Spatial Transcriptional Dynamics of CD74⁺ B Cells in Tertiary Lymphoid Structures Drive Immune Evolution in Penile Squamous Cell Carcinoma

Penile squamous cell carcinoma (PSCC) is a malignancy characterized by a poor prognosis and lack of reliable biomarkers, presenting considerable therapeutic challenges. Tertiary lymphoid structures (TLSs) are critical modulators of antitumor immunity; however, the immunological dynamics, particularly the roles of B cells and their interactions with naive T cells in PSCC tissues, remain inadequately understood. This study integrates transcriptomic approaches, including spatial transcriptomics, single-cell sequencing (scRNA-seq), and bulk RNA sequencing (bulk RNA-seq), and immunohistochemistry to elucidate the immune architecture of and functional mechanisms within TLSs. The results reveal a positive correlation between TLS density and patient survival, with CD74⁺ B cells tending to be enriched during early TLS formation. These cells exhibit strong immune activation and a propensity to differentiate into plasma cells. By engaging with naive T cells through HLA-DRA via ligand-receptor interactions, CD74⁺ B cells activate transcription factors, including NFKB1, NFKB2, NFATC1, NFATC2, FOS, and RUNX1, in naive T cells, thereby enhancing the immune response. Consequently, CD74⁺ B cells represent a compelling biomarker for and therapeutic target of PSCC, offering profound insights into the immunological mechanisms that drive PSCC progression and response to immunotherapy.