential in LIHC tumors
• Favorable dynamic range versus other cancers

✅ Very strong on-tumor signal in LIHC

3) Tumor vs Normal Specificity (Dominant Criterion)

LIHC tumor median: 80.0 TPM

Normal tissues (GTEx median TPM):

Vital tissues:
- Liver: 0.3
- Lung: 1.0
- Heart - Left Ventricle: 0.2
- Brain - Cortex: 0.3
- Kidney - Cortex: 0.5
- Colon - Transverse: 0.2
- Pancreas: 0.2
- Whole Blood: 0.1
- Spleen: 0.2
- Stomach: 0.3

Non-vital but notable:
- Testis: 2.0
- Ovary: 1.0

Dynamic range (tumor vs normal):

• LIHC vs liver: 80.0 vs 0.3 TPM (~267-fold)
• LIHC vs lung: 80.0 vs 1.0 TPM (80-fold)
• LIHC vs kidney: 80.0 vs 0.5 TPM (160-fold)
• LIHC vs brain: 80.0 vs 0.3 TPM (~267-fold)

Interpretation:
Normal adult liver expression is extremely low (0.3 TPM), which is critical for HCC targeting. Across all vital tissues, expression is ≤1.0 TPM. Even the highest normal tissue (testis at 2.0 TPM) is:

• Non-vital
• ~40-fold lower than LIHC

✅ Excellent tumor-to-normal differential
✅ Favorable safety profile based on transcript distribution

4) Safety Assessment

• Liver (vital organ): 0.3 TPM — very low baseline expression
• Brain, heart, lung, kidney all ≤1.0 TPM
• No high expression in hematopoietic tissues (Whole Blood 0.1 TPM; Spleen 0.2 TPM)

Potential considerations:
- GPI-anchored proteins can shed; soluble antigen could theoretically act as a sink (not evaluable from this dataset).
- Testis expression (2.0 TPM) suggests possible immune-privileged tissue expression, typically less dose-limiting.

Overall transcript-based safety risk appears low.

FINAL ASSESSMENT

Target: GPC3
Indication: Hepatocellular carcinoma (LIHC)

Surface Eligibility

Eligible — GPI-anchored cell-membrane protein with extracellular accessibility (0 transmembrane domains, cell membrane localization).

On-Tumor Signal

LIHC: 80.0 TPM (very high relative to other cohorts).

Specificity (Dominant Criterion)

• Liver (normal): 0.3 TPM
• Lung: 1.0 TPM
• Kidney: 0.5 TPM
• Brain cortex: 0.3 TPM
• Whole blood: 0.1 TPM

Tumor-to-normal differential: ~80–267-fold vs vital tissues.
Excellent tumor specificity.

Safety

Low expression across vital organs.
Highest normal tissue (testis 2.0 TPM) is non-vital and far below tumor levels.
Overall predicted on-target/off-tumor risk: low.

Tier

✅ Tier 1 — Strong Candidate

Rationale & Recommendation

GPC3 demonstrates all required properties of a high-priority cell-surface therapeutic target in HCC: clear extracellular accessibility, very high LIHC expression (80.0 TPM), and extremely low expression across vital adult tissues (≤1.0 TPM in all major organs, including liver at 0.3 TPM). The tumor-to-normal differential is exceptionally wide, strongly supporting both efficacy and safety.

Recommendation: Advance/continue prioritization of GPC3 for CAR-T, ADC, and T-cell engager strategies in hepatocellular carcinoma. It represents a benchmark Tier 1 solid tumor surface antigen based on expression and localization criteria.