Directing HIV-1 for degradation by non-target cells, using bi-specific single-chain llama antibodies

Abstract

While vaccination against HIV-1 has been so far unsuccessful, recently broadly neutralizing antibodies (bNAbs) against HIV-1 envelope glycoprotein were shown to induce long-term suppression in the absence of antiretroviral therapy in patients with antibody-sensitive viral reservoirs. The requirement of neutralizing antibodies indicates that the antibody mediated removal (clearance) of HIV-1 in itself is not efficient enough in these immune compromised patients. Here we present a novel, alternative approach that is independent of a functional immune system to clear HIV-1, by capturing the virus and redirecting it to non-target cells where it is internalized and degraded. We use bispecific antibodies with domains derived from small single chain Llama antibodies (VHHs). These bind with one domain to HIV-1 envelope proteins and with the other domain direct the virus to cells expressing epidermal growth factor receptor (EGFR), a receptor that is ubiquitously expressed in the body. We show that HIV envelope proteins, virus-like particles and HIV-1 viruses (representing HIV-1 subtypes A, B and C) are efficiently recruited to EGFR, internalized and degraded in the lysosomal pathway at low nM concentrations of bispecific VHHs. This directed degradation in non-target cells may provide a clearance platform for the removal of viruses and other unwanted agents from the circulation, including toxins, and may thus provide a novel method for curing.

Known and New Routes to Neutralize HIV-1 with Camelid Single Chain Antibody Fragments

“…An example of the latter turned out to provide a complete new potential therapeutic route to clear HIV-1. These bispecific VHH consist of a VHH recognizing CD4bs or another conserved region of the envelope protein of HIV-1, whereas the other VHH target the bispecific VHH -loaded with the virus -to cells not belonging to the immune system, providing a clearance route independent of the immune system [50]. This route may offer a therapy for immunocompromised persons, in particular HIV-1 infected persons that for other health reasons cannot use cART.…”