INTRODUCTION
The HIV-1 envelope (Env) trimer is protected by multiple mechanisms of humoral evasion, including conformational masking, glycan shielding, and sequence variation.Stabilization of the Env trimer through the incorporation of a disulfide (SOS) between residues 501 of gp120 and 605 of gp41 and the substitution of an isoleucine to a proline (IP) helped fix the trimer into a prefusion-closed conformation recognized by broadly neutralizing antibodies but not by non-neutralizing antibodies.While vaccine elicitation of tier-2 neutralizing responses has now been reported in multiple vaccine-test species including non-human primates,