Cancer treatment routinely involves taking out lymph nodes near the tumor in case they contain metastatic cancer cells. But new findings from a clinical trial by researchers at UC San Francisco and Gladstone Institutes have shown that immunotherapy can activate tumor-fighting T cells in nearby lymph nodes.

The team’s study of CD8+ T cell populations in human head and neck squamous cell carcinomas identified a role for lymph nodes in modulating antitumor responses in response to immune checkpoint blockade (ICB) immunotherapy. Results from the newly reported human study suggest that leaving lymph nodes intact until after immunotherapy could boost efficacy against solid tumors, only a small fraction of which currently respond to these newer types of treatments.

“This work really changes our thinking about the importance of keeping lymph nodes in the body during treatment,” said Matt Spitzer, PhD, an investigator for the Parker Institute for Cancer Immunotherapy and Gladstone-UCSF Institute of Genomic Immunology and senior author of the team’s study, which is published in Cell. In their paper, which is titled “Dynamic CD8+ T cell responses to cancer immunotherapy in human regional lymph nodes are disrupted in metastatic lymph nodes,”  the authors concluded, “These results lay a foundation for the future development of immunotherapies that optimally harness anti-tumor immunity in human LNs and inform immune-monitoring strategies for cancer patients treated with ICB.”

Immune checkpoint blockade (ICB) immunotherapy targeting the PD-1/PD-L1 axis has “revolutionized oncology,” the authors noted. “CD8+ T cells are central effector cells that mediate the efficacy of ICB and have been extensively studied in the tumor microenvironment (TME).” However, the mechanisms that underlie immunotherapy remain incompletely understood, especially in humans, they continued.

In settings such as cancer, antigen-specific CD8+ T cells can become exhausted. Studies in mice have shown that progenitor or precursor exhausted cells (Tpex) may differentiate into transitional intermediated exhausted cells (Tex-int) and subsequently into terminally exhausted cells (Tex-term), “losing proliferative capacity and effector functions as they differentiate,” the authors stated. Most immunotherapies are aimed only at reinvigorating  the potentially exhausted T cells in the tumor. But the new research shows that allowing the treatment to activate the immune response of the lymph nodes as well can play an important role in driving positive response to immunotherapy.

Lymph nodes are often removed because they are typically the first place metastatic cancer cells appear, and without surgery, it can be difficult to determine whether the nodes contain metastases. And as the team noted, “Despite the potential importance of the tdLN [tumor-draining lymph nodes] in ICB-driven CD8+ T cell responses, a lack of LN sampling in clinical datasets leaves many unanswered questions about the relationship between the immune responses in the LN and tumor in human cancer patients.”

“Immunotherapy is designed to jump start the immune response, but when we take out nearby lymph nodes before treatment, we’re essentially removing the key locations where T cells live and can be activated,” Spitzer said, noting that the evidence supporting the removal of lymph nodes is from older studies that predate the use of today’s immunotherapies.

Researchers have largely been working under the assumption that cancer immunotherapy works by stimulating the immune cells within the tumor, Spitzer continued. But in a 2017 study in mice, Spitzer showed that immunotherapy drugs are actually activating the lymph nodes. “That study changed our understanding of how these therapies might be working,” he said. Rather than the immunotherapy pumping up the T cells in the tumor, T cells in the lymph nodes are likely the source for T cells circulating in the blood. Such circulating cells can then go into the tumor and kill off the cancer cells. The authors further wrote, “… recent studies found that CD8+ T cells in the periphery, such as in secondary lymphoid organs (SLOs) including tumor-draining (td) lymph nodes (LNs), are integral for ICB response in mouse models.”

Having shown that intact lymph nodes can temper cancer’s hold in mice, Spitzer’s team wanted to know whether the same would prove true in human patients. They designed their trial to include patients with head and neck cancers because of the high number of lymph nodes in those areas. “We examined CD8+ T cells in human head and neck squamous cell carcinomas, regional LNs, and blood using mass cytometry, single-cell genomics, and multiplexed ion beam imaging.”

The study included 12 patients whose tumors hadn’t yet metastasized past the lymph nodes. Such patients would typically undergo surgery to remove the tumor, followed by other treatments if recommended. Instead, patients first received a single cycle of the anti-PD-L1 immunotherapy drug atezolizumab. A week or two later, Spitzer’s team measured how much the treatment had activated the patients’ immune systems.

As part of the study each patient’s tumor and nearby lymph nodes were surgically removed after immunotherapy and analyzed to determine how the immunotherapy had affected them. The team found that, after immunotherapy, the cancer-killing T cells in the lymph nodes began springing into action. They also found higher numbers of related immune cells in the patients’ blood. “Changes in uiLNs [uninvolved lymph nodes] correlated with an increase in proliferating Tex-int in peripheral blood.” Spitzer attributes some of the trial’s success to its design, which allowed the team to get a lot of information from a small number of patients by looking at the tissue before and after surgery, and by running detailed analyses.

“Being able to collect the tissue from surgery shortly after the patients had been given the drug was a really unique opportunity,” he said. “We were able to see, at the cellular level, what the drug was doing to the immune response.” That kind of insight would be challenging to get from a more traditional trial in patients with later-stage disease, who would not typically benefit from undergoing surgery after immunotherapy.

Another benefit of the study design was that it allowed researchers to compare how the treatment affected lymph nodes with and without metastases. “No one had looked at metastatic lymph nodes [metLNs] in this way before,” said Spitzer. “We could see that the metastases impaired the immune response relative to what we saw in the healthy lymph nodes.” The authors noted, “Patients with metLNs also experienced weaker CD8+ T cell responses in the blood following treatment, supporting an important role for LNs in generating circulating CD8+ T cell responses that associate with clinical response.” The results, they noted, “… add to a developing understanding of the impact of metastases in LN on the anti-tumor immune response.”

It could be that the T cells in these metastatic nodes were less activated by the therapy, Spitzer said. If so, that could explain, in part, the poor performance of some immunotherapy treatments. “ … regional lymph nodes with tumor metastasis (metLNs) exhibited an impairment in these responses to ICB associated with immunosuppressive cellular niches around Tpex and a reduction in the circulating CD8+ T cell response.”

Even so, the treatment prompted enough T-cell activity in the metastatic lymph nodes to consider leaving them in for a short period of time until treatment ends. “Removing lymph nodes with metastatic cancer cells is probably still important but taking them out before immunotherapy treatment may be throwing the baby out with the bathwater,” said Spitzer.

As the authors further concluded, “In summary, our data highlight the important role of CD8+ T cell responses in human LNs at steady-state and after ICB immunotherapy while also revealing the disruption of these key processes by LN metastasis … These results highlight a central role for uiLNs in mediating responses to ICB, which may create new opportunities for next-generation immunotherapies focused on optimally harnessing these responses.”

A subsequent goal of the current trial is to determine whether giving immunotherapy before surgery protects against the recurrence of tumors in the future. Researchers won’t know the answer to that until they’ve had a chance to monitor the participants for several years. “My hope is that if we can activate a good immune response before the tumor is taken out, all those T cells will stay in the body and recognize cancer cells if they come back,” Spitzer said.

Next, the team plans to study better treatments for patients with metastatic lymph nodes, using drugs that would be more effective at reactivating their immune responses.

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