Human Lymphoid Stromal Cells Contribute to Polarization of Follicular T Cells Into IL-4 Secreting Cells

Molecular Biomarkers in Prediction of High-Grade Transformation and Outcome in Patients with Follicular Lymphoma: A Comprehensive Systemic Review

Follicular lymphoma (FL) is the most prevalent indolent B-cell lymphoma entity, often characterized by the t(14;18) BCL2-IGH translocation. The malignancy represents a clinically and biologically highly heterogeneous disease. Most patients have favorable prognoses; however, despite therapeutic advancements, the disease remains incurable, with recurrent relapses or early disease progression. Moreover, transformation to an aggressive histology, most often diffuse large-B-cell lymphoma, remains a critical event in the disease course, which is associated with poor outcomes. Understanding the individual patient's risk of transformation remains challenging, which has motivated much research on novel biomarkers within the past four decades. This review systematically assessed the research on molecular biomarkers in FL transformation and outcome. Following the PRISMA guidelines for systemic reviews, the PubMed database was searched for English articles published from January 1984 through September 2024, yielding 6769 results. The identified publications were carefully screened and reviewed, of which 283 original papers met the inclusion criteria. The included studies focused on investigating molecular biomarkers as predictors of transformation or as prognostic markers of time-related endpoints (survival, progression, etc.). The effects of each biomarker were categorized based on their impact on prognosis or risk of transformation as none, favorable, or inferior. The biomarkers included genetic abnormalities, gene expression, microRNAs, markers of B cells/FL tumor cells, markers of the tumor microenvironment, and soluble biomarkers. This comprehensive review provides an overview of the research conducted in the past four decades, underscoring the persistent challenge in risk anticipation of FL patients.

Follicular lymphoma regulatory T-cell origin and function

Introduction

Follicular Lymphoma (FL) results from the malignant transformation of germinal center (GC) B cells. FL B cells display recurrent and diverse genetic alterations, some of them favoring their direct interaction with their cell microenvironment, including follicular helper T cells (Tfh). Although FL-Tfh key role is well-documented, the impact of their regulatory counterpart, the follicular regulatory T cell (Tfr) compartment, is still sparse.

Methods

The aim of this study was to characterize FL-Tfr phenotype by cytometry, gene expression profile, FL-Tfr origin by transcriptomic analysis, and functionality by in vitro assays.

Results

CD4+CXCR5+CD25hiICOS+ FL-Tfr displayed a regulatory program that is close to classical regulatory T cell (Treg) program, at the transcriptomic and methylome levels. Accordingly, Tfr imprinting stigmata were found on FL-Tfh and FL-B cells, compared to their physiological counterparts. In addition, FL-Tfr co-culture with autologous FL-Tfh or cytotoxic FL-CD8+ T cells inhibited their proliferation in vitro. Finally, although FL-Tfr shared many characteristics with Treg, TCR sequencing analyses demonstrated that part of them derived from precursors shared with FL-Tfh.

Discussion

Altogether, these findings uncover the role and origin of a Tfr subset in FL niche and may be useful for lymphomagenesis knowledge and therapeutic management.

Cell cross talk within the lymphoma tumor microenvironment: follicular lymphoma as a paradigm

ABSTRACT

Follicular lymphoma (FL) is an indolent yet incurable germinal center B-cell lymphoma retaining a characteristic follicular architecture. FL tumor B cells are highly dependent on direct and indirect interactions with a specific and complex tumor microenvironment (TME). Recently, great progress has been made in describing the heterogeneity and dynamics of the FL TME and in depicting how tumor clonal and functional heterogeneity rely on the integration of TME-related signals. Specifically, the FL TME is enriched for exhausted cytotoxic T cells, immunosuppressive regulatory T cells of various origins, and follicular helper T cells overexpressing B-cell and TME reprogramming factors. FL stromal cells have also emerged as crucial determinants of tumor growth and remodeling, with a key role in the deregulation of chemokines and extracellular matrix composition. Finally, tumor-associated macrophages play a dual function, contributing to FL cell phagocytosis and FL cell survival through long-lasting B-cell receptor activation. The resulting tumor-permissive niches show additional layers of site-to-site and kinetic heterogeneity, which raise questions about the niche of FL-committed precursor cells supporting early lymphomagenesis, clonal evolution, relapse, and transformation. In turn, FL B-cell genetic and nongenetic determinants drive the reprogramming of FL immune and stromal TME. Therefore, offering a functional picture of the dynamic cross talk between FL cells and TME holds the promise of identifying the mechanisms of therapy resistance, stratifying patients, and developing new therapeutic approaches capable of eradicating FL disease in its different ecosystems.

PI16+ reticular cells in human palatine tonsils govern T cell activity in distinct subepithelial niches

Fibroblastic reticular cells (FRCs) direct the interaction and activation of immune cells in discrete microenvironments of lymphoid organs. Despite their important role in steering innate and adaptive immunity, the age- and inflammation-associated changes in the molecular identity and functional properties of human FRCs have remained largely unknown. Here, we show that human tonsillar FRCs undergo dynamic reprogramming during life and respond vigorously to inflammatory perturbation in comparison to other stromal cell types. The peptidase inhibitor 16 (PI16)-expressing reticular cell (PI16⁺ RC) subset of adult tonsils exhibited the strongest inflammation-associated structural remodeling. Interactome analysis combined with ex vivo and in vitro validation revealed that T cell activity within subepithelial niches is controlled by distinct molecular pathways during PI16⁺ RC-lymphocyte interaction. In sum, the topological and molecular definition of the human tonsillar stromal cell landscape reveals PI16⁺ RCs as a specialized FRC niche at the core of mucosal immune responses in the oropharynx.

