Human immunodeficiency virus type 1 (HIV-1) vaccine immunogens capable of inducing broadly neutralizing antibodies (bNAbs) remain obscure. HIV-1 evades immune responses through enormous diversity and hides its conserved vulnerable epitopes on the envelope glycoprotein (Env) by displaying an extensive immunodominant glycan shield. In elite HIV-1 viremic controllers, glycan-dependent bNAbs targeting conserved Env epitopes have been isolated and are utilized as vaccine design templates. However, immunological tolerance mechanisms limit the development of these antibodies in the general population. The well characterized bNAbs monoclonal variants frequently exhibit extensive levels of somatic hypermutation, a long third heavy chain complementary determining region, or a short third light chain complementarity determining region, and some exhibit poly-reactivity to autoantigens. This review elaborates on the obstacles to engaging and manipulating the Env glycoprotein as an effective immunogen and describes an alternative reverse vaccinology approach to develop a novel category of bNAb-epitope-derived non-cognate immunogens for HIV-1 vaccine design.

• Keywords
• Broadly neutralizing antibodies, Combinatorial protein library, Glycans, HIV-1 vaccine, Non-cognate ligands, Protein mimicry,
• MeSH
• Epitopes immunology   MeSH
• env Gene Products, Human Immunodeficiency Virus immunology   MeSH
• HIV Infections immunology   MeSH
• HIV Antibodies * immunology   MeSH
• HIV-1 * immunology   MeSH
• Humans MeSH
• Ligands MeSH
• Molecular Mimicry immunology   MeSH
• Antibodies, Neutralizing * immunology   MeSH
• Polysaccharides immunology   MeSH
• AIDS Vaccines * immunology   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Epitopes MeSH
• env Gene Products, Human Immunodeficiency Virus MeSH
• HIV Antibodies * MeSH
• Ligands MeSH
• Antibodies, Neutralizing * MeSH
• Polysaccharides MeSH
• AIDS Vaccines * MeSH

Mucin-type O-glycosylation occurs on many proteins that transit the Golgi apparatus. These glycans impact structure and function of many proteins and have important roles in cellular biosynthetic processes, signaling and differentiation. Although recent technological advances have enhanced our ability to profile glycosylation of glycoproteins, limitations in the understanding of the biosynthesis of these glycan structures remain. Some of these limitations stem from the difficulty to track the biosynthetic process of mucin-type O-glycosylation, especially when glycans occur in dense clusters in repeat regions of proteins, such as the mucins or immunoglobulin A1 (IgA1). Here, we describe a series of nano-liquid chromatography (LC)-mass spectrometry (MS) analyses that demonstrate the range of glycosyltransferase enzymatic activities involved in the biosynthesis of clustered O-glycans on IgA1. By utilizing nano-LC-MS relative quantitation of in vitro reaction products, our results provide unique insights into the biosynthesis of clustered IgA1 O-glycans. We have developed a workflow to determine glycoform-specific apparent rates of a human UDP-N-acetylgalactosamine:polypeptide N-acetylgalactosaminyltrasnfersase (GalNAc-T EC 2.4.1.41) and demonstrated how pre-existing glycans affect subsequent activity of glycosyltransferases, such as core 1 galactosyltransferase and α2,3- and α2,6-specific sialyltransferases, in successive additions in the biosynthesis of clustered O-glycans. In the context of IgA1, these results have potential to provide insight into the molecular mechanisms implicated in the pathogenesis of IgA nephropathy, an autoimmune renal disease involving aberrant IgA1 O-glycosylation. In a broader sense, these methods and workflows are applicable to the studies of the concerted and competing functions of other glycosyltransferases that initiate and extend mucin-type core 1 clustered O-glycosylation.

