Immunogenicity of SARS-CoV-2 trimetric spike protein associated to Poly(I:C) plus Alum

Abstract

The SARS-CoV-2 pandemic has had a social and economic impact worldwide, and vaccination is an efficient strategy for diminishing those damages. New adjuvant formulations are required for the high vaccine demands, especially adjuvant formulations that induce a Th1 phenotype. Herein we assess a vaccination strategy using a combination of Alum and polyinosinic:polycytidylic acid (Poly(I:C)) adjuvants plus the SARS-CoV-2 spike protein in a prefusion trimeric conformation by an intradermal (ID) route. We found high levels of IgG anti-spike antibodies in the serum by enzyme linked immunosorbent assay (ELISA) and high neutralizing titers against SARS-CoV-2 in vitro by neutralization assay, after one or two boosts. By evaluating the production of IgG subtypes, as expected, we found that formulations containing Poly(I:C) induced IgG2a whereas Alum did not. The combination of these two adjuvants induced high levels of both IgG1 and IgG2a. In addition, cellular immune responses of CD4+ and CD8+ T cells producing interferon-gamma were equivalent, demonstrating that the Alum + Poly(I:C) combination supported a Th1 profile. Based on the high neutralizing titers, we evaluated B cells in the germinal centers, which are specific for receptor-binding domain (RBD) and spike, and observed that more positive B cells were induced upon the Alum + Poly(I:C) combination. Moreover, these B cells produced antibodies against both RBD and non-RBD sites. We also studied the impact of this vaccination preparation (S Ptn with Alum + Poly(I:C)) in the lungs of mice challenged with inactivated SARS-CoV-2 virus. We found a production of IgG, but not IgA, and a reduction in neutrophil recruitment in the bronchoalveolar lavage fluid (BALF) of mice, suggesting that our immunization scheme reduced lung inflammation. Altogether, our data suggest that Alum and Poly(I:C) together is a possible adjuvant combination for vaccines against SARS-CoV-2 by the intradermal route.

Intradermal Immunization of SARS-CoV-2 Original Strain Trimeric Spike Protein Associated to CpG and AddaS03 Adjuvants, but Not MPL, Provide Strong Humoral and Cellular Response in Mice

“…Recently, we demonstrated that the immunization of trimetric spike protein of SARS-CoV-2 that was associated to Poly(I:C) plus Alum was able to induce high neutralizing titers against SARS-CoV-2 in vitro by neutralization assay [7] by the i.d. route.…”

“…Nonetheless, many vaccine candidates against SARS-CoV-2 using the intradermal route (i.d.) have shown promising results, either on laboratory tests on different animal models [5][6][7][8], or in development with clinical trials [9,10]. The i.d.…”

“…Adjuvant usage in vaccination strategies against SARS-CoV-2 is absolutely important [15,16]. In fact, many adjuvants have already been evaluated with the spike protein (S ptn) and/or the receptor binding domain (RBD) portion of the S ptn regarding vaccination strategies, such as Matrix-M and AddaVax, both based on scalene [17,18], Alum [7,19], Poly(I:C) [7], and CpG [20]. Nonetheless, ours and other groups have already demonstrated that formulation with two different adjuvants may increase immunization efficacy [7,21].…”

“…In fact, many adjuvants have already been evaluated with the spike protein (S ptn) and/or the receptor binding domain (RBD) portion of the S ptn regarding vaccination strategies, such as Matrix-M and AddaVax, both based on scalene [17,18], Alum [7,19], Poly(I:C) [7], and CpG [20]. Nonetheless, ours and other groups have already demonstrated that formulation with two different adjuvants may increase immunization efficacy [7,21]. AddaS03 is a nanoemulsification adjuvant, with a formulation that is based on the adjuvant system AS03, that is capable of inducing transient nuclear factor-κB (NF-κB) activation, the production of cytokines, antigen-specific antibodies, and the migration of immune cells [22,23].…”

A SARS-CoV-2 Negative Antigen Rapid Diagnostic in RT-qPCR Positive Samples Correlates With a Low Likelihood of Infectious Viruses in the Nasopharynx

“…Microtitre plates (Immulon 2 HB) were coated with a trimeric mammalian-culture secreted ectodomain of the Spike protein—Wuhan in the pre-fusion conformation (Alvim et al, 2021 ) at 4 μg/ml or the nucleocapsid—Wuhan protein produced as described by dos-Santos et al ( 2021 ) at 1 μg/ml in 100 mM sodium carbonate-bicarbonate buffer (pH 9.6) and incubated overnight at 4°C. Excess protein was removed by washing five times with PBS + 0.05% Tween-20 (PBST, Sigma), and unbound sites were blocked using 5% BSA in PBST.…”