Humanized rabbit entry receptor complex supports HIV-1 entry into rabbit cells

Rabbits show promise as a model species for HIV-1, but exhibit a major block to infection at the level of viral entry. Here, minimally modified rabbit CD4 and CCR5 were sufficient to overcome this barrier and allowed efficient HIV-1 entry into rabbit cells.Based on in silico comparative structural modeling and sequence analysis, we generated several human-rabbit CD4 and CCR5 chimeras. All chimeric receptors localized to the cell surface, and the CD4 variants were down-modulated by the HIV-1 accessory proteins Nef and Vpu, similar to their parental counterparts. Importantly, HIV-1 bound to humanized rabbit CD4 with comparable efficiency to that observed with human CD4. Cell-cell and virion fusion assays revealed that the combination of humanized rabbit CD4 and humanized rabbit CCR5 enabled fusion mediated by CCR5-tropic HIV-1 Env. Notably, viral fusion was blocked by the CCR5 antagonist maraviroc, demonstrating its activity against humanized rabbit CCR5.In conclusion, computational modeling identified key residues in CD4 and CCR5, thereby overcoming a receptor-dependent block that restricts HIV-1 entry into rabbit cells. These findings constitute important steps toward the development of a fully permissive immunocompetent rabbit model of HIV-1 infection.