Synthesis and immunological evaluation of relevant bioconjugates to human health

Abstract

Leptospirosis is a zoonosis of global importance caused by the pathogenic bacteria Leptospira spp. that can affect humans and animals. Commercially available vaccines, in Brazil only for veterinary use, are prepared from inactivated bacteria and are serovar specific. The lipopolysaccharide (LPS) of leptospires is responsible for antigenic diversity and is less toxic to cells and animals than other LPS of Gram-negative bacteria. The genus Leptospira encompasses pathogenic and saprophytic species. There are more than 250 pathogenic serovars classified. Several proteins have been tested as vaccine candidates but only a few were able to induce partial protection against bacterial virulent challenge test. Many efforts and studies have been carried out with the aim of developing an efficient vaccine with the capacity to provide cross-protection to multiple serovars. The special laboratory of vaccine development from Butantan Institute, former Biotechnology Center, has been studying the use of chemical conjugation of bacterial capsular polysaccharides to carrier proteins and evaluating the potential of these conjugates as vaccine candidates. Conjugates of Haemophilus influenzae type b (Hib) and tetanus toxoid, Streptococcus pneumoniae serotypes 1, 6B, 14 and 23F with pneumococcal surface proteins (PspA) were synthesized and promising results achieved.This project aims to obtain and to characterize two LPS conjugates of Leptospira biflexa (saprophytic leptospira) with two leptospiral surface adhesins the Lsa45 and the Lsa66. In silico analysis indicated high level of similarity of Lsa45 among leptospiral pathogenic species and the gene that encodes the Lsa66 is present in the main serovars of L. interrogans (Icterohaemorrhagiae Copenhageni, Hardjo, Canicola, Pomona and). The Lsa45 adheres to laminin, binds to plasminogen with ability to generate plasmin and is able to induce humoral and cellular immune response in mice. The Lsa66 binds to laminin and fibronectin showing partial protection in leptospirosis hamster model. Both recombinant proteins react with antibodies present in human serum samples of patients with confirmed diagnosis of leptospirosis, suggesting their expression during infection. The influence of chemical conjugation on the immune response induced by LPS and by the Lsa45 and Lsa66 proteins will be evaluate. (AU)