Anti-CotH3 antibodies protect mice from mucormycosis by prevention of invasion and augmenting opsonophagocytosis.

Mucorales are fungal pathogens that cause mucormycosis, a lethal angioinvasive disease. Previously, we demonstrated that Rhizopus, the most common cause of mucormycosis, invades endothelial cells by binding of its CotH proteins to the host receptor GRP78. Loss of CotH3 renders the fungus noninvasive and attenuates Rhizopus virulence in mice. Here, we demonstrate that polyclonal antibodies raised against peptides of CotH3 protected diabetic ketoacidotic (DKA) and neutropenic mice from mucormycosis compared to mice treated with control preimmune serum. Passive immunization with anti-CotH3 antibodies enhanced neutrophil inlfux and triggered Fc receptor-mediated enhanced opsonophagocytosis killing of Rhizopus delemar. Monoclonal antibodies raised against the CotH3 peptide also protected immunosuppressed mice from mucormycosis caused by R. delemar and other Mucorales and acted synergistically with antifungal drugs in protecting DKA mice from R. delemar infection. These data identify anti-CotH3 antibodies as a promising adjunctive immunotherapeutic option against a deadly disease that often poses a therapeutic challenge.