Group B streptococcus (GBS) infection in the new-borns generally results from intrapartum acquisition of the organism from their rectovaginally colonised mothers. An effective maternal vaccine should protect the baby and prevent colonization in the pregnant woman to eliminate the risk of GBS transmission. Current GBS conjugate vaccine strategy (given parenterally) does not prevent maternal colonization, possibly due to its ability to induce only systemic (IgG), but not mucosal immunity (IgA) at the colonization site.
In this project we set up an alternative route for GBS vaccination, via sublingual administration. Advantage of using this route over parenteral administration is its potential to induce both systemic and mucosal immunity. Systemically generated IgG would be transferred trans-placentally to the foetus, whereas mucosal IgA prevents colonization at the mucosal surface of vagina, hence, effective immunization is achieved by inducing both protection to the foetus and prevention of maternal colonization.
Mice were immunised sublingually with GBS serotype III polysaccharide-tetanus toxoid conjugate with cholera toxin (CTX) or CT-B subunit adjuvants. The positive control mice (for systemic IgG) received subcutaneous GBS conjugate alone. Serum IgG and mucosal IgA levels at different mucosal sites were determined by ELISA.
Sublingual administration of GBS conjugate with CTX generated: i) serum IgG levels that were equivalent to the subcutaneous administration, and ii) while subcutaneous administration of GBS vaccine did not induce any mucosal IgA response, sublingual immunisation in the presence of CTX or CT-B induced substantial level of IgA antibodies to GBS polysaccharide in vaginal washes and in the intestines.