Fungal Vaccines and Immunotherapeutics: Current Concepts and Future Challenges

Purpose of review

The remarkable advances in modern medicine have paradoxically resulted in a rapidly expanding population of immunocompromised patients displaying extreme susceptibility to life-threatening fungal infections. There are currently no licensed vaccines, and the prophylaxis and therapy of fungal infections in at-risk individuals remains challenging, contributing to undesirable mortality and morbidity rates. The design of successful antifungal preventive approaches has been hampered by an insufficient understanding of the dynamics of the host-fungus interaction and the mechanisms that underlie heterogenous immune responses to vaccines and immunotherapy.

Recent findings

Recent advances in proteomics and glycomics have contributed to the identification of candidate antigens for use in subunit vaccines, novel adjuvants, and delivery systems to boost the efficacy of protective vaccination responses that are becoming available, and several targets are being exploited in immunotherapeutic approaches.

Summary

We review some of the emerging concepts as well as the inherent challenges to the development of fungal vaccines and immunotherapies to protect at-risk individuals.

     

Serology of histoplasmosis

We admit that the complete understanding of the serology of histoplasmosis has not as yet been realized. However, as laboratories continue to produce new and better techniques, not only for qualitative but also for quantitative assessment, we may be able to view a relatively complete picture in the near future.Paper read at the Eighth International Congresses for Tropical Medicine and Malaria, September 1968, Teheran (Iran).     

Serology of paracoccidioidomycosis

The purposes of the present work were: i) to study the positivity indices and compare titers obtained with the indirect immunofluorescence (II), tube precipitation (TP), complement fixation (CF) and double immunodiffusion on agar gel (ID) tests in the sera of 196 patients with paracoccidioidomycosis before treatment, and ii) to compare the initial titers of II with those obtained 1 year or more after treatment. II was the most sensitive serologic reaction (85.2%), and the positivity indices for CF, ID and TP were 67.7%, 66.0% and 50.0%, respectively. The sera tended to show parallel mean titers in II, CF and TP tests. One year after treatment there was a fall in titers of II in 66.2% of patients. The data, taken as a whole, demonstrate the usefulness of the indirect immunofluorescent test and the importance of using 2 or more serologic tests for the diagnosis and monitoring of patients with paracoccidioidomycosis.     

Serology of H-Y antigen

Summary Anti-H-Y antiserum is generally obtained from female inbred mice or rats that have been hyperimmunized with syngeneic male cells. The specificity of such antiserum is defined by its reactivity for male but not female cells. A number of conventional serological assays have been used to measure that reactivity. However, H-Y is a weak antigen, evidently represented sparingly on the surfaces of cells other than sperm, epidermal cells and brain cells; thus the srological assays for H-Y are technically difficult. Yet H-Y serology has enabled significant progress toward the understanding of primary sex differentiation.A recent advance in H-Y serology is the establishment of monoclonal anti-H-Y antisera which promise to facilitate analysis and clarification of the H-Y system.     

Serology of Aspergillus granuloma

A total of 21 cases of granuloma caused by Aspergillus species were encountered during the period 1972–79. The organs involved were nasal and paranasal sinuses, brain, orbit, subcutaneous tissue of cheek, lungs and endocardial valve in the decreasing order of their frequency. Aspergillus flavus was the main etiological agent. Immunodiffusion tests with various Aspergillus species as antigen showed a positivity of 17 out of 18 (94.4 per cent) cases. The role of precipitins in diagnosis and prognosis of the disease has been discussed.     

丙型肝炎病毒准种血清学检测技术的建立

目的:建立一种以血清学为基础的丙型肝炎病毒(HCV)准种检测技术。方法:自20份HCV血清中各挑选30个克隆进行测序比较,分析HCV准种的复杂程度;以HCV准种代表性抗原组合制备免疫芯片,用血清学检测技术分析上述20份HCV血清中的准种变异程度;比较两种方法之间的检出灵敏度和相关性。结果:测序法检出灵敏度为70.0%,血清学检测法检出灵敏度为95.0%,后者显著高于前者(P0.05);两种方法检测结果的相关性为74.7%(P0.01)。结论:血清学检测技术操作简单,且能够反映丙型肝炎患者的HCV准种变异程度,适于临床推广。     

Serology and yeast classification

When analysed by an immuno-fluorescent test method allSaccharomyces spp. examined were antigenically distinguishable, with no natural grouping of yeast strains. The sero-types exhibited a continuous spectrum of antigen combinations. Extensive cellular variation was detected in serological response, which principally resulted from physiological differences between individual yeast cells but mutation was a minor contributor. Combination of divisiveness of the current serological analysis and the presence of transient physiologically-based “antigenic variants” rendered serology of dubious significance for yeast taxonomy. The role of yeast serology is assured, however, in relation to rapid test procedures for yeast identification. The author wishes to thank the Directors of Bass Production Ltd., for permission to publish this Paper. Generous donations of rabbit antisera from Dr. I. Campbell, Heriot-Watt University, are gratefully acknowledged.     

