Development of monoclonal antibodies as therapeutic drugs against multiple drug resistant bacteria by using a unique screening platform based on breastmilk B cells

Misuse and overuse of antibiotics over the past few decades have led to an antibiotics resistance crisis. Instead of conventional antibiotics, we will develop monoclonal antibodies (mAbs) targeted against the bacterial type 3 secretion system (T3SS), which is a virulence mechanism utilized by many Gram-negative pathogens. Our goal is to develop mAbs that target T3SS components and block their activity, thereby inhibiting bacterial infectivity. It will be achieved by Isolation of B cells from human breastmilk, construction of a yeast display single-chain fragment variable (scFv) library derived from breastmilk-residing B cells, discovery of mAbs that target T3SS proteins by using the library, then cloning and expressing the discovered clones as IgGs and characterizing their activity. Preliminary results from FACS analysis of breastmilk cells show that on average 6% of total cells in breastmilk are B cells. To determine whether breastmilk antibodies are primed against Enterotoxigenic Escherichia coli (EPEC) T3SS proteins, we tested breastmilk samples against those proteins and found that breastmilk antibodies are indeed primed against these bacterial antigens. We perform another FACS analysis with fluorophore-conjugated bacterial antigens, to determine whether B cells in breastmilk are primed against these antigens. We found that there was indeed an indication of the presence of T3SS-specific B cells in breastmilk. These results suggest that B cells in breastmilk are potentially primed against EPEC-T3SS: therefore, the library constructed based on these B cells may be considered as a semi-immunized/primed library from which there should be a good chance of isolating anti-bacterial mAbs.