The invention features isolated human immunodeficiency virus (HIV) envelope (Env) trimers, in which the amino acid sequence of the Env polypeptides is optimized to stabilize formation of the trimers. The invention also features vaccines, nucleic acids, and vectors to deliver and/or facilitate production of the stabilized HIV Env trimers. In addition, the invention features methods of making and using the stabilized HIV Env trimers of the invention.