Helicobacter pylori Multiplex Serology

Background:  Helicobacter pylori infection is associated with severe gastrointestinal disease including cancer. It induces complex antibody responses that might vary depending on disease state but currently cannot be assessed adequately. The objective of this work was the development of a sensitive and specific H. pylori multiplex serology assay with high-throughput capability that allows simultaneous detection of antibodies to a protein array.
Methods:  Seventeen proteins of up to three H. pylori strains (26695, G27, 151), including CagA, VacA, UreA, Catalase, Omp, and GroEL, were recombinantly expressed as glutathione- S -transferase fusion proteins, affinity-purified, and used as antigens in a fluorescent bead-based antibody-binding assay. Reference sera (n   =   317) characterized by commercial assays (screening ELISA with Western blot confirmation) were used for validation.
Results:  H. pylori seropositivity by multiplex serology defined as reactivity with at least four proteins showed good agreement (kappa: 0.70) with commercial serologic assay classification, and a sensitivity of 89% and specificity of 82%. For individual antigens, agreement with Western blot was good for CagA (kappa: 0.77), moderate for UreA (kappa: 0.53), and weak for VacA (kappa: 0.12). Of the 13 proteins expressed from two strains, only VacA showed serologic strain differences. High antibody reactivity to CagA (Type I infection) was negatively associated with antibodies to GroEL, Cad, CagM, catalase, HcpC, NapA, and UreA, suggesting type-specific differences in protein expression patterns and/or immune response.
Conclusion:  With its high-throughput and simultaneous detection abilities, H. pylori multiplex serology appears suited as tool for large seroepidemiologic studies assessing H. pylori prevalence, antibody patterns, and associations with specific diseases.     

The Evolution of Fungal Metabolic Pathways

Fungi contain a remarkable range of metabolic pathways, sometimes encoded by gene clusters, enabling them to digest most organic matter and synthesize an array of potent small molecules. Although metabolism is fundamental to the fungal lifestyle, we still know little about how major evolutionary processes, such as gene duplication (GD) and horizontal gene transfer (HGT), have interacted with clustered and non-clustered fungal metabolic pathways to give rise to this metabolic versatility. We examined the synteny and evolutionary history of 247,202 fungal genes encoding enzymes that catalyze 875 distinct metabolic reactions from 130 pathways in 208 diverse genomes. We found that gene clustering varied greatly with respect to metabolic category and lineage; for example, clustered genes in Saccharomycotina yeasts were overrepresented in nucleotide metabolism, whereas clustered genes in Pezizomycotina were more common in lipid and amino acid metabolism. The effects of both GD and HGT were more pronounced in clustered genes than in their non-clustered counterparts and were differentially distributed across fungal lineages; specifically, GD, which was an order of magnitude more abundant than HGT, was most frequently observed in Agaricomycetes, whereas HGT was much more prevalent in Pezizomycotina. The effect of HGT in some Pezizomycotina was particularly strong; for example, we identified 111 HGT events associated with the 15 Aspergillus genomes, which sharply contrasts with the 60 HGT events detected for the 48 genomes from the entire Saccharomycotina subphylum. Finally, the impact of GD within a metabolic category was typically consistent across all fungal lineages, whereas the impact of HGT was variable. These results indicate that GD is the dominant process underlying fungal metabolic diversity, whereas HGT is episodic and acts in a category- or lineage-specific manner. Both processes have a greater impact on clustered genes, suggesting that metabolic gene clusters represent hotspots for the generation of fungal metabolic diversity.     

The Entry of Ammonia into Fungal Cells

When Scopulariopsis brevicaulis grown on an ammonia-free mediumis supplied with an ammonium salt ammonia enters the cells morerapidly than it is removed by assimilation, until an equilibriumlevel of ammonia is reached in the cells. The equilibrium concentrationin the cells is independent of metabolism and depends on theexternal concentration over a wide range. The internal concentra--tionof ammonia can be higher than the external under suitable conditionsof pH. The cells are shown to be permeable to ammonia also inthe outward direction, and the rate of entry or loss dependson the concentration difference between external and internalenvironment. The results support the view that ammonia enters the cells mainlyby the free diffusion of the undissociated molecule.