SSR4 Sustains Tertiary Lymphoid Structures by Regulation Quality Control of N-linked Glycosylation During B-cell Differentiation Into Plasmacyte in Colorectal Cancer.

Intratumoral tertiary lymphoid structure (TLS) fosters B-cell differentiation and antibody production, yet the intrinsic programs sustaining these functions remain unclear. By integrating spatial transcriptomics and single-cell RNA sequencing of colorectal cancer, we delineate a B-cell trajectory enriched for endoplasmic reticulum protein processing, autophagy, NF-κB signaling, and N-linked glycosylation, highlighting SSR4 as a progressively induced TRAP-complex component. SSR4 is further upregulated in B cells from anti-PD-1 responders. B-cell-specific Ssr4 deletion leads to peripheral B-cell loss, reduced antibody output, exacerbated colitis, and impaired mucosal immunity. Mechanistically, SSR4 interacts with DDOST to regulate BAFFR N-glycosylation, thereby sustaining B-cell activation and LTα1β2 expression via NF-κB signaling. In ApcMin/+ mice, Ssr4 deficiency accelerates tumorigenesis, disrupts TLS maturation, lowers serum IgG1, and increases high-mannose (HM) Ig. Conversely, SSR4 overexpression in CHO cells reduces high-mannose glycans and enhances IgG1 ADCC and CDC. These findings identify SSR4 as a central regulator of B-cell glycosylation and TLS-dependent anti-tumor immunity, offering translational implications for immunotherapy and antibody engineering.