The HIV-1-specific cytotoxic T lymphocyte (CTL) response is temporally associated with the decline in viremia during primary HIV-1 infection, but definitive evidence that it is of importance in virus containment has been lacking. Here we show that in a patient whose early CTL response was focused on a highly immunodominant epitope in gp 160, there was rapid elimination of the transmitted virus strain and selection for a virus population bearing amino acid changes at a single residue within this epitope, which conferred escape from recognition by epitope-specific CTL. The magnitude (> 100-fold), kinetics (30-72 days from onset of symptoms) and genetic pathways of virus escape from CTL pressure were comparable to virus escape from antiretroviral therapy, indicating the biological significance of the CTL response in vivo. One aim of HIV-1 vaccines should thus be to elicit strong CTL responses against multiple codominant viral epitopes.

Human immunodeficiency virus type 1 (HIV-1) Env-, Gag-, Pol-, Nef-, and Tat-specific cytotoxic Tlymphocyte (CTL) activities were quantitated temporally in five patients with symptomatic primary HIV-1 infection. A dominant CD8+-mediated, major histocompatibility complex class I-restricted CTL response to the HIV-1 envelope glycoprotein, gpl60, was noted in four of the five patients studied. The level of HIV-1-specific CTL activity in the five patients paralleled the efficiency of control of primary viremia. Patients who mounted strong gpl60-specific CTL responses showed rapid reduction of acute plasma viremia and antigenemia, while in contrast, primary viremia and antigenemia were poorly controlled in patients in whom virus-specific CTL activity was low or undetectable. These results suggest that HIV-1-specific CTL activity is a major component of the host immune response associated with the control of virus replication following primary HIV-1 infection and have important implications for the design of antiviral vaccines.

Among cells of the immune system, CD11c+ and DEC-205+ splenic dendritic cells primarily express the cellular receptor (α-dystroglycan [α-DG]) for lymphocytic choriomeningitis virus (LCMV). By selection, strains and variants of LCMV that bind α-DG with high affinity are associated with virus replication in the white pulp, show preferential replication in a majority of CD11c+ and DEC-205+ cells, cause immunosuppression, and establish a persistent infection. In contrast, viral strains and variants that bind with low affinity to α-DG are associated with viral replication in the red pulp, display minimal replication in CD11c+ and DEC-205+ cells, and generate a robust anti-LCMV cytotoxic T lymphocyte response that clears the virus infection. Differences in binding affinities can be mapped to a single amino acid change in the viral glycoprotein 1 ligand that binds to α-DG. These findings indicate that receptor–virus interaction on dendritic cells in vivo can be an essential step in the initiation of virus-induced immunosuppression and viral persistence.

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). Data presented in this paper indicate that the affinity of binding of LCMV to ␣-DG determines viral tropism and the outcome of infection in mice. To characterize this relationship, we evaluated the interaction between ␣-DG and several LCMV strains, variants, and reassortants. These viruses could be divided into two groups with respect to affinity of binding to ␣-DG, dependence on this protein for cell entry, viral tropism, and disease course. Viruses that exhibited high-affinity binding to ␣-DG displayed a marked dependence on ␣-DG for cell entry and were blocked from infecting mouse 3T6 fibroblasts by 1 to 4 nM soluble ␣-DG. In addition, high-affinity binding to ␣-DG correlated with an ability to infiltrate the white pulp (T-dependent) area of the spleen, cause ablation of the cytotoxic T-lymphocyte (CTL) response by day 7 postinfection, and establish a persistent infection. In contrast, viruses with a lower affinity of binding to ␣-DG were only partially inhibited from infecting ␣-DG ؊/؊ embryonic stem cells and required a concentration of soluble ␣-DG higher than 100 nM to prevent infection of mouse 3T6 fibroblasts. These viruses that bound at low affinity were mainly restricted to the splenic red pulp, and the host generated an effective CTL response that rapidly cleared the infection. Reassortants of viruses that bound to ␣-DG at high and low affinities were used to map genes responsible for the differences described to the S RNA, containing the virus attachment protein glycoprotein 1.

