Human cytomegalovirus (HCMV) strains that have been passaged in vitro rapidly acquire mutations that impact viral growth. These laboratory-adapted strains of HCMV generally exhibit restricted tropism, produce high levels of cell-free virus, and develop susceptibility to natural killer cells. To permit experimentation with a virus that retained a clinically relevant phenotype, we reconstructed a wild-type (WT) HCMV genome using bacterial artificial chromosome technology. Like clinical virus, this genome proved to be unstable in cell culture; however, propagation of intact virus was achieved by placing the RL13 and UL128 genes under conditional expression. In this study, we show that WT-HCMV produces extremely low titers of cell-free virus but can efficiently infect fibroblasts, epithelial, monocyte-derived dendritic, and Langerhans cells via direct cell-cell transmission. This process of cell-cell transfer required the UL128 locus, but not the RL13 gene, and was significantly less vulnerable to the disruptive effects of IFN, cellular restriction factors, and neutralizing antibodies compared with cell-free entry. Resistance to neutralizing antibodies was dependent on high-level expression of the pentameric gH/gL/gpUL128-131A complex, a feature of WT but not passaged strains of HCMV.virology | immune evasion | herpesvirus | HCMV | cell-cell spread H uman cytomegalovirus (HCMV) is a major cause of morbidity and mortality in the immunocompromised and the leading infectious cause of congenital malformation. As a result, a vaccine has been designated as a priority. However, basic studies of clinically relevant isolates that inform our understanding of the disease process are limited due to the rapid accumulation of genetic mutations during in vitro passage of HCMV. The same three genetic sites are reproducibly affected: the RL13 gene; the UL128 locus (UL128L), which comprises UL128, UL30, and UL131A; and the ∼15-kb U L /b′ gene region (1). Deletions in the U L /b′ region can affect tropism [UL148 (2)], latency [UL136 and UL138 (3-7)], and resistance to NK cells [UL141 (8-10), UL142 (11, 12), and UL135 (13)]. Disabling mutations in RL13 and UL128L independently contribute to the release of high-titer cell-free virus, whereas loss of UL128L restricts virus entry to fibroblasts alone by preventing assembly of a pentameric glycoprotein complex (gH/gL/pUL128/ pUL130/pUL131A) in the virion envelope (1,14,15).The rapid selection of mutations is a major obstacle to the propagation of genetically intact "clinical" strains of HCMV, which in turn has led to significant gaps in our understanding of the affiliated disease processes (16). In particular, HCMV is largely cell-associated in vivo (17), and clinical isolates exhibit a similar phenotype in vitro (17, 18), yet most studies in the field are based on laboratory strains that produce high titers of cell-free virus (19). As a consequence, little is known about the fundamental processes involved in the infectious spread of cell-associated HCMV.In this study, we used a system tha...

HPV-16 is the major causes of cervical cancer. Persistence of infection is a necessary event for progression of the infection to cancer. Among other factors, virus persistence is due the viral proteins fighting the immune response. HPV-16 E5 down-regulates MHC/HLA class I, which is much reduced on the cell surface and accumulates in the Golgi apparatus in cells expressing E5. This effect is observed also in W12 cells, which mimic early cervical intraepithelial progression to cervical cancer. The functional effect of MHC I down-regulation on human CD8 T cells is not known, because of the need for HLA-matched, HPV-specific T cells that recognise E5 expressing-cells. Here we employ a heterologous cell/MHC I system which uses mouse cells expressing both E5 and HLA-A2, and A2-restricted CTLs; we show that the E5-induced reduction of HLA-A2 has a functional impact by reducing recognition of E5 expressing cells by HPV specific CD8+ T cells.

Killer-cell immunoglobulin-like receptors (KIRs) are expressed predominantly on natural killer cells, where they play a key role in the regulation of innate immune responses. Recent studies show that inhibitory KIRs can also impact adaptive T cell-mediated immunity. In mice and in human T cells in vitro, inhibitory KIR ligation enhanced CD8+ T cell survival. To investigate the clinical relevance of these observations, we conducted an extensive immunogenetic analysis of multiple, independent cohorts of HIV-1, hepatitis C virus (HCV) and human T cell leukemia virus (HTLV-1)-infected individuals in conjunction with in vitro assays of T cell survival, analysis of ex vivo KIR expression and mathematical modeling of host-virus dynamics. Our data suggest that functional engagement of inhibitory KIRs enhances the CD8+ T cell response against HIV-1, HCV and HTLV-1 and is a significant determinant of clinical outcome in all three viral infections.

ABSTRACTmolecules is ideally suited for the capture of lipid antigens 3 . CD1 clefts derive from deep invaginations into the CD1 core structure and form two or four pockets 5,6,7,8,9. In general, the pockets surround a large portion of the lipidic antigens so that their hydrocarbon moieties are sequestered from solvent and the hydrophilic headgroups protrude for T cell contact. However, each of the four types of human CD1 proteins has a cavity with unique architecture, which endows each CD1 isoform with the ability to present specific types of lipids. Whereas MHC proteins allow broad access to peptides that span the entire platform, CD1 proteins possess an

SummaryAdaptive immunity requires the generation of memory T cells from naive precursors selected in the thymus. The key intermediaries in this process are stem cell-like memory T (TSCM) cells, multipotent progenitors that can both self-renew and replenish more differentiated subsets of memory T cells. In theory, antigen specificity within the TSCM pool may be imprinted statically as a function of largely dormant cells and/or retained dynamically by more transitory subpopulations. To explore the origins of immunological memory, we measured the turnover of TSCM cells in vivo using stable isotope labeling with heavy water. The data indicate that TSCM cells in both young and elderly subjects are maintained by ongoing proliferation. In line with this finding, TSCM cells displayed limited telomere length erosion coupled with high expression levels of active telomerase and Ki67. Collectively, these observations show that TSCM cells exist in a state of perpetual flux throughout the human lifespan.