NIH45-46

Broadly neutralizing antibodies (bNAbs) possess favorable safety, and passive immunization using these can prevent or control human immunodeficiency virus type 1 (HIV-1) infection. However, bNAbs generally used for monotherapy (IC₈₀ > 5 μg/mL) have limited breadth and potency and neutralize only 70-90% of all HIV-1 strains. To address the need for broader coverage of the HIV-1 epidemic and enhance the ability of bNAbs to target HIV-1, we fused the single-chain variable antibody fragment (scFv) of bNAbs (PG9, PGT123, or NIH45-46) with full-length ibalizumab (iMab) in an scFv-monoclonal antibody tandem format to construct bispecific bNAbs (BibNAbs). Additionally, we described the feasibility of BibNAb gene delivery mediated by recombinant adeno-associated virus 8 (rAAV8) for generating long-term expression with a single injection as opposed to short-term passive immunization requiring continuous injections. Our results showed that the expressed BibNAbs targeting two distinct epitopes exhibited neutralizing activity against 20 HIV-1 pseudoviruses in vitro. After injecting a single rAAV8 vector, the expression and neutralizing activity of the BibNAbs in serum were sustained for 24 weeks. To the best of our knowledge, very few studies have been published on BibNAb gene delivery using rAAV8 vectors against HIV-1. BibNAb gene delivery using rAAV8 vectors may be promising for passive immunization against HIV-1 infection.

HIV-1 broadly neutralizing antibodies (bNAbs) and engineered antibody-like inhibitors have been compared for their breadths, potencies, and in vivo half-lives. However, a key limitation in the use of antibodies to treat an established HIV-1 infection is the rapid emergence of fully resistant viruses. Entry inhibitors of similar breadths and potencies can differ in the ease with which viral escape variants arise. Here we show that HIV-1 escape from the potent and exceptionally broad entry inhibitor eCD4-Ig is more difficult than that from CD4-Ig or the bNAb NIH45-46. Indeed, full escape was not observed under conditions under which escape from CD4-Ig or NIH45-46 was readily detected. Moreover, viruses that were partially resistant to eCD4-Ig were markedly less infective and more sensitive to antibodies in the serum of an infected person. These data suggest that eCD4-Ig will be more difficult to escape and that even partial escape will likely extract a high fitness cost.