Quantitative analysis of long-term virus-specific CD8+-T-cell memory in mice challenged with unrelated pathogens

The consequences for the long-term maintenance of virus-specific CD8+-T-cell memory have been analyzed experimentally for sequential respiratory infections with readily eliminated (influenza virus) and persistent (gammaherpesvirus 68 [gammaHV68]) pathogens. Sampling a broad range of tissue sites established that the numbers of CD8+ T cells specific for the prominent influenza virus D(b)NP(366) epitope were reduced by about half in mice that had been challenged 100 days previously with gammaHV68, though the prior presence of a large CD8+ D(b)NP366+ population caused no selective defect in the gammaHV68-specific CD8+ K(b)p79+ response. Conversely, mice that had been primed and boosted to generate substantial gammaHV68-specific CD8+ D(b)p56+ populations did not show any decrease in prevalence for this set of CD8+ memory cytotoxic T lymphocytes (CTL) at 200 days after respiratory exposure to an influenza A virus. However, in both experiments, the total magnitude of the CD8+-T-cell pool was significantly diminished in those that had been infected with gammaHV68 and the influenza A virus. The broader implications of these findings, especially under conditions of repeated exposure to unrelated pathogens, are explored with a mathematical model which emphasizes that the immune effector and memory "phenome" is a function of the overall infection experience of the individual.     

Compromised influenza virus-specific CD8(+)-T-cell memory in CD4(+)-T-cell-deficient mice

The primary influenza A virus-specific CD8(+)-T-cell responses measured by tetramer staining of spleen, lymph node, and bronchoalveolar lavage (BAL) lymphocyte populations were similar in magnitude for conventional I-A(b+/+) and CD4(+)-T-cell-deficient I-A(b-/-) mice. Comparable levels of virus-specific cytotoxic-T-lymphocyte activity were detected in the inflammatory exudate recovered by BAL following challenge. However, both the size of the memory T-cell pool and the magnitude of the recall response in the lymphoid tissues (but not the BAL specimens) were significantly diminished in mice lacking the CD4(+) subset. Also, the rate of virus elimination from the infected respiratory tract slowed at low virus loads following challenge of na?ve and previously immunized I-A(b-/-) mice. Thus, though the capacity to mediate the CD8(+)-T-cell effector function is broadly preserved in the absence of concurrent CD4(+)-T-cell help, both the maintenance and recall of memory are compromised and the clearance of residual virus is delayed. These findings are consistent with mathematical models that predict virus-host dynamics in this, and other, models of infection.     

An optimized CD8+ T-cell response controls productive and latent gammaherpesvirus infection

Strategies to prime CD8(+) T cells against Murine gammaherpesvirus 68 (gammaHV68; MHV68) latency have, to date, resulted in only limited effects. While early forms of latency (<21 days) were significantly reduced, effects were not seen at later times, indicating loss of control by the primed CD8(+) T cells. In the present study, we evaluated CD8(+) T cells in an optimized system, consisting of OTI T-cell-receptor (TCR) transgenic mice, which generate clonal CD8(+) T cells specific for K(b)-SIINFEKL of OVA, and a recombinant gammaHV68 that expresses OVA (gammaHV68.OVA). Our aim was to test whether this optimized system would result in more effective control not only of acute infection but also of later forms of latent infection than was seen with previous strategies. First, we show that OTI CD8(+) T cells effectively controlled acute replication of gammaHV68.OVA in liver, lung, and spleen at 8 and 16 days after infection of OTI/RAG mice, which lack expression of B and CD4(+) T cells. However, we found that, despite eliminating detectable acute replication, the OTI CD8(+) T cells did not prevent the establishment of latency in the OTI/RAG mice. We next evaluated the effectiveness of OTI T cells in OTI/B6 animals, which express B cells--a major site of latency in wild-type mice--and CD4(+) T cells. In OTI/B6 mice OTI CD8(+) T cells not only reduced the frequency of cells that reactivate from latency and the frequency of cells bearing the viral genome at 16 days after infection (similar to what has been reported before) but also were effective at reducing latency at 42 days after infection. Together, these data show that CD8(+) T cells are sufficient, in the absence of B cells and CD4(+) T cells, for effective control of acute replication. The data also demonstrate for the first time that a strong CD8(+) T-cell response can limit long-term latent infection.     

