Passive immunotherapy for Middle East Respiratory Syndrome coronavirus infection with equine immunoglobulin or immunoglobulin fragments in a mouse model

•Healthy horses immunized with MERS-CoV virus-like particles rapidly generate high titers of virus neutralizing antibodies.•Passive transfer of equine immune antibodies significantly reduced virus titers from the lungs of MERS-CoV infected mice.•F(ab')2 fragments prepared by digestion of antibody with pepsin to reduce possible allergic responses.•Equine immune antibodies are polyclonal and recognize more antigen determinants in MERS-CoV spike protein.

Middle East Respiratory Syndrome (MERS) is a highly lethal pulmonary infection caused by a coronavirus (CoV), MERS-CoV. With the continuing spread of MERS-CoV, prophylactic and therapeutic treatments are urgently needed. In this study, we prepared purified equine F(ab')2 from horses immunized with MERS-CoV virus-like particles (VLPs) expressing MERS-CoV S, M and E proteins. Both IgG and F(ab')2 efficiently neutralized MERS-CoV replication in tissue culture. Passive transfer of equine immune antibodies significantly reduced virus titers and accelerated virus clearance from the lungs of MERS-CoV infected mice. Our data show that horses immunized with MERS-CoV VLPs can serve as a primary source of protective F(ab')2 for potential use in the prophylactic or therapeutic treatment of exposed or infected patients.