A non-toxic mucosal adjuvant is provided which may be admixed with further antigens to provide a vaccine administrable to mucosal surfaces in organisms including man. Preferably, the non-toxic mucosal adjuvant is a detoxified mutant of a bacterial ADP-ribosylating toxin, optionally comprising one or more amino acid additions, deletions or substitutions.

FIELD OF THE INVENTION

The present invention relates to an adjuvant useful for the administration of vaccines to organisms. In particular, the adjuvant of the invention allows the delivery of vaccines to mucosal surfaces to raise a secretory and systemic immune response.

BACKGROUND TO THE INVENTION

Current vaccination technology is based almost exclusively on systemic vaccination techniques wherein the vaccine is injected into the subject to be vaccinated. Only certain live/attenuated vaccines, such as the Sabin polio vaccine, may be taken orally.

The advantages of oral immunisation techniques are several fold. For instance, it is self-evident that a vaccine which may be fed to subjects is easier to administer on a large scale in the absence of specialised equipment, especially to subjects which may be difficult to handle or even locate, such as livestock and wild animals. The spread of infection by the re-use of needles in developing countries would thereby be avoided. Furthermore, an oral vaccine may be provided in the form of an edible solid, which is easier to handle under extreme conditions and is more stable than liquid suspensions as currently used.

Moreover, delivery of immunogens to a mucosal membrane, such as by oral or intranasal vaccination, would permit the raising of a secretory immune response.

The secretory immune response, mainly IgA-mediated, appears to be substantially separate from the systemic immune response. Systemic vaccination is ineffective for raising a secretory immune response. This is a considerable disadvantage when considering immunisation against pathogens, which often enter the subject across a mucosal surface such as the gut or lung.

Unfortunately, it is not possible to raise a secretory immune response to the vast majority of antigens simply by exposing mucosal surfaces to such antigens. Furthermore, no adjuvant capable of eliciting a secretory immune response to a given antigen is currently available.

The apparent difficulty is largely due to a phenomenon known as oral tolerance. The linings of the gut and the lungs are naturally tolerant to foreign antigens, which prevents an immune response being raised to ingested or inhaled substances, such as food and airborne particulate matter.

The ADP-ribosylating bacterial toxins, namely diphtheria toxin, pertussis toxin (PT), cholera toxin (CT), the E. coli heat-labile toxin (LT1 and LT2), Pseudomonas endotoxin A, C. botulinum C2 and C3 toxins as well as toxins from C. perfringens, C. spiriforma and C. difficile are potent toxins in man. These toxins are composed of a monomeric, enzymatically active A subunit which is responsible for ADP-ribosylation of GTP-binding proteins, and a non-toxic B subunit which binds receptors on the surface of the target cell and delivers the A subunit across the cell membrane. In the case of CT and LT, the A subunit is known to increase intracellular cAMP levels in target cells, while the B subunit is pentameric and binds to GM1 ganglioside receptors.

In 1975 and 1978 observations were made which demonstrated that CT is able to induce mucosal and systemic immunity against itself when administered intraduodenally (i.e. to a mucosal surface). The membrane-binding function of CT was shown to be essential for mucosal immugenicity, but cholera toxoid, also known as the B subunit of CT (CTB) was inactive in isolation (Pierce and Gowans, J. Exp. Med 1975; 142: 1550; Pierce, J. Exp Med 1978; 148: 195-206).

Subsequently, it was demonstrated that CT induces systemic and mucosal immunity to co-administered antigens, in other words functions as a mucosal adjuvant (Elson, Curr. Top. Microbiol. Immunal, 1989; 146: 29; Elson and Ealding, J. Immunol. 1984; 133: 2892-2897; Elson and Ealding, Ibid. 1984; 132: 2736-2741; Elson et al., J. Immunol. Methods 1984; 67: 101-118; Lycke and Homgren, Immunology 1986; 59: 301-338).

The experiments referred to above were conducted in mice, which are comparatively resistant to the toxic effects of CT. In contrast, wild-type CT is extremely toxic to humans, rendering the use of CT having any substantial residual toxicity as a mucosal adjuvant in humans entirely out of the question.

Two approaches have been taken in the prior art to address the problem of CT toxicity. The first approach has involved the use of CTB as a mucosal adjuvant. CTB is entirely non-toxic.

