Porphyromonas gingivalis adhesion protein Mfa1 enhances the anti-cancer effect of anti–PD-L1 antibody by immune activation

The Escherichia coli adhesion molecule, FimH, is known to induce the activation of immune cells, including dendritic cells (DCs) and T cells. While Mfa1 in Porphyromonas gingivalis plays a similar role, its potential immunostimulatory activity has not been extensively examined. Therefore, to explore this, recombinant Mfa1 was synthesized and extracted from E. coli . Recombinant Mfa1 upregulated co-stimulatory and major histocompatibility complex (MHC) molecules in a dose-dependent manner in bone marrow-derived DCs (BMDCs). Mfa1 administration to C57BL/6 mice increased the proportion and number of splenic DCs and enhanced the expression of C–C chemokine receptor type 7 (CCR7), indicating DC migration and maturation. Mfa1 treatment elevated the number of cDC1 and cDC2 subsets, upregulated co-stimulatory and MHC molecules, and increased pro-inflammatory cytokine levels in vivo. Mechanistically, in silico AI-based protein complex prediction and all-atom molecular dynamics simulation demonstrated that Mfa1 binds to TLR2 with high structural confidence and stability, while showing markedly lower binding stability toward TLR4. Consistently, the immune-activating effects observed in wild-type mice were absent in TLR2-knockout mice, confirming its dependence on TLR2 signaling. Furthermore, repeated Mfa1 treatment enhanced the intracellular production of IFN-γ and TNF-α in CD4 + and CD8 + T cells, indicating robust T cell activation. Finally, in a Lewis lung carcinoma model, Mfa1 enhanced the anti-tumor efficacy of anti–PD-L1 antibody therapy. Thus, Mfa1 may serve as a potential immunostimulatory adjuvant to enhance cancer immunotherapy.