Through extensive single-cell analysis, researchers at The University of Texas MD Anderson Cancer Center have created a spatial map of tumor-infiltrating B (TIB) cells and plasma cells (PCs) in early-stage lung cancers, highlighting previously unappreciated roles these immune cells play in tumor development and treatment outcomes.
The study, described in Cancer Discovery, represents is claimed to be the largest and most comprehensive single-cell atlas on tumor-infiltrating B cells and plasma cells to date, and which the researchers say can be used to develop novel immunotherapy strategies.
“We know the tumor microenvironment plays an important role in regulating tumor growth and metastasis, but we have an incomplete understanding of these interactions,” said Linghua Wang, MD, PhD, associate professor of Genomic Medicine. “So far, most of the focus has been on T cells. Our study provides much-needed understanding of the phenotypes of B cells and plasma cells, which also play critical roles in early lung cancer development.”
Wang is co-corresponding author of the team’s published paper, in Cancer Discovery, which is titled “The Single-Cell Immunogenomic Landscape of B and Plasma Cells in Early-Stage Lung Adenocarcinoma.” In their report the authors concluded, “This study provides a much-needed understanding of the transcriptional, clonotypic states and phenotypes of TIBs, unrevealing their potential roles in immunopathology of early-stage LUADs and constituting a roadmap for development of TIB-targeted immunotherapies for treatment of this morbid malignancy.’
Lung adenocarcinoma (LUAD) remains the most frequently diagnosed histological subtype of lung cancer, and accounts for most cancer deaths related to smoking, the team noted. Improved screening approaches have increased the proportion of lung cancers diagnosed at early stages. While surgery is curative for some patients, new treatment approaches are needed because many patients will experience a recurrence of their disease. “… the overall 5-year survival remains below 50%,” the team continued, citing American Cancer Society statistics that suggest the five-year survival rate drops to about seven percent for patients who developed distant metastases.
Understanding the early interactions between cancer cells and immune cells could reveal opportunities to block cancer growth or boost the anti-tumor immune response but, as the team further noted, “Such advances are severely limited by our lagging knowledge of the earliest changes in the tumor microenvironment (TME) during LUAD pathogenesis and that could thus lead to ideal targets for interception.”
Much research focused on understanding the immunobiology of lung cancer has been focused on T cells, and other cell types, in particular, tumor-infiltrating B and plasma cells, have been “mostly overlooked,” and their roles in pathogenesis of solid tumors such as LUAD remain poorly understood, the scientists stated.
Interestingly, previous research co-led by Wang and her colleagues discovered that B lineage cells are critical for responses to immunotherapy in patients with melanoma. Additionally, a study jointly led by Wang and co-corresponding author Humam Kadara, PhD, associate professor of Translational Molecular Pathology, found that B cells and plasma cells were enriched in early-stage lung cancers relative to normal lung tissue. Plasma cells are terminally differentiated B cells responsible for antibody production.
“Recent studies from our group and others demonstrated that TIBs can strongly impact patient responses to anti-cancer chemo- and immunotherapies as well as clinical outcomes in various cancers including melanoma and lung cancer,” the team continued.
To better understand the roles of these cells in early lung cancer development, the researchers performed single-cell analysis on 16 tumors and 47 matched normal lung tissues. The analysis was led by Dapeng Hao, PhD, and Guangchun Han, PhD, in the Wang laboratory, together with Ansam Sinjab, PhD, in the Kadara laboratory.
They performed single-cell RNA sequencing on roughly 50,000 unique B cells and plasma cells to analyze their gene expression profiles. They also completed single-cell B cell receptor (BCR) sequencing on more than 70,000 cells to understand the repertoires of B cell receptors, the membrane-bound proteins on the cell surface that recognize antigens.
“We studied BCRs from ~73K cells and transcriptomes of ~50K cells, the largest single-cell dataset on TIBs to date,” they wrote. “We also correlated TIB characteristics with major clinicopathological features including smoking, driver gene mutation and tumor stage, and assessed their clinical significance such as patient survival and response to immunotherapy.”
The results identified 12 different cell subsets, with more differentiated states (memory B cells and plasma cells) being highly enriched in the tumors relative to adjacent normal tissue. “We demonstrate extensive remodeling of TIBs in the TME [tumor microenvironment] of LUADs, characterized by markedly increased fractions of memory B cells and PCs with more differentiated states,” the team explained. “Our analyses suggest that various microenvironmental factors may have contributed to the altered TIB landscapes in LUADs.”
“This level of detailed analysis highlights the dynamic interplay between the tumor and its surrounding immune microenvironment,” said Kadara. “Our data reveal the importance of environmental factors, such as exposure to cigarette smoke, and molecular features of the tumor in contributing to the landscape of infiltrating B cells and plasma cells.”
For example, tumors from smokers had elevated plasma cells and decreased B-cell clonality compared with those of non-smokers. Further, lung tumors with EGFR mutations had lower levels of plasma cells and higher levels of less-differentiated B cells when compared to those with KRAS or other mutations.
By studying the single-cell data together with spatial information from the tumors, the researchers also demonstrated that most B cells and plasma cells were recruited to sites with high levels of CXCL13. Levels of this signaling molecule increase as tumors progress from precancerous lesions to invasive lung cancer.
The varied landscape of B cells and plasma cells in the tumor also appear to influence patient outcomes and treatment responses in early-stage lung cancers. Specifically, an enrichment of plasma cells in the tumor was associated most strongly with improved survival and responses to anti-PD-1/PD-L1 immune checkpoint inhibitors. “In terms of their clinical significance, our analysis clearly points to the PC (not B cell) subset, as the PC signature derived from this study notably showed the strongest correlation with patient survival across multiple LUAD cohorts and significantly associated with patient response to anti-PD-1/PD-L1-based immunotherapy,” the researchers noted.
“Most previous studies have treated tumor-infiltrating B cells or plasma cells as a homogeneous population, but our in-depth analysis highlights the heterogeneous nature of these cells and their crosstalk with other components of the tumor microenvironment,” Wang said. “Further studies are needed to fully understand their roles in tumor pathogenesis, but the evidence suggests the plasma cell signature may be a valuable biomarker to predict immunotherapy outcomes. Our findings also can be leveraged to identify new targets for immunotherapy that focus on tumor-infiltrating B cells and plasma cells.”
Future studies will build on the foundation provided by this study to clarify the precise roles of B cells and plasma cells in early lung tumor progression and to identify the most promising therapeutic strategies.
Noting limitations of their study, the researchers concluded, “… this study provides fundamental findings on yet uncharted phenotypic heterogeneity and roles of TIBs in the development and immunopathology of early stage LUAD, and it constitutes a valuable resource to leverage targets for the development of desperately needed novel immunotherapeutic strategies for early treatment of this morbid malignancy.”