Leaf saponins of Quillaja brasiliensis enhance long-term specific immune responses and promote dose-sparing effect in BVDV experimental vaccines

Abstract

Saponin-based adjuvants are promising adjuvants that enhance both humoral and T-cell-mediated immunity. One of the most used natural products as vaccine adjuvants are Quillaja saponaria bark saponins and its fraction named Quil A®. Despite that, its use has been restricted for human use due to safety issues. As an alternative, our group has been studying the congener species Quillaja brasiliensis saponins and its performance as vaccine adjuvants, which have shown to trigger humoral and cellular immune responses comparable to Quil A® but with milder side effects. Here, we studied a semi purified aqueous extract (AE) and a previously little characterized saponin-enriched fraction (QB-80) from Q. brasiliensis as vaccine adjuvants and an inactivated virus (bovine viral diarrhea virus, BVDV) antigen co-formulated in experimental vaccines in mice model. For the first time, we show the spectra pattern of the Q. brasiliensis saponins by MALDI-TOF, a novel and cost-effective method that could be used to characterize different batches during saponins production. Both AE and QB-80 exhibited noteworthy chemical similarities to Quil A®. In addition, the haemolytic activity and toxicity were assessed, showing that both AE and QB-80 were less toxic than Quil A®. When subcutaneously inoculated in mice, both fractions promoted long-term strong antibody responses encompassing specific IgG1 and IgG2a, enhanced the avidity of IgG antibodies, induced a robust DTH reaction and significantly increased IFN-ɣ production in T CD4 and T CD8 cells. Furthermore, we have proven herein that AE has the potential to promote dose-sparing, substantially reducing the dose of antigen required for the BVDV vaccines and still eliciting a mixed Th1/Th2 strong immune response. Based on these results, and considering that AE is a raw extract, easier and cheaper to produce than commercially available saponins, this product can be considered as candidate to be escalated from experimental to industrial uses.

Quillaja brasiliensis saponin-based nanoparticulate adjuvants are capable of triggering early immune responses

“…brasiliensis saponins and in particular their nanoparticles as potent vaccine adjuvants. We have demonstrated here that they are capable of promoting early immune responses that, considering our previous data, correlate with adequate adaptive immune responses 18 , 20 – 23 , 34 . In addition, Q .…”

“…The bovine viral diarrhea virus (BVDV) isolate EVI 001/94 was multiplied in Madin Darby Bovine Kidney cells (MDBK; originally ATCC CCL-22) as described elsewhere 20 , 24 . The infectious titre of the virus suspension prior to inactivation was 10 7.5 tissue culture infectious doses per mL.…”

“…Total anti-BVDV IgG1 and IgG2a were determined for each serum samples by ELISA, carried out essentially as previously described 20 , 24 using as antigen the BVDV suspension used for mouse immunization. Antibody titres were expressed in OD 492 nm.…”

“…brasiliensis were found to share structural and biological activities with Q . saponaria 17 – 20 , inducing lower levels of toxicity than Quil A ® in mice, and strongly potentiating humoral and cellular immune responses to viral antigens 18 , 20 – 23 . Indeed, these molecules were shown to up-regulate both Th1- and Th2-like immune responses and to promote a robust DTH reaction.…”

“…QB-90 and QB-80, two of the Q . brasiliensis saponin fractions, were shown to increase secretion of Th1-associated cytokines (IFN-γ and IL-2) and antigen-specific IFN-γ production by CD4 + and CD8 + T cells 20 , 24 when used as vaccine adjuvants.…”