Median inhibitory concentrations (IC50s) were defined as the concentration of MAb or the reciprocal dilution of plasma pool stock that resulted in 50% inhibition, calculated as described (Blish et al

Median inhibitory concentrations (IC50s) were defined as the concentration of MAb or the reciprocal dilution of plasma pool stock that resulted in 50% inhibition, calculated as described (Blish et al., 2007; Wu et al., 2006). et al., 2005)). HIV-1 specific NAb also have the potential to contribute to protection from infection, as evidenced by studies showing that passively administered HIV-1 specific monoclonal antibodies (MAbs) can prevent SHIV infection in non-human primates (reviewed in (Hu, 2005; Mascola, 2003)). However, antibodies capable of neutralizing a diverse spectrum of HIV-1 variants will be needed to achieve significant protection against circulating strains of HIV-1. While there are some HIV-1 specific NAbs that have broad specificity (Scheid et al., 2011; Walker et al., 2011; Walker et al., 2009; Wu et al., 2010; Wu et IMR-1A al., 2011), many virus isolates are not recognized by such MAbs, even those that target conserved regions of the virus (Blish et al., 2007; Blish et al., 2008; Blish et al., 2010; Scheid et al., 2011; Walker et al., 2011; Walker et al., 2009; Wu et al., 2010; Wu et al., 2011). The molecular basis for differences in neutralization sensitivity, especially in cases where the amino acid changes are outside of known epitope targets, remains poorly defined. The envelope protein (Env) surface unit (gp120) and the transmembrane protein (gp41) are both targets of NAbs, including several MAbs that have been studied in some detail (reviewed in (Burton et al., 2004; Zolla-Pazner and Cardozo, 2010)). Two of the most intensively studied MAbs, 2F5 and 4E10, target adjacent conserved epitopes in the membrane proximal external region (MPER) of gp41 [ELDKWA and NWF(D/N)IT, respectively; (Muster et al., 1993; Zwick et al., 2001). These MAbs bind to their peptide epitope target (Cardoso IMR-1A et al., 2005; Ofek et al., 2004), and they also bind weakly to membrane lipids but this binding alone does not induce neutralization (Julien et al., 2010; Xu et al., 2010). There are also multiple antibody targets IMR-1A in the surface unit gp120. The IgG1 MAb b12 targets a discontinuous epitope overlapping the CD4 binding pocket (Burton et al., 1994; Roben et al., 1994). MAb b12 neutralizes a majority of subtype B variants (Binley et al., 2004; Burton et al., 1994), but fewer variants of other subtypes (Blish et al., 2009; Blish et al., 2007; Wu et al., 2006). More recently, VRC01, another MAb that targets the CD4 binding site, has been identified; VRC01 exhibits increased breadth and potency compared to b12 (Wu et al., 2010). A collection of related MAbs targeted to a different epitope in gp120 but with similar breadth as VRC01, have also been described recently (Walker et al., 2009). These MAbs, PG9 and PG16, recognize an epitope formed by conserved regions of V2 and V3 (Walker et al., 2009). Early studies of antibody binding to HIV envelope focused on lab-adapted HIV-1 envelopes variants derived from virus grown in cell lines, which generally use the CXCR4 receptor. The study of these lab-adapted envelopes suggested that IMR-1A antibody neutralization correlated with binding to the envelope monomer (Parren et al., 1998a; Roben et al., 1994; Sattentau and Moore, 1995). Results of subsequent studies of envelope variants from viruses grown in primary cells, including CCR5-tropic variants that are more common in HIV-1 infection, suggested that antibody binding to monomeric envelope did not IMR-1A reliably predict neutralization potential (Fouts, 1997). Binding to the oligomeric form of envelope found on the virion has been correlated with neutralization sensitivity (Fouts, 1997; Sattentau and Moore, 1995; Stamatatos and Cheng-Mayer, 1995; Sullivan et al., 1995). However, there are numerous examples of MAbs that bind to virion-associated envelope protein, but do not neutralize the corresponding virus, suggesting that MAb binding alone is not sufficient to promote neutralization (Cavacini and Posner, 2004; Herrera et al., 2005; Leaman et al., 2010; Moore et al., Rabbit polyclonal to PDCL2 2006; Nyambi et al., 2000; Parren et al., 1998b). There is also evidence for binding between some trimeric envelope proteins and non-neutralizing antibodies in virion-capture assays (Poignard et al., 2003). Some of.