In one series of experiments, CTB was covalently coupled to horseradish peroxidase (HRP) and administered to mice intraduodenally. This gave rise to a powerful mucosal immune response to HRP (McKenzie and Halsey, J. Immunol 1984; 133: 1818-1824).

This result has subsequently been partially confirmed with other antigens (Liang et al., J. Immunol 1988; 141: 1495-1501; Czerkinsky et al., Infect. Immun. 1989; 57: 1072-1077). The same principle has also been established to be effective when chimeric antigens produced by gene fusion to sequences encoding CTB have been tested (Dertzbaugh and Elson, Infect. Immun. 1993; 61: 384-390; Dertzbaugh and Elson, Ibid. 1993; 61: 48-55; Sanchez et al., Res. Microbiol 1990; 141: 971-979; Holmgren et al., Vaccine 1993; 11: 1179-1184).

However, the production of chimeric or coupled antigens introduces a further step in the preparation of suitable vaccines, which essentially requires that antigens be prepared in a form conjugated with CTB especially for oral use. It would be for simpler and more economical if the adjuvant could be administered in simple admixture with the antigen.

An adjuvant effect for co-administered CTB has been alleged in a number of publications (Tamura et al., J. Immunol 1992; 149: 981-988; Hirabayashi et al., Immunology 1992; 75: 493-498; Gizurarson et al., Vaccine 1991; 9: 825-832; Kikuta et al., Vaccine 1970; 8: 595-599; Hirabayashi et al. Ibid. 1990; 8; 243-248; Tamura et al., Ibid. 1989; 7: 314-32-; Tamura et al., Ibid. 1989; 7: 257-262; Tamura et al., Ibid 1988; 6: 409-413; Hirabayashi et al., Immunology 1991; 72: 329-335 Tamura et al., Vaccine 1989; 7: 503-505).

However, a number of aspects of the observations reported above were not entirely convincing. For example, it was noted that the adjuvant effect ascribed to CTB was not H-2 restricted. It is known, however, that immune response to CTB is H-2 restricted (Elson and Ealding, Eur. J. Immunol. 1987; 17: 425-428). Moreover, the alleged adjuvant effect was observed even in individuals already immune to CTB.

Other groups were unable to observe any mucosal adjuvant effect attributable to CTB (Lycke and Holmgren, Immunology 1986; 59: 301-308; Lycke et al., Eur. J. Immunol. 1992; 22: 2277-2281). Experiments with recombinant CTB (Holmgren et al., Vaccine 1993; 11: 1179-1183) confirmed that the alleged effect is largely if not exclusively attributable to low levels of contamination of CTB preparations with CT.

Thus, it is presently accepted that CTB is not useful as a mucosal adjuvant.

A second approach to eliminating the toxicity of CT has been to mutate the CT holotoxin in order to reduce or eliminate its toxicity. The toxicity of CT resides in the A subunit and a number of mutants of CT and its homologue, LT, comprising point mutations in the A subunit are known in the art. See, for example, International Patent Application WO92/19265 (Amgen). It is accepted in the art that CT and LT are generally interchangeable, showing considerable homology.

However, the only mutant so far tested for mucosal adjuvanticity, an LT mutant having a Glu--Lys mutation at position 112, was found to be inactive as a mucosal adjuvant (Lycke et al; Eur. J. Immunol. 1992; 22: 2277-2251; Holmgren et al., Vaccine 1993; 11: 1179-1183). The authors of these publications conclude that there is a link between the ADP ribosylating activity of CT and/or LT and the adjuvant activity. It appears from these publications, therefore, that CTB or a non-toxic mutant of CT or LT would not be active as a mucosal adjuvant.

SUMMARY OF THE INVENTION

There therefore remains a need for an active mucosal adjuvant which may be used to increase the immunogenicity of an antigen when administered to a mucosal surface, such as orally or intranasally.

It has now been discovered that, in complete contradiction with the results and conclusions presented in the prior art, the toxic and adjuvant activities of the ADP-ribosylating toxins are separable. An entirely non-toxic mutant of such a toxin has been shown to be active as a mucosal adjuvant.

The present invention, in a first aspect, provides a pharmaceutical composition comprising a non-toxic mucosal adjuvant in admixture with a second antigen.

