The isolation of broadly-neutralizing antibodies from HIV-1 infected individuals raises the hope that a vaccine may elicit a similar immune response. These antibodies target the only viral protein on the surface of HIV, a metastable trimer of heterodimers, Env. A popular option for vaccine design is an engineered version of Env (named SOSIP) that is solubilized and stabilized. Production of many antigenically diverse SOSIP trimers for immunization studies is critical for an increased understanding of the development of neutralizing antibodies.