Vaccine against dental caries based on virulence-associated immunomodulatory extracellular proteins produced by the cariogenic bacteria Streptococcus sobrinus and Streptococcus mutans

FIELD OF THE INVENTION

Dental caries is considered one of the commonest infectious diseases affecting man. The development of a vaccine against dental decay has been exhaustively researched for several years. Streptococcus sobrinus and Streptococcus mutans are the main etiologic agents of dental caries in mammals, man inclusive. The said bacteria excrete into the culture medium virulence-associated immunomodulatory extracellular proteins (VIP), which have a mitogenic effect on the lymphocytes, suppress the immune response of the host and induce in the latter an early production of IL-10, an immunosuppressor cytokine. So, these VIP are important virulent factors to the produced microorganisms and closely associated with the respective bacterial pathogenicity. In this invention, we shall use these proteins as target antigens in a vaccine against dental caries resorting to the immunoneutralization of their immunobiological effects by immunization with submitogenic doses or by the inactivated VIP.

BACKGROUND OF THE INVENTION

The classical strategy in human vaccination based on the immunostimulation of the microorganism structural antigens has been somewhat disappointing. The number of authorized vaccines used to confer immunity in humans represents a very small percentage of all the pathogenic microorganisms known worldwide. There is not yet available any effective vaccine against fungi, protozoa or helminths. However, several findings suggest that vaccination proves to be efficacious when immunoneutralization of microbial agents associated with virulence occurs. Two of the most effective human vaccines, tetanus and diphtheria, are directed towards bacterial toxins and not to the bacteria structural epitopes. It is also worth mentioning that the vaccine against smallpox consists of a virus, not completely attenuated, since vesicles and pustules appear on the skin at the vaccination site. In previous studies, the inventors of the vaccine against dental caries have demonstrated that several pathogenic microorganisms release virulence-associated immunomodulatory proteins (1-.4). The immunoneutralization of these proteins developed a preventive action in the host, protecting it against systemic infections caused both by the fungus Candida albicans and the bacterium Streptococcus mutans (5,6). Furthermore, preventive vaccination against systemic candidiasis occurred for the first time in primates (marmosets) through immunization against the immunomodulatory protein produced by the fungus (D. Tavares, unpublished communication). Recently, it was reported that a racemase excreted by the protozoon Trypanosoma cruzi (7) preventively protects the host from the systemic infection caused by the parasite (Patent application PCT/IB00/02008, from the Pasteur Institute et al., submitted on Dec. 4, 2000).

The bacteria Streptococcus sobrinus and S. mutans have already been identified as the main etiologic agents of tooth decay in humans (8-11). The treatment of dental caries probably is the most expensive one at world level due to the disease high incidence all over (8,11). Both children and teenagers as well as adults can benefit from vaccination since it prevents pathological complications associated with cariogenicity. Actually, it is well known that Streptococci infections are responsible, in 55% of the cases, for endocarditis and are frequently detected in immunodepressed patients. Therefore, a vaccine against dental decay will reduce risk factors in patients suffering from congenital heart disease or having a heart implanted device and will have a helpful effect on other pathologies or clinical disorders associated with bacterial colonization.

The cariogenic bacteria S. sobrinus and S. mutans excrete into the culture medium proteins whose characteristics are identical to those reported in other microorganisms (1-4). These proteins have in common the following: i) they are mitogenic proteins, inducing lymphocyte polyclonal activation in the host (1-4); ii) they induce the early production of IL-10, an anti-inflammatory cytokine (12,13); iii) they are associated with the microorganism virulence once there is a direct relationship between its production and the microbe pathogenicity (4,14) and are iv) important to the survival of the microorganism in the host as the treatment of the latter with these proteins before occurring the infection enhances the parasitic loading (2,4,14). Consequently, the production of these immunomodulatory proteins seems to be an evasion mechanism used by some pathogens. The protein responsible for the immunosuppressor activity of the VIP produced by S. sobrinus was recently identified as an enolase according to a N-terminal basis and the gene that encodes it cloned, sequenced and expressed into a heterologous system in order to obtain the recombinant protein (15).

