Isolation of inhibiting anti-bacterial antibodies from infected patients. Mycobacterium tuberculosis: a model

Antibiotic-resistant bacteria became an increasing public health threat. Identifying natural anti-bacteria antibodies, as well as bacterial targets recognized by antibodies during natural infection is important and can contribute to the development of new anti-bacterial drugs and vaccines. In this study we focused on Mycobacterium tuberculosis (Mtb), the etiologic cause of the Tuberculosis disease, which infects approximately 1.8 million people yearly. We analyzed the B cell responses in an actively Mtb infected African-Israeli donor, Patient 004, who exhibited high serum reactivity against the Mtb ABC transporter phosphate binding protein PstS1. A monoclonal analysis of anti-PstS1 B cells from whole blood of Patient 004 revealed expanded clones and increased levels of somatic mutations, indicating affinity maturation. We cloned and expressed five distinct anti-PstS1 monoclonal antibodies (mAbs), which bound to PstS1 with picomolar affinity, as well as to the pathogenic Mtb bacteria. Two of these antibodies, P4-36 and P4-163, inhibited Mtb growth by 40-50%, both in vitro in whole blood assay, and in vivo when administered to Balb/c mice before Mtb challenge. By X-ray crystallography we solved the structure of P4-36:PstS1 complex at atomic resolution of 2.5 angstroms, thus revealing the complete P4-36 epitope on the surface of PstS1. Our results show for the first time that inhibiting natural anti-Mtb antibodies are elicited during infection. P4-36 and P4-163 isolated during our study can be tested as potential therapeutic modalities in Mtb-infected individuals who do not respond well to antibiotic treatment, and the epitope of P4-36 can be tested as a novel vaccine candidate.