TARGETING BACTERIAL BIOFILMS-MEDIATED DYSREGULATION OF IMMUNE CHECKPOINTS: A NEW DIMENSION FOR ANTI-PATHOGENIC IMMUNOTHERAPY
Bacterial infections associated with biofilms continue to be significant clinical problem due to their antibiotic resistance and immunosuppressive capabilities. The recent evidence indicates that the immune checkpoint signaling (PD-1/PD-L1) is involved in the immune impairment in chronic biofilm infections. The study examined the importance of such pathways and whether immune checkpoint inhibitors (ICIs) can be used with antibiotics to enhance the ability to eliminate bacteria and rebuild immune functions. Biofilms of Staphylococcus aureus and Pseudomonas aeruginosa in vitro also were developed and co-cultured with human peripheral blood mononuclear cells (PBMCs). They compared the following four groups: control, ciprofloxacin, antibodies against anti-PD-1/PD-L1 alone and the combination of these two types of antibodies. The crystal violet staining and the confocal microscopy method were used as methods of assessing biofilm biomass, whereas colony-forming unit (CFU) counts were used as the method of measuring viable bacteria. The flow cytometry analysis of PD-1/PD-L1 on T cells was complemented by the analysis of gene expression by qRT-PCR and the level of cytokines by ELISA. Results: Combination therapy yielded the best effect as it decreased biofilm biomass up to 70% in comparison with 35-45% reductions using one of the treatments. Bacterial viability in combination group was also much worse compared to monotherapy groups. Also, the PD-1/PD-L1 on the CD4+ and CD8+ T cells were significantly lowered, as well as TNF-a and IFN-g were elevated and IL-10 was lowered, with a shift up the pro-inflammatory immune response. These results indicate that immune checkpoint blockade is potentially able to augment antibiotic effects against infections caused by biofilms by reversing immunosuppression caused by infection. This integrated approach could be an effective treatment option against chronic and antimicrobial-resistant bacterial infections, but additional in vivo research is necessary to determine the effectiveness of the approach, the optimal dose level, and safety.