Stabilized gp120-specific CD4 for next-generation HIV-1 inhibitors

HIV-1 Env’s gp120 subunit uses the T-cell coreceptor CD4 to enter host cells in a manner that prevents the evolution of host resistance by sharing the binding epitope with the footprint of CD4’s natural ligands, class II MHC proteins ^1,2 . Consequently, CD4-containing biologics, such as CD4-Ig ^3,4 and derivatives ^5–9 , benefit from this conserved relationship and are promising broad-acting anti-HIV-1 agents that are resistant to viral mutational escape ¹⁰ . However, these biologics suffer from short serum half-lives in humans ^11,12 and animals ^3,13 , likely due to CD4’s poor thermostability ¹⁴ and/or off-target class II MHC binding ¹⁵ . This latter property also warrants caution for CD4-containing biologics that could indiscriminately recruit Fc-dependent effector functions against uninfected cells and/or compete with host CD4 for class II MHC during T cell interactions with antigen-presenting cells. Here, we describe gp120-specific CD4 (gCD4), which exhibits enhanced thermostability and retains Env, but not class II MHC, binding. CD4-Ig variants incorporating gCD4 did not bind class II MHC on human B cells, displayed greater longevity in human tonsil organoid cultures, showed half-lives equivalent to therapeutic IgG antibodies in mice, and neutralized HIV-1 more broadly and potently compared to the original CD4-Ig molecules. Encouragingly, one variant neutralized 100% of a panel of clinically-relevant HIV-1 strains at titers correlating to infection prevention in humans, outperforming known broadly neutralizing antibodies ^16,17 . Thus, gCD4 holds promise for the development of new CD4-containing biologics with best-in-class specificity, pharmacokinetic properties, and neutralization breadth and potency.