Detection of invasive Candida albicans infection using a specific 99mTc-labeled monoclonal antibody for the C. albicans germ tube

Accurate diagnosis is critical for effective treatment of the invasive infection by Candida albicans. Here, we investigated whether a ^99m technetium (Tc)-labeled Fab’ fragment of the monoclonal antibody specific for the C. albicans germ tube could specifically identify an invasive C. albicans infection. The germ tube of C. albicans was used as an immunogen to obtain monoclonal antibodies and the Fab’ fragment of MAb03.2 C1–C2 with highest affinity and specificity was labeled with ^99mTc. In vitro binding assays showed that the labeled Fab’ preferentially bound to the germ tubes of C. albicans (4.23 ± 0.17 × 10² Bq per 1 × 10⁷ cells). These values were significantly higher than those for blastospores of C. albicans, blastospores of heat-killed C. albicans, Aspergillus fumigatus, Staphylococcus aureus, and Escherichia coli (P < 0.05). By using in vivo biodistribution and planar imaging with single photon emission computed tomography, we demonstrated a significant specific accumulation of radioactivity in C. albicans-infected tissues. In summary, ^99mTc-MAb03.2 C1–C2 Fab’ is able to specifically accumulate in C. albicans-infected tissues, but not in tissue infected with A. fumigatus or bacteria or in a sterile inflammation. This study provides a new and specific radiopharmaceutical for the diagnosis of invasive C. albicans infections.