Adjuvants to increase immunogenicity of SARS-CoV-2 RBD and support maternal–fetal transference of antibodies in mice

Abstract

Adjuvants are important components of vaccines, increasing immunogenicity and modulating the immune response. SARS-CoV-2 vaccines are still being developed in order to improve worldwide access to immunization. Specific populations should be addressed in these investigations, such as pregnant women – to protect both mothers and neonates. In this study, female adult mice were immunized with Receptor-binding domain (RBD) from SARS-CoV-2 adjuvanted by a mixture of DDA and Saponin and put to mating to verify the maternal transference of IgG. For comparison, other group received RBD adjuvanted by OMVs from Neisseria meningitidis and Alum. The adjuvants enhanced IgG production and neutralization. DDA/Sap contributed to increase IgG1, IgG2a, IgG2b and IgG3 isotypes. Total IgG avidity was considered high, as well as IgG1, IgG2a and IgG2b avidity. IgG antibodies were effectively transferred to the offspring, predominantly IgG2a, IgG2b and IgG3. The passive transferred immunoglobulin maintained the neutralizing ability, although it lost avidity. ELISA data was confirmed in Dot-ELISA and Immunoblotting assays. DDA and Saponin seem a promising adjuvant mixture to enhance the humoral response of SARS-CoV-2 antigens. Further studies considering the effects of maternal immunization in the protection of offspring are needed, regardless the platform used in COVID-19 vaccines.

RBD-Adjuvanted Preparation: Evaluation of IgG and IgM Antibodies for One Year and Cross-Reactivity with Omicron Variant in Mice

“…In view of this, we studied an antigenic preparation using different adjuvants, aiming to induce a functional, durable and robust humoral and cellular response in mice. The first part of this study, published previously [19], showed that the same adjuvant contributed to the functionality of the humoral response and led to passive transfer of antibodies to the offspring. We used recombinant Receptor binding domain (RBD), due to its high immunogenicity and potential to induce neutralizing antibodies [4], associated with the following adjuvants mixtures: dimethyldioctadecylammonium bromide and saponin (DDA/Sap) or Outer membrane vesicles and aluminum hydroxide (OMV/AH).…”

“…We used recombinant Receptor binding domain (RBD), due to its high immunogenicity and potential to induce neutralizing antibodies [4], associated with the following adjuvants mixtures: dimethyldioctadecylammonium bromide and saponin (DDA/Sap) or Outer membrane vesicles and aluminum hydroxide (OMV/AH). We already published the results concerning IgG response and its functionality by avidity and neutralization against Wuhan strain [19]. In this manuscript, we continued the study, assessing IgM levels and avidity; IgG and IgM response one year after the immunization; neutralization against Omicron strain and memory-cellular response by ELISpot.…”

“…Both DDA and Sap were purchased (Sigma-Aldrich), prepared in 0.01 mM sterile saline solution for a final concentration of 1 µg of DDA/1 µg of Sap per dose, and filtered using 0.45 µm membrane as described in our previous manuscript [19]. These concentrations were safe to use according to the hemolysis test that we reported before [19].…”

“…meningitidis C:2a:P1.5 were isolated as described by De Gaspari and Zollinger (2001) [22], detoxified from LPS and used previously in our laboratory [11]. Final concentrations were 10 µg of OMVs and 0.1 mM of Aluminum hydroxide [19].…”

“…The antigenic preparations were: 0.5 µg RBD + 1 µg Sap + 1 µg DDA (the main focus of this study); 3 µg RBD + 10 µg OMVs of N. meningitidis C:2a:P1.5 + 0.1 mM AH (an antigenic preparation used before [12,13], for comparison); 3 µg RBD; and 1 µg Sap + 1 µg DDA. An extra control group was used, consisting of naïve mice [19].…”