NEW YORK – Three new studies published in Nature on Wednesday have found that the presence of B cells in compartments called tertiary lymphoid structures (TLS) in human tumors is associated with a favorable response to immunotherapy.
In a study led by MD Anderson Cancer Center's Jennifer Wargo, an international team of investigators performed bulk RNA sequencing on tumors from a cohort of melanoma patients from a previously conducted neoadjuvant immune checkpoint blockade (ICB) trial. They found that B cell markers were the most differentially expressed genes in the tumors of the patients who responded to treatment compared to those who did not respond.
Further, the researchers corroborated their findings using a computational method to estimate the immune and stromal composition of tumors in this cohort and in two other cohorts of melanoma and renal cell carcinoma patients treated with checkpoint inhibitors. As histological evaluations highlighted the localization of B cells within tertiary lymphoid structures, the researchers assessed the potential functional contributions of B cells via bulk and single-cell RNA sequencing. Mass cytometry showed that switched memory B cells were enriched in the tumors of responders.
"Together, these data provide insights into the potential role of B cells and tertiary lymphoid structures in the response to ICB treatment, with implications for the development of biomarkers and therapeutic targets," the authors wrote.
In a study led by INSERM's Wolf Fridman, researchers studied the variability of clinical response that patients with soft-tissue sarcomas have to therapies such as ICB. They studied gene expression profiles in 608 tumors across subtypes of soft-tissue sarcoma and established an immune-focused classification based on the composition of the tumor microenvironment in each tumor.
From this analysis, the team identified five distinct phenotypes: immune-low (A and B), immune-high (D and E), and highly vascularized (C) groups. In situ analysis of an independent validation cohort showed that class E was characterized by the presence of TLS that contained T cells and follicular dendritic cells, and which were particularly rich in B cells. The researchers also found that B cells were the strongest prognostic factor even in the context of high or low CD8-positive T cells and cytotoxic contents. Further, the class E group demonstrated improved survival and a high response rate to PD-1 blockade with pembrolizumab (Merck's Keytruda) in a Phase II clinical trial.
"Together, this work confirms the immune subtypes in patients with soft-tissue sarcoma, and unravels the potential of B-cell-rich tertiary lymphoid structures to guide clinical decision-making and treatments, which could have broader applications in other diseases," the authors wrote.
In the third study, which was led by Lund University's Göran Jönsson, researchers used metastatic melanoma clinical samples to investigate the role of B cells in anti-tumor response. They found that the co-occurrence of tumor-associated CD8-positive T cells and CD20-positive B cells was associated with improved survival, independent of other clinical variables.
The researchers conducted immunofluorescence staining of CXCR5 and CXCL13 in combination with CD20 to reveal the formation of TLS in the CD8-positive and CD20-positive tumors. They then derived a gene signature associated with TLS, which predicted clinical outcomes in cohorts of patients treated with ICB. Further, they found that tumors rich in B cells were accompanied by increased levels of memory T cells or increased levels of TCF7-positive naive cells. To further corroborate these findings, the researchers gathered digital spatial-profiling data, which showed that T cells in tumors without TLS had a dysfunctional molecular phenotype.
"Our results indicate that tertiary lymphoid structures have a key role in the immune microenvironment in melanoma, by conferring distinct T cell phenotypes," the authors wrote. "Therapeutic strategies to induce the formation of tertiary lymphoid structures should be explored to improve responses to cancer immunotherapy."
In an editorial accompanying the three studies, University of Pittsburgh immunology researcher Tullia Bruno noted that the papers provide doctors with new ways of predicting prognosis for patients who might be helped by immunotherapy.
"The presence of B cells in tumors has been considered to be a predictor of increased patient survival, but there are reports of both anti- and pro-tumor roles for B cells," Bruno said. "The presence of TLS in a tumor also correlates with increased patient survival in many cancer types. The three current studies confirm this trend in the context of immunotherapy, demonstrating that infiltration of B cells into a tumor, along with the presence of TLS, is associated with an improved response to this type of treatment."
The studies in metastatic melanoma and sarcoma patients both found that the presence of B cells in TLS in the tumor before treatment was associated with an increased chance that patients' tumors would respond to immunotherapy, Bruno noted. The third study corroborated these findings in metastatic melanoma patients and found that the same was true in renal cell carcinoma patients who had not yet undergone treatment.
Those authors also demonstrated that during treatment, TLS are more prevalent in people who have tumors that are responding to treatment than in those whose tumors are not, Bruno added. This timing is important because TLS could be considered a predictor of patient response to immunotherapy if they're present before treatment, but their presence during treatment could indicate that combinations of immune cells are inducing TLS formation.
"The three groups found that the B cell and TLS signature was often more pronounced in responders than in non-responders," Bruno wrote. "Furthermore, the signature was more prominent than typical T cell signatures currently used for understanding immunotherapy outcomes. This suggests that B cells and TLS could have a key role in anti-tumor immunity."
Bruno also pointed to unique findings in each study. For example, Jönsson and his colleagues found that B cells in TLS synergize with killer T cells that could ultimately target tumor cells. Fridman and his team described signatures characteristic of mature TLS in sarcoma, implying that mature TLS can exist in tumor sites that are not normally thought to be infiltrated by immune cells. This is "a phenomenon that has not previously been shown," Bruno wrote. And Wargo and her colleagues found increased diversity of B cell receptors in responders compared with non-responders, indicating that pools of B cells in responders might have a greater ability to specifically recognize tumor antigens than B cells of non-responders.
"With regard to clinical implications, the current studies suggest that therapeutics to enhance B cell responses should be prioritized as a complement to T cell-mediated immunotherapies," Bruno concluded. "Researchers should now ask whether B cells could be engineered to target specific tumor antigens, similar to current efforts to engineer antigen-targeting T cells."