RANKL-Induced Btn2a2 - A T Cell Immunomodulatory Molecule - During Osteoclast Differentiation Fine-Tunes Bone Resorption

An antibody targeting an immune checkpoint molecule BTN2A2 enhances anti-tumor immunity

Tumors exploit immune checkpoints to evade immune responses. Therefore, targeting these checkpoints has become a key strategy in cancer immunotherapy. In this study, we have developed a novel immune checkpoint inhibitor (ICI) targeting the B7 family-related molecule BTN2A2. The human BTN2A2 protein, which was highly expressed in some tumor tissues and activated antigen-presenting cells (APCs), can inhibit T cell activation and proliferation. The anti-BTN2A2 monoclonal antibody (mAb) can neutralize the inhibitory effect of BTN2A2 on T cells. In mouse models of pancreatic cancer and glioma, compared to the control group, the anti-BTN2A2 treatment group exhibited tumor shrinkage of 35.8 % (P < 0.05) and 51.2 % (P < 0.01), respectively, along with increased CD8+ tumor-infiltrating lymphocytes (TILs) by 1.7-fold (P < 0.001) and 2.2-fold (P < 0.001), respectively. In addition, anti-BTN2A2 mAb also increased the infiltration of B cells, M1 macrophages, and the expression of inflammatory cytokines in T cells, while reducing the infiltration of M2 macrophages, myeloid-derived suppressor cells (MDSCs), and regulatory T cells (Tregs). Thus, anti-hBTN2A2 mAb normalizes the immunodeficient tumor microenvironment (TME) and inhibits tumor growth. Our results suggest that targeting the BTN2A2 immune checkpoint may represent a novel strategy for cancer treatment, especially in immunosuppressive 'cold' tumors.

Butyrophilin 2a2 (Btn2a2) expression on thymic epithelial cells promotes central T cell tolerance and prevents autoimmune disease

Butyrophilins are surface receptors belonging to the immunoglobulin superfamily. While several members of the butyrophilin family have been implicated in the development of unconventional T cells, butyrophilin 2a2 (Btn2a2) has been shown to inhibit conventional T cell activation. Here, we demonstrate that in steady state, the primary source of Btn2a2 are thymic epithelial cells (TEC). Absence of Btn2a2 alters thymic T cell maturation and bypasses central tolerance mechanisms. Furthermore, Btn2a2-/- mice develop spontaneous autoimmunity resembling human primary Sjögren's Syndrome (pSS), including formation of tertiary lymphoid structures (TLS) in target organs. Ligation of Btn2a2 on developing thymocytes is associated with reduced TCR signaling and CD5 levels, while absence of Btn2a2 results in increased TCR signaling and CD5 levels. These results define a novel role for Btn2a2 in promoting central tolerance by modulating TCR signaling strength and indicate a potential mechanism of pSS development.

Butyrophilins: γδ T Cell Receptor Ligands, Immunomodulators and More

Butyrophilins (BTN) are relatives of the B7 family (e.g., CD80, PD-L1). They fulfill a wide range of functions including immunomodulation and bind to various receptors such as the γδ T cell receptor (γδTCR) and small molecules. One intensively studied molecule is BTN3A1, which binds via its cytoplasmic B30.2 domain, metabolites of isoprenoid synthesis, designated as phosphoantigen (PAg), The enrichment of PAgs in tumors or infected cells is sensed by Vγ9Vδ2 T cells, leading to the proliferation and execution of effector functions to remove these cells. This article discusses the contribution of BTNs, the related BTNL molecules and SKINT1 to the development, activation, and homeostasis of γδ T cells and their immunomodulatory potential, which makes them interesting targets for therapeutic intervention.

The Rising Era of “Immunoporosis”: Role of Immune System in the Pathophysiology of Osteoporosis

Discoveries in the last few years have emphasized the existence of an enormous breadth of communication between bone and the immune system in maintaining skeletal homeostasis. Originally, the discovery of various factors was assigned to the immune system viz. interleukin (IL)-6, IL-10, IL-17, tumor necrosis factor (TNF)-α, receptor activator of nuclear factor kappa B ligand (RANKL), nuclear factor of activated T cells (NFATc1), etc., but now these factors have also been shown to have a significant impact on osteoblasts (OBs) and osteoclasts (OCs) biology. These discoveries led to an alteration in the approach for the treatment of several bone pathologies including osteoporosis. Osteoporosis is an inflammatory bone anomaly affecting more than 500 million people globally. In 2018, to highlight the importance of the immune system in the pathophysiology of osteoporosis, our group coined the term “immunoporosis”. In the present review, we exhaustively revisit the characteristics, mechanism of action, and function of both innate and adaptive immune cells with the goal of understanding the potential of immune cells in osteoporosis. We also highlight the Immunoporotic role of gut microbiota (GM) for the treatment and management of osteoporosis. Importantly, we further discuss whether an immune cell-based strategy to treat and manage osteoporosis is feasible and relevant in clinical settings.