Distinct Roles of HHLA2 and PD-L1 in the Immune Cell and Prognosis of Hepatocellular Carcinoma.

BACKGROUND

HHLA2, a member of the B7 family, is extensively expressed in various cancers and plays a pivotal role in modulating the immune microenvironment. However, its prognostic significance in hepatocellular carcinoma (HCC) remains poorly understood. This study aims to elucidate the expression patterns of HHLA2 and PD-L1 in HCC, their associations with tumor-infiltrating lymphocytes (TILs), and their impact on clinical outcomes.

METHODS

Immunohistochemistry (IHC) was employed to evaluate HHLA2 and PD-L1 expression in 547 HCC tissue samples. PD-L1 positivity was defined as ≥1% membranous or cytoplasmic staining. Hematoxylin and eosin (H&E) staining was utilized to quantify TILs (percentage/area), while IHC was used to measure the densities of CD3+, CD4+, and CD8+ TILs (cells/mm²).

RESULTS

HHLA2 and PD-L1 exhibited similar positivity rates. HHLA2 positivity was associated with older age, lower alpha-fetoprotein (AFP) levels, well-differentiated tumors, and improved overall survival (OS). HHLA2 expression was inversely correlated with stromal TIL density. In contrast, tumor cell (TC)-PD-L1 and inflammatory cell (IC)-PD-L1 positivity were positively correlated with higher stromal TIL density and increased levels of CD3+, CD4+, and CD8+ TILs. Patients with HHLA2(+)/PD-L1(-) status demonstrated the longest OS. A novel classification system based on HHLA2/PD-L1 expression identified distinct immune profiles and prognostic subgroups.

CONCLUSION

HHLA2 significantly influences the immune microenvironment of HCC and serves as an independent prognostic marker. The combined assessment of HHLA2 and PD-L1 expression facilitates risk stratification, providing a framework to optimize immunotherapy strategies. These findings contribute to the advancement of precision medicine in the management of HCC.