LTK63

LTK63 is a genetically detoxified mutant of the *Escherichia coli* heat-labile enterotoxin (LT), created by substituting serine with lysine at position 63 in the A subunit. This mutation results in complete loss of enzymatic (ADP-ribosyltransferase) activity, making it non-toxic while retaining strong immunostimulatory properties[2][4]. LTK63 functions as a potent mucosal adjuvant and has been shown to enhance both humoral and cellular immune responses to co-administered antigens when delivered via mucosal routes such as intranasal administration[1][2][4]. It acts by mimicking airway infection, activating alveolar macrophages, recruiting T and B cells as well as innate immune cells to the lung, and establishing a protective environment that limits respiratory infections[4]. LTK63 has been evaluated in preclinical models for its adjuvant effect with various vaccines (e.g., influenza, measles virus nucleoprotein) and was tested clinically as an adjuvant for intranasal vaccines including HIV gp140 protein; however, clinical development was discontinued after phase 1 trials[3].