CCR5 mimicry by sulfated human anti-HIV-1 antibodies

A potential antibody repertoire diversification mechanism through tyrosine sulfation for biotherapeutics engineering and production

The diversity of three hypervariable loops in antibody heavy chain and light chain, termed the complementarity-determining regions (CDRs), defines antibody's binding affinity and specificity owing to the direct contact between the CDRs and antigens. These CDR regions typically contain tyrosine (Tyr) residues that are known to engage in both nonpolar and pi stacking interaction with antigens through their complementary aromatic ring side chains. Nearly two decades ago, sulfotyrosine residue (sTyr), a negatively charged Tyr formed by Golgi-localized membrane-bound tyrosylprotein sulfotransferases during protein trafficking, were also found in the CDR regions and shown to play an important role in modulating antibody-antigen interaction. This breakthrough finding demonstrated that antibody repertoire could be further diversified through post-translational modifications, in addition to the conventional genetic recombination. This review article summarizes the current advances in the understanding of the Tyr-sulfation modification mechanism and its application in potentiating protein-protein interaction for antibody engineering and production. Challenges and opportunities are also discussed.

Structural characterization of the ICOS/ICOS-L immune complex reveals high molecular mimicry by therapeutic antibodies

The inducible co-stimulator (ICOS) is a member of the CD28/B7 superfamily, and delivers a positive co-stimulatory signal to activated T cells upon binding to its ligand (ICOS-L). Dysregulation of this pathway has been implicated in autoimmune diseases and cancer, and is currently under clinical investigation as an immune checkpoint blockade. Here, we describe the molecular interactions of the ICOS/ICOS-L immune complex at 3.3 Å resolution. A central FDPPPF motif and residues within the CC' loop of ICOS are responsible for the specificity of the interaction with ICOS-L, with a distinct receptor binding orientation in comparison to other family members. Furthermore, our structure and binding data reveal that the ICOS N110 N-linked glycan participates in ICOS-L binding. In addition, we report crystal structures of ICOS and ICOS-L in complex with monoclonal antibodies under clinical evaluation in immunotherapy. Strikingly, antibody paratopes closely mimic receptor-ligand binding core interactions, in addition to contacting peripheral residues to confer high binding affinities. Our results uncover key molecular interactions of an immune complex central to human adaptive immunity and have direct implications for the ongoing development of therapeutic interventions targeting immune checkpoint receptors.

Cell Proteins Interacting with the Human Immunodeficiency Virus in Immunoblotting can be Detected by R5- or X4- Tropic Human Immunodeficiency Virus Particles

Introduction:

The present study reported a new immunoblot assay, with revelation by R5- or X4-whole free human immunodeficiency virus (HIV) particles or recombinant gp160.

Materials and Methods:

The assay was optimized to identify cell proteins interacting with HIV. Whole cell lysates were prepared from peripheral blood lymphocytes (PBLs), dendritic cells (DC), monocyte-derived macrophage (MDM), and Henrietta Lacks (Hela, wild-type or transfected with DC-specific intracellular adhesion molecule-3-Grabbing Non-Integrin, HeLa) and Human endometrial cells (HEC-1A) lines; HIV particles used were the R5-tropic HIV-1_JRCSF and the X4-tropic HIV-1_NDK.

Results:

Experiments with PBL lysates and both viruses demonstrated different bands, including a unique band at 105–117 kDa in addition to nonspecific bands. The 105–117 kDa band migrated at the same level of that observed in controls using total PBL lysate and anti-CD4 mAb for detection and thus likely corresponds to the cluster difference (CD) 4 complex. Blots using lysates of DCs, MDM, HeLa cell line, and HEC-1A cell line allowed identifying several bands that positions were similar to that seen by recombinant gp160 or whole R5- or X4-HIV particles.

Conclusion:

Blot of whole lysates of various HIV target cells is recognized by free HIV particles and allows identifying a wide range of HIV-interacting cell proteins. Such optimized assay could be useful to recognize new cellular HIV attachment proteins.

