The protection afforded by active cathepsin B was suggested to be partly due to its ability to activate components of the innate immune system in a non-specific manner as the cysteine peptidase papain from plants [11, 13] and the papain-like cathepsin L1, FhCL1, of the related trematode Fasciola hepatica [14, 15], also had the capacity to induce protection against S. mansoni. Notwithstanding, we felt it judicious to pursue SmCB1 as a protective vaccine molecule rather than these other peptidases for schistosomiasis because it was derived from the parasite itself. This evidence concerns the gene CTSL and schistosomiasis.