The Neutralizing Anti-HIV Antibody 2G12
The human monoclonal antibody (mAb) 2G12 was isolated from an asymptomatic HIV-1 infected patient in 1990. In 1994, its neutralizing activity against HIV-1 strains and binding to the glycoprotein 120 (gp120) was described for the first time (Buchacher et
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The Neutralizing Anti-HIV Antibody 2G12 Renate Kunert
6.1
The Anti HIV-1 Neutralizing Antibody 2G12 and It’s Neutralizing Activity
The human monoclonal antibody (mAb) 2G12 was isolated from an asymptomatic HIV-1 infected patient in 1990. In 1994, its neutralizing activity against HIV-1 strains and binding to the glycoprotein 120 (gp120) was described for the first time (Buchacher et al. 1994; Purtscher et al. 1994; Trkola et al. 1995). At that time a recombinantly expressed 2G12 IgG1 protein was already available (see below) and characterization was exclusively done with this recombinant molecule so that a confusion between hybridoma derived and recombinantly expressed 2G12 could be precluded. In principle, mAbs possess different ways to counteract HIV-1, (a) cell free neutralization, (b) complement mediated activities and (c) antibody dependent cellular cytotoxicity (ADCC), all of which have been shown to be employed by mAb 2G12 and seem to be responsible for its broad reactivity against primary and T-cell line adapted strains of HIV-1 (Trkola et al. 1996). Due to its broad biological activities, mAb 2G12 is able to defend against infection with primary HIV isolates from various clades, either by direct virus neutralization or in combination with other effector cells and complement activation. This was shown impressively with the HIV-1-MN strain (Trkola et al. 1996) which is not neutralized in a cell free assay. However, in combination with activated human complement, HIV-1-MN was unable to form syncytia of AA-2 lymphoblastoid cells, indicator cells with syncytia formation upon HIV infection. The specific effect of complement activation was confirmed by deposition of complement factor C3 on infected cells. ADCC activity was evaluated with different HIV-1 infected cell lines in a 51Cr release assay (Klein et al. 2010; Trkola et al. 1996). In this assay, the infected target
R. Kunert (*) University of Natural Resources and Life Sciences, Muthgasse 18, 1190 Vienna, Austria e-mail: [email protected] P. Kosma and S. M€uller-Loennies (eds.), Anticarbohydrate Antibodies, DOI 10.1007/978-3-7091-0870-3_6, # Springer-Verlag/Wien 2012
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cells were labelled with Na251CrO4 and in addition to mAb 2G12, peripheral blood mononuclear cells (PBMCs) isolated from healthy HIV-1 negative donors, were added as effector cells. The percentage of released 51Cr was then calculated relative to the total amount of 51Cr released by 1% Triton X-100 treatment. This test revealed that 2G12 is a potent mediator of ADCC and induces specific lysis of various infected cells (recombinant gp120/IIIB CEM.NKR cells, HIV-1 IIIB infected CEM.NKR cells, HIV-1 MN infected CEM.NKR cells).
6.2
Binding of mAb 2G12 to gp120
Already in the early 1990s the specificity of mAb 2G12 for N-linked glycans in the domains C2, C3, V4 and C4 of the HIV-1 gp120 became evident from binding studies. The combination of glycan trees on different constant and variable regions of gp120 forms a unique structure in a special arrangement allowing
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