SUMMARY OF THE INVENTION

This invention uses virulence-associated immunomodulatory extracellular proteins (VIP). Though the vaccination strategy is identical to the one described for the already mentioned microbes, there are some innovative differences that deserve special reference: I) the etiologic agents are the bacteria S. sobrinus and S. mutans; II) dental caries is the infection caused by these bacteria; III) tooth infection occurs via oral; IV) vaccination routes are: oral, intranasal and subcutaneous; V) this vaccination has two main objectives: prevention and infection treatment when it occurs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows evaluation of dental caries scores on proximal (A) and sulcal (B) molar surfaces involving enamel lesions in Wistar rats sham-immunized and active- or heat-inactivated-VIP-immunized. Data show means.+-.SD of 10 to 12 rats per group. Statistical difference in mean score among the 3 groups was assessed by ANOVA. Multiple comparisons among groups indicated a significantly different mean score of active- or inactive-VIP-immunized in comparison with sham-immunized (p<0.001). No differences were detected between active- and heat-inactivated-VIP-immunized groups. FIG. 1 shows results of 1 of 3 representative independent experiments.

FIG. 2 shows caries lesions on sulcal (A) and interproximal (B) enamel and dentine (C) of molar surfaces in sham-immunized and ENO-immunized rats. Values are the mean caries scores.+-.the standard deviations of 10 to 12 Wistar rats and are one of three representative independent experiments. Comparison among groups indicated a significant difference between ENO-immunized and sham-immunized animals (p<0.001).

FIG. 3 shows numbers of S. sobrinus CFU (Log 10) recovered from oral cavities of different groups of Wistar rats orally infected with S. sobrinus 4 days before immunization. Results are the means.+-.SD of 10 to 12 rats per group rats and are one of three representative independent experiments. Comparison among groups indicated a significant difference between ENO-immunized (...) and sham-immunized () animals (p<0.001).

DETAILED DESCRIPTION OF THE INVENTION

This invention aims at marketing a vaccine against dental decay, obtained from the supernatant over cultures of the cariogenic bacteria known as Streptococcus sobrinus and S. mutans.

According to this invention, the vaccine consists of extracellular proteins or recombinant enolase.

The said proteins induce the suppression of the immune response in the host through the early production of IL-10, an anti-inflammatory cytokine.

In addition, those proteins are factors of virulence to the host and enhance the respective bacterial colonization.

This vaccine induces the immunoneutralization of the immunobiological effects caused by virulence-associated immunomodulatory extracellular proteins (VIP) through the host immunization with submitogenic doses of VIP or inactivated VIP.

Further to this invention, the vaccine against dental decay is prepared to be administered intranasally, orally or subcutaneously to mammals.

This vaccine may be used as a preventive measure against dental caries, i.e., immunization with VIP is performed before bacterial infection.

Alternatively, this vaccine may be administered as an effective treatment of dental caries by immunization with VIP after bacterial infection

EXPERIMENTAL PART

Preparation Procedure

Preparation of Virulence-Associated Immumodulatory Extracellular Proteins (VIP)

I) Preparation of the Set of Extracellular Proteins from the Bacteria S. sobrinus and S. mutants

The bacteria were cultured anaerobically in a broth medium of Todd-Hewitt for 2 days at 37.degree. C. in a starting concentration of 10.sup.8 microorganisms/ml as previously reported (14,16). Cultures were centrifuged at 29,000.times.g during 30 mm and the supernatants successively filtered using 1.2 .mu.m, 0.45 .mu.m and 0.2 .mu.m filters (Schleicher & Schuell). The supernatants were then concentrated by ultracentrifugation (dialysis membrane of 10 kDa porosity) in a Vivaflow 200 (Masterfiex, easy-load) system. These products were generically designated as crude extracellular proteins of their respective bacteria (CEP-Ss and CEP-Sm).

II) CEPs Fractionation

CEPs were subject to an ion-exchange chromatography as previously described (16). The different fractions were concentrated by means of vacuum dialysis on membranes of 12 kDa porosity. Protein concentration was determined according to the Lowry's method (17). Fractions with biological activity (described below) were subfractionated by isoelectric focusing in 2.5-10 saccharose gradient, using an ampholyte mixture of pH 2.5-5.0 and 4.5-6.0 (Pharmacia) as already reported (16). The eluted fractions with biological activity and a pH 4.0-5.0 were designated as protein fractions with virulence-associated immunomodulatory activity, VIP in short.

III) Isolation and Purification of Recombinant Enolase

Cultures of Escherichia coli M-15 cells under exponential growth (A.sub.600=0.6-0.8) and expression vector pQE-31 were induced into the fusion protein expression during 3 hrs at 37.degree. C. by adding 1 mM IPTG (15). The cells were collected by centrifugation at 5000.times.g for 20 min and resuspended in phosphate buffer (1 mM Na.sub.2HPO.sub.4.2H.sub.2O, 1 mM NaH.sub.2PO.sub.4.H.sub.2O, 50 mM NaCl, pH 7.4) containing 10 mM imidazole. The sample was incubated on ice during 30 min in the presence of 100 .mu.g/ml lysozyme and 1% Triton X-100. The cells were sonicated at maximum intensity in 3 cycles of 10 sec. The insoluble material was removed by centrifugation at 10000.times.g for 15 min. The supernatant was filtered using filters of 0.45 .mu.m porosity and introduced into a His-trap column. The recombinant enolase was eluted by imidazole under native conditions. Protein concentration was measured by the Lowry's method (17). The purity of the recombinant protein was determined by SDS-PAGE on gel at 17.5%.

