Jodie S. Haring

Accelerated CD8+ T-cell memory and prime-boost response after dendritic-cell vaccination.

Efficient boosting of memory T-cell numbers to protective levels generally requires a relatively long interval between immunizations. Decreasing this interval could be crucial in biodefense and cancer immunotherapy, in which rapid protective responses are essential. Here, we show that vaccination with peptide-coated dendritic cells (DCs) generated CD8+ T cells with the phenotype and function of memory cells within 4–6 d. These early memory CD8+ T cells underwent vigorous secondary expansion in response to a variety of booster immunizations, leading to elevated numbers of effector and memory T cells and enhanced protective immunity. Coinjection of CpG oligodeoxynucleotides, potent inducers of inflammation that did not alter the duration of DC antigen display, prevented the rapid generation of memory T cells in wild-type mice but not in mice lacking the interferon (IFN)-γ receptor. These data show that DC vaccination stimulates a pathway of accelerated generation of memory T cells, and suggest that events of inflammation, including the action of IFN-γ on the responding T cells, control the rate of development of memory CD8+ T cells.

Mouse hepatitis virus

Abstract Inoculation of mice with most neurotropic strains of the coronavirus mouse hepatitis virus results in an immune response-mediated demyelinating disease that serves as an excellent animal model for the human disease multiple sclerosis. Recent work has shown that either virus-specific CD4+ or CD8+ T cells are able to mediate demyelination and also that the antibody response is crucial for clearing infectious virus. Another exciting advance is the development of recombinant coronaviruses, which, for the first time, will allow genetic manipulation of the entire viral genome.

Constitutive activation of Wnt signaling favors generation of memory CD8 T cells

T cell factor-1 (TCF-1) and lymphoid enhancer-binding factor 1, the effector transcription factors of the canonical Wnt pathway, are known to be critical for normal thymocyte development. However, it is largely unknown if it has a role in regulating mature T cell activation and T cell-mediated immune responses. In this study, we demonstrate that, like IL-7Rα and CD62L, TCF-1 and lymphoid enhancer-binding factor 1 exhibit dynamic expression changes during T cell responses, being highly expressed in naive T cells, downregulated in effector T cells, and upregulated again in memory T cells. Enforced expression of a p45 TCF-1 isoform limited the expansion of Ag-specific CD8 T cells in response to Listeria monocytogenes infection. However, when the p45 transgene was coupled with ectopic expression of stabilized β-catenin, more Ag-specific memory CD8 T cells were generated, with enhanced ability to produce IL-2. Moreover, these memory CD8 T cells expanded to a larger number of secondary effectors and cleared bacteria faster when the immunized mice were rechallenged with virulent L. monocytogenes. Furthermore, in response to vaccinia virus or lymphocytic choriomeningitis virus infection, more Ag-specific memory CD8 T cells were generated in the presence of p45 and stabilized β-catenin transgenes. Although activated Wnt signaling also resulted in larger numbers of Ag-specific memory CD4 T cells, their functional attributes and expansion after the secondary infection were not improved. Thus, constitutive activation of the canonical Wnt pathway favors memory CD8 T cell formation during initial immunization, resulting in enhanced immunity upon second encounter with the same pathogen.

Dynamic Regulation of IFN-γ Signaling in Antigen-Specific CD8+ T Cells Responding to Infection

IFN-γ plays a critical role in the CD8+ T cell response to infection, but when and if this cytokine directly signals CD8+ T cells during an immune response is unknown. We show that naive Ag-specific CD8+ T cells receive IFN-γ signals within 12 h after in vivo infection with Listeria monocytogenes and then become unresponsive to IFN-γ throughout the ensuing Ag-driven expansion phase. Ag-specific CD8+ T cells regain partial IFN-γ responsiveness throughout the contraction phase, whereas the memory pool exhibits uniform, but reduced, responsiveness that is also modulated during the secondary response. The responsiveness of Ag-specific CD8+ T cells to IFN-γ correlated with modulation in the expression of IFN-γR2, but not with IFN-γR1 or suppressor of cytokine signaling-1. This dynamic regulation suggests that early IFN-γ signals participate in regulation of the primary CD8+ T cell response program, but that evading or minimizing IFN-γ signals during expansion and the memory phase may contribute to appropriate regulation of the CD8+ T cell response.

Bystander CD8 T Cell-Mediated Demyelination After Viral Infection of the Central Nervous System

Multiple sclerosis, a chronic inflammatory disease of the CNS, is characterized by immune-mediated demyelination. Many patients have a remitting-relapsing course of disease with exacerbations often following unrelated microbial illnesses. The relationship between the two events remains obscure. One possibility is that T cells specific for the inciting microbial pathogen are able to effect demyelination at a site of ongoing inflammation within the CNS. This possibility was examined in mice infected with mouse hepatitis virus, a well-described model of virus-induced demyelination. Using transgenic TCR/recombination activation gene 2−/− mice with only non-mouse hepatitis virus-specific T cells, we show that CD8 T cells are able to cause demyelination in the absence of cognate Ag in the CNS, but only if specifically activated. These findings demonstrate a novel mechanism for immune-mediated neuropathology and show that activated CD8 T cells may serve as important mediators of bystander demyelination during times of infection, including in patients with multiple sclerosis.