It has been demonstrated that an LT mutant which completely lacks toxicity is active as a mucosal adjuvant and protects subjects against subsequent challenge with a lethal dose of the immunogen. Although the Applicants do not wish to be bound by any particular theory, it is postulated that the results of Lycke et al. and Holmgren et al. quoted above may be contradicted at least in part because they fail to take into account the stability of the mutant being made. Inter alia by ensuring that the non-toxic mutant of the invention is stable at the site of delivery, it has been demonstrated that the adjuvant effect of CT and/or LT may be maintained while its toxic effects are eliminated.

Preferably, therefore, the non-toxic mucosal adjuvant is a detoxified mutant of a bacterial ADP-ribosylating toxin, optionally comprising one or more amino acid additions, deletions or substitutions.

Particularly suitable are detoxified mutants of CT or LT. For example, a mutant LT in accordance with the invention may possess an Arg7 to Lys7 substitution at position 7 of the A subunit, the so-called LTK7 mutant.

Alternative mutants are known to those skilled in the art and are preferred molecules for use in the present invention. Examples include PT mutated at position 129, in particular PT having a Glu 129.fwdarw.Gly mutation. Further mutants include PT mutated at one or both of Trp 26 and Arg 9, optionally in combination with the Glu 129 mutation.

The mutant used in the invention may moreover be a mutant wherein the mutation has been effected in a part of the molecule which results in the prevention of proteolytic cleavage of the A subunit of the toxin, such that enzymatic activity is not brought about. Such mutants are described in Grant et al. Inf. and Immunity (1994) 62(10) 4270-4278. For example, the mutant may comprise an Arg 192.fwdarw.Gly mutation in LT or a corresponding mutation in another ADP-ribosylating toxin.

The mutant of the invention is preferably in the form of a holotoxin, comprising the mutated A subunit and the B subunit, which may be oligomeric, as in the wild-type holotoxin. The B subunit is preferably not mutated. However, it is envisaged that a mutated A subunit may be used in isolation from the B subunit, either in an essentially pure form or complexed with other agents, which may replace the B subunit and/or its functional contribution.

Methods for the design and production of mutants of CT and/or LT are known in the art. Suitable methods are described in International Patent Application WO93/13202 (Biocine Sclavo), the disclosure of which is incorporated herein by reference, as well as WO92/19265 (Amgen).

The adjuvant of the invention is preferably administered in admixture with a suitable antigen against which it is desired to raise an immune response. If the antigen and the adjuvant are not in admixture, it is preferred that they be administered within a relatively short time of each other, at the same site of administration. It has been observed that the adjuvant effect provided by wild-type CT is short lived (see Lycke and Homgren, Immunology 1986; 59: 301-308). In an alternative embodiment, the mucosal adjuvant of the invention may be administered, optionally in isolation from other antigens, as a boost following systemic or mucosal administration of a vaccine.

The precise formulation of the vaccine may vary in accordance with the nature of the immunogen. For example, if the antigen is enclosed in slow-releasing microspheres to liposomes, the mucosal adjuvant may be similarly enclosed so that the antigen and the adjuvant may interact simultaneously with the mucosal immune system. Alternatively, separate mucosal administration of the adjuvant of the invention may be used to enhance mucosal response to parentally-administered vaccines.

In a second aspect, the present invention provides the use of a non-toxic mutant of CT or LT as a mucosal adjuvant in the preparation of a composition for mucosal administration.

Preferably, the composition is a vaccine and is useful for the immunisation of a subject against a disease or the treatment of a subject suffering from a disease.

Preferably, the mutant comprises one or more amino acid additions, substitutions or deletions in the amino acid sequence of the A subunit of CT or LT which is or are effective to abolish the toxicity of the toxin.

According to a third aspect of the invention, there is provided a method for the prevention or treatment of a disease in a subject comprising administering to the subject an immunologically effective dose of an antigen adjuvanted with a non-toxic CT or LT mutant by contacting a mucosal surface of the subject with said adjuvanted antigen.

The mucosal surface may be any suitable mucosal surface of the subject. For example, the administration may be carried out by inhalation, by means of a rectal or vaginal suppository, or a pessary, by feeding or other buccal administration, by means of an aerosol, by intranasal delivery or direct application to mucosal surfaces. Especially preferred are oral and intranasal administration.

The subject may be any organism susceptible to immunisation. Especially indicated are humans and other mammals such as livestock, pets and wildlife.

