Longitudinal Biopsies in mBC Map Immune Response to HER2 Tri-Blockade

Resistance remains a defining challenge in HER2+ metastatic breast cancer, particularly after multiple lines of targeted therapy. While immunotherapy combinations have shown signals of activity, clinicians still lack clarity on why some tumors respond and others rapidly fail. But longitudinal tissue profiling may help bridge this gap by revealing how the tumor microenvironment evolves under therapy.

A 2025 study published in the Journal for ImmunoTherapy of Cancer integrates serial tumor biopsies with single-cell analyses to examine immune dynamics during combined HER2 and checkpoint blockade. Rather than cataloging static biomarkers, the study focuses on changes over time that distinguish response from resistance.

Here’s an in-depth look at its design and findings.

A Phase II Trial Built Around Serial Tumor Sampling

The multicenter phase II trial enrolled patients with HER2+ metastatic breast cancer resistant to prior HER2-directed regimens. Patients received KN046, a bispecific PD-L1 and CTLA-4 antibody, combined with KN026, a dual-epitope anti-HER2 bispecific antibody. The objective response rate was 47.2%, with a median progression-free survival of 5.6 months.

Seventeen patients underwent pretreatment and/or on-treatment biopsies, enabling longitudinal single-cell RNA and T-cell receptor sequencing across more than 330,000 cells. Tumors were categorized as responders or non-responders using RECIST criteria.

Responders Show Preserved Immune Architecture Under Therapy

In responding tumors, CD8+ T cells demonstrated clonal expansion, particularly among precursor exhausted subsets known to mediate checkpoint responsiveness. Natural killer cell and dendritic cell populations were preserved.

And rather than an immune cell influx, response was characterized by immune durability. Effector populations survived treatment and remained functionally engaged—a finding that contrasts with the rapid immune attrition seen in non-responders.

Immune Collapse, Not Baseline Absence, Defines Non-Response

A central and clinically striking finding was that non-response was driven by immune loss during treatment. Despite comparable baseline immune infiltration, non-responding tumors showed rapid depletion of CD8+ T cells, CD4+ T cells, natural killer cells, and dendritic cells after therapy initiation.

Single-cell analyses linked this decline to increased apoptosis rather than physical exclusion. In effect, treatment coincided with collapse of the immune compartments required for both checkpoint activity and HER2 antibody–mediated mechanisms.

Macrophage Burden Signals Resistance Before Treatment Starts

Baseline myeloid composition strongly differentiated outcomes. Non-responders entered therapy with higher levels of tumor-associated macrophages and monocytes expressing immunosuppressive features.

During treatment, macrophages in responders shifted toward inflammatory and antigen-presenting programs, while those in non-responders remained refractory to activation. This finding suggests that macrophage burden and plasticity may represent a more actionable resistance marker than lymphocyte counts alone, with potential implications for patient selection or combination strategies.

Tumor and Vascular Context Reinforces Immune Failure

Non-responding tumors also showed fewer lymphatic endothelial cells, a feature associated with impaired tumor-draining lymphatic function and reduced peripheral T-cell priming. The ratio of macrophages to lymphatic endothelial cells emerged as a composite indicator of resistance, integrating immune and stromal features into a single risk signal.

What Longitudinal Tissue Profiling Adds to Combination Strategy Design

This study suggests that successful HER2 tri-blockade requires preservation and activation of a multi-cellular immune network. Resistance appears to emerge from baseline immunosuppression compounded by the treatment-associated loss of effector populations rather than the failure of checkpoint engagement alone.

For clinicians, a key insight is that baseline macrophage burden and early immune collapse may help identify patients unlikely to benefit from this therapy. While limited by sample size and lesion accessibility, the findings support longitudinal tissue analysis as a tool to identify resistance mechanisms early and guide rational combination strategies in HER2+ metastatic disease.

Reference:
Liao JY, Wang J, Li H, et al. Longitudinal tissue analysis reveals microenvironmental changes correlate with combined immunotherapy and targeted therapy response in metastatic breast cancer. J Immunother Cancer. 2025;13(10):e012629. Published 2025 Oct 5. doi:10.1136/jitc-2025-012629