• Keywords
• IgA1 hinge region, polypeptide GalNAc-transferase, LC–MS, clustered glycosylation, mucin-type glycosylation,
• MeSH
• Glycosylation MeSH
• Glycosyltransferases metabolism   MeSH
• Immunoglobulin A metabolism   MeSH
• Humans MeSH
• Polysaccharides analysis   biosynthesis   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Glycosyltransferases MeSH
• Immunoglobulin A MeSH
• Polysaccharides MeSH

HIV-1 envelope (Env) N-glycosylation impact virus-cell entry and immune evasion. How each glycan interacts to shape the Env-protein-sugar complex and affects Env function is not well understood. Here, analysis of two Env variants from the same donor, with differing functional characteristics and N-glycosylation-site composition, revealed that changes to key N-glycosylation sites affected the Env structure at distant locations and had a ripple effect on Env-wide glycan processing, virus infectivity, antibody recognition, and virus neutralization. Specifically, the N262 glycan, although not in the CD4-binding site, modulated Env binding to the CD4 receptor, affected Env recognition by several glycan-dependent neutralizing antibodies, and altered site-specific glycosylation heterogeneity, with, for example, N448 displaying limited glycan processing. Molecular-dynamic simulations visualized differences in glycan density and how specific oligosaccharide positions can move to compensate for a glycan loss. This study demonstrates how changes in individual glycans can alter molecular dynamics, processing, and function of the Env-glycan shield.

• Keywords
• Biochemistry, Biological Sciences, Glycobiology, Microbiology, Virology,
• Publication type
• Journal Article MeSH

BACKGROUND: The development of an effective vaccine preventing HIV-1 infection is hindered by the enormous antigenic variability and unique biochemical and immunological properties of HIV-1 Env glycoprotein, the most promising target for HIV-1 neutralizing antibody. Functional studies of rare elite neutralizers led to the discovery of broadly neutralizing antibodies. METHODS: We employed a highly complex combinatorial protein library derived from a 5 kDa albumin-binding domain scaffold, fused with support protein of total 38 kDa, to screen for binders of broadly neutralizing antibody VRC01 paratope. The most specific binders were used for immunization of experimental mice to elicit Env-specific antibodies and to test their neutralization activity using a panel of HIV-1 clade C and B pseudoviruses. FINDINGS: Three most specific binders designated as VRA017, VRA019, and VRA177 exhibited high specificity to VRC01 antibody. Immunized mice produced Env-binding antibodies which neutralize eight of twelve HIV-1 Tier 2 pseudoviruses. Molecular modelling revealed a shape complementarity between VRA proteins and a part of VRC01 gp120 interacting surface. INTERPRETATION: This strategy based on the identification of protein replicas of broadly neutralizing antibody paratope represents a novel approach in HIV-1 vaccine development. This approach is not affected by low immunogenicity of neutralization-sensitive epitopes, variability, and unique biochemical properties of HIV-1 Env used as a crucial antigen in the majority of contemporary tested vaccines. FUND: Czech Health Research Council 15-32198A, Ministry of Health, Czech Republic.

• Keywords
• Albumin-binding domain scaffold, Antibody paratope mimetics, Combinatorial protein library, HIV-1 vaccine, Neutralizing antibody, Protein docking,
• MeSH
• Antigens, Viral chemistry   immunology   MeSH
• Epitopes chemistry   immunology   MeSH
• HIV Infections immunology   virology   MeSH
• HIV Envelope Protein gp120 immunology   MeSH
• HIV Antibodies blood   immunology   MeSH
• HIV-1 immunology   MeSH
• Immunoglobulin G blood   immunology   MeSH
• Protein Conformation MeSH
• Humans MeSH
• Disease Models, Animal MeSH
• Models, Molecular MeSH
• Mice MeSH
• Antibodies, Neutralizing blood   immunology   MeSH
• Amino Acid Sequence MeSH
• AIDS Vaccines immunology   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Antigens, Viral MeSH
• Epitopes MeSH
• HIV Envelope Protein gp120 MeSH
• HIV Antibodies MeSH
• Immunoglobulin G MeSH
• Antibodies, Neutralizing MeSH
• AIDS Vaccines MeSH