The present invention features antibodies and antibody fragments that specifically bind a CD4-inducible HIV gp120 epitope that is enhanced by binding a co-receptor for HIV, such as CCR5 or CXCR4, and pharmaceutical compositions comprising the antibodies or antibody fragments. The invention also features nucleic acids encoding the antibodies or antibody fragments, pharmaceutical compositions comprising the nucleic acids encoding the antibodies or antibody fragments, vectors comprising the nucleic acids, and cells comprising the vectors. The invention further features methods of identifying antibodies or antibody fragments with broadly neutralizing activity against HIV. The invention also features methods of inhibiting HIV entry into cells and methods of inhibiting replication of HIV in mammals, using the antibodies and nucleic acids of the invention.