Protective immunity against murine candidiasis elicited by Candida albicans ribosomal fractions

Current trends to control fungal pathogens: exploiting our knowledge in the host-pathogen interaction

Human fungal infections remain a major challenge in medicine. Only a limited number of antifungal drugs are available, which are often related to severe adverse effects. In addition, there is an increased emergence related to resistant strains, which makes imperative to understand the host-pathogen interactions as well as to develop alternative treatments. Host innate and adaptive immunity play a crucial role controlling fungal infections; therefore, vaccines are a viable tool to prevent and treat fungal pathogens. Innate immunity is triggered by the interaction between the cell surface pattern recognition receptors (PRRs) and the pathogen-associated molecular patterns (PAMPs). Such an initial immunological response is yet little understood in fungal infections, in part due to the complexity and plasticity of the fungal cell walls. Described host cell-fungus interactions and antigenic molecules are addressed in this paper. Furthermore, antigens found in the cell wall and capsule, including peptides, glycoproteins, glycolipids, and glycans, have been used to trigger specific immune responses, and an increased production of antibodies has been observed when attached to immunogenic molecules. The recent biotechnological advances have allowed the development of vaccines against viral and bacterial pathogens with positive results; therefore, this technology has been applied to develop anti-fungal vaccines. Passive immunization has also emerged as an appealing alternative to treat disseminated mycosis, especially in immunocompromised patients. Those approaches have a long way to be seen in clinical cases. However, all studies discussed here open the possibility to have access to new therapies to be applied alone or in combination with current antifungal drugs. Herein, the state of the art of fungal vaccine developments is discussed in this review, highlighting new advances against Candida albicans, Aspergillus fumigatus, Cryptococcus neoformans, Paracoccidioides brasiliensis, and Sporothrix spp.

Experimental in Vivo Models of Candidiasis

Candidiasis is a multifaceted fungal disease including mucosal-cutaneous, visceral, and disseminated infections caused by yeast species of the genus Candida. Candida infections are among the most common human mycoses. Candida species are the third to fourth most common isolates from bloodstream infections in neutropenic or immunocompromised hospitalized patients. The mucosal-cutaneous forms-particularly vaginal infections-have a high prevalence. Vaginitis caused by Candida species is the second most common vaginal infection. Hence, candidiasis is a major subject for research, including experimental in vivo models to study pathogenesis, prevention, or therapy of the disease. The following review article will focus on various experimental in vivo models in different laboratory animals, such as mammals (mice, rats, rabbits), the fruit fly-Drosophila melanogaster, the larvae of the moth Galleria mellonella, or the free-living nematode Caenorhabditis elegans. The review will describe the induction of the different clinical forms of candidiasis in the various models and the validity of such models in mimicking the human clinical situations. The use of such models for the assessment of antifungal drugs, evaluation of potential vaccines to protect before candidiasis, exploration of Candida virulence factors, and comparison of pathogenicity of different Candida species will be included in the review. All of the above will be reported as based on published studies of numerous investigators as well as on the research of the author and his group.

Testing Antifungal Vaccines in an Animal Model of Invasive Candidiasis and in Human Mucosal Candidiasis

The following article will concentrate on the NDV-3 anti-Candida and Staphylococcus vaccine. The vaccine is composed of the N-terminal portion of the Candida albicans agglutinin-like sequence 3 protein (Als3p) and aluminum hydroxide as adjuvant. The vaccine conferred protection to mice against experimental vaginal, oral, and intravenous challenge with C. albicans. Due to the sequence and structural homology of the Als3p with Staphylococcus aureus surface proteins, the vaccine also protected against experimental skin and IV infection with S. aureus. The vaccine has reached the stage of human trials: phase 1 clinical studies have shown that the vaccine is safe and immunogenic. The latest brief conference abstract reports of vaccination in women suffering from recurrent vaginal candidiasis, indicating that the recurrence rates were lower in the women receiving the vaccine.

