Monoclonal antibodies to Cryptococcus neoformans glucuronoxylomannan enhance fluconazole efficacy

Monoclonal antibody (MAb) 2H1, which binds to the capsular glucuronoxylomannan (GXM) of the fungus Cryptococcus neoformans, prolonged survival and decreased fungal burden in an experimental routine infection. Fluconazole (FLU) is a triazole antibiotic which is effective against C. neoformans. The efficacy of MAb 2H1 in combination with FLU was studied in vitro with the murine macrophage-like cell line J7741.16 and in vivo in mice infected intravenously. In vitro, the combination of MAb 2H1 and FLU was more effective than either agent alone in reducing the number of CFU of C. neoformans cocultured with J774.16 cells. In combination with FLU, GXM- binding MAbs of the immunoglobulin M (IgM), IgG1, IgG2a, IgG2b, IgG3, and IgA isotypes were effective in reducing the numbers of CFU in C. neoformans- J774.16 cocultures. For the in vivo experiments, A/JCr mice were infected intravenously with 5 x 10⁵ organisms treated with MAb and FLU. The therapeutic effect of MAb 2H1 was primarily to reduce the number of CFU in the lung and the serum GXM level, whereas FLU was most effective in reducing the number of CFU in the brain. Mice receiving combination therapy had lower numbers of CFU in the lung and serum GXM levels than mice treated with FLU alone. Administration of MAb 2H1 with or without FLU had little or no effect on the number of CFU in the brain. The results provide support for combined therapy.