Plant‐derived recombinant immune complexes as self‐adjuvanting TB immunogens for mucosal boosting of BCG

Abstract

SummaryProgress with protein-based tuberculosis (TB) vaccines has been limited by poor availability of adjuvants suitable for human application. Here, we developed and tested a novel approach to molecular engineering of adjuvanticity that circumvents the need for exogenous adjuvants. Thus, we generated and expressed in transgenic tobacco plants the recombinant immune complexes (RICs) incorporating the early secreted Ag85B and the latency-associated Acr antigen of Mycobacterium tuberculosis, genetically fused as a single polypeptide to the heavy chain of a monoclonal antibody to Acr. The RICs were formed by virtue of the antibody binding to Acr from adjacent molecules, thus allowing self-polymerization of the complexes. TB-RICs were purified from the plant extracts and shown to be biologically active by demonstrating that they could bind to C1q component of the complement and also to the surface of antigen-presenting cells. Mice immunized with BCG and then boosted with two intranasal immunizations with TB-RICs developed antigen-specific serum IgG antibody responses with mean end-point titres of 1 : 8100 (Acr) and 1 : 24 300 (Ag85B) and their splenocytes responded to in vitro stimulation by producing interferon gamma. 25% of CD4+ proliferating cells simultaneously produced IFN-c, IL-2 and TNF-a, a phenotype that has been linked with protective immune responses in TB. Importantly, mucosal boosting of BCG-immunized mice with TB-RICs led to a reduced M. tuberculosis infection in their lungs from log 10 mean = 5.69 AE 0.1 to 5.04 AE 0.2, which was statistically significant. We therefore propose that the plant-expressed TB-RICs represent a novel molecular platform for developing self-adjuvanting mucosal vaccines.

Novel vaccination approach for dengue infection based on recombinant immune complex universal platform

“…Plant-expressed RIC were first shown to be immunogenic and protective against C. tetani challenge [20]. More recently, we reported that Ebola RIC could induce protective antibodies against the Ebola virus [1,21], while similar studies performed elsewhere showed that tuberculosis-based RIC (TB-RIC) [22] confer statistically significant protection against M. tuberculosis infection. Others have shown that immune complexes can substantially enhance antibody responses to HIV gp120 [17][18][19].…”

“…Studies by Hioe and coworkers indicate that immune complexes substantially enhanced antibody responses against HIV gp120 [17][18][19]. We and others have explored the possibility of designing immune complex vaccines against a number of pathogens including Clostridium tetani [20], Ebola virus [1,21] and Mycobacterium tuberculosis [22]. This approach is based on generating recombinant immune complexes (RIC) using a monoclonal antibody specific for a particular antigen and expressed in fusion with that antigen (at the C-terminus of the heavy chain).…”

An overview of tuberculosis plant-derived vaccines

“…IFN-g was also activated when either Ag85B or Acr stimulus was present. Remarkably, in terms of immunoprotection, BCG-immunized mice boosted with TB-RICs showed a significant reduction on lung M. tuberculosis infection, at lower levels than the observed in the group immunized only with BCG [68]. The successful use of immune complexes based on antibody chains was previously proven in plant systems by targeting an HIV antigen and thus this technology is considered a convenient configuration leading to high immunogenicity [69,70].…”

Chikungunya virus vaccines: Current strategies and prospects for developing plant-made vaccines

“…Using similar approaches, multiple antigens have been expressed in tobacco being able to induce both humoral and cellular immune responses that protected against intracellular pathogens such as Mycobacterium tuberculosis. Intranasal immunization of mice with ICs boosted the Bacillus Calmette-Guerin strain vaccine (BCG)-induced immunity and, importantly, conferred further protection against M. tuberculosis infection [92]. Remarkably, these methodologies have been applied to target viruses.…”