TMEFF1 is a neuron-specific restriction factor for herpes simplex virus

The brain is highly sensitive to damage caused by infection and inflammation. Herpes simplex virus-1 (HSV-1) is a neurotropic virus and the cause of herpes simplex encephalitis. It is unknown whether neuron-specific antiviral factors control virus replication to prevent infection and excessive inflammatory responses, hence protecting the brain. Using genome-wide CRISPR screening for HSV-1 restriction factors, we identified TMEFF1, which is expressed specifically in CNS neurons and not regulated by type I interferon, as the best-known innate antiviral system controlling virus infections. Depletion of TMEFF1 in stem-cell-derived human neurons led to elevated viral replication and neuronal death upon HSV-1 infection. TMEFF1 blocked the HSV-1 replication cycle at the level of viral entry through interactions with Nectin-1 and non-muscle myosin heavy chain IIA/B, which are core proteins in virus-cell binding and virus-cell fusion, respectively. Importantly, Tmeff1-/- mice exhibited increased susceptibility to HSV-1 infection in the brain but not in the periphery. Within the brain, elevated viral load was observed specifically in neurons. Our study identifies TMEFF1 as a neuron-specific restriction factor essential for prevention of HSV-1 replication in the CNS. Cas9+ SK-N-SH 614 cells were transduced with lentiviral preparations of GeCKO v2 CRISPR library (library part A for screen 1 and library part B for screen 2). Subsequently, the library transduced cell populations were infected with HSV-1-K26GFP at an MOI of 0.25, 17 h after infection cells with high GFP expression was sorted by FACS. Analysis was performed by comparing the GFPhigh sample with the non-sorted control.