Opportunistic fungi and fungal infections: the challenge of a single, general antifungal vaccine

A vaccine made up by an algal beta-glucan (laminarin), conjugated with a protein component, protects against infections by different fungi and induces antibodies capable of inhibiting fungal growth. Although taking a premium on a common molecular theme, this remains a sort of 'cross-kingdom' vaccine because the immunizing antigen and the vaccination target belong to organisms from two different kingdoms and this is certainly the first case in the field of human vaccines. Thus, it is possible to convey in a single immunological tool the potential to protect against multiple infections, in theory all those caused by beta-glucan-expressing fungi. The generation of antibodies with the potential to directly inhibit the growth of, or kill the fungal cells also opens an exciting perspective for both active and passive vaccination in immunocompromised subjects.

Candida vaccines development from point view of US patent application

Candidiasis is the fourth most common bloodstream infection in hospitalized patients in the United States. Moreover, the mortality rate from Candida infections remains high, even after treatment with antifungal therapy. Vaccination would be a promising strategy for prevention of invasive fungal infections. In order to examine the main trends in anticandidal vaccine patenting activity, we conducted an analysis for anticandidal vaccine patents. We find 190 issued patent and 940 patent application documents containing the keywords Candida and vaccine within claims in the USA. Candida vaccines development, as evidenced by the numbers of issued patents, has decreased since the year 2002. Furthermore, the number of patent applications in Candida vaccines may indicate the strength of engaged resources were also in the status of stagnation during 2005-2007 and even a decline in 2008. Academic and nonprofit research institutions not only account for a large share of Candida vaccines patents but also apply for patents continually. Based on this analysis, the strength of Candida vaccines resources seems to remain stagnant in recent years due to patent prosecution or technical barrier in the filed of Candida vaccines. Therefore, we consider that Candida vaccines technology to still be under development and the researchers are still looking for scientific breakthrough in the filed.

Vaccines under study: non-HIV vaccines

The development of effective vaccines has been an amazing public health achievement and has resulted in countless lives being saved. Dermatologic therapy has recently been greatly advanced by the licensure of an effective human papillomavirus vaccine and herpes zoster vaccine. Despite these successes, many infectious diseases do not currently have a preventive vaccine. We review potential vaccines against selected infectious agents, including viruses, bacteria, fungi, and protozoa that have cutaneous and mucocutaneous manifestations. The road to licensure of a new vaccine begins with exhaustive preclinical and clinical studies, and many of these will fail before a successful vaccine candidate is approved. This article focuses on vaccines that have yet to be approved for licensure.

Immunization protocols for use in animal models of candidiasis

Immunoprotection during most forms of candidiasis (oropharyngeal, invasive) is lacking since most candidiasis patients are immunosuppressed either as a result of their allogeneic transplant, cancer chemotherapy, or HIV infection. Consequently, immunization might be considered as an unlikely way to protect patients from such infection. Nonetheless, there are a number of investigations that indicate active immunization or the passive treatment with hyperimmune, specific antibodies can result in protection in models of experimental candidiasis. The former subject, active immunization, is the subject of this chapter. We focus on recent efforts with the Als family of cell wall proteins to serve as a model, and also offer immunization methods in candidiasis models that can be adapted to any antigen of the organism.

Is a vaccine needed against Candida albicans?

The development of a useful Candida vaccine is a distinct possibility despite the fact that individuals with a lifetime of commensal sensitization do not develop sterile immunity to the organism. An effective Candida vaccine would be invaluable in preventing hematogenously disseminated candidiasis, as well as mucocutaneous disease. This review is a discussion of our current understanding of the interplay between commensal and pathogenic forms of Candida albicans and approaches toward active and passive immunoprevention against candidiasis.

Antifungal activity of amphotericin B-lipid admixtures in experimental systemic candidosis in naive mice

