Evaluation of Monoclonal Antibody MC3 as a Diagnostic Antibody for Invasive Candidiasis

Abstract

Candida species are the most common cause of invasive fungal infections in immunocompromised humans. Invasive candidiasis (IC) has an associated mortality rate of around 50%, with the diploid, pleomorphic yeast, Candida albicans responsible for up to 60% of cases. Current immunodiagnostic tests for IC are based on the detection of circulating mannan antigen (Mn) and anti-mannan antibody (A-Mn) in a patient’s serum, using an enzyme-linked immunosorbent assay (ELISA) format. The high rate of false negative results in immunocompromised patients unable to produce sufficient levels of antibody, and false positive results in patients with superficial, non-invasive colonisation has encouraged the development of new non-invasive immunodiagnostic tests that rapidly and more accurately detect IC. In this study, hybridoma technology was used to produce a murine monoclonal antibody (MAb), MC3, which binds to a carbohydrate epitope present on an extracellular mannan-containing antigen in C. albicans yeast and hyphal morphotypes. The MAb is highly specific, reacting with antigens from several Candida species known to cause IC, but not with antigens from a large number of clinically important fungi, including the invasive human pathogens Cryptococcus neoformans and Aspergillus fumigatus. The MAb was used in combination with a standard mycological growth medium to develop an ELISA for differentiation of C. albicans from other pathogenic yeasts in single and mixed species cultures, substantially improving in vitro detection methods using mycological culture. In future, the MAb will be incorporated into the rapid, point-of-care lateral-flow device (LFD) diagnostic format, previously used successfully in the detection of invasive aspergillosis (IA). The use of MAb MC3 in these diagnostic tests would allow high risk patient groups to be routinely monitored for IC.