Follicular lymphoma dynamics

Follicular lymphoma (FL) is an indolent yet challenging disease. Despite a generally favorable response to immunochemotherapy regimens, a fraction of patients does not respond or relapses early with unfavorable prognosis. For the vast majority of those who initially respond, relapses will repeatedly occur with increasing refractoriness to available treatments. Addressing the clinical challenges in FL warrants deep understanding of the nature of treatment-resistant FL cells seeding relapses, and of the biological basis of early disease progression. Great progress has been made in the last decade in the description and interrogation of the (epi)genomic landscape of FL cells, of their major dependency to the tumor microenvironment (TME), and of the stepwise lymphomagenesis process, from healthy to subclinical disease and to overt FL. A new picture is emerging, in which an ever-evolving tumor-TME duo sparks a complex and multilayered clonal and functional heterogeneity, blurring the discovery of prognostic biomarkers, patient stratification and reliable designs of risk-adapted treatments. Novel technological approaches allowing to decipher both tumor and TME heterogeneity at the single-cell level are beginning to unravel unsuspected cell dynamics and plasticity of FL cells. The upcoming drawing of a comprehensive functional picture of FL within its ecosystem holds great promise to address the unmet medical needs of this complex lymphoma.

B cell/stromal cell crosstalk in health, disease, and treatment: Follicular lymphoma as a paradigm

Stromal cells organize specific anatomic compartments within bone marrow (BM) and secondary lymphoid organs where they finely regulate the behavior of mature normal B cells. In particular, lymphoid stromal cells (LSCs) form a phenotypically heterogeneous compartment including various cell subsets variably supporting B-cell survival, activation, proliferation, and differentiation. In turn, activated B cells trigger in-depth remodeling of LSC networks within lymph nodes (LN) and BM. Follicular lymphoma (FL) is one of the best paradigms of a B-cell neoplasia depending on a specific tumor microenvironment (TME), including cancer-associated fibroblasts (CAFs) emerging from the reprogramming of LN LSCs or poorly characterized local BM precursors. FL-CAFs support directly malignant B-cell growth and orchestrate FL permissive cell niche by contributing, through a bidirectional crosstalk, to the recruitment and polarization of immune TME subsets. Recent studies have highlighted a previously unexpected level of heterogeneity of both FL B cells and FL TME, underlined by FL-CAF plasticity. A better understanding of the signaling pathways, molecular mechanisms, and kinetic of stromal cell remodeling in FL would be useful to delineate new predictive markers and new therapeutic approaches in this still fatal malignancy.

Lymphoid stromal cells-more than just a highway to humoral immunity

The generation of high-affinity long-lived antibody responses is dependent on the differentiation of plasma cells and memory B cells, which are themselves the product of the germinal centre (GC) response. The GC forms in secondary lymphoid organs in response to antigenic stimulation and is dependent on the coordinated interactions between many types of leucocytes. These leucocytes are brought together on an interconnected network of specialized lymphoid stromal cells, which provide physical and chemical guidance to immune cells that are essential for the GC response. In this review we will highlight recent advancements in lymphoid stromal cell immunobiology and their role in regulating the GC, and discuss the contribution of lymphoid stromal cells to age-associated immunosenescence.

The Tumor Microenvironment in Follicular Lymphoma: Its Pro-Malignancy Role with Therapeutic Potential

In the follicular lymphoma (FL) microenvironment, CXCR5⁺ICOS⁺PD1⁺BCL6⁺ follicular helper T (Tfh) cells, which closely correlate with FL B cells in neoplastic follicles, play a major role in supporting FL. Interleukin-4 secreted by Tfh cells triggers the upregulation of the lymphocyte chemoattractant CXCL12 in stromal cell precursors, in particular by fibroblastic reticular cells (FRCs). In turn, mesenchymal stem cells (MSCs) can be committed to FRC differentiation in the bone marrow and lymph nodes involved by FL. Noteworthy, MSCs can promote the differentiation of Tfh cells into highly immunosuppressive T-follicular regulatory cells. The tumor suppressor HVEM is highly mutated in FL cells, and its deficiency increases Tfh cell frequency. In contrast, PI3Kδ inhibition impedes the recruitment of Tfh/regulatory T cells and impairs the proliferation of follicular dendritic cells (FDCs) and FDC-induced angiogenesis. Since TIGIT ligands are expressed by FDCs, the immune checkpoint receptor TIGIT plays an important role in tumor-infiltrating T cells. Thus, TIGIT blockade might invigorate cytotoxic T cells in the FL microenvironment. Given their potential to simultaneously reduce the neoplastic B cells, Tfh, and TFR cells could also reinforce the effects of the cytotoxic T cells. This combinatory strategy should be explored as a treatment option to tackle FL.

Conversations that count: Cellular interactions that drive T cell fate

The relationship between the extrinsic environment and the internal transcriptional network is circular. Naive T cells first engage with antigen‐presenting cells to set transcriptional differentiation networks in motion. In turn, this regulates specific chemokine receptors that direct migration into distinct lymph node niches. Movement into these regions brings newly activated T cells into contact with accessory cells and cytokines that reinforce the differentiation programming to specify T cell function. We and others have observed similarities in the transcriptional networks that specify both CD4+ T follicular helper (T_FH) cells and CD8+ central memory stem‐like (T_SCM) cells. Here, we compare and contrast the current knowledge for these shared differentiation programs, compared to their effector counterparts, CD4+ T‐helper 1 (T_H1) and CD8+ short‐lived effector (T_SLEC) cells. Understanding the interplay between cellular interactions and transcriptional programming is essential to harness T cell differentiation that is fit for purpose; to stimulate potent T cell effector function for the elimination of chronic infection and cancer; or to amplify the formation of humoral immunity and longevity of cellular memory to prevent infectious diseases.