Characterization of a novel monoclonal antibody candidate that targets bacterial GAPDH and protects neonatal mice from infections caused by <i>Streptococcus pneumoniae</i> or <i>Streptococcus agalactiae</i>

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a highly conserved bacterial enzyme essential for glycolysis, yet it also plays important non-metabolic, "moonlighting" roles, including host immunomodulation. Here, we describe the generation and characterization of a monoclonal antibody (mAb01) that targets extracellular GAPDH from <i>Streptococcus agalactiae</i> (GBS) and <i>Streptococcus pneumoniae</i>. Using bio-layer interferometry (BLI) and surface plasmon resonance (SPR), we demonstrate that mAb01 binds with high affinity, exhibiting dissociation constants in the low nanomolar range for both antigens. Functionally, mAb01 significantly improves survival in a neonatal murine model of sepsis caused by either GBS or <i>S. pneumoniae</i>, two relevant neonatal pathogens. The addition of mAb01 to <i>ex vivo</i> cultures of human peripheral blood infected with GBS or <i>S. pneumoniae</i> induced a significant decrease in bacterial replication, further supporting its protective potential. These results provide the first demonstration of a high-affinity anti-GAPDH monoclonal antibody that is effective in both <i>in vivo</i> and <i>ex vivo</i> models of streptococcal infection.