Diseases against which the subject may be immunised include all diseases capable of being treated or prevented by immunisation, including viral diseases, allergic manifestations, diseases caused by bacterial or other pathogens which enter through or colonise mucosal surfaces, AIDS, autoimmune diseases such as systemic Lupus Erythe-matosus, Alzheimer's disease and cancers. Examples of viral infections which may be treated or prevented using the invention include infection by DNA viruses, such as EBV and VZV, and in particular herpesviridae, for example HSV and HCMV, adenoviridae, papovaviridae, such as HPV, hepadna-viridae, such as HBV, infection by RNA viruses, such as picorvaviridae, especially polivirus and HAV, rhinoviruses and FMDV, togaviridae, flaviviridae, coronaviridae, paramyxo-viridae, such as RSV, orthomyoxoviridae, such as influenza virus, and retroviridae, especially HIV. Vaccination against HCV and HDV is also envisaged.

Examples of bacterial infections suitable for treatment or prophylaxis by the invention include infection with Helicobacter pylori, streptococci, meningococcus A, B, and C, bordetella pertussis and chlamydia and trachomatis.

Vaccine formulation suitable for delivery at mucosal surfaces may be prepared as set out hereinbelow, while further formulations will be apparent to those of skill in the art. Suitable administration regimes are, likewise, set out below while modifications of the exemplified values will be apparent to those of skill in the art.

Moreover, the invention provides a mutant of CT or LT which is a non-toxic mucosal adjuvant and a second antigen for simultaneous separate or sequential administration. Simultaneous administration of the adjuvant and the second antigen when combined in a single vehicle, carrier or particle, as exemplified below, is particularly preferred.

The second antigen may be any antigen to which it is desired to raise an immune response in the subject. Suitable antigens comprise bacterial, viral and protozoan antigens derived from pathogenic organisms, as well as allergens, allogens and antigens derived from tumours and self-antigens. Typically, the antigen will be a protein, polypeptide or peptide antigen, but alternative antigenic structures, such as nucleic acid antigens, carbohydrate antigens, and whole or attenuated or inactivated organisms such as bacteria, viruses or protozoa are not excluded. The invention further provides a method for the manufacture of an adjuvanted vaccine comprising the steps of: a) performing site-diected mutagenesis on the A-subunit of a bacterial ADP-ribosylating toxin in order to detoxify the toxin; and b) bringing the detoxified toxin into association with a second antigen, such that it functions as a mucosal adjuvant.

Specific examples of antigens useful in the present invention include HSV gD, gB and other glycoproteins; HIV gp120 and other proteins; CMV gB or gH; HCV antigens; HDV delta antigen; HAV antigens; EBV and VZV antigens; B. pertussis antigens and H. pylori antigens.

In general, the second antigen may be the immunogenic component of the vaccine intended for injection. Such vaccines, and the immunogenic components thereof, may be subunit vaccines, whole inactivated or attenuated organisms or polynucleotide vaccines.

The vaccines according to the invention may either be prophylactic (to prevent infection) or therapeutic (to treat disease after infection).

These vaccines may either be prophylactic (to prevent infection) or therapeutic (to treat disease after infection).

Such vaccines comprise antigen or antigens, usually in combination with "pharmaceutically acceptable carriers," which include any carrier that does not itself induce the production of antibodies harmful to the individual receiving the composition.

Suitable carriers are typically large, slowly metabolized macromolecules such as proteins, polysaccharides, polylactic acids, polyglycolic acids, polymeric amino acids, amino acid copolymers, lipid aggregates (such as oil droplet emulsions or liposomes), and inactive virus particles. Such carriers are well known to those of ordinary skill in the art. In preferred aspects of the invention, these carriers may function as immunostimulating agents ("adjuvants"). Furthermore, the antigen may be conjugated to a bacterial toxoid, such as a toxoid from diphtheria, tetanus, cholera, H. pylori, etc. pathogens.

