The effect of an anti-HLA-B27 immune response on CTL recognition of Chlamydia.

The interplay between triggering bacteria and HLA-B27 in the pathogenesis of the spondyloarthropathies remains one of the most active areas of investigation in the rheumatic diseases. This has proved difficult to study systematically in the clinical setting, and in this study we utilized a rat model to address the influence that B27-related immunity may have on the process of generating anti-Chlamydia immunity. When splenocytes from HLA-B27 DNA-immunized Lewis (LEW) animals received restimulation in vitro with Chlamydia-treated cells from B27-transgenic LEW rats, we observed that in addition to the expected CTL recognition of HLA-B27, there was also anti-Chlamydia CTL killing of Chlamydia-sensitized syngeneic fibroblast targets. This was not seen when responding cells in vitro were naive LEW splenocytes. To confirm the existence of CTLs recognizing both HLA-B27 and Chlamydia, LEW rats were immunized with B27-transgenic LEW cells, instead of the B27 DNA construct. Splenocytes from the immune rats were restimulated in vitro with Chlamydia-treated B27-transgenic LEW cells. In this instance, the CTLs retained the allele-specific recognition of HLA-B27, as well as recognition of Chlamydia-sensitized syngeneic fibroblasts. Thus, if there is prior expansion of an immune response against HLA-B27, then the resulting splenocytes demonstrate a reduced threshold for generating a primary anti-Chlamydia CTL response. These studies implicate a dynamic interrelationship between recognition of HLA-B27 and Chlamydia trachomatis. The results may have implications for deciphering the cellular basis of Chlamydia-induced reactive arthritis.     

Sharing of an HLA-B27-restricted H-Y antigen between rat and mouse

The purpose of this work was twofold: 1 to learn whether rats transgenic for HLA-B27 and the human ₂-microglobulin gene HB2M can mount B27-restricted cytolytic T lymphocyte (CTL) responses to the male H-Y antigen, and 2 to learn whether such CTLs would recognize both rat and mouse H-Y in the context of HLA-B27. Female rats of the B27/HB2M transgenic line 21-4L were primed in vivo with cells from males of the same line. CTL effectors were generated from lymph node cells of these females following culture with irradiated antigen-presenting cells from either male 21-4L rats or male mice of the B27/HB2M transgenic 56-3 line. The CTLs showed male-specific, B27-specific lysis of both rat and mouse targets. Lysis of B27 targets was inhibitable by monoclonal antibodies specific for B27 or rat CD8. Specific lysis of male B27 rat and mouse targets was inhibitable equally by either rat or mouse male B27 cold targets, but not significantly by female or nontransgenic cold targets. The B27-restricted CTLs neither recognized nor were inhibited by B27⁺ or B27^- male or female human targets. These results demonstrate that CD8⁺, B27-restricted, anti-H-Y CTLs recognize and evolutionarily conserved H-Y peptide antigen in both rats and mice. In addition, they establish the transgenic rat as a model system for examining the T-cell response to antigen presented by class I HLA molecules. Correspondence to: J. D. Taurog.     

Vaccination with mRNAs encoding tumor-associated antigens and granulocyte-macrophage colony-stimulating factor efficiently primes CTL responses, but is insufficient to overcome tolerance to a model tumor/self antigen

Immunization of mice with dendritic cells transfected ex vivo with tumor-associated antigen (TAA)-encoding mRNA primes cytotoxic T lymphocytes (CTL) that mediate tumor rejection. Here we investigated whether direct injection of TAA mRNA, encapsulated in cationic liposomes, could function similarly as cancer immunotherapy. Intradermal and intravenous injection of ovalbumin (OVA) mRNA generated specific CTL activity and inhibited the growth of OVA-expressing tumors. Vaccination studies with DNA have demonstrated that co-administration of antigen (Ag)- and cytokine-encoding plasmids potentiate the T cell response; in analogous fashion, the inclusion of granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA enhanced OVA-specific cytotoxicity. The ability of this GM-CSF-augmented mRNA vaccine to treat an established spontaneous tumor was evaluated in the Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) mouse, using the SV40 large T Ag (TAg) as a model tumor/self Ag. Repeated vaccination elicited vigorous TAg-specific CTL activity in nontransgenic mice, but tumor-bearing TRAMP mice remained tolerant. Adoptive transfer of naïve splenocytes into TRAMP mice prior to the first vaccination restored TAg reactivity, and slowed tumor progression. The data from this study suggests that vaccination with TAA mRNA is a simple and effective means of priming antitumor CTL, and that immunogenicity of the vaccine can be augmented by co-delivery of GM-CSF mRNA. Nonetheless, limitations of such vaccines in overcoming tolerance to tumor/self Ag may mandate prior or simultaneous reconstitution of the autoreactive T cell repertoire for this form of immunization to be effective.     