We have shown previously that admixtures of amphotericin B (AMB) and Intralipid (AMB-IL) obtained by vigorous and prolonged agitation are stable and can be standardized. These preparations exhibited in-vitro activity against various Candida spp., and had significantly lower toxicity. The present study was undertaken to evaluate the activity of AMB-IL admixtures in vivo in comparison with the conventional formulation of AMB (Fungizone), using a murine model of experimental systemic candidosis. ICR female mice (4-6 weeks old) were injected iv with 5 x 10(4) Candida albicans CBS 562. The animals developed a lethal infection (100%) within 10 days. Systemic candidosis was demonstrated by the presence of fungal elements in kidneys and spleen tissue, and by enumeration of cfu of Candida in the tissue homogenates. AMB-IL or AMB was administered iv 48 h post-Candida inoculation for 5 consecutive days. Four experiments with 108 mice treated with AMB 5 x 0.4 mg/kg and followed up for 6 weeks, showed that the mean survival percentages at the end of the experiment were 0, 24.9 and 52.5% for the untreated group, conventional AMB-treated and AMB-IL-treated groups, respectively. The mean survival time (MST) was 7.4, 25 and 30 days for the untreated, conventional AMB-treated and AMB-IL-treated groups, respectively. Use of increased doses of AMB showed that conventional AMB at doses greater than 5 x 1 mg/kg caused immediate animal death. AMB-IL was used at doses of AMB up to 5 x 2 mg/kg. Experiments with 104 mice revealed that the mean survival percentage at the end of the experiment was 0, 34.5, 58.6 and 97% for the untreated, conventional AMB-treated (5 x 1 mg/kg), AMB-IL-1-treated (5 x 1 mg/kg) and AMB-IL-2-treated (5 x 2 mg/kg) groups, respectively. The MST was 7, 27.8, 34.8 and 41.4 days for the untreated, conventional AMB-treated, AMB-IL-1-treated and AMB-IL-2-treated groups, respectively. The results of this study reveal that AMB-IL is significantly more effective in treating systemic murine candidosis than conventional AMB.

Liposomes containing Candida albicans ribosomes as a prophylactic vaccine against disseminated candidiasis in mice

This study describes the development of prophylactic anti-Candida vaccine which combines the advantages of Candida albicans ribosomes as antigen(s) and of liposomes as carrier/adjuvant with minimal side-effects, which could be suitable for human use. The liposomal vaccine was composed of C. albicans ribosomes and the lipids dimyristoyl phosphatidyl choline (DMPC) and dimyristoyl phosphatidyl glycerol (DMPG) (9:1 molar ratio). Some of the vaccines contained Lipid-A (LA) as an additional adjuvant. The vaccine was prepared by two methods: (I) dehydration by lyophylization of small liposomes in the presence of the Candida ribosomes (DRV method); (II) colyophylization of DMPC/DMPG (9:1 mole ratio) in tertiary butanol with aqueous dispersion of Candida ribosomes. In both cases a dry powder was obtained which was rehydrated to form large multilamellar vesicles. The efficacy of the vaccines in mice was tested by their protectivity against a challenge with C. albicans, as assessed by survival rate, induction of cell mediated immunity (measured by delayed type hypersensitivity-DTH) and anti-Candida antibody titer. Unimmunized mice and mice vaccinated by ribosomes supplemented with incomplete Freund's adjuvant (IFA) were used as controls. The results indicated that the liposomal vaccines were effective at least as the IFA-based vaccine. The study indicates the feasibility of developing an efficacious anti-Candida vaccine for human use.

Plasma amylase levels as a marker of disease severity in an isogenic murine model of paracoccidioidomycosis

Survival patterns after peritoneal infection with Paracoccidioides brasiliensis vary according to the mouse strain and to the virulence of the fungal isolate. It has previously been observed that a significant increase in plasma amylase levels occurs only when susceptible mice (B10.A) were infected with a virulent isolate (Pb18). In order to verify if increased amylase levels correlate with susceptibility to P. brasiliensis infection, 12 mouse strains with different susceptibility patterns to this fungus were investigated after infection with Pb18. When compared with their respective controls, C57BI/6, B10D2/oSn, B10D2/nSn, C3H/HeJ, B10.A and BALB/c mice showed a conspicuous amylase increase and AKR, (NZB x NZW)F1, CBA/J, (A/Sn x B10.A)F1, A/Sn and DBA/2 absence of alteration. The influence of the infecting fungal isolate on this enzymatic parameter was investigated using B10.A mice and fungal isolates with diverse degrees of virulence. When compared with their non-infected controls, mice infected with Pb45 or Pb47 showed a very high amylase increase, with Pb44 or Pb18 a high one and with Pb50 or Pb265 a discrete increase. On the whole, there is an inverse correlation between survival times after infection and the increase in amylase levels. Thus, measurement of plasma amylase is a satisfactory parameter to evaluate the severity of paracoccidioidomycosis in mice.

