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1.  Ontogeny of Recognition Specificity and Functionality for the Broadly Neutralizing Anti-HIV Antibody 4E10 
PLoS Pathogens  2014;10(9):e1004403.
The process of antibody ontogeny typically improves affinity, on-rate, and thermostability, narrows polyspecificity, and rigidifies the combining site to the conformer optimal for binding from the broader ensemble accessible to the precursor. However, many broadly-neutralizing anti-HIV antibodies incorporate unusual structural elements and recognition specificities or properties that often lead to autoreactivity. The ontogeny of 4E10, an autoreactive antibody with unexpected combining site flexibility, was delineated through structural and biophysical comparisons of the mature antibody with multiple potential precursors. 4E10 gained affinity primarily by off-rate enhancement through a small number of mutations to a highly conserved recognition surface. Controverting the conventional paradigm, the combining site gained flexibility and autoreactivity during ontogeny, while losing thermostability, though polyspecificity was unaffected. Details of the recognition mechanism, including inferred global effects due to 4E10 binding, suggest that neutralization by 4E10 may involve mechanisms beyond simply binding, also requiring the ability of the antibody to induce conformational changes distant from its binding site. 4E10 is, therefore, unlikely to be re-elicited by conventional vaccination strategies.
Author Summary
4E10 is an antibody that neutralizes a broad variety of HIV strains. However, 4E10 is uncommon in infected patients and has not been successfully elicited by any vaccine approach attempted. Hurdles to re-eliciting 4E10 include the accumulation of many mutations during development, demonstrated reactivity against host proteins and significant structural flexibility. Lacking a confirmed sequence for precursors of 4E10, we studied the recognition and biophysical properties of an ensemble of eight of the likeliest candidates. Surprisingly, 4E10 gained host reactivity and structural flexibility, but lost stability during development when compared to candidate precursors. However, recognition of HIV was remarkably conserved, despite a considerable improvement in binding. Since these results run counter to those expected from conventional vaccination protocols, 4E10 is unlikely to serve as the basis of a useful HIV vaccine.
doi:10.1371/journal.ppat.1004403
PMCID: PMC4177983  PMID: 25254371
2.  Autoreactivity and Exceptional CDR Plasticity (but Not Unusual Polyspecificity) Hinder Elicitation of the Anti-HIV Antibody 4E10 
PLoS Pathogens  2013;9(9):e1003639.
The broadly-neutralizing anti-HIV antibody 4E10 recognizes an epitope in the membrane-proximal external region of the HIV envelope protein gp41. Previous attempts to elicit 4E10 by vaccination with envelope-derived or reverse-engineered immunogens have failed. It was presumed that the ontogeny of 4E10-equivalent responses was blocked by inherent autoreactivity and exceptional polyreactivity. We generated 4E10 heavy-chain knock-in mice, which displayed significant B cell dysregulation, consistent with recognition of autoantigen/s by 4E10 and the presumption that tolerance mechanisms may hinder the elicitation of 4E10 or 4E10-equivalent responses. Previously proposed candidate 4E10 autoantigens include the mitochondrial lipid cardiolipin and a nuclear splicing factor, 3B3. However, using carefully-controlled assays, 4E10 bound only weakly to cardiolipin-containing liposomes, but also bound negatively-charged, non-cardiolipin-containing liposomes comparably poorly. 4E10/liposome binding was predominantly mediated by electrostatic interactions rather than presumed hydrophobic interactions. The crystal structure of 4E10 free of bound ligands showed a dramatic restructuring of the combining site, occluding the HIV epitope binding site and revealing profound flexibility, but creating an electropositive pocket consistent with non-specific binding of phospholipid headgroups. These results strongly suggested that antigens other than cardiolipin mediate 4E10 autoreactivity. Using a synthetic peptide library spanning the human proteome, we determined that 4E10 displays limited and focused, but unexceptional, polyspecificity. We also identified a novel autoepitope shared by three ER-resident inositol trisphosphate receptors, validated through binding studies and immunohistochemistry. Tissue staining with 4E10 demonstrated reactivity consistent with the type 1 inositol trisphosphate receptor as the most likely candidate autoantigen, but is inconsistent with splicing factor 3B3. These results demonstrate that 4E10 recognition of liposomes competes with MPER recognition and that HIV antigen and autoepitope recognition may be distinct enough to permit eliciting 4E10-like antibodies, evading autoimmunity through directed engineering. However, 4E10 combining site flexibility, exceptional for a highly-matured antibody, may preclude eliciting 4E10 by conventional immunization strategies.
Author Summary
4E10 is an example of an anti-HIV, broadly neutralizing antibody that is uncommon in infected patients and has not been successfully elicited by any vaccine approach attempted. 4E10 has been proposed to neutralize HIV through a mechanism that requires broad recognition of other antigens, including membrane phospholipids. Such a mechanism would also block the generation of 4E10 during B cell development, confounding vaccination strategies. Analysis of B cell development in 4E10 heavy-chain knock-in mice confirmed that 4E10 does recognize self-antigens. However, a previously proposed autoantigen candidate, the mitochondrial lipid cardiolipin, was not consistent with binding studies which showed that while 4E10 does bind liposomes containing cardiolipin, it does so only weakly and nonspecifically, also binding liposomes without cardiolipin. Using a synthetic human peptidome, 4E10 was shown to be polyreactive, binding peptides from various proteins, but only in a limited manner. Three of the top five hits are from types 1, 2 and 3 inositol trisphosphate receptors, with high scoring peptides sharing a conserved sequence motif. Validation of the top hits was performed by binding analyses and staining of tissue sections, which combined to identify the type 1 inositol trisphosphate receptor as the most likely 4E10 physiological autoantigen.
doi:10.1371/journal.ppat.1003639
PMCID: PMC3784475  PMID: 24086134
3.  B7h-expressing dendritic cells and plasma B cells mediate distinct outcomes of ICOS costimulation in T cell-dependent antibody responses 
BMC Immunology  2012;13:29.
Background
The ICOS-B7h costimulatory receptor-ligand pair is required for germinal center formation, the production of isotype-switched antibodies, and antibody affinity maturation in response to T cell-dependent antigens. However, the potentially distinct roles of regulated B7h expression on B cells and dendritic cells in T cell-dependent antibody responses have not been defined.
Results
We generated transgenic mice with lineage-restricted B7h expression to assess the cell-type specific roles of B7h expression on B cells and dendritic cells in regulating T cell-dependent antibody responses. Our results show that endogenous B7h expression is reduced on B cells after activation in vitro and is also reduced in vivo on antibody-secreting plasma B cells in comparison to both naïve and germinal center B cells from which they are derived. Increasing the level of B7h expression on activated and plasma B cells in B-B7hTg mice led to an increase in the number of antibody-secreting plasma cells generated after immunization and a corresponding increase in the concentration of antigen-specific high affinity serum IgG antibodies of all isotypes, without affecting the number of responding germinal center B cells. In contrast, ICOS costimulation mediated by dendritic cells in DC-B7hTg mice contributed to germinal center formation and selectively increased IgG2a production without affecting the overall magnitude of antibody responses.
Conclusions
Using transgenic mice with lineage-restricted B7h expression, we have revealed distinct roles of ICOS costimulation mediated by dendritic cells and B cells in the regulation of T cell-dependent antibody responses.
doi:10.1186/1471-2172-13-29
PMCID: PMC3477010  PMID: 22686515
ICOS; B7h; Costimulation; Antibody; Germinal center; Plasma cell; Dendritic cell

Results 1-3 (3)