Induction in vitro of primary cytotoxic T-lymphocyte responses with DNA encoding herpes simplex virus proteins.

Vaccines which successfully protect against virus infections usually need to induce a broadly reactive immune response which includes the induction of cytotoxic T lymphocytes (CTL). In this study, we have used a convenient in vitro approach to investigate if plasmid DNAs encoding proteins of herpes simplex virus (HSV) are capable of inducing primary CD8+ CTL. Dendritic cells or macrophages were transfected with either plasmid DNA encoding glycoprotein B or DNA encoding the immediate-early protein ICP27. These antigen-presenting cells (APC) were then used to stimulate enriched populations of naive T cells in microcultures for 5 days in vitro. Antigen-specific CD8+ CTL which reacted both with specific protein-expressing targets and with syngeneic targets infected with HSV could be demonstrated. Dendritic cells, as APC, generated the maximal responses, but such cells needed to be transfected with DNA in the presence of a cationic lipid. However, macrophages could act as APC when they were exposed to purified DNA. HSV-primed splenocytes were also shown to generate specific CTL responses when they were stimulated with purified DNA encoding ICP27. The novel approach described in this paper promises to be extremely useful, since defining immunogenicity profiles and identifying epitopes on viral proteins should be easier and more convenient when working with DNA and investigating variables in vitro. This is particularly the case with complex viruses such as HSV, most of whose encoded proteins have yet to be isolated in sufficient quantity or purity to perform in vivo immunological studies.     

IFN-alpha beta promote priming of antigen-specific CD8+ and CD4+ T lymphocytes by immunostimulatory DNA-based vaccines

Immunostimulatory sequence (ISS) DNA containing unmethylated CpG dinucleotides stimulate NK and APC to secrete proinflammatory cytokines, including IFN-alphabeta and -gamma, TNF-alpha, and IL-6 and -12, and to express costimulatory surface molecules such as CD40, B7-1, and B7-2. Although ISS DNA has little direct effect on T cells by these criteria, immunization of wild-type mice with ISS DNA and OVA results in Ag-specific CTL and Th1-type T helper activity. This investigation examines the mechanisms by which ISS DNA primes CD8(+) and CD4(+) lymphocyte activities. In this report we demonstrate that ISS DNA regulates the expression of costimulatory molecules and TAP via a novel autocrine or paracrine IFN-alphabeta pathway. Coordinated regulation of B7 costimulation and TAP-dependent cross-presentation results in priming of Ag-specific CD8(+) CTL, whereas CD40, B7, and IL-12 costimulation is required for priming of CD4(+) Th cells by ISS-based vaccines.     

Anti-tumor immunity against CT26 colon tumor in mice immunized with plasmid DNA encoding beta-galactosidase fused to an envelope protein of endogenous retrovirus