CD103- and CD103+ bronchial lymph node dendritic cells are specialized in presenting and cross-presenting innocuous antigen to CD4+ and CD8+ T cells

Dendritic cells (DC) are able to capture, process, and present exogenous Ag to CD8(+) T lymphocytes through MHC class I, a process referred to as cross-presentation. In this study, we demonstrate that CD103(+) (CD11c(high)CD11b(low)) and CD103(-) (CD11c(int)CD11b(high)) DC residing in the lung-draining bronchial lymph node (brLN) have evolved to acquire opposing functions in presenting innocuous inhaled Ag. Thus, under tolerogenic conditions, CD103(-) DC are specialized in presenting innocuous Ag to CD4(+) T cells, whereas CD103(+) DC, which do not express CD8alpha, are specialized in presenting Ag exclusively to CD8(+) T cells. In CCR7-deficient but not in plt/plt mice, Ag-carrying CD103(+) DC are largely absent in the brLN, although CD103(+) DC are present in the lung of CCR7-deficient mice. As a consequence, adoptively transferred CD8(+) T cells can be activated under tolerizing conditions in plt/plt but not in CCR7-deficient mice. These data reveal that CD103(+) brLN DC are specialized in cross-presenting innocuous inhaled Ag in vivo. Because these cells are largely absent in CCR7(-/-) mice, our findings strongly suggest that brLN CD103(+) DC are lung-derived and that expression of CCR7 is required for their migration from the lung into its draining lymph node.     

MHC class Ib-restricted CTL provide protection against primary and secondary Listeria monocytogenes infection

Infection of B6 mice with the intracellular pathogen Listeria monocytogenes (LM) results in the activation of CD8(+) T cells that respond to Ag presented by both MHC class Ia and class Ib molecules. Enzyme-linked immunospot analysis reveals that these CTL populations expand and contract at different times following a primary sublethal LM infection. Between days 4 and 6 postinfection, class Ib-restricted CTL exhibit a rapid proliferative response that is primarily H2-M3 restricted. The peak response of class Ia-restricted CD8(+) T cells occurs a few days later, after the majority of bacteria have been cleared. Although class Ia-restricted CTL exhibit a vigorous recall response to secondary LM infection, we observe limited expansion of class Ib-restricted memory CTL, even in MHC class Ia-deficient mice (B6.K(b-/-)D(b-/-)). Despite this lack of enhanced expansion in vivo, class Ib-restricted memory CTL retain the ability to proliferate and expand when provided with Ag in vitro. Furthermore, we demonstrate that in vivo depletion of CD8(+) T cells in LM-immune B6.K(b-/-)D(b-/-) mice severely impairs memory protection. Together, these data demonstrate that class Ib-restricted CTL play an important role in clearing a primary LM infection and generate a memory population capable of providing significant protection against subsequent infection.     

CD8alpha+ and CD11b+ dendritic cell-restricted MHC class II controls Th1 CD4+ T cell immunity

The activation, proliferation, differentiation, and trafficking of CD4 T cells is central to the development of type I immune responses. MHC class II (MHCII)-bearing dendritic cells (DCs) initiate CD4(+) T cell priming, but the relative contributions of other MHCII(+) APCs to the complete Th1 immune response is less clear. To address this question, we examined Th1 immunity in a mouse model in which I-A(beta)(b) expression was targeted specifically to the DCs of I-A(beta)b-/- mice. MHCII expression is reconstituted in CD11b(+) and CD8alpha(+) DCs, but other DC subtypes, macrophages, B cells, and parenchymal cells lack of expression of the I-A(beta)(b) chain. Presentation of both peptide and protein Ags by these DC subsets is sufficient for Th1 differentiation of Ag-specific CD4(+) T cells in vivo. Thus, Ag-specific CD4(+) T cells are primed to produce Th1 cytokines IL-2 and IFN-gamma. Additionally, proliferation, migration out of lymphoid organs, and the number of effector CD4(+) T cells are appropriately regulated. However, class II-negative B cells cannot receive help and Ag-specific IgG is not produced, confirming the critical MHCII requirement at this stage. These findings indicate that DCs are not only key initiators of the primary response, but provide all of the necessary cognate interactions to control CD4(+) T cell fate during the primary immune response.     

