Identification of vaccine candidates for Chagas’ disease by immunization with sequential fractions of an epimastigote-subtracted trypomastigote cDNA expression library.

VALERIA SONIA TEKIEL; C. ALBA-SOTO; M. POSTAN; GONZALEZ-CAPPA, S.M.; SANCHEZ, D.O.

Rio de Janeiro

Congreso; 13th International Congress of Immunology.; 2007

International Union of Immunological Societies

The trypomastigote is the Trypanosoma cruzi extracellular parasite stage involved in tissue dissemination and cell invasion in the mammalian host, so it seems the most promising target for drug or vaccine development. The objective of this work was to identify trypomastigote-specific antigens capable of confering protection against T. cruzi infection, by means of a modification of the technique expression library immunization (ELI). Briefly, a previously constructed epimastigote-subtracted trypomastigote cDNA library (TcT-E library) was re-cloned into an eukaryotic expression vector. Peptide-producing clones were selected to compose the expression library ELI_TcT-E. Mice (6 animals/group) were immunized (3 doses, 100 ug/dose) with plasmid DNA of the whole ELI_TcT-E library (~1000 clones), with empty vectors or with each one of 3 sub-libraries  (ELI_TcT-E 1, 2 or 3; ~330 clones each). Ten days after the last immunization mice were challenged with 10 lethal doses of T. cruzi. Results showed a 50% of survival in vaccinated mice with one of the sub-libraries (vs. 0% survival in control mice).  Next, we fractionated the protective sub-library ELI_TcT-E_2 into 4 new sub-libraries (2A, 2B, 2C, 2D) and performed another round of immunization and challenge. As the ELI_TcT-E_2D sub-library was protective, we sequence all clones. Gene fragments identified could be grouped into 3 categories: (a) not annotated CDS or ESTs, (b) MASP/mucin-like/trans-sialidase genes and (c) “other genes”. These results demonstrate that immunization with sequential fractions of a cDNA library is a powerful strategy for identifying protective antigens from gene categories not generally predicted to be good sources of vaccine candidates.