Protective ribosomal preparation from Shigella sonnei as a parenteral candidate vaccine

A parenteral Shigella ribosomal vaccine (SRV) was investigated in animals for safety, antibody-inducing capacity, and protective activity. Ribosomal preparations from a Shigella sonnei phase I avirulent strain were obtained and shown to possess chemical, sedimentation, and other properties typical of bacterial ribosomes. No endotoxin contamination was revealed by a ketodeoxyoctonate assay, although the presence of some kind of O antigen was evidenced by serological findings and the high activity of SRV in inducing the O-antibody response and immunological memory in animals. SRV was nontoxic in mice, guinea pigs, and monkeys and induced no local reactions when injected subcutaneously in reasonable doses. Significant protection against a local Shigella infection (Sereny test) was seen in guinea pigs injected with SRV (efficiency index, about 60%) and the specificity of the protection was evident from cross-challenge experiments. The protective efficiency of SRV was especially high in rhesus monkeys challenged orally with virulent Shigella cells (89%, as calculated from the summarized data of several experiments in 71 animals). Protection in monkeys was long lasting and could be demonstrated several months after injection of SRV. An inexpensive technique can be used for the production of SRV on a large scale. The high immunogenicity of SRV is discussed in terms of the amplifying effect of the ribosome, which serves as a delivery system for polysaccharide O antigen. Further study of SRV as a candidate vaccine for humans seems justified by the data obtained.

Vaccines against fungal infections

The state-of-the-art reached in developing protective immunity against fungal infections through vaccination makes a survey of methodologies and results timely. This review describes experimental vaccinations against dermatophytes, pathogenic yeasts, and dimorphic fungi with special attention to the anti-Coccidioides immitis vaccine, which has reached clinical trials, and to the anti-Candida albicans and anti-Histoplasma capsulatum ribosomal vaccines. Also covered are vaccination experiments in compromised hosts aimed at eliciting acquired resistance to opportunistic fungal infections which constitute risk factors for these hosts. Immunization procedures include live, killed, and attenuated organisms, as well as different subcellular fractions such as cytoplasmic extracts, fungal culture filtrates, cell walls, or ribosomal fractions. A variety of experimental animal models and isolated human trials constitute the subjects in these studies. Acquired immunity has been evaluated through assessment of resistance to infection and determination of specific immune responses. It has been demonstrated that fungal vaccines do elicit both humoral and cell-mediated immunity in the immunized host. For some vaccines (e.g., H. capsulatum), a correlation between the induced immunity and protection was observed and the immunity could be adoptively transferred. In view of the potential of vaccines against fungal infections, a perspective on their applicability, significance, and value for human use is discussed.

Systemic candidiasis in mice immunized with Candida albicans ribosomes

In view of our previous findings that vaccination of mice with Candida albicans ribosomes protects them against experimental systemic candidiasis, the aim of this study was to investigate the effect of this vaccination on the course of infection in immunized animals. Since the kidney is the major target in systemic candidal infection, we concentrated in this research on studying the histopathology and determining quantitatively the candidal colonization of this organ. The experiments were carried out at various time intervals after intravenous inoculation with live C. albicans. The colonization of kidneys in immunized mice was markedly lower than that in controls. The maximal difference in renal colonization between immunized and non immunized animals was observed when relatively low challenge doses were used. The inhibition of candidal multiplication in immunized mice seemed to be correlated to their increased resistance against lethal challenge, as expressed by a significantly higher survival rate. Histopathological changes and fungal elements were found in kidneys of control mice as early as 20 h post infection, while the kidneys of immunized mice did not seem affected by the disease. Moreover, even 3 days post infection, the kidneys of vaccinated animals still seemed normal. In conclusion, apparently the ribosomal vaccination leads to diminished colonization of the major site of infection in candidiasis, thus affording protection to the immunized animals against these infections.

Immune responses elicited by vaccinations with Candida albicans ribosomes in cyclophosphamide treated animals

This study describes humoral and cell mediated immune (CMI) responses detected in cyclophosphamide (CY) treated animals who were vaccinated with Candida albicans ribosomes and were protected against systemic candidiasis (previous study). Mice treated with CY and vaccinated with C. albicans ribosomes revealed CMI responses towards the ribosomes as measured in vivo by the foot pad swelling test and in vitro by the lymphocyte transformation assay. Both reactions were higher in CY treated and ribosome vaccinated mice than in controls (mice that were only vaccinated). Humoral immune responses were measured by the enzyme linked immunosorbent assay (ELISA). Anti ribosomal antibody titer contrary to the CMI responses was lower in CY treated animals than in non treated controls. These data point to a possible explanation of the mechanisms underlying the ribosomal vaccinations in CY treated hosts, and show the potential of such vaccinations in compromised individuals.

