Abstract
Inactivated polio vaccines (IPV) have an important role at the final stages of poliomyelitis eradication programs, reducing the risks associated with the use of attenuated polio vaccine (OPV). An affordable option to enhance vaccine immunogenicity and reduce costs of IPV may be the use of an effective and renewable adjuvant. In the present study, the adjuvant activity of aqueous extract (AE) and saponin fraction QB-90 from Quillaja brasiliensis using poliovirus antigen as model were analyzed and compared to a preparation adjuvanted with Quil-A, a well-known saponin-based commercial adjuvant. Experimental vaccines were prepared with viral antigen plus saline (control), Quil-A (50 µg), AE (400 µg) or QB-90 (50 µg). Sera from inoculated mice were collected at days 0, 28, 42 and 56 post-inoculation of the first dose of vaccine. Serum levels of specific IgG, IgG1 and IgG2a were significantly enhanced by AE, QB-90 and Quil-A compared to control group on day 56. The magnitude of enhancement was statistically equivalent for QB-90 and Quil-A. The cellular response was evaluated through DTH and analysis of IFN-γ and IL-2 mRNA levels using in vitro reestimulated splenocytes. Results indicated that AE and QB-90 were capable of stimulating the generation of Th1 cells against the administered antigen to the same extent as Quil-A. Mucosal immune response was enhanced by the vaccine adjuvanted with QB-90 as demonstrated by increases of specific IgA titers in bile, feces and vaginal washings, yielding comparable or higher titers than Quil-A. The results obtained indicate that saponins from Q. brasiliensis are potent adjuvants of specific cellular and humoral immune responses and represent a viable option to Quil-A.
Highlights
More than 25 years after ‘‘The World Health Organization Polio Eradication Initiative’’ was established with the intention of eradicating poliomyelitis, a highly contagious disease that affects nerves and can lead to partial or full paralysis, remarkable success has been achieved in this field, with the reduction of global cases by 99% in 2013 [1]
This study provides for the first time a direct comparison of the effect of Q. brasiliensis aqueous extract (AE) and QB-90 versus commercial Quil-A as vaccine adjuvants for triggering immune responses against a relevant human pathogen, including mucosal immunity, an important feature in polio vaccine
Poliovirus-specific IgG and the subclasses in mice Serum anti-poliovirus IgG, IgG1 and IgG2a were significantly higher in mice immunized with vaccine formulations containing QB-90 50 mg, AE 400 mg or Quil-A 50 mg, when compared to the control group on tests performed on samples collected on day 56 (Fig. 1)
Summary
More than 25 years after ‘‘The World Health Organization Polio Eradication Initiative’’ was established with the intention of eradicating poliomyelitis, a highly contagious disease that affects nerves and can lead to partial or full paralysis, remarkable success has been achieved in this field, with the reduction of global cases by 99% in 2013 [1]. In line with this observation, it has further been shown that aqueous extract (AE) and fraction QB-90 of the Brazilian species were able to stimulate both humoral and cellular immune responses against bovine herpesvirus types I (BoHV-1) and 5 (BoHV-5) in mice in a comparable manner to Quil-A saponins [9,10]. We further advance knowledge on the adjuvant activity of saponins from leaves of Q. brasiliensis by analyzing the use of AE and QB90 in an inactivated poliovirus vaccine, following immunization of mice.
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