Triple-Negative Breast Tumours Induce Functional Impairment of Peripheral Natural Killer Cells

Background:
Breast cancer is the most common cancer diagnosed in women worldwide. 15-20% of breast
tumours are classified as triple-negative breast cancer (TNBC), meaning that these tumours lack
common targets used for cancer therapy, making them hard to treat. Moreover, TNBC is a very
aggressive subtype of breast cancer with higher likelihood of metastasis to distant organs than
in other subtypes. As distant metastases are the main cause of patient death, there is great
need for novel therapeutic approaches.
Natural killer (NK) cells are innate lymphoid cells capable of limiting distant metastasis by
eliminating tumour cells in the blood stream. However, NK-cell function is often suppressed by
the cancer microenvironment, e.g. through the activation of immune checkpoints. Thus, the aim
of this project is to analyse changes occurring in blood NK cells during the progression of
metastatic TNBC to find novel therapeutic targets improving NK cell function.
Methods:
Blood NK cells from primary TNBC tumour-bearing mice and healthy controls were subjected to
10x Genomics single-cell RNA sequencing. The identified targets and NK-cell functionality were
validated ex vivo and in vitro using a co-cultivation system of NK and TNBC cells. In addition,
flow cytometric analysis of various organs was performed at the primary tumour stage of the
TNBC mouse model. Various organs were used to determine the presence of a premetastatic
niche.
Results:
Single-cell RNA sequencing showed a strong enrichment of blood NK cells with an activated
signature in primary-tumour bearing mice at the stage of premetastatic niche formation.
However, NK cell function- and degranulation-related genes were downregulated in this cluster.
Ex vivo functional analysis confirmed the reduced degranulation potential of peripheral NK cells
from tumour-bearing mice. Similar changes in the NK cell phenotype could be mimicked by an in
vitro co-cultivation system of NK and TNBC cells. Moreover, in vitro co-cultivation assays
suggest that NK cells need direct contact to TNBC cells to become functionally impaired.
Currently, targeting of relevant genes that might reverse the observed phenotype is explored.
Discussion:
Systemic alterations in NK cells are already present at the primary tumour stage, which
potentially dampens their potential to limit TNBC metastasis. Further analysis of factors
contributing to this functional impairment could provide new therapeutic targets to limit
metastasis formation in patients and thus improve their survival.