Dendritic cell-derived IL-12 is not required for the generation of cytotoxic, IFN-gamma-secreting, CD8(+) CTL in vivo.

By using adoptive transfer of Ag-loaded bone marrow-derived dendritic cells (BMDC), we have established an in vivo model of CTL priming. Activation of CTL in these experiments required both CD4(+) T cells and CD154, demonstrating that this model reflects CD4(+) T cell-dependent dendritic cell (DC) licensing. Because IL-12 has been suggested to play an important role in CTL activation by DC, we examined the ability of BMDC to prime CTL in the complete absence of IL-12 using p40-deficient mice. We observed that the absence of IL-12 does not affect the phenotype or allostimulatory function of BMDC after in vitro maturation. Moreover, there was no difference in the ability of Ag-loaded DC to elicit CTL cytotoxicity, whether the Ag was delivered by virus infection or peptide pulsing. Equal frequencies of Ag-specific, IFN-gamma-secreting CD8(+) T cells developed in both wild-type and IL-12-deficient backgrounds. Finally, CTL generated in the IL-12-deficient environment were capable of protecting immunized mice against tumor challenge, demonstrating that these CTL were fully functional, despite the absence of IL-12 during the maturation process in vivo. These results indicate that IL-12 is not critical for the development of IFN-gamma secreting, CD8(+) T cells and that another mechanism must be used by licensed DC to prime and activate CTL.     

A marked reduction in priming of cytotoxic CD8+ T cells mediated by stress-induced glucocorticoids involves multiple deficiencies in cross-presentation by dendritic cells

Protracted psychological stress elevates circulating glucocorticoids, which can suppress CD8(+) T cell-mediated immunity, but the mechanisms are incompletely understood. Dendritic cells (DCs), required for initiating CTL responses, are vulnerable to stress/corticosterone, which can contribute to diminished CTL responses. Cross-priming of CD8(+) T cells by DCs is required for initiating CTL responses against many intracellular pathogens that do not infect DCs. We examined the effects of stress/corticosterone on MHC class I (MHC I) cross-presentation and priming and show that stress/corticosterone-exposed DCs have a reduced ability to cross-present OVA and activate MHC I-OVA(257-264)-specific T cells. Using a murine model of psychological stress and OVA-loaded β(2)-microglobulin knockout "donor" cells that cannot present Ag, DCs from stressed mice induced markedly less Ag-specific CTL proliferation in a glucocorticoid receptor-dependent manner, and endogenous in vivo T cell cytolytic activity generated by cross-presented Ag was greatly diminished. These deficits in cross-presentation/priming were not due to altered Ag donation, Ag uptake (phagocytosis, receptor-mediated endocytosis, or fluid-phase uptake), or costimulatory molecule expression by DCs. However, proteasome activity in corticosterone-treated DCs or splenic DCs from stressed mice was partially suppressed, which limits formation of antigenic peptide-MHC I complexes. In addition, the lymphoid tissue-resident CD11b(-)CD24(+)CD8α(+) DC subset, which carries out cross-presentation/priming, was preferentially depleted in stressed mice. At the same time, CD11b(-)CD24(+)CD8α(-) DC precursors were increased, suggesting a block in development of CD8α(+) DCs. Therefore, glucocorticoid-induced changes in both the cellular composition of the immune system and intracellular protein degradation contribute to impaired CTL priming in stressed mice.     