Measles virus (MV), a member of the family Paramyxoviridae and an exclusively human pathogen, is among the most infectious viruses. A progressive fatal neurodegenerative complication, subacute sclerosing panencephalitis (SSPE), occurs during persistent MV infection of the CNS and is associated with biased hypermutations of the viral genome. The observed hypermutations of A-to-G are consistent with conversions catalyzed by the adenosine deaminase acting on RNA (ADAR1). To evaluate the role of ADAR1 in MV infection, we selectively disrupted expression of the IFN-inducible p150 ADAR1 isoform and found it caused embryonic lethality at embryo day (E) 11-E12. We therefore generated p150-deficient and WT mouse embryo fibroblast (MEF) cells stably expressing the MV receptor signaling lymphocyte activation molecule (SLAM or CD150). The p150 −/− but not WT MEF cells displayed extensive syncytium formation and cytopathic effect (CPE) following infection with MV, consistent with an anti-MV role of the p150 isoform of ADAR1. MV titers were 3 to 4 log higher in p150 −/− cells compared with WT cells at 21 h postinfection, and restoration of ADAR1 in p150 −/− cells prevented MV cytopathology. In contrast to infection with MV, p150 disruption had no effect on vesicular stomatitis virus, reovirus, or lymphocytic choriomeningitis virus replication but protected against CPE resulting from infection with Newcastle disease virus, Sendai virus, canine distemper virus, and influenza A virus. Thus, ADAR1 is a restriction factor in the replication of paramyxoviruses and orthomyxoviruses. M easles virus (MV), a member of the family Paramyxoviridae, infects more than 10 million persons worldwide each year, resulting in several hundred thousand deaths (1, 2). A serious complication is the persistent infection of the CNS known as subacute sclerosing panencephalitis (SSPE) that occurs at a frequency of 4-11 cases per 100,000 cases of MV infection. SSPE is a progressive fatal neurodegenerative disease with characteristic features of replication of MV in neurons in the presence of high titers of MV antibodies, modest infiltration of T and B cells into the CNS, and replication of defective MV in the CNS with biased mutation of U-to-C and A-to-G in the viral genome (3-5). These hypermutations occur primarily in the matrix (M) gene but are also observed to a lesser extent in the fusion (F) and hemagglutinin (H) genes (3, 4). A transgenic mouse model that expresses the human MV receptor CD46 recapitulates all the features of SSPE on infection with MV, with biased hypermutations of U-to-C and A-to-G accounting for more than 95% of point mutations in the M gene (3,4,6). Interestingly, these biased hypermutations play a direct role in the pathogenesis of SSPE by facilitating a significant prolongation of MV persistence within the CNS, as opposed to mere accumulation as a result of persistent infection (7). In support of a direct role of M gene hypermutations in the establishment of SSPE, MV generated by reverse genetics and containing a hypermutated M...

Monoclonal hybridoma antibodies directed against the polypeptides of murine hepatitis virus-4 (JHM strain) were tested for their ability to alter the course of a normally lethal intracerebral virus challenge. Three monoclonal antibodies directed against two distinct epitopes on the E2 glycoprotein of MHV-4 protected mice against lethal virus challenge and converted the infection from fatal encephalomyelitis to demyelination. A single neutralizing antibody directed against a third epitope on E2 as well as seven nonneutralizing antibodies to E2, E1, and N polypeptides did not protect against challenge. In mice which received protective antibody, MHV-4 infection was not blocked, however, virus grew to lower titers in liver and brain, and virus replication in the CNS was more restricted than in unprotected mice. Decreased involvement of neurons in the brains of protected mice was observed, and no evidence of neuronal infection in the spinal cords was found. In contrast, oligodendrocytes were infected in the presence of protective antibody, and evidence of demylination associated with mononuclear cell infiltration was found. These studies demonstrate that antibody to a single epitope on a viral glycoprotein can substantially alter the course and phenotype of disease.

The mechanism(s) by which infectious material is cleared by the host is an area of intensive study. This is especially so with the realization that persistent viral infection is a cause of chronic disease in humans and presents a major health problem. We have used the murine model of infection with lymphocytic choriomeningitis virus to evaluate immune clearance. Mice with a targeted disruption of the IFN-gamma gene mount effective cytotoxic T lymphocyte (CTL) responses after an acute viral challenge and clear virus. CD4+ T cells are not required but CD8+ T cells are mandatory. In contrast, CTL from mice with targeted disruption of the IFN-gamma gene are unable to clear virus from persistently infected mice. In addition to the requirement for IFN-gamma, CD4+ T cells are essential for maintaining a CD8(+)-mediated cure of persistent viral infection.