Strategies to elaborate a vaccine for mucosal candidiasis should take into account what type of immune response is protective under natural conditions, but should not necessarily be limited to mimicking the natural history of mucosal infection and protection. Hence, several studies have focused on different strategies to induce protection against vaginal candidiasis. In particular, it has been reported that vaccination with the recombinant N terminus of the candidal adhesin rAls3p-N protects mice against disseminated and oropharyngeal and vaginal candidiasis by a cell-mediated immune response (Th1/Th17). Antibodies have also been generated but their titers did not correlate with protection. The rAls3p-N vaccine is a promising new vaccine candidate for further exploration to prevent systemic and mucosal candidal infections (Spellberg et al.,
2006). It has recently completed a Phase 1 clinical trial and proved to be safe and immunogenic. In particular, this research group reported that vaginal and systemic protective responses could be achieved by vaccination with rAls3-N which stimulates Th1/Th17 lymphocytes to produce high levels of IFN-γ and IL-17A, as well as the chemokines KC and MIP-1. These cytokines enhance the capacity of phagocytes to kill the pathogen. This vaccine protects immunocompetent mice from both vaginal candidiasis and lethal disseminated candidiasis and it also significantly reduces oral fungal burden in the corticosteroid-treated mouse model of OPC. Human trials with the rAls3-N vaccine are in final preparation (Liu and Filler,
2011). An additional approach to achieve protection against mucosal infection was immunization with
C. albicans dsDNA which induces host resistance in newborn mice against gastrointestinal
C. albicans infection. The protective properties of dsDNA are related to an increased number of CD4
+ T cells secreting IFN-γ (Remichkova et al.,
2009).
One attempt to develop a mucosal vaccination was by using an aspartyl proteinase (Sap2), a very well known enzyme belonging to a family of virulence factors of
C. albicans (Naglik et al.,
2003). Previous clinical and experimental work strongly suggested that Sap2 and possibly other Saps were involved in vaginal infection (Cassone et al.,
1987; De Bernardis et al.,
1990). Mice immunized with Sap2 showed significantly reduced fungal burdens both orally and vaginally, and rats receiving intravaginal administration of anti-Sap2 antibodies were protected by an intravaginal challenge by
C. albicans. These studies demonstrated that Sap2 is an immunogenic antigen capable of inducing protective responses against
C. albicans colonization and infection, and tentatively supports its targeting as a potential vaccine candidate (Rahman et al.,
2007). The role of Sap2 in inducing protection against mucosal candidiasis has more recently been underscored by Sandini et al. (
2011). These authors generated a recombinant truncated Sap2 protein (rSap2t) and reported that intravaginal immunization with this antigen and cholera toxin as an adjuvant protected from the challenge of a highly vaginopathic strain of
C. albicans. Protection was possibly due to the elicitation of specific antibodies IgM and IgG anti-rSap2t. More recently rSap2t was incorporated into influenza virosomes, an adjuvant/carrier formulation already used in other human vaccines, which avoids the necessity for a toxin adjuvant. This formulation generated a potent serum antibody response in the mouse and rat following intramuscular immunization. In a rat model of candidal vaginitis the intravaginal or intramuscular administration of rSap2t induced production of anti-Sap2 IgG and IgA in the vaginal fluid, which conferred a consistent degree of protection against vaginal
C. albicans infection (De Bernardis et al.,
2012).
In another study, murine mAb (KT4, IgG1) was used, neutralizing
in vitro the anti-
Candida activity as an Id vaccine to elicit Abs. An effective protection that correlated with a significant decrease in vaginal
Candida CFU was obtained in Id-vaccinated animals compared with controls. The protection was associated with rising vaginal titers of anti-idiotypic Abs (IdAb), prevalently of the IgA isotype, that were able to passively transfer the protective state to non-immunized animals (Polonelli et al.,
1994). Since the receptor of the killer toxin recognized by the mAbKT4 is a beta-glucan molecule, it is possible that the protection conferred by the Id vaccine somewhat parallels the protection conferred by the β-glucan-conjugate vaccine (see below).
In a further work, immunization was performed with
C. albicans heat shock protein 90

kDa (hsp90-CA). Intradermal priming with recombinant hsp90-CA protein, followed by an intranasal or intradermal booster with recombinant hsp90-CA protein, induced significant increases of specific IgG and IgA antibodies in both serum and vaginal fluid. The specific IgG isotype increased after vaginal
Candida infection, suggesting that
Candida has the ability to induce a local hsp90-specific antibody (IgG) response during VVC (Raska et al.,
2008).
A vaccine composed of β-glucan has been considered a candidate against
Candida and other fungi. A non-fungal source of β-glucan, laminarin, has been used in these studies. Because polysaccharides are poor immunogens, laminarin was conjugated with the diphtheria toxoid CRM197. This novel glyco-conjugate vaccine administered with human-compatible adjuvant resulted immunogenic and protective as a prophylactic against experimental systemic and mucosal infections by
C. albicans (Torosantucci et al.,
2005). The protection has been ascribed to the production of antibodies to β-(1,3)-glucan (Bromuro et al.,
2010). The protective capacity of this β-glucan-conjugate vaccine formulated with the human-compatible MF59 adjuvant was assessed in a murine model of vaginal candidiasis exploiting an
in vivo imaging technique to monitor the infection. The vaccine conferred significant protection, which was associated to anti-β-glucan IgG antibodies in the serum and in the vagina. The efficacy of the antibodies was demonstrated by the passive transfer of the immune vaginal fluid or anti-β-glucan monoclonal antibodies to naïve mice before infection (Pietrella et al.,
2010). The main vaccine candidates are reported in Table .
| Table 1Vaccine candidates for protection against candidiasis. |