Project Summary HIV-1 vaccines that can elicit broadly neutralizing antibodies (bnAbs) are a primary goal. To date, it has been demonstrated that a single bnAb lineage (VRC01-class) can be specifically activated in human trials. Antibodies from this trial do not neutralize HIV-1 and heterologous sequential immunization is thought to be required to develop bnAbs. Heterologous sequential immunization has been employed to generate bnAbs in pre-clinical models. While VRC01-class antibodies isolated from infected individuals can be quite broad, the limit of breadth for VRC01-class antibodies induced by these types of vaccination strategies in people is unknown. Therefore, we are developing an alternative bnAb lineage targeting vaccine (VH1-46 class) through advanced protein engineering approaches and assessment in newly generated human immunoglobulin knock-in mice harboring VH1-46 germline antibodies. Further, we are pursuing innovative approaches to develop a dual bnAb lineage targeting vaccine which could synergize with current VRC01-class vaccines. Individual lineage targeting vaccines may not succeed at fully maturating these lineages, thus severely limiting the neutralization breadth and ultimate effectiveness of these vaccines. Dual lineage targeting may be critical for success of the first bnAb- eliciting HIV-1 vaccine.