A human anti-IL-2 antibody that potentiates regulatory T cells by a structure-based mechanism . Previous studies showed that IL-2 is highly flexible 8,9 and exists in different conformations that favor either the high-affinity trimeric IL-2R or intermediate-affinity dimeric IL-2R, resulting in the activation of different immune cells 9 . This plasticity has complicated the use of the approved drug Proleukin at high doses to treat metastatic melanoma and renal cell carcinoma 10 , due to the role of IL-2 as an essential growth factor for T regs [11][12][13] . Moreover, adverse effects of high-dose IL-2 therapy have greatly limited its use 14,15 . Several studies have shown that low-dose IL-2 therapy preferentially activates T regs due to the constitutive high expression of IL-2Rα 16 and other cell-intrinsic factors that increase signal transduction sensitivity 17 . Treatment of mice and humans with low doses of IL-2 has been shown to ameliorate autoimmune diseases and graft-versus-host disease (GvHD) as well as delaying organ allograft rejection [18][19][20][21][22] . However, IL-2 therapy has some limitations, including difficulty in predicting the efficacious dose, off-target effects on different cell populations and a short in vivo half-life 23,24 . Thus, attempts have been made to engineer or modify the IL-2 structure to improve its therapeutic potential by modulating its ability to selectively target either T effs or T regs [25][26][27][28][29][30][31] . Selective antibodies against IL-2 can alter its conformation by binding a number of potential epitopes, thereby modifying the binding interaction of IL-2 to any of the IL-2R subunits and resulting in selective expansion of T regs or T eff cell subsets 32,33 . For example, it has been demonstrated that a rat anti-mouse IL-2 monoclonal antibody (JES6-1) can be administered in complex with wild-type mouse IL-2 and used to preferentially enhance T reg populations 26 . Binding of JES6-1 to IL-2 alters its conformation to lower the affinity of mIL-2 for CD25, such that CD25 high T regs compete favorably for IL-2 binding and expansion against T effs 33 . The therapeutic potential of IL-2 to selectively activate the tolerogenic immune response, combined with the imperative to develop a human T reg -selective IL-2 compound, led us to develop a mechanism-based screening strategy to identify human antibodies against human IL-2 that exhibit an in vivo T reg potentiation profile when complexed with hIL-2. This class of monoclonal antibody, exemplified by F5111.2, blocked IL-2Rβ binding and reduced IL-2Rα binding to IL-2, and, when administered in complex with hIL-2, preferentially promoted T reg expansion and was effective in models of autoimmune disease including type 1 diabetes and experimental autoimmune encephalomyelitis (EAE) in addition to GvHD. ResultsSelective IL-2 stimulation in T regs . To directly compare T reg and T eff sensitivity to IL-2, the pSTAT5 signaling response of T regs was analyzed in a mixed population of peripheral blood mononuclear cells (PBMCs).

HIV-1 has been the target of intensive research at the molecular and biochemical levels for >25 years. Collectively, this work has led to a detailed understanding of viral replication and the development of 24 approved drugs that have five different targets on various viral proteins and one cellular target (CCR5). Although most drugs target viral enzymatic activities, our detailed knowledge of so much of the viral life cycle is leading us into other types of inhibitors that can block or disrupt proteinprotein interactions. Viruses have compact genomes and employ a strategy of using a small number of proteins that can form repeating structures to enclose space (i.e. condensing the viral genome inside of a protein shell), thus minimizing the need for a large protein coding capacity. This creates a relatively small number of critical protein-protein interactions that are essential for viral replication. For HIV-1, the Gag protein has the role of a polyprotein precursor that contains all of the structural proteins of the virion: matrix, capsid, spacer peptide 1, nucleocapsid, spacer peptide 2, and p6 (which contains protein-binding domains that interact with host proteins during budding). Similarly, the Gag-Pro-Pol precursor encodes most of the Gag protein but now includes the viral enzymes: protease, reverse transcriptase (with its associated RNase H activity), and integrase. Gag and Gag-Pro-Pol are the substrates of the viral protease, which is responsible for cleaving these precursors into their mature and fully active forms (see Fig. 1A).The Gag and Gag-Pro-Pol precursors assemble at the plasma membrane of the cell, with the membrane ultimately being pinched off from the cell surface to create a membrane-bound virion with a diameter of ϳ120 nm, representing a volume of ϳ0.9 attoliters (Fig. 1). The host ESCRT (endosomal sorting complex required for transport) pathway that is subverted to drive the membrane fission event needed for virion budding has been reviewed in detail (1-3). The virion assembly process that takes place at the cell membrane results in a finite number of each viral protein within the particle. The budded particle has ϳ2400 Gag molecules embedded in the membrane via the N-terminal matrix (MA) 3 protein domain, which, in a 120-nm sphere, gives Gag a concentration of ϳ4.4 mM, with a crude estimate that the Gag molecules occupy 50 -60% of the volume of the sphere (4). There are also ϳ120 Gag-Pro-Pol molecules (5). The embedded protease (PR) must dimerize, release itself from the Gag-Pro-Pol precursor, and then cleave the other PR cleavage sites in Gag and Gag-Pro-Pol (6). From these cleaved products, the nucleocapsid (NC) condenses and stabilizes the viral dimeric RNA, and ϳ1500 copies of the processed capsid (CA) protein reform to make the mature conical capsid structure around viral RNA to create an infectious particle (7). In this minireview, we examine outstanding issues surrounding the HIV-1 PR, the role of protein processing and rearrangement in the assembly pathway, the impact of PR inhibi...

CD4 + effector lymphocytes (Teff) are traditionally classified by the cytokines they produce. To determine the states that Teff actually adopt in frontline tissues in vivo , we applied single-cell transcriptome and chromatin analysis on colonic Teff cells, in germ-free or conventional mice, or after challenge with a range of phenotypically biasing microbes. Subsets were marked by expression of interferon-signature or myeloid-specific transcripts, but transcriptome or chromatin structure could not resolve discrete clusters fitting classic T H subsets. At baseline or at different times of infection, transcripts encoding cytokines or proteins commonly used as T H markers distributed in a polarized continuum, which was also functionally validated. Clones derived from single progenitors gave rise to both IFN-γ and IL17-producing cells. Most transcriptional variance was tied to the infecting agent, independent of the cytokines produced, and chromatin variance primarily reflected activity of AP1 and IRF transcription factor families, not the canonical subset master regulators T-bet, GATA3, RORγ.

No abstract

Priming of human NK cells with IL-2 is necessary to render them functionally competent upon NKG2D engagement. We examined the underlying mechanisms that control NKG2D responsiveness in NK cells and found that IL-2 up-regulates expression of the amino acid transporters solute carrier family 1 member 5 (SLC1A5)2 and CD98. Using specific inhibitors to block SLC1A5 and CD98 function, we found that production of IFNγ and degranulation by CD56bright and CD56dim NK cells following NKG2D stimulation were dependent on both transporters. IL-2 priming increased the activity of the mammalian target of rapamycin complex 1 (mTORC1) and inhibition of mTORC1 abrogated the ability of the IL-2-primed NK cells to produce IFNγ in response to NKG2D-mediated stimulation. This study identifies a series of IL-2-induced cellular changes that regulates the NKG2D responsiveness in human NK cells.