Reviving exhausted T cells to tackle immunotherapy-resistant cancers

LA JOLLA, CALIF. – May 03, 2023 – When the cells of our immune system are under constant stress due to cancer or other chronic diseases, the T cells of the immune system shut down in a process called T cell exhaustion. Without active T cells, which kill tumor cells, it’s impossible for our bodies to fight back against cancer. One of the biggest goals of immunotherapy is to reverse T cell exhaustion to boost the immune system’s ability to destroy cancerous cells.

Researchers at Sanford Burnham Prebys studying melanoma have found a new way to make this happen. Their approach, described in Cell Reports, can reduce T cell exhaustion even in tumors that are resistant to clinically approved immunotherapies. It can also help T cells from becoming exhausted.

“Slowing or reversing T cell exhaustion is a huge focus in cancer research, and many researchers are working on different ways to accomplish this,” says first author Jennifer Hope, Ph.D., who completed this research as a postdoctoral researcher at Sanford Burnham Prebys and is now an assistant professor at Drexel University. “This new approach could be a viable treatment on its own, but it also has tremendous potential to work synergistically with existing therapies.”

Although there are established immunotherapies that target T cell exhaustion, the new approach is unique in that it targets several different aspects of the process at once. This means that it could help people overcome resistance to various anti-cancer immunotherapies that are currently available.

“One of the foundational ideas of modern cancer treatment is not relying on a single therapy, since this can cause the cancer to become resistant to that treatment,” says senior author Linda Bradley, Ph.D., a professor in the Cancer Metabolism and Microenvironment Program at Sanford Burnham Prebys. “The more tools at our disposal to slow down or reverse T cell exhaustion in different ways, the better chance we have of improving precision medicine and helping more people with cancer benefit from immunotherapy.”

Their approach hinges on a protein called PSGL-1, which is found in most blood cells. By studying mice with a genetic deficiency in PSGL-1, the researchers determined that this protein helps facilitate T cell exhaustion, a major roadblock to effective anti-cancer immunity.

The researchers then used an antibody to block the activity of PGSL-1 in mice with immunotherapy-resistant melanoma. They found that targeting PSGL-1 slowed the process of T cell exhaustion and helped exhausted T cells switch back into functioning T cells. These two effects significantly reduced tumor growth in the mice.

“One of the things that makes this approach unique compared to existing immunotherapies is that it directly alters the way T cells become exhausted and helps them regain their function,” says Hope. “I think this is going to be crucial in terms of its translational potential.”

The researchers were also able to replicate this effect in mice with mesothelioma, suggesting that the approach could be applicable to a wide range of cancers. Although the treatment they used in this study is not yet suited for clinical use in humans, the overall approach of using antibodies or recombinant proteins for immunotherapy is well established. This means that translating these results for people with cancer may just be a matter of time and testing.

“Once we’ve done all the necessary science, this could be really valuable, or even lifesaving, for a lot of people with cancers that are resistant to current treatments,” says Bradley. “We still have a long way to go, but I’m optimistic that we’re onto something game-changing here.”

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Additional authors on the study include Dennis C. Otero, Eun-Ah Bae, Christopher J. Stairiker, Ashley B. Palete, Hannah A. Faso, Michelle Lin, Monique L., Henriquez, Sreeja Roy, Xue Lei, Eric S. Wang, Savio Chow, Roberto Tinoco, Kevin Yip, Alexandre Rosa Campos, Jun Yin, Peter D. Adams and Linda M. Bradley, Sanford Burnham Prebys; Anjana Rao and Hyungseok Seo, La Jolla Institute for Immunology; and Gregory A. Daniels, Moores Cancer Center at UC San Diego Health.

The study was supported by grants from the American Cancer Society (PF-20-113-01-LIB), the National Institutes of Health (T32 AI125209, R01 AI106895, R21 CA249353, R21 CA216678, R03 CA252144, R01 AI040127, R01 AI109842, P30 CA030199), the Melanoma Research Alliance (MRA 696326), the Department of Defense (W81XWH-20-1-0324), the American Association of Immunologists, the San Diego Cancer Centers Council (C3 2018), the Association of Immunologists Careers in Immunology Fellowship Program, and was supported in part by the following Sanford Burnham Prebys Core facilities: Flow Cytometry, Vivarium, Histology, Bioinformatics, Proteomics, and Cancer Metabolism.

The study’s DOI is 10.1016/j.celrep.2023.112436

About Sanford Burnham Prebys

Sanford Burnham Prebys is an independent biomedical research institute dedicated to understanding human biology and disease and advancing scientific discoveries to profoundly impact human health. For more than 45 years, our research has produced breakthroughs in cancer, neuroscience, immunology and children’s diseases, and is anchored by our NCI-designated Cancer Center and advanced drug discovery capabilities. For more information, visit us at SBPdiscovery.org or on Facebook facebook.com/SBPdiscovery and on Twitter @SBPdiscovery.