Properties of a neutralizing antibody that recognizes a conformational form of epitope ERDRD in the gp41 C-terminal tail of human immunodeficiency virus type 1

Abstract

The possibility that epitopes from the C-terminal tail of the gp41 transmembrane protein of human immunodeficiency virus type 1 (HIV-1) are exposed the surface of the virion has long been contentious. Resolution of this has been hampered by the absence of any neutralizing monoclonal antibodies, but we have recently epitope-purified a neutralizing polyclonal IgG specific for one of the putative gp41 tail epitopes, 746 ERDRD 750 . This was obtained from mice immunized parenterally with a plant virus chimera expressing residues 731-752 from the gp41 tail. The ERDRD epitope is highly conformational and is conserved in 81 % of B clade viruses. Here, it is shown that this polyclonal ERDRD-specific IgG is highly potent, with an affinity of 2n2i10 8 M N1 , and a neutralization rate constant (NK neut ) of 7n8i10 4 M N1 s N1 that exceeds that of nearly all other known HIV-1-neutralizing antibodies. ERDRD-specific IgG gave 50 % neutralization at 0n1-0n2 µg/ml and 90 % neutralization at approximately 3 µg/ml. It also neutralized virus that was already attached to target cells, and this and other data suggest that it neutralized by inhibiting a virion event that precedes the fusion-entry process. Consistent with this conclusion was the finding that neutralizing amounts of ERDRD-specific IgG did not inhibit the attachment of free virus to target cells. ERDRDspecific IgG was also cross-reactive and neutralized all but one of six B clade T cell line-adapted strains tested.

Human Recombinant Antibodies againstPlasmodium falciparumMerozoite Surface Protein 3 Cloned from Peripheral Blood Leukocytes of Individuals with Immunity to Malaria Demonstrate Antiparasitic Properties

“…Previous work on an invasion-inhibiting anti-circumsporozoite antibody has reported a K D of approximately 300 nM (k on , Ϸ4 ϫ 10 3 ; k off , Ϸ1.2 ϫ 10 Ϫ3 ) (51), and HIV neutralizing antibodies have been shown to have a K D of 4.6 nM (k on , Ϸ8.4 ϫ 10 4 ; k off , Ϸ3.9 ϫ 10 Ϫ4 ) (8), showing that the RAM antibodies described here indeed have affinities within a biologically relevant range. RAM1 had the fastest kinetics of the three; i.e., RAM1 was rapidly binding to the antigen and was also released from the antigen more quickly than the other two clones.…”

The complex antigenicity of a small external region of theC-terminal tail of the HIV-1 gp41 envelope protein: a lesson in epitope analysis

“…This epitope is constitutively expressed and virus is still neutralised when particle-IgG complexes are separated from free antibody. In addition there are other non-neutralising MAbs that bind gp41 C-terminal tail loop epitopes adjacent to the neutralisation epitopes, and prevent binding of neutralising antibody [16,19]. Consistent with their external location, the interaction with all tail-specific MAbs is abrogated by digestion of virions with trypsin or thermolysin [17].…”

“…However, MAb SAR1 differs from EPES IgG, in that it gives PAN and NIP, but little or no STAN [19]. The location of the EPES IgG and SAR1 epitopes in the C-terminal tail was confirmed by their failure to neutralise a gp41 tail-truncated mutant virus [16,19]. In addition, further mapping showed that prebinding to virions of the non-neutralising MAb 1575 prevented binding of MAb 1577 to FHV-L2-A and the neutralisation of virions by EPES IgG [16].…”

“…d Gives 90% neutralisation of IIIB in human PBMC at 50.9 mg/ml, but no significant neutralisation of several TCLA viruses in C8166 cells, unless complement is present. IgG preparations have very similar biological properties, and give strong STAN and PAN (Table 1; [6,[16][17][18]31]). They also have a high affinity (K D , 5 nM) and a high neutralisation rate constant [16], the latter being only 5-fold lower than that of the gp120-specific 'gold-standard' MAb b12 [16].…”

Single-Chain Antibody Fragment Specific forPlasmodium vivaxDuffy Binding Protein

“…Surface plasmon response measurements showed that the three antibodies had affinities (K D ) in the nanomolar range. Previous work on an invasion-inhibiting anticircumsporozoite antibody (K D Ϸ 300 nM) (35), HBV neutralizing antibodies (K D Ϸ 160 nM) (22), and human immunodeficiency virus neutralizing antibodies (K D Ϸ 4.6 nM) (11) showed that the SFDBII antibody series described here indeed has affinities within a biologically relevant range. Hans et al (15) estimated that the binding constant of the PvRII-DARC is 8.7 nM.…”