BTLA: An Emerging Immune Checkpoint Target in Cancer Immunotherapy.

B and T lymphocyte attenuator (BTLA) is a unique co-inhibitory receptor of the CD28 immunoglobulin superfamily that exhibits dual regulatory functions in immune activation and tolerance. Unlike PD-1 or CTLA-4, BTLA interacts bidirectionally with its ligand HVEM, forming a complex signaling network that shapes immune homeostasis within the tumor microenvironment. Dysregulated BTLA expression has been associated with tumor immune evasion and poor prognosis in several cancers. Owing to its distinctive molecular features and multifaceted immunoregulatory roles, BTLA represents an emerging therapeutic target, particularly in tumors unresponsive to conventional immune checkpoint inhibitors. This review provides a comprehensive overview of BTLA's structure, signaling mechanisms, and functional implications in tumor immunity and discusses current advances and challenges in BTLA-targeted therapy. Finally, we outline future perspectives on leveraging BTLA modulation to enhance cancer immunotherapy outcomes.