Adeno-associated virus (AAV) vectors are the preferred gene delivery tool in gene therapy owing to their safety, long-term gene expression, broad tissue tropism, and low immunogenicity. Affinity ligands that can bind multiple AAV serotypes endure harsh clean-in-place (CIP) conditions and are critical for industrial-scale purification. However, current ligands lack broad serotype recognition and adequate alkaline stability, which limits their reusability in large-scale manufacturing. In this study, we employed a competitive biopanning strategy to isolate a single-domain antibody (VHH) that simultaneously binds AAV2, AAV8, and AAV9. The VHH retained structural integrity and binding activity after exposure to 0.1 M NaOH, demonstrating robust alkaline stability. Structural modeling revealed that the VHH primarily recognizes the DE loop region of the VP3 capsid protein across the three serotypes, explaining its cross-serotype reactivity. Affinity chromatography using the VHH yielded infectious AAV particles, confirming its potential for downstream processing. This strategy provides a versatile platform for developing high-performance AAV affinity ligands and may be extended to other viral vector systems.

Monocarboxylate transporter 4 (MCT4/SLC16A3) is frequently upregulated in human cancers and associated with aggressive progression and poor clinical outcomes. To elucidate its functional role, we establish MCT4 homozygous knockout BALB/c mice (MCT4^-/-) using CRISPR/Cas9-EGE technology. Compared with wild-type counterparts, MCT4^-/- mice exhibit ~40% reduction in allograft tumor volume, which is partly attributable to diminished IGF1 production, as circulating and tumor interstitial IGF1 levels decrease by 40–45%. Exogenous IGF1 supplementation restores tumor growth, confirming this dependency. Moreover, MCT4 deficiency enhances antitumor immunity, characterized by increased infiltration of CD4⁺ and CD8⁺ T cells, NK cells, and macrophages, with a pronounced shift from immunosuppressive M2 to pro-inflammatory M1 macrophages. Consistently, across three independent carcinogenesis models (breast, lung, oral squamous cancers), MCT4^-/- mice develop fewer and smaller lesions, underscoring its critical role in tumor incidence. Collectively, these findings identify MCT4 as a key driver of carcinogenesis through IGF1 regulation and immune modulation, highlighting its therapeutic potential.