Memory CD8 T cells are a critical component of protective immunity and inducing effective memory T cell responses is a major goal of vaccines against chronic infections and tumors 1-3. Considerable effort has gone into designing vaccine regimens that will increase the magnitude of the memory response but there has been minimal emphasis on developing strategies to improve the functional qualities of memory T cells 4. In this study we show that mTOR, the mammalian target of rapamycin 5, is a major regulator of memory CD8 T cell differentiation and in contrast to what we expected the mTOR specific inhibitor rapamycin, an immunosuppressive drug, had surprising immunostimulatory effects on the generation of memory CD8 T cells. Treatment of mice with rapamycin following acute lymphocytic choriomeningitis virus (LCMV) infection enhanced not only the quantity but also the quality of virus specific CD8 T cells. Similar effects were seen after immunization of mice with a non-replicating VLP based vaccine. In addition, rapamycin treatment also enhanced memory T cell responses in non-human primates following vaccination with MVA (modified vaccinia virus - Ankara). Rapamycin was effective during both the expansion and contraction phases of the T cell response; during the expansion phase it increased the number of memory precursors and during the contraction phase (effector to memory transition) it accelerated the memory T cell differentiation program. Experiments using RNAi to inhibit mTOR, raptor or FKBP12 expression in antigen specific CD8 T cells showed that mTOR acts intrinsically through the mTORC1 pathway to regulate memory T cell differentiation. Thus, these studies identify a molecular pathway regulating memory formation and provide an effective strategy for improving the functional qualities of vaccine or infection induced memory T cells.

We evaluated the ability of neonatal porcine islets to engraft and restore glucose control in pancreatectomized rhesus macaques. Although porcine islets transplanted into nonimmunosuppressed macaques were rapidly rejected by a process consistent with cellular rejection, recipients treated with a CD28-CD154 costimulation blockade regimen achieved sustained insulin independence (median survival, >140 days) without evidence of porcine endogenous retrovirus dissemination. Thus, neonatal porcine islets represent a promising solution to the crucial supply problem in clinical islet transplantation.

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Many chronic viral infections are marked by pathogen persistence and a generalized immunosuppression. The exact mechanisms by which this occurs are still unknown. Using a mouse model of persistent lymphocytic choriomeningitis virus (LCMV) infection, we demonstrate viral targeting of fibroblastic reticular cells (FRC) in the lymphoid organs. The FRC stromal networks are critical for proper lymphoid architecture and function. High numbers of FRC were infected by LCMV clone 13, which causes a chronic infection, whereas few were infected by the acute strain, LCMV Armstrong. The function of the FRC conduit network was altered after clone 13 infection by the action of CD8 ؉ T cells. Importantly, expression of the inhibitory programmed death ligand 1, which was up-regulated on FRC after infection, reduced early CD8 ؉ T cell-mediated immunopathology and prevented destruction of the FRC architecture in the spleen. Together, this reveals an important tropism during a persistent viral infection. These data also suggest that the inhibitory PD-1 pathway, which likely evolved to prevent excessive immunopathology, may contribute to viral persistence in FRC during chronic infection.immunopathology ͉ stromal cells ͉ viral infection M any acute and chronic viral infections induce a generalized immunosuppression (1, 2). This suppression of immunity is often transient, occurring during the acute phase of infection; however, prolonged suppression can also occur during certain chronic viral infections. The mechanisms of virus-induced immunosuppression are complex and varied (1-3). Infection of mice with lymphocytic choriomeningitis virus (LCMV) is a useful model to dissect the mechanisms of viral persistence and immunosuppression. The clone 13 (CL-13) strain of LCMV results in a chronic infection in adult mice, marked by persisting virus and a generalized immunosuppression. Viral load rises rapidly within days and remains high over a prolonged period, suppressing specific immunity by inducing an hierarchical loss of CD8 ϩ T cell function (4, 5). This CL-13 chronic infection is also associated with increased susceptibility to opportunistic secondary infections (6-8).Chronic LCMV infection results in reduced cellularity and altered splenic architecture (9). Enhanced infection of dendritic cells (DC), resulting in reduced T cell stimulatory capacity and destruction of the DC, has been proposed as one mechanism by which CL-13 initiates immunosuppression within the host (8, 10). Although DC in the spleen can be infected by LCMV CL-13, this represents a relatively small proportion of total infected cells. It follows that other cell types are infected by CL-13 and likely contribute to the pronounced immunosuppression and architectural disruption of lymphoid organs that are observed after infection.Through a detailed kinetic examination of the cell types infected during LCMV CL-13 infection we discovered that fibroblastic reticular cells (FRC) are an important target of infection by this virus. Secondary lymphoid tissues are supported by a c...