Nonconventional CD8+ T cell responses to Listeria infection in mice lacking MHC class Ia and H2-M3

CD8(+) T cells restricted to MHC class Ib molecules other than H2-M3 have been shown to recognize bacterial Ags. However, the contribution of these T cells to immune responses against bacterial infection is not well defined. To investigate the immune potential of MHC class Ib-restricted CD8(+) T cells, we have generated mice that lack both MHC class Ia and H2-M3 molecules (K(b-/-)D (b-/-)M3(-/-)). The CD8(+) T cells present in K(b-/-)D (b-/-)M3(-/-) mice display an activated surface phenotype and are able to secrete IFN-γ rapidly upon anti-CD3 and anti-CD28 stimulation. Although the CD8(+) T cell population is reduced in K(b-/-)D (b-/-)M3(-/-) mice compared with that in K(b-/-)D (b-/-) mice, this population retains the capacity to expand significantly in response to primary infection with the bacteria Listeria monocytogenes. However, K(b-/-)D (b-/-)M3(-/-) CD8(+) T cells do not expand upon secondary infection, similar to what has been observed for H2-M3-restricted T cells. CD8(+) T cells isolated from Listeria-infected K(b-/-)D (b-/-)M3(-/-) mice exhibit cytotoxicity and secrete proinflammatory cytokines in response to Listeria-infected APCs. These T cells are protective against primary Listeria infection, as Listeria-infected K(b-/-)D (b-/-)M3(-/-) mice exhibit reduced bacterial burden compared with that of infected β(2)-microglobulin-deficient mice that lack MHC class Ib-restricted CD8(+) T cells altogether. In addition, adoptive transfer of Listeria-experienced K(b-/-)D (b-/-)M3(-/-) splenocytes protects recipient mice against subsequent Listeria infection in a CD8(+) T cell-dependent manner. These data demonstrate that other MHC class Ib-restricted CD8(+) T cells, in addition to H2-M3-restricted T cells, contribute to antilisterial immunity and may contribute to immune responses against other intracellular bacteria.     

Establishment and maintenance of long-term murine gammaherpesvirus 68 latency in B cells in the absence of CD40

Murine gammaherpesvirus 68 (gammaHV68), like Epstein-Barr virus (EBV), establishes a chronic infection in its host by gaining access to the memory B-cell reservoir, where it persists undetected by the host's immune system. EBV encodes a membrane protein, LMP1, that appears to function as a constitutively active CD40 receptor, and is hypothesized to play a central role in EBV-driven differentiation of infected naive B cells to a memory B-cell phenotype. However, it has recently been shown that there is a critical role for CD40-CD40L interaction in B-cell immortalization by EBV (K.-I. Imadome, M. Shirakata, N. Shimizu, S. Nonoyama, and Y. Yamanashi, Proc. Natl. Acad. Sci. USA 100:7836-7840, 2003), indicating that LMP1 does not adequately recapitulate all of the necessary functions of CD40. The role of CD40 receptor expression on B cells for the establishment and maintenance of gammaHV68 latency is unclear. Data previously obtained with a competition model, demonstrated that in the face of CD40-sufficient B cells, gammaHV68 latency in CD40-deficient B cells waned over time in chimeric mice (I.-J. Kim, E. Flano, D. L. Woodland, F. E. Lund, T. D. Randall, and M. A. Blackman, J. Immunol. 171:886-892, 2003). To further investigate the role of CD40 in gammaHV68 latency in vivo, we have characterized the infection of CD40 knockout (CD40(-/-)) mice. Here we report that, consistent with previous observations, gammaHV68 efficiently established a latent infection in B cells of CD40(-/-) mice. Notably, unlike the infection of normal C57BL/6 mice, significant ex vivo reactivation from splenocytes harvested from infected CD40(-/-) mice 42 days postinfection was observed. In addition, in contrast to gammaHV68 infection of C57BL/6 mice, the frequency of infected naive B cells remained fairly stable over a 3-month period postinfection. Furthermore, a slightly higher frequency of gammaHV68 infection was observed in immunoglobulin D (IgD)-negative B cells, which was stably maintained over a period of 3 months postinfection. The presence of virus in IgD-negative B cells indicates that gammaHV68 may either directly infect memory B cells present in CD40(-/-) mice or be capable of driving differentiation of naive CD40(-/-) B cells. A possible explanation for the apparent discrepancy between the failure of gammaHV68 latency to be maintained in CD40-deficient B cells in the presence of CD40-sufficient B cells and the stable maintenance of gammaHV68 B-cell latency in CD40(-/-) mice came from examining virus replication in the lungs of infected CD40(-/-) mice, where we observed significantly higher levels of virus replication at late times postinfection compared to those in infected C57BL/6 mice. Taken together, these findings are consistent with a model in which chronic virus infection of CD40(-/-) mice is maintained through virus reactivation in the lungs and reseeding of latency reservoirs.     

