Impact of immune microenvironment on immune checkpoint inhibitor response in HER2-overexpressing urothelial carcinoma

The biological interaction between human epidermal growth factor receptor 2 (HER2) overexpression and the tumor immune microenvironment (TIME) in urothelial carcinoma (UC) has not been comprehensively elucidated, which limits the rational integration of HER2-targeted therapies with Immune checkpoint Inhibitors (ICIs). This study aimed to characterize the immune landscape associated with HER2 expression and evaluate its clinical implications.

Using transcriptomic datasets from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO), patients were stratified based on an exploratory threshold, with the highest 20% of ERBB2 mRNA expression defined as HER2-high. Integrated bioinformatic analyses were validated via immunohistochemistry (IHC) in 21 UC specimens. Additionally, a real-world cohort of 29 patients with locally advanced or metastatic UC (la/mUC) treated with disitamab vedotin (RC48), as monotherapy or combined with PD-1 inhibitors, was evaluated for clinical efficacy.

In this exploratory analysis, HER2-high tumors were associated with an immunologically suppressed phenotype, characterized by reduced immune/stromal infiltration and increased tumor purity. Notably, these tumors exhibited a selective enrichment of FOXP3 + regulatory T cells (Tregs) (P < 0.001) alongside significantly lower expression of canonical immune checkpoints, including CTLA-4, PD-1, and PD-L2 (all P < 0.001). These findings suggest a distinct immune regulatory pattern characterized by regulatory cell enrichment and relatively low expression of classical immune checkpoint molecules.

HER2 expression in urothelial carcinoma was associated with a distinct immune microenvironmental profile characterized by Treg enrichment and relatively low immune checkpoint expression, as supported by our protein-level validation. These findings provide additional biological context for the potential therapeutic benefit of combining RC48 with ICIs. Given the exploratory nature of the HER2-high definition and the limited sample size of the validation cohorts, further prospective studies are warranted to confirm these observations.