The molecular composition and binding epitopes of the immunoglobulin G (IgG) antibodies that circulate in blood plasma after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection are unknown. Proteomic deconvolution of the IgG repertoire to the spike glycoprotein in convalescent subjects revealed that the response is directed predominantly (>80%) against epitopes residing outside the receptor binding domain (RBD). In one subject, just four IgG lineages accounted for 93.5% of the response, including an amino (N)-terminal domain (NTD)–directed antibody that was protective against lethal viral challenge. Genetic, structural, and functional characterization of a multidonor class of “public” antibodies revealed an NTD epitope that is recurrently mutated among emerging SARS-CoV-2 variants of concern. These data show that “public” NTD-directed and other non-RBD plasma antibodies are prevalent and have implications for SARS-CoV-2 protection and antibody escape.

Many γ-herpesviruses encode candidate oncogenes including homologues of host bcl-2 and cyclin proteins (v-bcl-2, v-cyclin), but the physiologic roles of these genes during infection are not known. We show for the first time in any virus system the physiologic role of v-bcl-2. A γ-herpesvirus v-bcl-2 was essential for efficient ex vivo reactivation from latent infection, and for both persistent replication and virulence during chronic infection of immunocompromised (interferon [IFN]-γ−/−) mice. The v-cyclin was also critical for the same stages in pathogenesis. Strikingly, while the v-bcl-2 and v-cyclin were important for chronic infection, these genes were not essential for viral replication in cell culture, viral replication during acute infection in vivo, establishment of latent infection, or virulence during acute infection. We conclude that v-bcl-2 and v-cyclin have important roles during latent and persistent γ-herpesvirus infection and that herpesviruses encode genes with specific roles during chronic infection and disease, but not acute infection and disease. As γ-herpesviruses primarily cause human disease during chronic infection, these chronic disease genes may be important targets for therapeutic intervention.

Tunneling nanotubes (TNTs) represent a novel route of intercellular communication. While previous work has shown that TNTs facilitate the exchange of viral or prion proteins from infected to naïve cells, it is not clear whether the viral genome is also transferred via this mechanism and further, whether transfer via this route can result in productive replication of the infectious agents in the recipient cell. Here we present evidence that lung epithelial cells are connected by TNTs, and in spite of the presence of neutralizing antibodies and an antiviral agent, Oseltamivir, influenza virus can exploit these networks to transfer viral proteins and genome from the infected to naïve cell, resulting in productive viral replication in the naïve cells. These observations indicate that influenza viruses can spread using these intercellular networks that connect epithelial cells, evading immune and antiviral defenses and provide an explanation for the incidence of influenza infections even in influenza-immune individuals and vaccine failures.

After a brief period of antigenic stimulation, T cells become committed to a program of autonomous expansion and differentiation. We investigated the role of antigen-specific T cell precursor frequency as a possible cell-extrinsic factor impacting T cell programming in a model of allogeneic tissue transplantation. Using an adoptive transfer system to incrementally raise the precursor frequency of antigen-specific CD8+ T cells, we found that donor-reactive T cells primed at low frequency exhibited increased cellular division, decreased development of multifunctional effector activity, and an increased requirement for CD28- and CD154-mediated costimulation relative to those primed at high frequency. The results demonstrated that recipients with low CD4+ and CD8+ donor-reactive T cell frequencies exhibited long-term skin graft survival upon CD28/CD154 blockade, whereas simultaneously raising the frequency of CD4+ T cells to ∼0.5% and CD8+ T cells to ∼5% precipitated graft rejection despite CD28/CD154 blockade. Antigenic rechallenge of equal numbers of cells stimulated at high or low frequency revealed that cells retained an imprint of the frequency at which they were primed. These results demonstrate a critical role for initial precursor frequency in determining the CD8+ T cell requirement for CD28- and CD154-mediated costimulatory signals during graft rejection.