Isolation of broadly protective monoclonal antibodies for Crimean Congo Hemorrhagic Fever

Background/Rationale: Crimean-Congo Hemorrhagic Fever (CCHF) is the most widely distributed tick-borne viral hemorrhagic fever infection in the world. CCHF is potentially fatal and there is currently no vaccine or specific therapy for this disease. Monoclonal antibodies (mAbs) have been discovered that have shown ability to protect; however, their limited protective breadth are a liability. Objectives: The premise of this grant is that the humoral response raised against natural CCHF infection in humans leads to antibody responses that can be protective. The hypothesis is that cross-protective anti- CCHFV mAbs can be found and isolated from humans. We have data demonstrating that mouse monoclonal antibodies can be protective, and have isolated GP38 and GC mAbs from humans. The specific aims of this proposal are 1) Develop a cohort of CCHF survivors and isolate a panel of monoclonal antibodies against CCHFV envelope subjects with broad responses to Gc, Gn, and/or GP38. 2) Test the efficacy of anti-CCHFV envelope mAbs for their ability for cross-clade protection in a lethal mouse model. 3) Define the fine specificity of the broadly protective human mAb(s) against CCHFV. Methods: We will develop a cohort, analyze blood samples from 120 CCHF survivors in Turkey, and identify the patients with the broadest breadth and neutralization, and undertake a detailed isolation and characterization of up to 75 anti-CCHFV glycoprotein antibodies. Nine antibodies will then be selected for sequential efficacy testing in the IFNAR-/- mouse model in up to five separate strains representing different clades to identify broadly cross-protective mAbs. Four cross-protective mAbs will be chosen for fine epitope mapping. Monoclonal antibodies in complex with a variety of CCHFV antigens will undergo x-ray crystallography and cryo-EM. Impact: If our hypothesis proves correct, the isolation of human monoclonal antibodies that are cross-protective will represent a breakthrough, and will be candidates for further pre-clinical and clinical testing. In addition, the identification of an epitope would have implications for vaccine design against this virus.