en Vaccine development, efficacy and safety evaluation Vaccine development, efficacy and safety evaluation Original article Original article <strong>Introduction:</strong> Vaccination of hamsters with Schistosoma mansoni adjuvant-free recombinant cathepsin B1 (SmCB1) and L3 (SmCL3) have been shown to elicit highly significant (P < 0.005) protection against challenge <em>Schistosoma haematobium</em> that was not very superior to that achieved by the cysteine peptidase, papain.&nbsp; Sterilizing immunity might, however, be induced if hamsters were vaccinated against S. haematobium infection with a homologous cysteine peptidase, i.e., S. haematobium cathepsin L (ShCL).&nbsp;&nbsp; <strong>Methods:</strong> Standards methods, techniques, and primers based on the published nucleotide sequence of ShCL were used to clone, amplify and express DNAs encoding the target enzyme in a bacterial expression vector.&nbsp; Repeat immunization trials were performed using recombinant ShCL alone or in combination with the vaccine candidate S. mansoni recombinant glyceraldehyde 3-phosphate dehydrogenase, in parallel with S. mansoni lecucine aminopeptidase.&nbsp; <strong>Results:</strong> The results together indicated that our adjuvant-free, cysteine peptidase-based vaccine elicits highly significant (P < 0.0001) reduction in challenge worm burden and parasite egg viability.&nbsp; Protection was associated with whole blood cultures release of type 1, type 2, and type 17 cytokines, and modest, yet significant (P < 0.05) humoral response to ShCL.&nbsp; <strong>Conclusion:</strong> Sterilizing immunity was, however, not achieved in any trial, likely because of the preponderant role of cysteine peptidases-induced nonspecific factors in amplifying and antagonizing its protective potential.&nbsp; Experiments are planned in an aim to identify these elusive factors and their exact role. Schistosoma haematobium, Hamsters, Cysteine peptidases, Vaccine, Recombinant proteins, Antibody response 1 8 http://vacres.pasteur.ac.ir/browse.php?a_code=A-10-741-1&slc_lang=en&sid=1 Nada Abdel Aziz nadabdelaziz@gmail.com 0000-0002-7616-3645 No Faculty of SCience, Cairo University Hatem Tallima hatemtallima@gmail.com 0000-0003-3714-641X No Faculty of Science, Cairo University Marwa Abou El Dahab m_aboueldahab_78@yahoo.com No Faculty of Science, Ein Shams University Rashika El Ridi rashikaelridi@hotmail.com 0000-0001-5094-6994 Yes Zoology Department, Faculty of Science, Cairo University