Modulation of CD8+ T cell response to antigen by the levels of self MHC class I

The response of H-Y-specific TCR-transgenic CD8(+) T cells to Ag is characterized by poor proliferation, cytolytic activity, and IFN-gamma secretion. IFN-gamma secretion, but not cytotoxic function, can be rescued by the B7.1 molecule, suggesting that costimulation can selectively enhance some, but not all, effector CD8(+) T cell responses. Although the H-Y epitope binds H-2D(b) relatively less well than some other epitopes, it can induce potent CTL responses in nontransgenic mice, suggesting that the observed poor responsiveness of transgenic CD8(+) T cells cannot be ascribed to the epitope itself. Previously reported reactivity of this TCR to H-2A(b) is also not the cause of the poor responsiveness of the H-Y-specific CD8(+) T cells, as H-Y-specific CD8(+) T cells obtained from genetic backgrounds lacking H-2A(b) also responded poorly. Rather, reducing the levels of H-2(b) class I molecules by breeding the mice to (C57BL/6 x B10.D2)F(1) or TAP1(+/-) backgrounds partially restored cytotoxic activity and enhanced proliferative responses. These findings demonstrate that the self MHC class I gene dosage may regulate the extent of CD8(+) T cell responsiveness to Ag.     

An MHC class Ib-restricted CD8+ T cell response to lymphocytic choriomeningitis virus

Conventional MHC class Ia-restricted CD8(+) T cells play a dominant role in the host response to virus infections, but recent studies indicate that T cells with specificity for nonclassical MHC class Ib molecules may also participate in host defense. To investigate the potential role of class Ib molecules in anti-viral immune responses, K(b-/-)D(b-/-)CIITA(-/-) mice lacking expression of MHC class Ia and class II molecules were infected with lymphocytic choriomeningitis virus (LCMV). These animals have a large class Ib-selected CD8(+) T cell population and they were observed to mediate partial (but incomplete) virus clearance during acute LCMV infection as compared with K(b-/-)D(b-/-)β(2)-microglobulin(-/-) mice that lack expression of both MHC class Ia and class Ib molecules. Infection was associated with expansion of splenic CD8(+) T cells and induction of granzyme B and IFN-γ effector molecules in CD8(+) T cells. Partial virus clearance was dependent on CD8(+) cells. In vitro T cell restimulation assays demonstrated induction of a population of β(2)-microglobulin-dependent, MHC class Ib-restricted CD8(+) T cells with specificity for viral Ags and yet to be defined nonclassical MHC molecules. MHC class Ib-restricted CD8(+) T cell responses were also observed after infection of K(b-/-)D(b-/-)mice despite the low number of CD8(+) T cells in these animals. Long-term infection studies demonstrated chronic infection and gradual depletion of CD8(+) T cells in K(b-/-)D(b-/-)CIITA(-/-) mice, demonstrating that class Ia molecules are required for viral clearance. These findings demonstrate that class Ib-restricted CD8(+) T cells have the potential to participate in the host immune response to LCMV.     

