Soluble HER2 Drives CD8⁺ T-Cell Exhaustion and Limits Immunotherapy Response in HER2-Low Triple-Negative Breast Cancer
Key Insights
HER2 (search)-low TNBC patients exhibit a shift in CD8⁺ T-cell differentiation toward effector and effector-memory phenotypes with increased exhaustion marker expression.
Elevated circulating soluble HER2 extracellular domain (search) (HER2 (search) ECD) was identified in HER2-low TNBC and shown to directly induce T-cell exhaustion in vitro.
HER2 (search)-low tumors demonstrated a significantly reduced pathological complete response rate following PD-1 (search)-based immunotherapy compared to HER2-zero tumors.
A retrospective translational analysis has uncovered a distinct immune microenvironment in HER2-low triple-negative breast cancer (search) (TNBC) that may explain the heterogeneous response to immunotherapy observed in this clinically relevant subgroup. The findings, published in Nature, reveal that soluble HER2 (search) antigen shedding drives chronic CD8⁺ T-cell dysfunction, ultimately limiting the effectiveness of PD-1 (search)-based immunotherapy.
The study analyzed peripheral blood mononuclear cells (PBMCs) from patients with HER2 (search)-zero and HER2-low TNBC using flow cytometry to characterize CD8⁺ T-cell differentiation and functional states. While overall proportions of peripheral T cells were comparable between groups, a notable shift emerged in the HER2-low cohort: CD8⁺ T cells displayed a bias toward effector and effector-memory phenotypes, accompanied by increased expression of exhaustion markers.
Soluble HER2 (search) ECD as a Driver of Immune Dysfunction
Circulating levels of soluble HER2 extracellular domain (search) (HER2 (search) ECD) were quantified by ELISA, revealing significantly elevated levels in patients with HER2-low disease. To investigate the functional consequences, researchers performed in vitro assays using purified recombinant HER2 ECD. The experiments demonstrated that recombinant HER2 ECD was sufficient to induce time-dependent activation followed by exhaustion-like phenotypes in CD8⁺ T cells. Furthermore, HER2 blockade in tumor-derived conditioned media partially attenuated these immunomodulatory effects, confirming the role of shed HER2 antigen in driving T-cell dysfunction.
Serum cytokine profiles were assessed using Luminex assays, providing additional context to the systemic immune alterations associated with HER2 (search)-low disease.
Clinical Implications for Immunotherapy
The clinical relevance of these findings was underscored by comparing responses to neoadjuvant chemotherapy with or without PD-1 (search)-based immunotherapy between HER2 (search)-low and HER2-zero subgroups. HER2-low tumors showed a significantly reduced pathological complete response (pCR) rate following PD-1-based immunotherapy, suggesting that the antigen-driven T-cell exhaustion state compromises the therapeutic benefit of immune checkpoint blockade.
In vivo validation using a syngeneic mouse model further supported the translational findings. HER2 (search)-targeted therapy, when combined with PD-1 (search) blockade, enhanced antitumor efficacy and improved CD8⁺ T-cell function, pointing toward a rational combination strategy to overcome the immunosuppressive effects of chronic HER2 antigen exposure.
A Model of Antigen-Mediated Immune Evasion
Taken together, the findings support a model in which tumor antigen shedding contributes to systemic immune modulation and may limit responsiveness to immunotherapy. The authors conclude that targeting HER2 (search)-associated antigen dynamics may represent a potential strategy to improve immunotherapeutic outcomes in HER2-low TNBC, a population for whom current PD-1 (search)-based regimens may be suboptimal due to underlying T-cell exhaustion driven by soluble HER2.