APPLICATION EXAMPLES

Animal models: C57BL/6 mice aged 8-10 weeks born at the Gulbenkian Institute for Science, Oeiras, were used in immunobiological assays. Male and female 16-day old Wistar rats born at the animal quarters of the Faculty of Medicine in Coimbra were used in dental caries experiments. The rats were weaned when they were 20 days old and started a cariogenic diet on the 16.sup.th day following birth.

Bacteria: Streptococcus sobrinus, strain 6715, obtained from the "American Type Culture Collection (ATCC, Manassas, Va.) and Streptococcus mutans (kind gift of Institute Pasteur, Paris), stored at -70.degree. C. in a culture medium of "Brain Heart Infusion Broth" (Difco, Detroit, Mich.) with 25% (v/v) glycerol.

Example A1

Evaluation of the Immunobiological Activity of VIP and of the Protein Recombinant Enolase of S. sobrinus

As it has been previously described (16), the polyclonal activation induced by VIP was determined 5 days after the VIP mice inoculation by the number of non-specific immunoglobulin producing spleen cells, the IgM and IgG isotypes. The isotype profile obtained was IgG2a>IgG2b>IgG1>-IgG3>IgM. The analysis of cell activation markers of the splenic lymphocyte total population 6 hrs (CD69) and on days 3 and 5 (CD25) after treatment with VIP showed a preferential increase in the expression of both markers in the population of B lymphocytes. The immunosuppressor effect was determined following injection of VIP or recombinant enolase 4 days before intraperitoneal immunization with sheep red blood cells (SRBC), as previously reported (15,16,). It was observed an evident suppression of the specific response against SRBC in comparison with the controls. It was also detected that this VIP and the recombinant enolase induced in the inoculated mice a fast increase in the serum levels of interleukin-10 (IL-10) with the maximum rise observed 2 hrs after i.p. injection.

Example A2

Experimental Immunoprotection Assay Using the VIP from Streptococcus sobrinus and Recombinant Enolase.

Protocol for Dental Caries Experiments with Wistar Rats

I) Antigens and adjuvant. The VIP of Streptococcus sobrinus was used as active VIP in a submitogenic dose or inactivated VIP and the recombinant enolase was used in a dose unable to induce immunosuppression. Alum, a kind gift of Erik Lindblad (Biosector, Denmark), was used as adjuvant.

II) Immunizations. Male and female Wistar rats were used in these experiments. Groups of 10-12 animals each were subject to the following treatment:

TABLE-US-00001 Group II Group III Group I (immunized (immunized Group IV (Sham.-immunized intranasally with intranasally with (immunized orally with or control) active VIP) inactivated VIP) Recombinant enolase) 16.sup.th day Cariogenic diet Cariogenic diet Cariogenic diet Cariogenic diet 17.sup.th-21.sup.st Colonization of Colonization of Colonization of the Colonization of the day the oral cavity the oral cavity oral cavity with 10.sup.9 oral cavity with 10.sup.9 with 10.sup.9 cells of with 10.sup.9 cells of cells of S. cells of S. sobrinus S. sobrinus sobrinus S. sobrinus 4 days 1.sup.st intranasal 1.sup.st i.n. 1.sup.st i.n. 1.sup.st oral immunization later (i.n.) or oral immunization with immunization with with recombinant immunization with active VIP + alum inactivated enolase + alum PBS + Alum VIP + alum 3 weeks 2.sup.nd i.n. or oral. 2.sup.nd i.n. 2.sup.nd i.n. 2.sup.nd oral immunization later immunization with immunization with immunization with with recombinant PBS + active VIP + alum inactivated Enolase + alum Alum VIP + alum 10 The animals were The animals were The animals were The animals were weeks sacrificed and sacrificed and sacrificed and sacrificed and later dental caries dental caries dental caries dental caries evaluated evaluated evaluated evaluated

Evaluation of Dental Caries in the Experimental Groups

The rats of the different groups were sacrificed when they were 120 days old and identified with codified numbers before being sent to another laboratory to evaluate dental caries incidence and severity. The jaws were removed and sectioned longitudinally, stained with silver nitrate at 5% for 72 hrs and cut sagittally. The extent of enamel or dentine caries lesions in the 1.sup.st, 2.sup.nd and 3.sup.rd molars teeth of all rats (caries score) was microscopically evaluated by a modified method of Keyes (18).

