“We’ve been quite successful with our multiplex service, and the Vectra® imaging system has helped our investigators to perform cellular phenotyping in the tumor microenvironment,” said Dr. Chanthaphavong.
Our next speaker was Dr. Kristin G. Anderson, a Senior Postdoctoral Research Fellow in the Greenberg Lab at Fred Hutchinson. She offered her perspective as a frequent user of the multiplex immunohistochemistry (mIHC) services from the Experimental Histopathology Core Lab.
One of the main hypotheses being tested in the Greenberg lab is how engineered T cells can be used to treat ovarian cancer, specifically high-grade serous carcinoma – the most common and most deadly ovarian cancer.
Dr. Anderson and her colleagues have developed CD8 T cells engineered to express a high-affinity T-cell receptor specific for an ovarian cancer antigen. They aim to use these T cells to slow tumor growth and prolong survival in patients.
The team uses the ID8VEGF mouse model in their research because it recapitulates characteristics of human ovarian cancer. Vascular endothelial growth factor (VEGF) and mesothelin, a self-protein thought to promote excessive growth, are both overexpressed in this model as well as in high-grade serous ovarian cancer.
In Dr. Anderson’s presentation, she focused on her lab’s efforts to target mesothelin with their engineered T cells. In an early experiment, they observed that while engineered mesothelin-specific T cells can infiltrate ID8VEGF tumors, they do not persist for very long. Additionally, when the engineered T cells were taken out of the tumor 21 days after infiltration, it was observed that the cells lost their ability to make anti-tumor cytokines. This correlated with the expression of markers thought to be inhibitory receptors.
To understand this phenomenon, the Greenberg lab worked closely with the Experimental Histopathology Core Lab to characterize the tumor microenvironment and determine how the expression of suppressive ligands might be contributing to the dysfunction of T cells in tumors.
Dr. Anderson mentioned a paper published this year, which evaluated the expression of inhibitory receptors on T cells from human ovarian cancer using flow cytometry. Using this technique, they quantified the number of inhibitory receptors on T cells extracted from tumors, showing that T cells can display between 0 to 3 inhibitory receptors.
She noted that while this paper was important, it was lacking in spatial context.
“This [paper] suggests that there are multiple negative signals that these T cells are getting in the tumor microenvironment. But one thing that this particular analysis was lacking, because it was a flow cytometry experiment, was spatial resolution,” said Dr. Anderson.
Using mIHC services from the Experimental Histopathology Core Lab, Dr. Anderson’s team imaged tumor tissues to identify where these inhibitory receptors are being expressed in the ID8VEGF mouse model. The Core Lab developed panels for the Vectra® system to visualize the engineered T cells and inhibitory receptors Lag-3, PD-1, and Tim-3. They observed that the T cells with inhibitory receptors were clustering in the center of the tumor, suggesting that there is a spatial component involved in the cells recognizing antigens.
CD8+ T cells in human (top) and mouse (bottom) ovarian tumors can
co-express PD-1, Tim-3 and Lag-3 (Images courtesy of Dr. Kristin Anderson)