SAN ANTONIO – Researchers at MD Anderson Cancer Center in Houston and the University of New South Wales (UNSW) in Sydney are among teams from around the world working toward human breast cell atlas development using single-cell genomics, and their efforts to date have yielded new understanding of both the normal breast cell ecosystem and the breast cancer tumor microenvironment.
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The work at MD Anderson, for example, has led to the identification of a number of new gene markers and multiple cell states within breast cell types, according to Tapsi Kumar Seth, who reported early findings from an analysis of more than 32,000 cells from normal breast tissue during a presentation at the San Antonio Breast Cancer Symposium.
At the UNSW’s Garvan Institute of Medical Research, Alexander Swarbrick, PhD, and his colleagues are working to better define the tumor microenvironment at the single-cell level. At the symposium, Dr. Swarbrick presented interim findings from cellular analyses in the first 23 breast cancer cases of about 200 that will be studied in the course of the project.
Improved understanding of the cellular landscape of both normal breast tissue and breast cancer tissue should lead to new stromal- and immune-based therapies for the treatment of breast cancer, the investigators said.
The normal breast cell ecosystem
The MD Anderson researchers studied 32,148 stromal cells from pathologically normal breast tissues collected from 11 women who underwent mastectomy at the center.
Unbiased expression analysis identified three major cell types, including epithelial cells, fibroblasts, and endothelial cells, as well as several minor cell types such as macrophages, T-cells, apocrine cells, pericytes, and others, said Ms. Seth, a graduate student in the department of genetics at the center and a member of the Navin Laboratory there.
The work is designed to help identify the presence and function of cells and explain how they behave in a normal breast ecosystem, she said.
“We know that a female breast undergoes a lot of changes due to age, pregnancy, or when there is a disease such as cancer, so it’s essential to chart out what a normal cell reference would look like,” she said.
Toward that goal, a protocol was developed to dissociate the tissue samples within 2 hours due to the decline in viability seen in cells and RNA over time. Analysis of the cell states revealed different transcriptional programs in luminal epithelial cells (hormone receptor positive and secretory), basal epithelial cells (myoepithelial or basement-like), endothelial cells (lymphatic or vascular), macrophages (M1 or M2) and fibroblasts (three subgroups) and provided insight into progenitors of each cell types, she said.
A map was created to show gene expression and to identify transcriptomally similar cells.
“We were able to identify most of the major cell types that are present in human breasts,” she said. “What was interesting was that the composition of these cells also varied across women.”
For example, the proportion of fibroblasts was lower in 3 of the 11 patients, and even though the cells were pathologically normal, immune cell populations, including T-cells and macrophages, were also seen.
Adipocytes cannot be evaluated using this technology because they are large and the layer of fat cells must be removed during dissociation to prevent clogging of the machines, she noted, adding that “this is really a limitation of our technology.”
A closer look was taken at each of the major cell types identified.