Investigate how IgM drives complement-mediated killing of Klebsiella pneumoniae

Antibiotic resistance of bacteria requires the development of alternative therapies against bacterial infections. A promising strategy is developing antibodies capable of boosting the human immune system. An important mechanism by which these antibodies clear bacterial infections is by stimulating the human complement system. Upon binding to the bacterial surface, antibodies trigger activation of the complement cascade, leading to direct killing of bacteria by Membrane Attack Complex (MAC) pores. Also, antibody-dependent complement activation can stimulate uptake of bacteria via phagocytes, such as neutrophils, and subsequent intracellular killing.  Currently, Immunoglobulin G (IgG) is considered superior for pharmaceutical development, because of its high affinity, and ample know-how on large-scale production and clinical development. However, for bacteria, it is established that the larger pentameric Immunoglobulin M (IgM) is more potent in driving immune-mediated killing. Still, the exact mechanism underlying the superior activity has not been elucidated.

To help unravel this, we aim to first identify a large panel of functionally dissimilar monoclonal IgMs that target the human pathogen Klebsiella pneumoniae (Kpn). Using a recently developed method in our lab, memory B cells targeting Kpn will be isolated via single-cell sorting and using the mRNA of single these B cells, monoclonal IgMs will be produced. The targets of these IgMs will be identified through transposon mutagenesis, while their function will be assessed via antibody binding, complement activation, and phagocytosis assays.

Next, we want to elucidate how IgM potently drives complement activation. Therefore, we will investigate the differences between IgG and IgM. Using recombinant antibody engineering to swap IgMs to IgG and vice versa. Utilizing both flowcytometric- and microscopy-based assays we will reveal the effect these antibody isotypes have on the different steps of the complement cascade.

Finally, previous data showed that anti-capsular mAbs can synergize. I showed that this is also true for IgM, I will further investigate if IgMs against other capsule structures have the potential to act synergistically with other antibodies. Together, this will result in a deeper understanding of how IgM mediates protection against bacterial infections.

Contact 
Stan Baijens