It has been estimated that 700,000 to 1 million new cases of leishmaniasis occur annually worldwide. This neglected tropical disease, endemic in countries where there is poverty and malnutrition, is transmitted by phlebotomine sand flies infected with the Leishmania protozoan parasite. It can manifest as cutaneous leishmaniasis (CL) - the most prevalent form of the disease -, mucocutaneous leishmaniasis, or visceral leishmaniasis (VL) also known as Kala-azar - the most fatal form of the disease. Leishmania tropica, L. major, L. infantum and L. donovani are the major etiologic agents in the Old World (the Eastern Hemisphere). In the New World (i.e. the Western Hemisphere/American continent), the main species are from the L. mexicana complex (L. mexicana and L. amazonensis) and the subgenus Viannia (L. braziliensis, L. guyanensis, L. panamensis, and L. peruviana). The treatment of leishmaniasis depends on the clinical manifestations, the infecting Leishmania spp. and the specific geographic locations where cases are encountered (Leishmaniasis Fact sheets, 2023; Prevention CfDCa, 2023). The antileishmanial drugs currently on the market (e.g. pentavalent antimonials, paromomycin, amphotericin, pentamidine, miltefosine) present serious adverse side-effects including nephrotoxicity (amphotericin), ototoxicity, impairment of liver function (paromomycin), and drug-resistant Leishmania strains have already emerged following exposure to these drugs (Haldar et al., 2011; Sundar et al., 2007a, 2007b; Sundar and Olliaro, 2007). Early trials seeking to design and develop an anti-Leishmania vaccine used live and pathogenic Leishmania (leishmaniasation), but such a hazardous immunisation method is no longer practiced (Khalil et al., 2000). Trials using killed and attenuated organisms have also been carried out, but with limited success (Armijos et al., 2003). The use of crude antigens with specific adjuvants has been reported, but efficacy was found to be restricted to CL and Leishmania spp. from specific geographic locations (Mohebali et al., 2004). The use of second- and third-generation vaccines such as Leish-F1+MPL-SE, ChAd63-KH/DNA has recently been described, but these require further investigations and final approval (Gillespie et al., 2016; Osman et al., 2017).

The zinc metalloprotease gp63 (known as leishmanolysin) is an integral component of the Leishmania glycocalyx. It is a major surface antigen and virulence factor with a key role in the developmental stages of Leishmania promastigotes and amastigotes and their survival in the host's macrophages. As such, it has been identified as an antigenic structure for vaccine design and as a promising target for new antileishmanial drugs (Murase et al., 2018; Chan et al., 2021; Mukherjee et al., 2021; Yao et al., 2003; Mercado-Camargo et al., 2020). The aim of this study was twofold. The first goal was to design a full vaccine construct based on the highly immunogenic and conserved cytotoxic T-lymphocyte (CTL) and helper T-lymphocyte (HTL) epitopes of gp63 from Old and New World Leishmania spp using immunoinformatics. Such an approach helps predict, with high sensitivity and specificity, epitopes from antigenic proteins and characterise their interactions with the corresponding major histocompatibility complex (MHC) molecules (Patronov and Doytchinova, 2013). It has also previously been used to design epitopes for vaccines against influenza, hepatitis B and C viruses (Staneková and Varečková, 2010; Sominskaya et al., 2010; He et al., 2015). The second goal was to identify new antileishmanial molecules with the potential to target gp63 using in silico studies such as molecular docking and molecular dynamics simulations. The molecules investigated were selected phytochemicals isolated from medicinal plants with known antileishmanial activity (Sidana and Farooq, 2015).