Endogenous retroviral gene products have been recognized as being expressed in human cancerous tissues. However, these products have not been shown to be antigenic targets for T-cells, possibly due to immune tolerance. Since carcinogen-induced colon tumor CT26 expresses an envelope protein, gp70, of an endogenous ecotropic murine leukemia virus that is comparable to human tumor-associated antigens, we examined whether a DNA vaccine containing the gp70 gene induces protective immunity against CT26 cells. Injection of mice with plasmid DNA (pDNA) encoding gp70 alone failed to induce anti-gp70 antibody (Ab) or anti-CT26 cytotoxic T lymphocyte (CTL) responses. However, immunization with pDNA encoding the beta-galactosidase (beta-gal)/gp70 fusion protein induced anti-gp70 Ab and anti-CT26 CTL responses and conferred protective immunity against CT26 cells. These results indicate that beta-gal acts as an immunogenic carrier protein that helps in the induction of immune responses against the poorly immunogenic gp70. Considering these results, it is possible that potential tolerance to the endogenous retroviral gene products expressed by human tumors may be overcome by DNA vaccines that contain an endogenous retroviral gene fused to genes encoding immunogenic carrier proteins.     

A decaepitope polypeptide primes for multiple CD8+ IFN-gamma and Th lymphocyte responses: evaluation of multiepitope polypeptides as a mode for vaccine delivery

Proteins are generally regarded as ineffective immunogens for CTL responses. We synthesized a 100-mer decaepitope polypeptide and tested its capacity to induce multiple CD8(+) IFN-gamma and Th lymphocyte (HTL) responses in HLA transgenic mice. Following a single immunization in the absence of adjuvant, significant IFN-gamma in vitro recall responses were detected for all epitopes included in the construct (six A2.1-, three A11-restricted CTL epitopes, and one universal HTL epitope). Immunization with truncated forms of the decaepitope polypeptide was used to demonstrate that optimal immunogenicity was associated with a size of at least 30-40 residues (3-4 epitopes). Solubility analyses of the truncated constructs were used to identify a correlation between immunogenicity for IFN-gamma responses and the propensity of these constructs to form particulate aggregates. Although the decaepitope polypeptide and a pool of epitopes emulsified in IFA elicited similar levels of CD8(+) responses using fresh splenocytes, we found that the decaepitope polypeptide more effectively primed for in vitro recall CD8(+) T cell responses. Finally, immunogenicity comparisons were also made between the decaepitope polypeptide and a corresponding gene encoding the same polypeptide delivered by naked DNA immunization. Although naked DNA immunization induced somewhat greater direct ex vivo and in vitro recall responses 2 wk after a single immunization, only the polypeptide induced significant in vitro recall responses 6 wk following the priming immunization. These studies support further evaluation of multiepitope polypeptide vaccines for induction of CD8(+) IFN-gamma and HTL responses.     

Overcoming T cell tolerance to the hepatitis B virus surface antigen in hepatitis B virus-transgenic mice

The sequence of the hepatitis B virus (HBV) major envelope (Env) protein (ayw subtype) was scanned for the presence of H-2(d,b) motifs. Following binding and immunogenicity testing, two new H-2(d)-restricted epitopes (Env.362 and Env.364) were identified. These epitopes induced CTLs capable of recognizing naturally processed HBV-Env, but were apparently generated with lower efficiency than the previously defined dominant Env.28 epitope. Next, HBV-transgenic mice that express all of the HBV proteins and produce fully infectious particles were immunized with a mixture of lipopeptides encompassing the Env.28, Env.362, and Env.364 epitopes. Significant CTL responses were obtained, but they had no effect on viral replication in the liver, nor did they induce an inflammatory liver disease. However, in adoptive transfer experiments, CTL lines generated from the HBV-transgenic mice following immunization were able to inhibit viral replication in vivo without causing hepatitis. This is in contrast to CTL lines derived from nontransgenic mice that displayed both antiviral and cytopathic effects, presumably because they displayed higher avidity for the viral epitopes than the transgenic CTLs. These results suggest that T cell tolerance to HBV can be broken with appropriate immunization but the magnitude and characteristics of the resultant T cell response are significantly different from the response in HBV-naive individuals since their antiviral potential is stronger than their cytotoxic potential. This has obvious implications for immunotherapy of chronic HBV infection.     

