Cruzipain, the major cysteinyl
proteinase of Trypanosoma cruzi, is expressed by all developmental forms and strains of the parasite and stimulates potent humoral and cellular immune responses during
infection in both humans and mice. This information suggested that
cruzipain could be used to develop an effective T. cruzi
vaccine. To study whether
cruzipain-specific T cells could inhibit T. cruzi intracellular replication, we generated
cruzipain-reactive CD4(+) Th1 cell lines. These T cells produced large amounts of
gamma interferon when cocultured with infected macrophages, resulting in NO production and decreased intracellular parasite replication. To study the protective effects in vivo of
cruzipain-specific Th1 responses against systemic T. cruzi challenges, we immunized mice with recombinant
cruzipain plus
interleukin 12 (IL-12) and a neutralizing anti-IL-4 MAb. These immunized mice developed potent
cruzipain-specific memory Th1 cell responses and were significantly protected against normally lethal systemic T. cruzi challenges. Although
cruzipain-specific Th1 responses were associated with T. cruzi protective immunity in vitro and in vivo, adoptive transfer of
cruzipain-specific Th1 cells alone did not protect BALB/c histocompatible mice, indicating that additional immune mechanisms are important for
cruzipain-specific immunity. To study whether
cruzipain could induce mucosal immune responses relevant for
vaccine development, we prepared recombinant attenuated Salmonella enterica serovar Typhimurium
vaccines expressing
cruzipain. BALB/c mice immunized with salmonella expressing
cruzipain were significantly protected against T. cruzi mucosal
infection. Overall, these data indicate that
cruzipain is an important T. cruzi
vaccine candidate and that protective T. cruzi
vaccines will need to induce more than CD4(+) Th1 cells alone.