Diagnostic evaluation of a novel recombinant multi-epitope protein for paucibacillary and multibacillary leprosy

The diagnosis of leprosy remains challenging due to its clinical similarity with other infectious diseases and the variable sensitivity and specificity of current laboratory tests. Therefore, the identification and/or development of novel antigens is crucial for improving diagnostic accuracy. In this study, we designed a novel recombinant multi-polypeptide construct, termed M3, which was composed of specific B-cell epitopes from nine Mycobacterium leprae proteins, previously shown to be antigenic in leprosy. The recombinant M3 protein was expressed, purified, and evaluated as an antigen for the diagnosis of both paucibacillary (PB) and multibacillary (MB) disease, by using paired serum and urine samples from 380 participants. ELISA was performed using samples from PB (n = 50) and MB (n = 55) leprosy patients, their household contacts [PBC (n = 30) and MBC (n = 40), respectively], healthy individuals living in endemic region (n = 55), and patients with visceral (n = 30) and tegumentary (n = 45) leishmaniasis, Chagas disease (n = 35), tuberculosis (n = 15), and HIV-infection (n = 25). In serum-based ELISA, M3 showed sensitivity, specificity, positive and negative predictive values, and Youden index of 94.5 %, 100 %, 96.8 %, 97.4 %, and 0.91, respectively; whilst in a urine-based ELISA, the corresponding values were 96.4 %, 100 %, 98.8 %, 98.2 %, and 0.96, respectively. Additionally, paired serum and urine samples from 15 PB and 20 MB patients collected before and after treatment, revealed that anti-M3 antibodies decreased by more than 50 % post-therapy when using both analytes. These pilot findings suggest a potential biological role of the recombinant M3 protein for diagnosis of PB and MB leprosy.