Stabilized diverse HIV-1 envelope trimers for vaccine design

One of the major goals in HIV-1 vaccine development is to achieve properly folded and stabilized envelope glycoprotein (Env) trimers that mimic the native Env on the mature virion. Here, we design and characterize uncleaved prefusion-optimized (UFO) trimers for 12 Envs currently circulating in China. Biochemical and biophysical characterization of these UFO trimers identified two subtype B/B' Envs, CNE6 and MG13, which exhibited the highest trimer content and stability at a level comparable to the subtype A reference, BG505. Replacing the gp41 ectodomain (gp41_ECTO) of CRF01_AE trimers with that of CNE6, MG13, and BG505 resulted in chimeric constructs with significantly improved trimer content and stability. Negative-stain electron microscopy (EM) confirmed the structural integrity of these chimeric UFO trimers with CNE6 gp41_ECTO. Antibody binding assays showed that the chimeric trimers shared similar antigenic profiles to those with their original gp41_ECTO domains. Our results thus revealed the intrinsic differences among HIV-1 Envs of diverse origins and the critical role of gp41_ECTO in stabilizing the trimeric spike. By taking advantage of naturally stable Envs, gp41_ECTO swapping may represent a universal approach for the generation of stable trimers with the desired structural and antigenic properties for downstream in vivo evaluation and vaccine development.