Mechanisms of monocyte cell death triggered by dengue virus infection

Arthropod-borne viral diseases caused by dengue virus (DENV) are major re-emerging public health problem worldwide. In spite of intense research, DENV pathogenesis is not fully understood and remains enigmatic; however, current evidence suggests that dengue progression is associated with an inflammatory response, mainly in patients suffering from a second DENV infection. Monocytes are one of the main target cells of DENV infection and play an important role in pathogenesis since they are known to produce several inflammatory cytokines that can lead to endothelial dysfunction and therefore vascular leak. In addition, monocytes play an important role in antibody dependent enhancement, infection with consequences in viral load and immune response. Despite the physiological functions of monocytes in immune response, their life span in the bloodstream is very short, and activation of monocytes by DENV infection can trigger different types of cell death. For example, DENV can induce apoptosis in monocytes related with the production of Tumor necrosis factor alpha (TNF-α). Additionally, recent studies have shown that DENV-infected monocytes also exhibit a cell death process mediated by caspase-1 activation together with IL-1 production, referred to as pyroptosis. Taken together, the aforementioned studies strongly depict that multiple cell death pathways may be occurring in monocytes upon DENV-2 infection. This review provides insight into mechanisms of DENV-induced death of both monocytes and other cell types for a better understanding of this process. Further knowledge in cell death induced by DENV will help in the developing novel strategies to prevent disease progression.

Regulation of human immunodeficiency virus type 1 envelope glycoprotein fusion by a membrane-interactive domain in the gp41 cytoplasmic tail

Truncation of the human immunodeficiency virus (HIV) or simian immunodeficiency virus (SIV) gp41 cytoplasmic tail (CT) can modulate the fusogenicity of the envelope glycoprotein (Env) on infected cells and virions. However, the CT domains involved and the underlying mechanism responsible for this "inside-out" regulation of Env function are unknown. HIV and SIV CTs are remarkably long and contain amphipathic alpha-helical domains (LLP1, LLP2, and LLP3) that likely interact with cellular membranes. Using a cell-cell fusion assay and a panel of HIV Envs with stop codons at various positions in the CT, we show that truncations of gp41 proximal to the most N-terminal alpha helix, LLP2, increase fusion efficiency and expose CD4-induced epitopes in the Env ectodomain. These effects were not seen with a truncation distal to this domain and before LLP1. Using a dye transfer assay to quantitate fusion kinetics, we found that these truncations produced a two- to fourfold increase in the rate of fusion. These results were observed for X4-, R5-, and dual-tropic Envs on CXCR4- and CCR5-expressing target cells and could not be explained by differences in Env surface expression. These findings suggest that distal to the membrane-spanning domain, an interaction of the gp41 LLP2 domain with the cell membrane restricts Env fusogenicity during Env processing. As with murine leukemia viruses, where cleavage of a membrane-interactive R peptide at the C terminus is required for Env to become fusogenic, this restriction of Env function may serve to protect virus-producing cells from the membrane-disruptive effects of the Env ectodomain.

Prospects for an AIDS vaccine: three big questions, no easy answers

The unremitting devastation created by the AIDS pandemic will probably only be controlled when a vaccine is developed that is safe, effective, affordable, and simple enough to permit implementation in developing countries where the impact of AIDS is most severe. Although formidable practical, political, economic, social, and ethical challenges face the AIDS vaccine development effort, the most fundamental challenges now reside at the level of the basic biology of HIV-1 infection and pathogenesis. Of these biological considerations, three questions loom especially large: can we design immunogens that will elicit neutralising antibodies that are reactive against a wide variety of primary HIV isolates; will vaccine-elicited cytotoxic T cells be fundamentally better at controlling HIV-1 replication and ameliorating disease progression than those responses that arise during natural HIV infection; and to what extent will the tremendous global genetic diversity of HIV-1 compromise the breadth of vaccine-elicited protective immunity and the overall effectiveness of an AIDS vaccine? Although these are three exceptionally challenging questions, they are now being approached with clear hypotheses whose testing is being facilitated by an ever-improving array of technologies for vaccine design and immunological characterisation. The extent to which the field of AIDS vaccine research can now come together to answer these questions in the best coordinated, most efficient manner will probably be an important determinant of how and when an effective AIDS vaccine will be developed.