Preferred adjuvants to enhance effectiveness of the composition include, but are not limited to: (1) aluminum salts (alum), such as aluminum hydroxide, aluminum phosphate, aluminum sulfate, etc; (2) oil-in-water emulsion formulations (with or without other specific immunostimulating agents such as muramyl peptides (see below) or bacterial cell wall components), such as for example (a) MF59 (PCT Publ. No. WO 90/14837), containing 5% Squalene, 0.5% Tween 80, and 0.5% Span 85 (optionally containing various amounts of MTP-PE (see below), although not required) formulated into submicron particles using a microfluidizer such as Model 110y microfluidizer (Microfluidics, Newton, Mass.), (b) SAF, containing 10% Squalane, 0.4% Tween 80, 5% pluronic-blocked polymer L121, and thr-MDP (see below) either microfluidized into a submicron emulsion or vortexed to generate a larger particle size emulsion, and (c) RIBI.TM. adjuvant system (RAS), (Ribi Immunochem, Hamilton, Mo.) containing 2% Squalene, 0.2% Tween 80, and one or more bacterial cell wall components from the group consisting of monophosphorylipid A (MPL), trehalose dimycolate (TDM), and cell wall skeleton (CWS), preferably MPL+CWS (DETOX.TM.); (3) saponin adjuvants, such as STIMULON.TM. (Cambridge Bioscience, Worcester, Mass.) may be used or particles generated therefrom such as ISCOMs (immunostimulating complexes); (4) Complete Freunds Adjuvant (CFA) and Incomplete Freunds Adjuvant (IFA); (5) cytokines, such as interleukins (e.g., IL-1, IL-2, IL-4, IL-5, IL-6, IL-7, IL-12, etc.), interferons (e.g., gamma interferon), macrophage colony stimulating factor (M-CSF), tumor necrosis factor (TNF), etc; and (6) other substances that act as immunostimulating agents to enhance the effectiveness of the composition. Alum and MF59 are preferred.

As mentioned above, muramyl peptides include, but are not limited to, N-acetyl-muramyl-L-threonyl-D-isoglutamine (thr-MDP), N-acetyl-normuramyl-1-alanyl-d-isoglutamine (nor-MDP), N-acetylmuramyl-1-alanyl-d-isoglutaminyl-1-alanine-2-(1'-2'-dipalmitoyl-s- n-glycero-3-huydroxyphosphoryloxy)-ethylamine (MTP-PE), etc.

The immunogenic compositions (e.g., the antigen, pharmaceutically acceptable carrier, and adjuvant) typically will contain diluents, such as water, saline, glycerol, ethanol, etc.

Additionally, auxiliary substances, such as wetting or emulsifying agents, pH buffering substances, and the like, may be present in such vehicles.

Typically, the immunogenic compositions are prepared as injectables, either as liquid solutions or suspensions; solid forms suitable for solution in, or suspension in, liquid vehicles prior to injection may also be prepared. The preparation also may be emulsified or encapsulated in liposomes for enhanced adjuvant effect, as discussed above under pharmaceutically acceptable carriers.

Immunogenic compositions used as vaccines comprise an immunologically effective amount of the antigenic polypeptides, as well as any other of the above-mentioned components, as needed. By "immunologically effective amount", it is meant that the administration of that amount to an individual, either in a single dose or as part of a series, is effective for treatment or prevention. This amount varies depending upon the health and physical condition of the individual to be treated, the taxonomic group of individual to be treated (e.g., nonhuman primate, primate, etc.), the capacity of the individual's immune system to synthesize antibodies, the degree of protection desired, the formulation of the vaccine, the treating doctor's assessment of the medical situation, and other relevant factors. It is expected that the amount will fall in a relatively broad range that can be determined through routine trials.

The immunogenic compositions are conventionally administered parenterally, e.g., by injection, either subcutaneously or intramuscularly. Additional formulations suitable for other modes of administration include oral and pulmonary formulations, suppositories, and transdermal applications. Dosage treatment may be a single dose schedule or a multiple dose schedule. The vaccine may be administered in conjunction with other immunoregulatory agents.

Examples of suitable immunostimulatory agents include interleukins, such as interleukins 1,2, 4-7 and 12, and interferons, especially .gamma.-interferon.

 

Claim 1 of 64 Claims

1. An immunogenic composition comprising an immunologically effective amount of an antigen selected from the group consisting of a viral antigen and a bacterial antigen, and a mucosal adjuvant, comprising a detoxified mutant A subunit of a cholera toxin (CT) or an E. coli heat labile toxin (LT1 or LT2), wherein said detoxified mutant comprises one or more amino acid substitutions as compared to wild-type sequence of said toxin, and wherein said mucosal adjuvant is not said antigen.

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