Optimization and production of a GLP-grade recombinant Sm29 vaccine against schistosomiasis: From expression to preclinical assessment.

Schistosomiasis remains a major neglected tropical disease, and the development of a safe, effective vaccine is a global priority. Sm29, a Schistosoma mansoni surface antigen associated with naturally acquired resistance, has emerged as a promising vaccine candidate; however, its translational advancement requires both high-quality antigen production and evaluation with clinically acceptable adjuvants. Here, we report a Good Laboratory Practice-aligned process for generating tag-free recombinant Sm29 in Escherichia coli, including multi-step anion-exchange chromatography followed by subsequent removal of residual impurities. Analytical validation demonstrated high purity, minimal host cell proteins and residual DNA and low endotoxin levels compliant with international regulatory standards. We then assessed the immunogenicity and protective efficacy of recombinant Sm29 formulated with alum or the squalene-based emulsion (CTVad1) in a murine model of S. mansoni infection. Both formulations elicited robust humoral immune responses, characterized by high titers of total IgG, IgG1, and IgG2c, and moderate levels of IgG3 and IgE anti-Sm29. Regarding cytokines, Sm29 formulated with alum induced a mixed Th1/Th2 immunological profile while Sm29 adjuvanted with CTVad1 engendered a Th2-like response. Following cercarial challenge, CTVad1 + Sm29 or Alum+Sm29 vaccinated mice displayed reduced worm burdens and liver pathology when compared to adjuvant controls. These findings demonstrate that a regulatory-compliant Sm29 antigen, combined with human-compatible adjuvants, induces robust immunity and protection against infection and supports further clinical advancement as a schistosomiasis vaccine candidate.