New strategies for Leptospira vaccine development based on LPS removal

Abstract

Pathogenic spirochetes from genus Leptospira are etiologic agents of leptospirosis. Cellular vaccines against Leptospira infection often elicit mainly response against the LPS antigen of the serovars present in the formulation. There is no suitable protein candidate capable of replacing whole-cell vaccines, thus requiring new approaches on vaccine development to improve leptospirosis prevention. Our goal was to develop a whole-cell vaccine sorovarindependent based on LPS removal and conservation of protein antigens exposure, to evaluate the protective capacity of monovalent or bivalent vaccines against homologous and heterologous virulent Leptospira in hamster. Leptospire were subjected to heat inactivation, or to LPS extraction with butanol and in some cases further inactivation with formaldehyde. Hamsters were immunized and challenged with homologous or heterologous virulent serovars, blood and organs were collected from the survivors for bacterial quantification, chemokine evaluation, and analysis of sera antibody reactivity and cross-reactivity by Western blot. Immunization with either heated or low LPS vaccines with serovar Copenhageni or Canicola resulted in 100% protection of the animals challenged with homologous virulent bacteria. Notably, different from the whole-cell vaccine, the low LPS vaccines produced with serovar Canicola provided only partial protection in heterologous challenge with the virulent Copenhageni serovar. Immunization with bivalent formulation results in 100% protection of immunized animals challenged with virulent serovar Canicola. All vaccines produced were able to eliminate bacteria from the kidney of challenged animals. All the vaccines raised antibodies capable to recognize antigens of serovars not present in the vaccine formulation. Transcripts of IFNγ, CXCL16, CCL5, CXCL10, CXCR6, and CCR5, increased in all immunized animals. Conclusion: Our results showed that bivalent vaccines with reduced LPS may be an interesting strategy for protection against heterologous virulent serovars. Besides the desirable multivalent protection, the low LPS vaccines are specially promising due to the expected lower reatogenicity.

Leptospira borgpetersenii Leucine-Rich Repeat Proteins Provide Strong Protective Efficacy as Novel Leptospiral Vaccine Candidates

“…The greatest challenge for the development of a vaccine against leptospirosis is to identify antigens that provide long-lasting, cross-protective, and sterilizing immunity. To develop a fully protective, sterilizing immune response to a leptospiral vaccine, mixed strong humoral and cell-mediated immune responses are obligatory [ 14 , 15 , 16 , 20 , 29 , 30 , 45 , 48 , 49 , 50 ]. Since Leptospira is an extracellular bacterium, the predominant immunological effector response is humoral immunity, whereby IgG antibodies would inactivate the Leptospira because of complement-mediated lysis and/or via opsonization for phagocytosis.…”

“…It is interesting to note that the rhKU_Sej_LRR_2271 protein can activate both Th1 and Th2 immune responses as a single protein. It has been previously reported that cell-mediated immunity is required for protection against bovine leptospirosis [ 16 , 48 , 50 ] and in a hamster model of acute leptospirosis [ 20 , 29 , 30 , 45 , 49 , 61 ]. The results in the present study are in agreement with the data reported by Tansiri et al The 2271 antigen, including LL17 and SL19 peptides, stimulated splenocyte proliferative responses on cultured splenocytes isolated from the 2271 vaccinated hamster spleens.…”

“…Although the 2271 protein is supposed to function as bacterial host-pathogen interactions, membrane anchoring, and invasion, such as proteins Internalin A, B and J, YopM, and LRR20 [ 34 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 ], the 2271 vaccine could not provide a sterilizing immunity against challenging with virulent L. interrogans serovar Pomona in immunized hamsters. However, the protein alleviated severe inflammatory lesions in vital tissues; therefore, it is interesting to investigate further the 2271 vaccine activity against homologous Leptospira such as L. borgpetersenii and additional cross-immunity against heterologous strains from L. interrogans as previously studied [ 20 , 21 , 64 ].…”

“…However, these multivalent whole-cell leptospiral vaccines usually do not achieve sufficient coverage against the spectrum of serovars important for animal health [ 15 ]. Although several research groups recently presented a novel approach for the preparation of whole-cell leptospiral vaccines with cross-protective immunity, the disadvantages of the bacterin vaccine are still a concern [ 20 , 21 ]. Adverse effects of the whole-cell vaccines are contaminated medium components resulting in serious side effects, the requirement for ongoing surveillance to identify new bacterin serovars for the preparation of multivalent whole-cell vaccines, and the maintenance of virulent strains in bacterin formulations [ 14 , 15 , 22 ].…”

Leptospiral Immunoglobulin-Like Domain Proteins: Roles in Virulence and Immunity

“…For this reason, whole cell vaccines typically contain a combination of serovars prevalent locally ( 144 ). In some studies, heterologous protection against unrelated serovars has been observed ( 145 , 146 ), including cases with altered or depleted LPS ( 147 – 149 ). As discussed in a recent review on leptospirosis vaccines ( 150 ), these varying results may also stem from different levels of immunoprotective protein antigens, such as the Lig proteins, whose expression varies according to the culture conditions used to grown the antigen source or challenge strain.…”