B subunit of Shiga toxin-based vaccines synergize with alpha-galactosylceramide to break tolerance against self antigen and elicit antiviral immunity

The nontoxic B subunit of Shiga toxin (STxB) targets in vivo Ag to dendritic cells that preferentially express the glycolipid Gb(3) receptor. After administration of STxB chemically coupled to OVA (STxB-OVA) or E7, a polypeptide derived from HPV, in mice, we showed that the addition of alpha-galactosylceramide (alpha-GalCer) resulted in a dramatic improvement of the STxB Ag delivery system, as reflected by the more powerful and longer lasting CD8(+) T cell response observed even at very low dose of immunogen (50 ng). This synergy was not found with other adjuvants (CpG, poly(I:C), IFN-alpha) also known to promote dendritic cell maturation. With respect to the possible mechanism explaining this synergy, mice immunized with alpha-GalCer presented in vivo the OVA(257-264)/K(b) complex more significantly and for longer period than mice vaccinated with STxB alone or mixed with other adjuvants. To test whether this vaccine could break tolerance against self Ag, OVA transgenic mice were immunized with STxB-OVA alone or mixed with alpha-GalCer. Although no CTL induction was observed after immunization of OVA transgenic mice with STxB-OVA, tetramer assay clearly detected specific anti-OVA CD8(+) T cells in 8 of 11 mice immunized with STxB-OVA combined with alpha-GalCer. In addition, vaccination with STxB-OVA and alpha-GalCer conferred strong protection against a challenge with vaccinia virus encoding OVA with virus titers in the ovaries reduced by 5 log compared with nonimmunized mice. STxB combined with alpha-GalCer therefore appears as a promising vaccine strategy to more successfully establish protective CD8(+) T cell memory against intracellular pathogens and tumors.     

Cross-priming as a predominant mechanism for inducing CD8(+) T cell responses in gene gun DNA immunization.

DNA immunization induces CD8(+) CTL responses by bone marrow-derived APCs, which are directly transfected with a plasmid DNA and/or acquire Ags from DNA-transfected non-APCs. To investigate the relative contribution of DNA-transfected APCs vs non-APCs to the initiation of CD8(+) T cell responses, we used tissue-specific promoter-directed gene expression and adoptive transfer systems in gene gun DNA immunization. In this study, we demonstrated that non-APC-specific gene expressions induced significant CD8(+) CTL and IFN-gamma-producing cells and Ab responses, whereas APC-specific gene expressions led to moderate CTL and IFN-gamma-producers, but no Ab responses. Interestingly, mice immunized with a non-APC-specific plasmid induced more rapid, vigorous, and prolonged proliferation of adoptively transferred Ag-specific CD8(+) T cells than APC-specific plasmid-immunized mice. In addition, the in vivo proliferative responses elicited by a non-APC-specific plasmid administration were dependent on TAP, but were independent of CD4(+) T cell help. Collectively, our results suggest that cross-priming, in which Ags expressed in non-APCs are taken up, processed, and presented by APCs, plays an important role in the initiation, magnitude, and maintenance of CD8(+) T cell responses in gene gun DNA immunization.     

Tolerance induction by transcutaneous immunization through ultraviolet-irradiated skin is transferable through CD4+CD25+ T regulatory cells and is dependent on host-derived IL-10

UV radiation of the skin impairs immune responses to haptens and to tumor Ags. Transcutaneous immunization (TCI) is an effective method of inducing immune responses to protein and peptide Ag. We explore the effect of UV irradiation on TCI. The generation of Ag-specific CTL to OVA protein, but not class I MHC-restricted OVA peptide, is inhibited by TCI through UV-irradiated skin. Consequently, the induction of protein contact hypersensitivity and in vivo Ag-specific CTL activity following OVA protein immunization is prevented. Application of haptens to UV-exposed skin induces hapten-specific tolerance. We demonstrate that application of protein or class II MHC-restricted OVA peptide to UV-irradiated skin induces transferable Ag-specific tolerance. This tolerance is mediated by CD4(+)CD25(+) T regulatory (T(reg)) cells. These Ag-specific T(reg) cells inhibit the priming of CTL following protein immunization in the presence of CpG adjuvant. IL-10 deficiency is known to prevent hapten-specific tolerance induction. In this study, we demonstrate, using IL-10-deficient mice and adoptive T cell transfer, that IL-10 is required for the direct inhibition of CTL priming following immunization through UV-irradiated skin. However, IL-10 is not required for the induction of T(reg) cells through UV-irradiated skin as IL-10-deficient T(reg) cells are able to mediate tolerance. Rather, host-derived IL-10 is required for the function of UV-generated T(reg) cells. These experiments indicate that protein and peptide TCI through UV-irradiated skin may be used to induce robust Ag-specific tolerance to neo-Ags and that UV-induced T(reg) cells mediate their effects in part through the modulation of IL-10.     

