Combination immunotherapy of MAb B6.1 with fluconazole augments therapeutic effect to disseminated candidiasis.

We recently reported that IgM MAb B6.1, specific for β-1, 2-mannotriose on the cell wall of Candida albicans, is therapeutic to disseminated candidiasis due to C. albicans. In the current study, we examined if MAbB6.1 enhances therapeutic effect of fluconazole (FLC) to the disseminated disease. To assess the combination effect, determination by the kidneys-colony forming unit and survival times were used. Results showed that the therapeutic effect of FLC on mice with disseminated candidiasis was dose-dependent, but a FLC dose at 0.8 mg/kg body weight of mice was ineffective. To determine combination effect, mice treated intraperitoneally with a combination of FLC plus MAb B6.1 at 1 h post-infection - a condition of developing partial therapeutic activity - enhanced survival times beyond the effect by only antibody (p < 0.05). The resulting MST (mean survival times) value from the combination-received mice was almost the same as MST value from 3.2 mg FLC dose-given animals (p < 0.05). Another combination of 1.6 mg FLC dose and B6.1 reduced severity of the disseminated disease at almost the same rate as combination efficacy of 0.8 mg FLC dose plus B6.1. This data indicates that B6.1 acts in concert with FLC and that this combination therapy augments protection, which suggests a possibility of reducing FLC dose. The augmentation response was specific because an irrelevant IgM MAb S9 was not effective to the disseminated disease. Thus, our present studies demonstrate that this combination immunotherapy may be a way of solving the problem of limited antifungal drug choices caused by drug-resistant C. albicans.