Full Length Single Chain Fc Protein (FLSC IgG1) as a Potent Antiviral Therapy Candidate: Implications forIn VivoStudies

Abstract

We have previously shown that FLSC, a chimeric protein containing HIV-1 BAL gp120 and the D1 and D2 domains of human CD4, blocks the binding and entry of HIV-1 into target cells by occluding CCR5, the major HIV-1 coreceptor. In an effort to improve the antiviral potential of FLSC, we fused it with the hinge-C H 2-C H 3 region of human IgG1. The IgG moiety should increase both the affinity and stability in vivo of FLSC, due to the resultant bivalency and an extended serum half-life, thereby increasing its antiviral potency. We previously showed that (FLSC) IgG1 indeed had greater antiviral activity against T cell infections. Here we extend these results to macrophages, for which (FLSC) IgG1 has a more potent antiviral activity than FLSC alone, due in part to its higher binding affinity for CCR5. We also test both compounds in a relevant humanized mouse model and show that, as anticipated, the IgG1 moiety confers a greatly extended half-life. These data, taken together with previous results, suggest potential clinical utility for (FLSC) IgG1 and support further developmental work toward eventual clinical trials.

Humanized NSG Mouse Models of HIV-1 Infection and Pathogenesis

“…with 20,000 of 50% tissue culture infective dose (TCID50%) of HIV-1 Bal, they developed a productive infection. 6 Quantifying CD4+ T cells, CCR5+ cells, and CCR5 expression levels to evaluate and validate the NSG adult mouse model, we showed that levels of both CD4+ and CCR5+ cells from within the CD4+ T cell population remained stable in non-infected mice up to 4 weeks post engraftment. 6 As expected, infected mice showed a steep decline in CD4+ T cells and CCR5+ cells, as well as somewhat reduced CCR5 expression levels.…”

“…6 Quantifying CD4+ T cells, CCR5+ cells, and CCR5 expression levels to evaluate and validate the NSG adult mouse model, we showed that levels of both CD4+ and CCR5+ cells from within the CD4+ T cell population remained stable in non-infected mice up to 4 weeks post engraftment. 6 As expected, infected mice showed a steep decline in CD4+ T cells and CCR5+ cells, as well as somewhat reduced CCR5 expression levels. 6 A second approach, based upon the injection of HSC into newborn mice supports longer-term experiments and allows multilineage development of human immune cells.…”

“…Clearly this model is a good option for short term experiments of up to 4 weeks following HIV-1 infection. 5,6 The model was used to engraft human PBMCs into adult mice to study the effects of HIV-1 entry blockage by INK128, a prototype TOR-KI (the catalytic inhibitor, in dual targeting of mTORC-1/2). 7 It was also reported that in comparison with all immunodeficient strains, the NSG mouse model has highest human HSC engraftment levels.…”

Identifying CCR5 coreceptor populations permissive for HIV-1 entry and productive infection: implications for in vivo studies

“…Both cell lines showed a decrease in mAb binding to CCR5 when cells were pretreated with full length single chain IgG1 (FLSC IgG1), a chimeric protein containing HIV-1 BaL gp120 and the D1 and D2 domains of human CD4. FLSC IgG1 competitively binds the coreceptor at two different regions, the NT and ECL2 [ 17 , 18 ]. As expected, the visualized CCR5 signal was correspondingly lower in the JC10 cell line due to lower CCR5 expression (Additional file 1 : Fig.…”

“…It was demonstrated that dimerization of CCR5 contributes to the conformational diversity of G-protein coupled receptors (GPCRs), which is a promising avenue of research for the prevention of HIV-1 entry [ 13 ]. Recognition of CCR5’s role has led to the development of effective antiviral drugs, including CCR5 antagonists and inverse agonists such as Maraviroc (MVC) [ 14 – 16 ] and fusion proteins that target the NT and other relevant sites in CCR5 [ 17 , 18 ], as well as various anti-CCR5 antibodies [ 19 – 21 ].…”