Tertiary Lymphoid Structures Validated as Biomarker

New trial data confirm the potential of so-called tertiary lymphoid structures (TLS) as a predictive biomarker of responsiveness to checkpoint blockade, with evidence that combining anti–PD-1/PD-L1 agents with angiogenesis inhibitors can enhance treatment efficacy and improve how patients with TLS-positive tumors fare.

TLSs are lymph node–like clusters of immune cells that form at sites of prolonged inflammation, including tumors. Comprised mostly of B cells, T cells, and supporting dendritic cells—along with specialized blood vessels known as high endothelial venules (HEV) that help facilitate immune cell recruitment—these structures are increasingly recognized as important orchestrators of an organized antitumor immune response.

Retrospective analyses previously linked TLS presence to improved outcomes after checkpoint blockade therapy. However, prospective trial data were lacking—which is where the REGOMUNE trial comes in.

Led by Sophie Cousin, MD, and Antoine Italiano, MD, PhD, both of Institut Bergonié in Bordeaux, France, REGOMUNE is a single-arm, multicohort study of the PD-L1 inhibitor avelumab (Bavencio; EMD Serono/Pfizer) with regorafenib (Stivarga; Bayer), a multikinase-directed drug with anti-angiogenic activity owing to its dual targeted VEGFR–TIE2 inhibition.

The trial included 38 patients with 19 types of progressive cancer, each exhibiting signs of TLSs, as identified through a double-staining technique that tests for the co-occurrence of CD20-expressing B cells and CD23-positive dendritic cells. It is the first-ever histology-neutral study of patients recruited based on TLS positivity alone.

“The approach is truly tumor-agnostic,” says Joseph Skitzki, MD, of Roswell Park Comprehensive Cancer Center in Buffalo, NY, who was not involved in the trial. “Responses appear to be impressive in tumors that are not typically known to be sensitive to immunotherapy and thus validates their rationale.”

Among the 34 patients evaluated for efficacy, eight experienced a clinical response and nine others displayed less-pronounced signs of tumor shrinkage. The median progression-free and overall survival times were 3.6 months and 8.6 months, respectively. Grade 3 and 4 adverse events included hand-foot syndrome, skin rashes, fatigue, and mouth sores.

Notably, positive responses were observed in tumors typically refractory to anti–PD-1/PD-L1 therapy, including sarcoma, biliary tract cancer, and small bowel cancer. And 6 months after initiating treatment, 12 of the 34 patients remained progression free—all indications that the drug regimen is helping patients with TLS-positive tumors achieve “durable responses even in traditionally immunotherapy-resistant indications,” says Italiano, who presented the findings at the Society for Immunotherapy of Cancer (SITC) Annual Meeting in San Diego, CA, November 3–5.

Why the drug combination is eliciting such favorable responses is unclear. Without molecular analyses, it's difficult to say what's happening biologically, notes Sapna Patel, MD, of The University of Texas MD Anderson Cancer Center in Houston. And without a trial arm in which patients with TLS-positive tumors receive regorafenib monotherapy, researchers can't say whether the anti-angiogenesis effect alone or the synergy of the drugs provides the clinical benefit, she says.

By normalizing tumor blood vessels and blocking immunosuppressive cells, regorafenib may remodel the tumor microenvironment to potentiate the effects of the anti–PD-L1 therapy. Or the anti-VEGFR therapy may induce the formation of HEVs, leading to enhanced immune cell infiltrates upon which the checkpoint-blocking drugs can act.

“The results are quite striking,” Patel says. “But the missing link here is the on-treatment biopsy.”

Another uncertainty arises from the way the study authors tested for TLS positivity. Whereas the Bergonié team used CD20/CD23 staining, others have relied on more traditional histochemical techniques. For example, Genentech scientists, in an exploratory analysis of phase III data involving patients who had non–small cell lung cancer treatment with its anti–PD-L1 drug atezolizumab (Tecentriq) or chemotherapy, defined TLSs by the presence of dense lymphoid aggregates and at least one germinal center, finding improved survival among immunotherapy recipients with TLS-positive tumors.

The company reported the results at the SITC meeting—and they were not alone in stratifying by TLS signature. “Using TLS as a biomarker for response in clinical trials and/or entry is something that is gaining traction,” says Tullia Bruno, PhD, of the UPMC Hillman Cancer Center in Pittsburgh, PA. “Almost every SITC presentation that I went to with clinical trials talked about incorporating this.”

However, the absence of standardized criteria for assessing TLS presence raises concerns about the comparability and consistency of the various analyses associated with these structures. “I do not believe there is yet a bona fide marker for mature TLS,” says James Mulé, PhD, of the Moffitt Cancer Center in Tampa, FL. “Until we figure this out,” he adds, “using TLS as a biomarker needs more work.” –Elie Dolgin