Two studies published in the latest issue of the journal cell Researchers at the University of Pittsburgh have discovered how immunotherapies that target the immune checkpoints PD1 and LAG3 work together to activate immune responses. The findings shed light on why combination therapies that target both checkpoints may improve outcomes for melanoma patients compared with monotherapies that target only PD1.

Using data from a human clinical trial and animal models, researchers studied the responses of tumor-killing CD8+ T cells. During protracted battles against cancer, immune checkpoints accumulate on the surface of T cells, acting like brakes on their activity and leading to exhaustion. Immune checkpoint inhibitors that help release these brakes and combat T cell exhaustion have revolutionized cancer treatment. However, because many patients do not respond, more research is needed to understand how these drugs can be combined to improve their effectiveness.

These studies are the first in-depth investigation of the immune system’s response to blocking PD1 and LAG3. We found that targeted blocking of PD1 versus PD1 and LAG3 modulated CD8+ T cell function in surprisingly different ways. Understanding these mechanisms is relevant to our thinking about combination therapies and to optimizing the best drug combinations.”

Dario AA Vignali, Ph.D., chair and distinguished professor of the Department of Immunology at Pitt, lead author of two of the papers

In 2022, the LAG3-targeting drug relatlimab was approved by the U.S. Food and Drug Administration as a combination treatment with nivolumab, which targets PD1, for patients with metastatic melanoma. This combination has significantly improved patient outcomes compared to nivolumab alone, but according to Vignali, the mechanisms underlying this enhanced anti-tumor immunity were unknown. These new studies help fill that gap.

For the first study, Vignali teamed up with co-senior authors John Kirkwood, M.D., Distinguished Service Professor of Medicine at Pitt and director of the Melanoma and Skin Cancer Program at UPMC Hillman Cancer Center, and Tullia Bruno, Ph.D., assistant professor of immunology at Pitt, and lead author Anthony Cillo, Ph.D., assistant professor of immunology at Pitt. The researchers conducted a clinical trial to examine the immune responses of melanoma patients who received relatlimab, nivolumab, or both drugs.

By analyzing blood and tumor samples, they found that patients who received both drugs had enhanced CD8+ T cell responses associated with improved cancer-killing power compared to patients treated with only one of the two drugs, although the cells continued to show the hallmarks of exhaustion.

“We were surprised to see that blocking PD1 and LAG3 simultaneously resulted in much larger changes than would be expected when adding together the effects of blocking PD1 or LAG3 alone,” said Cillo. “These results demonstrate that these immune checkpoints inhibit different aspects of CD8+ T cell function, allowing them to act in unexpected synergy.”

Another key finding from the analysis of patient samples, the researchers say, is that relatlimab is not inert. This study was unique in that patients first received four weeks of therapy with relatlimab alone, nivolumab alone, or in combination, allowing researchers to examine the effect of each regimen. Several previous studies have found that relatlimab alone does not improve anti-tumor immunity, but is only effective when combined with nivolumab. By showing how relatlimab affects T cell responses, the new findings suggest that the therapy could be combined with other immunotherapies to improve responses.

“We are particularly excited about this research because the analyses were performed on samples from patients who had not previously received immunotherapy. This allowed us to assess the impact of LAG3 and PD1 alone and in combination on the immune response in these patients’ tumors,” Bruno said. “This will give us further insight into smart immunotherapy combinations for patients with the hope of improved efficacy.”

The second study, led by Dr. Lawrence Andrews, a senior scientist at Arcellx who conducted this work as a research scientist in Vignali’s lab, and Samuel Butler, a current graduate student in Vignali’s lab, used mice that had been genetically modified so that their CD8+ T cells did not produce PD1, LAG3, or both.

In a mouse model of melanoma, T cells lacking both immune checkpoints improved tumor clearance and survival compared to T cells lacking either PD1 or LAG3, confirming the clinical trial results. Furthermore, their experiments revealed mechanisms whereby PD1 and LAG3 act synergistically to hamper anti-tumor immunity.

A third study, published in the same issue of cellled by researchers at the University of Pennsylvania and co-authored by Vignali, agreed with these observations and provided additional insights into how LAG3 and PD1 contribute differently to T cell exhaustion.

Taken together, these three articles provide mechanistic insights into how PD1 and LAG3 work alone and in combination and suggest opportunities for further clinical development.