Retro-inverso peptide analogues of Trypanosoma cruzi B13 protein epitopes fail to be recognized by human sera and peripheral blood mononuclear cells

Retro inverso (RI) analogues of antigenic synthetic peptides, which are mad e of D-amino acids with a reversed sequence, may mimic the side chain confo rmation of natural all-L peptides. RI analogues were cross-reactively recog nized by antibodies and CD4+ T cells reactive against natural all-L synthet ic peptides or native proteins in animal models. Since peptides containing D-amino acids are highly resistant to proteolytic digestion, cross-reactive RI analogues may be ideal for in vivo administration to humans as syntheti c peptide vaccines or immunomodulators. B13 is an immunodominant tandemly r epetitive protein from Trypanosoma cruzi, a protozoan parasite that is the causative antigen of Chagas' disease. In order to test whether RI peptides can be recognized by human antibody and T cells, we synthesized two all-L p eptides containing the immunodominant B (S12) and T (S15.7) cell epitopes o f B13 protein from T. cruzi and their retro (R, made of all-L amino acids w ith reversed sequence), inverse (I, made of all-D amino acids) and RI analo gues. Recognition of peptides S12, S12-R, S12-I and S12-RI by anti-B13 anti bodies in sera from T. cruzi-infected patients was tested in competitive EL ISA assay with recombinant B13 protein as the solid phase antigen. Peptides S15.7 and its topological analogues were tested at the 10-50 muM range in proliferation assays on peripheral blood mononuclear cells (PBMC) from S15. 7-responder individuals. The median percentage inhibition of B13 ELISA for peptide S12 was 94%. while those of the RI analogue or the other topologica l analogues were below 12%. While peptide S15.7 was recognized by PBMC from all subjects tested, none recognized the RI analogue of the S15.7 T cell e pitope. Our results indicate that cross-reactivity with natural epitopes is not an universal property of RI analogues. This may limit the general appl icability of the use of cross-reactive RI analogues as human vaccines and i mmunotherapeutic agents. (C) 2001 Elsevier Science Inc. All rights reserved .