Scientific Publications by FDA Staff

J Virol 2018 Apr 13;92(9):e02065-17

HAVCR1 (CD365) and its mouse ortholog are functional hepatitis A virus (HAV) cellular receptors that mediate HAV infection.

Costafreda MI, Kaplan G

The Hepatitis A virus (HAV) cellular receptor 1 (HAVCR1), classified as CD365, was initially discovered as a HAV cellular receptor using an expression cloning strategy. Due to the lack of HAV receptor-negative replication-competent cells, it was not possible to fully prove that HAVCR1 was a functional HAV receptor. However, biochemistry, classical virology, and epidemiology studies further supported the functional role of HAVCR1 as a HAV receptor. Here, we show that an anti-HAVCR1 monoclonal antibody that protected African green monkey (AGMK) cells against HAV infection only partially protected monkey Vero E6 cells and human hepatoma Huh7 cells indicating that these two cell lines express alternative yet unidentified HAV receptors. Therefore, we focused our work on AGMK cells to further characterize the function of HAVCR1 as a HAV receptor. Advances in CRISPR/Cas9 technology allowed us to knock out HAVCR1 in AGMK cells. The resulting AGMK HAVCR1 KO cells lost susceptibility to HAV infection including HAV free viral particles (vpHAV) and exosomes purified from HAV-infected cells (exo-HAV). Transfection of HAVCR1 cDNA into AGMK HAVCR1 KO cells restored susceptibility to vpHAV and exo-HAV infection. Furthermore, transfection of the mouse ortholog of HAVCR1, mHavcr1, also restored the susceptibility of AGMK HAVCR1 KO cells to HAV infection. Taken together, our data clearly show that HAVCR1 and mHavcr1 are functional HAV receptors that mediate HAV infection. This work paves the way for the identification of alternative HAV receptors to gain a complete understanding of their interplay with HAVCR1 in the cell entry and pathogenic processes of HAV. IMPORTANCE: HAVCR1, a HAV receptor, is expressed in different cell types including regulatory immune cells and antigen presenting cells. How HAV evades the immune response during a long incubation period of up to 4 weeks and the mechanism by which the subsequent necroinflammatory process clears the infection remain a puzzle that most likely involves the HAV-HAVCR1 interaction. Based on negative data, a recent paper from the Lemon and Maury laboratories (1) suggested that HAVCR1 is neither a functional HAV receptor nor required for HAV infection. However, our data based on regain of HAV-receptors function in HAVCR1 knockout cells transfected with the HAVCR1 cDNA disagree with their findings. Our positive data show conclusively that HAVCR1 is indeed a functional HAV receptor and lays the ground for the identification of alternative HAV receptors and how they interact with HAVCR1 in cell entry and pathogenesis of HAV.