Contribution of antigen-primed CD8+ T cells to the development of airway hyperresponsiveness and inflammation is associated with IL-13

The role of Th2/CD4 T cells, which secrete IL-4, IL-5, and IL-13, in allergic disease is well established; however, the role of CD8(+) T cells (allergen-induced airway hyperresponsiveness (AHR) and inflammation) is less clear. This study was conducted to define the role of Ag-primed CD8(+) T cells in the development of these allergen-induced responses. CD8-deficient (CD8(-/-)) mice and wild-type mice were sensitized to OVA by i.p. injection and then challenged with OVA via the airways. Compared with wild-type mice, CD8(-/-) mice developed significantly lower airway responsiveness to inhaled methacholine and lung eosinophilia, and exhibited decreased IL-13 production both in vivo, in the bronchoalveolar lavage (BAL) fluid, and in vitro, following Ag stimulation of peribronchial lymph node (PBLN) cells in culture. Reconstitution of sensitized and challenged CD8(-/-) mice with allergen-sensitized CD8(+) T cells fully restored the development of AHR, BAL eosinophilia, and IL-13 levels in BAL and in culture supernatants from PBLN cells. In contrast, transfer of naive CD8(+) T cells or allergen-sensitized CD8(+) T cells from IL-13-deficient donor mice failed to do so. Intracellular cytokine staining of lung as well as PBLN T cells revealed that CD8(+) T cells were a source of IL-13. These data suggest that Ag-primed CD8(+) T cells are required for the full development of AHR and airway inflammation, which appears to be associated with IL-13 production from these primed T cells.     

Novel role of CD8(+) T cells and major histocompatibility complex class I genes in the generation of protective CD4(+) Th1 responses during retrovirus infection in mice

CD4(+) Th1 responses to virus infections are often necessary for the development and maintenance of virus-specific CD8(+) T-cell responses. However, in the present study with Friend murine retrovirus (FV), the reverse was also found to be true. In the absence of a responder H-2(b) allele at major histocompatibility complex (MHC) class II loci, a single H-2D(b) MHC class I allele was sufficient for the development of a CD4(+) Th1 response to FV. This effect of H-2D(b) on CD4(+) T-cell responses was dependent on CD8(+) T cells, as demonstrated by depletion studies. A direct effect of CD8(+) T-cell help in the development of CD4(+) Th1 responses to FV was also shown in vaccine studies. Vaccination of nonresponder H-2(a/a) mice induced FV-specific responses of H-2D(d)-restricted CD8(+) cytotoxic T lymphocytes (CTL). Adoptive transfer of vaccine-primed CD8(+) T cells to naive H-2(a/a) mice prior to infection resulted in the generation of FV-specific CD4(+) Th1 responses. This novel helper effect of CD8(+) T cells could be an important mechanism in the development of CD4(+) Th1 responses following vaccinations that induce CD8(+) CTL responses. The ability of MHC class I genes to facilitate CD4(+) Th1 development could also be considerable evolutionary advantage by allowing a wider variety of MHC genotypes to generate protective immune responses against intracellular pathogens.     

Cutting edge: selective impairment of CD8+ T cell function in mice lacking the TNF superfamily member LIGHT

Interactions of LIGHT and its receptors, herpesvirus entry mediator on T cells and lymphotoxin beta receptor on stromal cells, are implicated in the regulation of lymphoid organogenesis, costimulation of T cells, and activation of dendritic cells. In this work we report that LIGHT-deficient mice had normal lymphoid organs with T cells and APCs that normally responded to Ag stimulation and normally stimulated T cells. Although the number of Vbeta8(+) T cells in naive LIGHT(+/+) and LIGHT(-/-) mice was identical, Vbeta8(+)CD8(+) T cell proliferation in response to staphylococcal enterotoxin B was significantly lower in LIGHT(-/-) mice. Consistently, induction and cytokine secretion of CD8(+) CTL to MHC class I-restricted peptide was also reduced in LIGHT(-/-) mice. However, the proliferative response of Vbeta8(+)CD4(+) T cells to staphylococcal enterotoxin B was comparable in LIGHT(-/-) and LIGHT(+/+) mice. Our results suggest that LIGHT is required for activation of normal CD8(+) T cells but not CD4(+) T cells.     