Bacterial Recoveries

S. sobrinus infection levels were assessed after systematic swabbing of teeth, sonication, and plating of appropriate dilutions on Todd-Hewitt agar (Difco) with Strreptococcus Selective Supplement (0.001 mg of colistin sulphate and 0.5 .mu.g of oxalinic acid per ml) (Oxoid). The plates were incubated at 37.degree. C. in aerobiose for 48 hrs, and S. sobrinus CFU were then enumerated microscopically.

Statistical Analysis

The level of significance of the results in all groups of rats was determined by one-way ANOVA, calculated with Microsoft Excel 2000 software.

Example A3

Increased Resistance to Streptococcus sobrinus-Induced Dental Caries in Rats by Intranasal or Oral Therapeutic Vaccination with the VIP or with Recombinant Enolase, Respectively.

We conducted these experiments to investigate the protective effect of therapeutic immunization with the active- or inactivated-VIP or with recombinant enolase in S. sobrinus-induced dental caries in Wistar rats.

The differences in enamel sulcal caries score between sham-immunized group and the other two immunized groups were statistically significant (p<0.001), with a 34% reduction in caries lesions in both immunized groups of rats (FIG. 1A). The protective effect of VIP immunization on caries lesions was more marked in the enamel proximal caries score (FIG. 1B). Indeed, the differences in the proximal caries scores between the sham-immunized group and the two VIP-immunized groups were statistically relevant (p<0.001), with a 60% reduction in the caries lesions in both VIP-immunized groups (FIG. 1B). No statistical differences were found between active- and inactivated-VIP-immunized groups (p=1.000). Therefore, immunization with either active or inactivated VIP conferred protection against S. sobrinus-induced dental caries in Wistar rats.

The evaluation of S. sobrinus colonization in the oral cavities of the rats showed that VIP-immunized groups exhibited a significant reduction in S. sobrinus levels, while the sham-immunized group maintained high levels of bacteria throughout the study.

TABLE-US-00002 TABLE Reduction of S. sobrinus Oral Colonization in Acive- or Heat-inactivated-VIP-immunized Rats.sup.a Mean Response (log CFU .+-. log SD.sup.b Days after Sham- Active-VIP- Heat-inactivated- Immunization immunized immunized VIP-immunized 30 7.62 .+-. 0.66 6.76 .+-. 0.65 6.62 .+-. 0.54 60 6.60 .+-. 0.56 5.43 .+-. 0.58 5.61 .+-. 0.68 90 5.89 .+-. 0.74 4.23 .+-. 0.60 4.27 .+-. 0.61 .sup.aNumbers of S. sobrinus CFU recovered from the oral cavities of the different groups of Wistar rats orally infected with S. sobrinus 4 days before immunization (post-infection immunization). .sup.bResults are means .+-. SD of 10 to 12 Wistar rats per group. The significantly higher differences between sham-immunized and active- or heat-inactivated-VIP-immunized groups are underlined (p < 0.001). Statistical difference in mean score among the 3 groups was assessed by ANOVA.

The evaluation of dental caries in the animal group orally immunized with recombinant enolase showed that cariogenic lesions in these rats were significantly lower either on the enamel or dentine in comparison with the controls (p<0.001). Therefore, as shown in FIG. 2A there was a reduction of 45% reduction in the enamel sulcal caries score on ENO-immunized group comparatively with sham-immunized animals. This protective effect of enolase immunization on teeth lesions was more evident in the enamel interproximal caries score (FIG. 2B). Indeed, a 71% reduction was observed in the interproximal caries lesions on the ENO-immunized group when compared with the sham-immunized. Moreover, a reduction of 46% in the dentine lesions on the ENO-immunized group was observed when compared with sham-immunized animals (FIG. 2C).

The evaluation of S. sobrinus colonization in the rats oral cavity showed a significant reduction in S. sobrinus levels on ENO-immunized rats when compared with the sham-immunized group, throughout the study (FIG. 3). This reduction of S. sobrinus colonization in oral cavity of ENO-immunized group, in comparison with sham-immunized animals, is correlated with the reduction of caries lesions observed in ENO-immunized rats.

The greater resistance against dental caries observed in the animals immunized against VIP or against the recombinant enolase is in agreement with the important role played by these proteins as to colonization enhancement brought about by the producing bacteria.

BIBLIOGRAPHY

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