- Regulatory T cells are particularly good at suppressing the anticancer immune response.
- Immunosuppression occurs because current immunotherapy targets molecules present both on regulatory T cells in the tumor and regulatory T cells outside of the tumor.
- Targeting molecules that are selectively present in the tumor can improve efficacy of immunotherapy.
A subset of our immune cells (called regulatory T cells) that are highly abundant in the tumor microenvironment and are particularly good at suppressing the anticancer immune response.
In two independent studies, published in Immunity
, scientists describe the distinct features and differences in molecules expressed by regulatory T cells inside of human breast, colon, and lung tumors compared to normal tissue that could be potential biomarkers or therapeutic targets.
‘Targeting molecules on regulatory T cells are selectively present in the tumor can result in comparable efficacy and fewer adverse events.’
While immunotherapy have been successful for some types of tumors, such as melanoma, up to 40% of patients report serious adverse events.
"Our working hypothesis is that most of the adverse effects that patients experience with these immunotherapy treatments is because they are targeting molecules that are present both on regulatory T cells in the tumor and regulatory T cells outside of the tumor," says Sergio Abrignani, co-lead author on one of the studies with Massimiliano Pagani.
Targeting molecules that are selectively present in the tumors, can result in comparable efficacy and fewer adverse events.
"We are discovering a lot of new markers for these cells that can be used to make future therapies safer."adds Pagani.
Their study, analyzed tissue samples collected from nearly 200 patients with colon and lung cancer and compared them to normal tissue and peripheral blood.
The researchers identified specific signature molecules and genes not previously associated with regulatory T cells that could be detected in both primary and metastatic tumors.
Certain molecules may even be potential biomarkers for poor prognosis.
"We know that tumors that are highly infiltrated with regulatory T cells are bad, but our paper also shows that tumors with the highest expression of signature molecules on intratumoral regulatory T cells had the worst outcomes," Abrignani says.
The other Immunity study, led by Alexander Rudensky of the Ludwig Center at Memorial Sloan Kettering Cancer Center, looked specifically at the distinct feature of regulatory T cells from over 100 human breast tumors removed during surgery.
They found that compared to normal tissue and peripheral blood, breast tumors possess an increased presence of regulatory T cells and that the most aggressive breast cancers have the highest number of the cells.
In the analysis of the immune cells by Rudensky's team, the most notable contrast was increased expression of chemokine receptor protein CCR8 in the tumor-resident cells in breast and other cancers
(also found to be overexpressed in colon and lung tumors in Abrignani and Pagani's study).
"What's remarkable is the differential expression of CCR8; it is a very clear and clean marker that distinguishes regulatory T cells in the tumor," says Rudensky, also of the Howard Hughes Medical Institute. "This suggests one path to a more selective strategy to deplete regulatory T cells present in breast and other types of cancer."
The studies reveal a more complete picture of the interactions between different immune cell types and the tumor microenvironment.
Both sets of researchers hope to use what they have learned about the unique properties of regulatory T cells in tumor sites to improve cancer immunotherapies--drugs that stimulate immune cells to attack cancer cells.