Effective control of chronic gamma-herpesvirus infection by unconventional MHC Class Ia-independent CD8 T cells

Control of virus infection is mediated in part by major histocompatibility complex (MHC) Class Ia presentation of viral peptides to conventional CD8 T cells. Although important, the absolute requirement for MHC Class Ia-dependent CD8 T cells for control of chronic virus infection has not been formally demonstrated. We show here that mice lacking MHC Class Ia molecules (K(b-/-)xD(b-/-) mice) effectively control chronic gamma-herpesvirus 68 (gammaHV68) infection via a robust expansion of beta2-microglobulin (beta2-m)-dependent, but CD1d-independent, unconventional CD8 T cells. These unconventional CD8 T cells expressed: (1) CD8alphabeta and CD3, (2) cell surface molecules associated with conventional effector/memory CD8 T cells, (3) TCRalphabeta with a significant Vbeta4, Vbeta3, and Vbeta10 bias, and (4) the key effector cytokine interferon-gamma (IFNgamma). Unconventional CD8 T cells utilized a diverse TCR repertoire, and CDR3 analysis suggests that some of that repertoire may be utilized even in the presence of conventional CD8 T cells. This is the first demonstration to our knowledge that beta2-m-dependent, but Class Ia-independent, unconventional CD8 T cells can efficiently control chronic virus infection, implicating a role for beta2-n-dependent non-classical MHC molecules in control of chronic viral infection. We speculate that similar unconventional CD8 T cells may be able to control of other chronic viral infections, especially when viruses evade immunity by inhibiting generation of Class Ia-restricted T cells.     

The murine gammaherpesvirus 68 v-cyclin gene is an oncogene that promotes cell cycle progression in primary lymphocytes

Several gammaherpesviruses contain open reading frames encoding proteins homologous to mammalian D-type cyclins. In this study, we analyzed the expression and function of the murine gammaherpesvirus 68 (gammaHV68) viral cyclin (v-cyclin). The gammaHV68 v-cyclin gene was expressed in lytically infected fibroblasts as a leaky-late mRNA of approximately 0.9 kb encoding a protein of approximately 25 kDa. To evaluate the effect of the gammaHV68 v-cyclin on cell cycle progression in primary lymphocytes and to determine if the gammaHV68 v-cyclin gene is an oncogene, we generated transgenic mice by using the lck proximal promoter to express the gammaHV68 v-cyclin in early T cells. Expression of the gammaHV68 v-cyclin significantly increased the number of thymocytes in cell culture, as determined by measuring both DNA content and incorporation of 5-bromo-2-deoxyuridine following in vivo pulse-labeling. Expression of the gammaHV68 v-cyclin interfered with normal thymocyte maturation, as shown by increased numbers of CD4(+) CD8(+) double-positive thymocytes and decreased numbers of CD4(+) or CD8(+) single-positive and T-cell-receptor-bright thymocytes and splenocytes in transgenic mice. Despite increased numbers of cycling thymocytes, gammaHV68-v-cyclin-transgenic mice did not have proportionately increased thymocyte numbers, and staining by terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling demonstrated increased apoptosis in the thymi of v-cyclin-transgenic mice. Fifteen of 38 gammaHV68-v-cyclin-transgenic mice developed high-grade lymphoblastic lymphoma between 3 and 12 months of age. We conclude that (i) the gammaHV68 v-cyclin is expressed as a leaky-late gene in lytically infected cells, (ii) expression of the gammaHV68 v-cyclin in thymocytes promotes cell cycle progression and inhibits normal T-cell differentiation, and (iii) the gammaHV68 v-cyclin gene is an oncogene.     

