Isolation of a nanobody specific to the PstS-1 protein and evaluation of its immunoreactivity with structural components of Mycobacterium tuberculosis granuloma

M. tuberculosis (Mtb) causes infectious granulomatous disease tuberculosis (TB). Within TB granuloma, foci of Mtb secreted antigens anchored on the surface of either bacilli or host cells may serve as targetable biomarkers for antibody based molecular imaging of TB. Nanobody is better suited over conventional antibody or its fragment derivatives for molecular imaging due to its quick localization in target tissue and rapid clearance from off-target organs. Here, we report the production of a high affinity nanobody against PstS-1 protein of Mtb which helps bacilli in phosphate uptake as well as host cell adhesion. C8 nanobody was isolated from a phage display library displaying nanobodies which was constructed from a camel immunized with secretory proteins of Mtb. C8 Nb was characterized in vitro and in vivo for its immunoreactivity against PstS-1 protein. Ability of C8 Nb to bind PstS-1 protein present on the surface of Mtb bacilli or adhered on macrophages and its localization around BCG cells injected intramuscularly in mice demonstrate its potential in the development of molecular imaging for tuberculosis.