Detection of antibodies against Candida albicans ribosomes by the enzyme linked immunosorbent assay

Enzyme linked immunosorbent assay was found to be a convenient method for the investigation of antibodies in mice immunized with Candida albicans ribosomes. Antibodies against the ribosomal antigen were detected in all the sera of mice (ICR and BALB/c) immunized with ribosomes and incomplete Freund's adjuvant and in some of the sera of mice immunized with ribosomes only; the titer of antibodies varied from 1:320 to 1:10 240. Vaccination of mice with ribosomal protein and IFA resulted in a high titer of antiribosomal antibodies. Treatment of ribosomes with pronase abrogated the capacity of the ribosomes to elicit anti ribosomal humoral responses, suggesting that the antibodies detected were directed against the protein moiety of the ribosomes. The presence of antibodies in sera of immunized mice could not be correlated with the protection afforded by the ribosomal vaccination.

Cell-mediated immunity following experimental vaccinations with Candida albicans ribosomes

The aim of the present study was to ascertain whether cell-mediated immunity (CMI) is induced in animals by vaccination with Candida albicans ribosomes. Delayed type hypersensitivity (DTH) was detected in vivo in ribosome-vaccinated mice and guinea pigs by the footpad swelling and skin tests, respectively. The observed DTH was similar to that induced by live C. albicans organisms. A lymphocyte transformation assay was used for in vitro detection of CMI. The tritiated thymidine incorporation assays revealed that spleen lymphocytes from mice immunized with C. albicans ribosomes were stimulated by the ribosomal antigen. The findings establish that C. albicans ribosomes are able to induce CMI in experimental animals.

Candida albicans-induced agglutinin and immunoglobulin E responses in mice

Mice varied in their ability to make detectable antibody responses to cell surface determinants of Candida albicans depending upon the antigen preparation and the immunization schedule used. Immunoglobulin M (IgM) appeared to be the major class of antibody responsible for the C. albicans-agglutinating activity of the immune sera. Various inbred strains of mice injected with a ribosomal fraction from C. albicans produced a low titer (average, 4 to 8) of yeast cell agglutinins and a higher titer (64 to 512) of IgE antibodies detected by passive cutaneous anaphylaxis (PCA) in rats. The two kinds of antibodies appeared to be specific for different antigens because the agglutinin, but not IgE, could be removed by absorbing the serum with a polysaccharide from the cell wall of C. albicans, but the polysaccharide did not provoke the PCA reaction. C. albicans-specific IgE antibodies showed cross-reactivity (PCA) with ribosomal antigens from a strain of C. albicans and C. tropicalis, but PCA reactions could not be elicited with similar antigen preparations from other yeast species. IgE responses were also detected in over 20% of the mice infected intravenously or intraperitoneally with live C. albicans.

Influence of preformed antibody on the pathogenesis of experimental Candida albicans endocarditis

The influence of preformed antibody on the induction of experimental Candida albicans endocarditis was investigated by both in vitro and in vivo techniques. Preincubation of C. albicans with immune serum (raised in rabbits by intravenous injection of Formalin-killed yeast cells) decreased adhesion to the constituents of nonbacterial thrombotic endocarditis, e.g., fibrin plus platelets, in vitro. Two different methods, with radiolabeled or viable yeast cells, were confirmatory and demonstrated decreased adhesion of immune serum-treated C. albicans cells to 0 to 7.8% of control values (P less than 0.001). These results correlated with protection from the development of C. albicans endocarditis in the immunized rabbits. The mean (+/- standard deviation) infectious dose for 50% of the animals was 10(5.29) +/- 10(0.07) in 48 control animals versus 10(7.11) +/- 10(0.22) in 37 immunized rabbits (P less than 0.001). These studies suggest that humoral antibody may protect against C. albicans endocarditis, perhaps through inhibition of adhesion, a crucial early step in the pathogenesis of endocarditis.