# High levels of circulating miR-19a-3p in patients with metastatic HER2 + breast cancer are associated with a favorable prognosis and anti-tumor immune responses

## TL;DR

High levels of miR-19a-3p in the blood of HER2-positive breast cancer patients are linked to better outcomes and stronger immune responses.

## Contribution

The study identifies that elevated miR-19a-3p may result from effective NK cell activity and Th1 cell activation in HER2 + breast cancer patients.

## Key findings

- In vitro ADCC by NK cells increases miR-19a-3p levels in supernatants after killing cancer cells.
- CD4 + Th1 cells secrete more miR-19a-3p than Th2 cells and develop a TCM phenotype.
- Patients with high miR-19a-3p levels have more activated T and NK cells and better prognosis.

## Abstract

Trastuzumab, combined with chemotherapy, is the current standard treatment for both metastatic and early-stage HER2-positive (HER2 +) breast cancer. One of the mechanisms of action of trastuzumab is antibody-dependent cellular cytotoxicity (ADCC), which involves engaging FcγRIIIA (CD16) on natural killer (NK) cells. A competent immune system and properly functioning NK cells are crucial for effective ADCC, as they can influence favorable clinical outcomes. Resistance to trastuzumab often develops after about one year. We previously reported that elevated levels of miR-19a-3p in the serum of patients with metastatic HER2 + breast cancer treated with trastuzumab were associated with a favorable prognosis. Here, we aim to identify the mechanism and the immune cells responsible for elevated serum levels of miR-19a-3p.

Peripheral blood mononuclear cells (PBMCs) from healthy individuals were used to isolate naïve CD4 + T cells and NK cells. Naïve CD4 + T cells were polarized into CD4 + Th1 and CD4 + Th2 cells. NK cells were utilized for the ADCC assay. Levels of transcription factors, cytokines, and miR-19a-3p were measured using RT-qPCR. Surface markers and cytokines were analyzed by flow cytometry to characterize immune cell phenotypes.

In vitro NK cell-mediated ADCC resulted in increased levels of miR-19a-3p released into the supernatants after killing breast cancer cells. In vitro polarized CD4 + Th1 cells expressed and secreted higher levels of miR-19a-3p than CD4 + Th2 cells. Over a long-term in vitro culture (24 days), anti-CD3/CD28 restimulation sustained higher levels of miR-19a-3p in CD4 + Th1 cells compared to CD4 + Th2 cells and their respective supernatants. CD4 + Th1 cells developed a central memory T (TCM) phenotype (CD45RO + CCR7 + CD62L +) and expressed and secreted higher levels of miR-19a-3p than CD4 + Th2 cells. In patients with HER2 + metastatic breast cancer, those with elevated serum levels of miR-19a-3p and a favorable prognosis had a larger percentage of circulating activated T cells and NK cells in their blood compared to patients with lower serum levels of miR-19a-3p and a poor prognosis. The small cohort (n = 15) limits the statistical power of our retrospective study.

Our findings suggest that elevated levels of miR-19a-3p in the serum of patients with HER2 + metastatic breast cancer may result from effective NK cell-mediated ADCC and activation of CD4 + Th1 cells, which could be responsible for the anti-tumor immune response associated with a favorable prognosis. Blood levels of miR-19a-3p might help identify breast cancer patients who have effective trastuzumab-induced anti-tumor immune responses.

The online version contains supplementary material available at 10.1186/s13058-025-02174-8.