Peter Mac scientists have described in unprecedented detail how the immune system responds to breast cancer, identifying a potential new target for immunotherapy treatments.

The study, led by Professor Sherene Loi, involved a genetic analysis of more than 6300 white blood cells found within tumour samples collected from 129 Peter Mac patients with breast cancer.

These cells, primarily the immune system’s killer T Cells, are Tumour Infiltrating Lymphocytes (TILs) and the study was the first to divide TILs from breast cancer into distinct sub-types.

Results of the ground-breaking study - also a collaboration with The Peter Doherty Institute for Infection and Immunity, and the Walter and Eliza Hall Institute of Medical Research - are published online today in the journal Nature Medicine.

“For some time we’ve known that patients who have more TILs detectable in their tumours generally have better outcomes from cancer treatment, as this indicates a stronger immune response,” says Prof Loi, who is Peter Mac’s head of the Translational Breast Cancer Genomics and Therapeutics Laboratory.

“Our study has taken the next step of identifying the distinct TILs subsets that are driving this enhanced response in some patients, giving us important insights into how we can better use immunotherapies to treat breast cancer.”

One subset - CD8+ T Cells with features of tissue-resident memory - emerged as a common factor across breast cancer tumours that had high numbers of TILs.

A further analysis involving a broader pool of patient genetic information found this same T Cell subset was associated with improved relapse-free, and overall, survival in patients who had Triple Negative breast cancer – the most aggressive form of breast cancer.

It is thought this T Cell subset is the key modulator of the immune response against breast cancer – particularly in Triple Negative breast cancer – and existing and new immunotherapies targeting this may lead to improved treatments.

The paper titled “Single-cell profiling of breast cancer T cells reveals a tissue-resident memory subset associated with improved prognosis” is available online at journal Nature Medicine.