Induction of in vivo functional Db-restricted cytolytic T cell activity against a putative phosphate transport receptor of Mycobacterium tuberculosis

Using plasmid vaccination with DNA encoding the putative phosphate transport receptor PstS-3 from Mycobacterium tuberculosis and 36 overlapping 20-mer peptides spanning the entire PstS-3 sequence, we determined the immunodominant Th1-type CD4(+) T cell epitopes in C57BL/10 mice, as measured by spleen cell IL-2 and IFN-gamma production. Furthermore, a potent IFN-gamma-inducing, D(b)-restricted CD8(+) epitope was identified using MHC class I mutant B6.C-H-2(bm13) mice and intracellular IFN-gamma and whole blood CD8(+) T cell tetramer staining. Using adoptive transfer of CFSE-labeled, peptide-pulsed syngeneic spleen cells from naive animals into DNA vaccinated or M. tuberculosis-infected recipients, we demonstrated a functional in vivo CTL activity against this D(b)-restricted PstS-3 epitope. IFN-gamma ELISPOT responses to this epitope were also detected in tuberculosis-infected mice. The CD4(+) and CD8(+) T cell epitopes defined for PstS-3 were completely specific and not recognized in mice vaccinated with either PstS-1 or PstS-2 DNA. The H-2 haplotype exerted a strong influence on immune reactivity to the PstS-3 Ag, and mice of the H-2(b, p, and f) haplotype produced significant Ab and Th1-type cytokine levels, whereas mice of H-2(d, k, r, s, and q) haplotype were completely unreactive. Low responsiveness against PstS-3 in MHC class II mutant B6.C-H-2(bm12) mice could be overcome by DNA vaccination. IFN-gamma-producing CD8(+) T cells could also be detected against the D(b)-restricted epitope in H-2(p) haplotype mice. These results highlight the potential of DNA vaccination for the induction and characterization of CD4(+) and particularly CD8(+) T cell responses against mycobacterial Ags.     

Identification of major epitopes of Mycobacterium tuberculosis AG85B that are recognized by HLA-A*0201-restricted CD8+ T cells in HLA-transgenic mice and humans

CD8(+) T cells are thought to play an important role in protective immunity to tuberculosis. Although several nonprotein ligands have been identified for CD1-restricted CD8(+) CTLs, epitopes for classical MHC class I-restricted CD8(+) T cells, which most likely represent a majority among CD8(+) T cells, have remained ill defined. HLA-A*0201 is one of the most prevalent class I alleles, with a frequency of over 30% in most populations. HLA-A2/K(b) transgenic mice were shown to provide a powerful model for studying induction of HLA-A*0201-restricted immune responses in vivo. The Ag85 complex, a major component of secreted Mycobacterium tuberculosis proteins, induces strong CD4(+) T cell responses in M. tuberculosis-infected individuals, and protection against tuberculosis in Ag85-DNA-immunized animals. In this study, we demonstrate the presence of HLA class I-restricted, CD8(+) T cells against Ag85B of M. tuberculosis in HLA-A2/K(b) transgenic mice and HLA-A*0201(+) humans. Moreover, two immunodominant Ag85 peptide epitopes for HLA-A*0201-restricted, M. tuberculosis-reactive CD8(+) CTLs were identified. These CD8(+) T cells produced IFN-gamma and TNF-alpha and recognized Ag-pulsed or bacillus Calmette-Guérin-infected, HLA-A*0201-positive, but not HLA-A*0201-negative or uninfected human macrophages. This CTL-mediated killing was blocked by anti-CD8 or anti-HLA class I mAb. Using fluorescent peptide/HLA-A*0201 tetramers, Ag85-specific CD8(+) T cells could be visualized in bacillus Calmette-Guérin-responsive, HLA-A*0201(+) individuals. Collectively, our results demonstrate the presence of HLA class I-restricted CD8(+) CTL against a major Ag of M. tuberculosis and identify Ag85B epitopes that are strongly recognized by HLA-A*0201-restricted CD8(+) T cells in humans and mice. These epitopes thus represent potential subunit components for the design of vaccines against tuberculosis.