Evaluation of Cryptococcus neoformans galactoxylomannan–protein conjugate as vaccine candidate against murine cryptococcosis

• Published in: Vaccine Vol. 29; no. 10; pp. 1891 - 1898
• Main Authors: Chow, Siu-Kei, Casadevall, Arturo
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 24.02.2011; Elsevier; Elsevier Limited
• Subjects: Adjuvants, Immunologic - administration & dosage; Allergy and Immunology; Animals; Antibodies, Fungal - blood; Antigens, Bacterial - chemistry; Antigens, Bacterial - immunology; Apoptosis; Applied microbiology; Bacillus anthracis; Bacterial Toxins - chemistry; Bacterial Toxins - immunology; Biological and medical sciences; Capsule; Carbohydrates; Cryptococcosis - immunology; Cryptococcosis - prevention & control; Cryptococcus neoformans; Cryptococcus neoformans - chemistry; Cryptococcus neoformans - immunology; ELISA; Enzyme-Linked Immunosorbent Assay; Female; Fluorescent Antibody Technique; Fundamental and applied biological sciences. Psychology; Fungal Vaccines - chemistry; Fungal Vaccines - immunology; Galactoxylomannan; HIV; Human immunodeficiency virus; Immune system; Immunoglobin; Immunoglobulin G - blood; Immunoglobulin M - blood; Mice; Mice, Inbred BALB C; Microbiology; Miscellaneous; Mycology; Opsonin Proteins - immunology; Phenols; Polysaccharide; Polysaccharides; Polysaccharides, Bacterial - immunology; Polysaccharides, Bacterial - isolation & purification; Proteins; Serum Albumin, Bovine - chemistry; Serum Albumin, Bovine - immunology; Studies; Survival Analysis; Tetanus; Vaccines; Vaccines, antisera, therapeutical immunoglobulins and monoclonal antibodies (general aspects); Vaccines, Conjugate - chemistry; Vaccines, Conjugate - immunology; Immunoglobin; Capsule; Cryptococcus neoformans; Polysaccharide; Galactoxylomannan; ELISA; Yeast; Mycosis; Rodentia; Cryptococcosis; Vaccine; Protein; Fungi; Infection; Microorganism capsule; Vertebrata; Mammalia; Mouse; Fungi Imperfecti; ELISA assay
• ISSN: 0264-410X; 1873-2518
• DOI: 10.1016/j.vaccine.2010.12.134

Abstract Galactoxylomannan (GalXM) is a complex polysaccharide produced by the human pathogenic fungus Cryptococcus neoformans that mediates profound immunological derangements in murine models. GalXM is essentially non-immunogenic and produces immune paralysis in mice. Previous studies have attempted to enhance immunogenicity by conjugating GalXM to a protein carrier, but only transient antibody responses were elicited. Here we report the generation of two GalXM conjugates with bovine serum albumin (BSA) and protective antigen (PA) of Bacillus anthracis , respectively, using 1-cyano-4-dimethylaminopyridinium tetrafluoroborate (CDAP) as the cyanylating reagent. Both conjugates induced potent and sustained antibody responses as detected by both cross antigen-based and CovaLink direct ELISAs. We confirmed the specificity of the response to GalXM by inhibition ELISA and immunofluorescence. The isotype composition analysis revealed that IgG and IgM were abundant in the immune sera against GalXM, consistent with the induction of a T cell-dependent response. IgG1 was the predominant IgG subclass against GalXM, while immunization with Quil A as adjuvant elicited a significantly higher production of IgG2a than with Freund's adjuvant. Immune sera were not opsonic for C. neoformans and there was no survival difference between immune and non-immune mice challenged with C. neoformans . These results demonstrated the effectiveness of the GalXM–protein conjugate to induce robust immune responses although no evidence was obtained that such responses contributed to host defense.