Constitutive Expression of IL-7 Receptor α Does Not Support Increased Expansion or Prevent Contraction of Antigen-Specific CD4 or CD8 T Cells following Listeria monocytogenes Infection

Expression of IL-7Rα (CD127) has been suggested as a major determinant in the survival of memory T cell precursors. We investigated whether constitutive expression of IL-7Rα on T cells increased expansion and/or decreased contraction of endogenous Ag-specific CD4 and CD8 T cells following infection with Listeria monocytogenes. The results indicate that constitutive expression of IL-7Rα alone was not enough to impart an expansion or survival advantage to CD8 T cells responding to infection, and did not increase memory CD8 T cell numbers over those observed in wild-type controls. Constitutive expression of IL-7Rα did allow for slightly prolonged expansion of Ag-specific CD4 T cells; however, it did not alter the contraction phase or protect against the waning of memory T cell numbers at later times after infection. Memory CD4 and CD8 T cells generated in IL-7Rα transgenic mice expanded similarly to wild-type T cells after secondary infection, and immunized IL-7Rα transgenic mice were fully protected against lethal bacterial challenge demonstrating that constitutive expression of IL-7Rα does not impair, or markedly improve memory/secondary effector T cell function. These results indicate that expression of IL-7Rα alone does not support increased survival of effector Ag-specific CD4 or CD8 T cells into the memory phase following bacterial infection.

CD4 T-Cell-Mediated Demyelination Is Increased in the Absence of Gamma Interferon in Mice Infected with Mouse Hepatitis Virus

ABSTRACT Mice infected with the murine coronavirus, mouse hepatitis virus, strain JHM (MHV) develop an immune-mediated demyelinating encephalomyelitis. Adoptive transfer of MHV-immune splenocytes depleted of either CD4 or CD8 T cells to infected mice deficient in recombination activation gene 1 resulted in demyelination. We showed previously that the process of CD8 T-cell-mediated demyelination was strongly dependent on the expression of gamma interferon (IFN-γ) by donor cells. In this report, we show, in contrast, that demyelination and lymphocyte infiltration were increased in recipients of IFN-γ−/− CD4 T cells when compared to levels in mice receiving C57BL/6 CD4 T cells.

High-Magnitude, Virus-Specific CD4 T-Cell Response in the Central Nervous System of Coronavirus-Infected Mice

ABSTRACT The neurotropic JHM strain of mouse hepatitis virus (MHV) causes acute encephalitis and chronic demyelinating encephalomyelitis in rodents. Previous results indicated that CD8 T cells infiltrating the central nervous system (CNS) were largely antigen specific in both diseases. Herein we show that by 7 days postinoculation, nearly 30% of the CD4 T cells in the acutely infected CNS were MHV specific by using intracellular gamma interferon (IFN-γ) staining assays. In mice with chronic demyelination, 10 to 15% of the CD4 T cells secreted IFN-γ in response to MHV-specific peptides. Thus, these results show that infection of the CNS is characterized by a large influx of CD4 T cells specific for MHV and that these cells remain functional, as measured by cytokine secretion, in mice with chronic demyelination.

Aberrant Contraction of Antigen-Specific CD4 T Cells after Infection in the Absence of Gamma Interferon or Its Receptor

ABSTRACT Several lines of evidence from different model systems suggest that gamma interferon (IFN-γ) is an important regulator of T-cell contraction after antigen (Ag)-driven expansion. To specifically investigate the role of IFN-γ in regulating the contraction of Ag-specific CD4 T cells, we infected IFN-γ−/− and IFN-γR1−/− mice with attenuated Listeria monocytogenes and monitored the numbers of Ag-specific CD4 T cells during the expansion, contraction, and memory phases of the immune response to infection. In the absence of IFN-γ or the ligand-binding portion of its receptor, Ag-specific CD4 T cells exhibited normal expansion in numbers, but in both strains of deficient mice there was very little decrease in the number of Ag-specific CD4 T cells even at time points later than day 90 after infection. This significant delay in contraction was not due to prolonged infection, since mice treated with antibiotics to conclusively eliminate infection exhibited the same defect in contraction. In addition to altering the number of Ag-specific CD4 T cells, the absence of IFN-γ signaling also changed the phenotype of cells generated after infection. IFN-γR1−/− Ag-specific CD4 T cells reacquired expression of CD127 more quickly than wild-type cells, and more IFN-γR1−/− CD4 T cells were capable of producing both IFN-γ and interleukin 2 following Ag stimulation. From these data we conclude that IFN-γ regulates the contraction, phenotype, and function of Ag-specific CD4 T cells generated after infection.

TNF Receptor-Associated Factor 5 Is Required for Optimal T Cell Expansion and Survival in Response to Infection

Receptors belonging to the TNF-receptor (TNF-R) superfamily include important costimulatory molecules, many of which specifically affect T cell activation. TNF receptor-associated factors (TRAFs) are recruited to many TNF-R superfamily members and are important modulators of the proximal signaling events that occur at the time of receptor engagement and activation. TRAF5 has been shown to be a positive regulator of a number of these receptors that are involved in T cell costimulation. However, the potential importance of TRAF5 in cellular immune responses to infection or in T cell expansion and memory have not been studied. We report in this study that TRAF5 was required for optimal CD8+ T cell responses following infection with Listeria monocytogenes expressing OVA (LM-OVA). TRAF5 was necessary for optimal T cell expansion following primary infection with LM-OVA, and its absence resulted in fewer memory CD8+ T cells following LM-OVA infection, together with higher bacterial loads in the liver. The effect of TRAF5 on CD8+ T cell expansion was T cell intrinsic and not due to effects of TRAF5 deficiency on APCs. Although their proliferative ability remained intact, CD8+ T cells from TRAF5−/− mice were more sensitive to apoptosis and were unresponsive to the prosurvival effects of the TNF-R superfamily costimulator CD27. Collectively, these studies identify TRAF5 as an important positive signaling element that enhances T cell expansion and pathogen containment by providing a survival advantage to responding Ag-specific CD8+ T cells during infection.