Enhanced immune response to the melanoma antigen gp100 using recombinant adenovirus-transduced dendritic cells

Glycoprotein 100 (gp100) is one of a series of well-characterized human melanoma-associated antigens expressed by most melanoma cells. Immunization of C57BL/6 mice with an adenovirus (Ad) vector encoding human gp100 (Adhgp100) has been shown to induce limited protective immunity against challenge with murine melanoma B16 cells. In the current study we determined whether gp100-specific immunity can be enhanced using bone-marrow-derived dendritic cells (DCs) transduced with Adhgp100 ex vivo. Subcutaneous injection of Adhgp100-infected DCs resulted in potent T-cell-mediated protective immunity and a greater than 80% reduction of established tumors when administered to B16 tumor-bearing hosts. Compared to direct injection of Adhgp100 vector alone, immunization with Adhgp100-infected DCs induced markedly greater antitumor activity. In vitro CTL analysis demonstrated that DC-Adhgp100 immunization activated both CD4(+) and CD8(+) CTLs, while no lytic activity was generated by vaccination with Adhgp100 alone. In vivo depletion of CD4(+) T cells, but not CD8(+) T cells, completely abrogated CTL activity, suggesting that Adhgp100-transduced DCs result in activation of both CD4(+) and CD8(+) CTLs via a CD4(+)-dependent mechanism. We speculate that this improved efficacy of Adhgp100-transduced DCs compared to direct immunization with Adhgp100 may be the result of direct DC-mediated CD4(+) T cell activation. These results emphasize the importance of CD4(+) T cells in the development of therapeutic antigen-specific cancer vaccines.     

Protective cellular immunity: cytotoxic T-lymphocyte responses against dominant and recessive epitopes of influenza virus nucleoprotein induced by DNA immunization.

DNA immunization offers a novel means to induce cellular immunity in a population with a heterogeneous genetic background. An immunorecessive cytotoxic T-lymphocyte (CTL) epitope in influenza virus nucleoprotein (NP), residues 218 to 226, was identified when mice were immunized with a plasmid DNA encoding a full-length mutant NP in which the anchor residues for the immunodominant NP147-155 epitope were altered. Mice immunized with wild-type or mutant NP DNA were protected from lethal cross-strain virus challenge, and the protection could be adoptively transferred by immune splenocytes, indicating the role of cell-mediated immunity in the protection. DNA immunization is capable of eliciting protective cellular immunity against both immunodominant and immunorecessive CTL epitopes in the hierarchy seen with virus infection.     

Regulatory CD8+ T cells control neonatal tolerance to a Th2-mediated autoimmunity

Exposure of newborn animals to a foreign Ag may result in immunological tolerance to that specific Ag, a phenomenon called neonatal tolerance. We have previously reported that neonatal administration to Brown-Norway rats of mercury, a heavy metal toxicant, induces a dominant tolerance, specific for the chemical otherwise responsible for Th2 cell-mediated autoimmune responses in this susceptible strain of rats. Neonatal exposure to Ags can prime immunity, rather than inactivate or delete responses, and sustain regulatory functions effective against autoreactive T cells. Here, we address whether such a tolerant response is due to the generation of regulatory cells. The results suggest that the CD8(+) T cell subset is involved in neonatal tolerance to mercuric salt-induced Th2 autoimmune disease. Thus, we demonstrate that in vivo CD8 depletion breaks tolerance following mercury recall in animals under a neonatal tolerance protocol. Furthermore, adoptive cotransfer of splenocytes from naive and tolerant rats as well as transfer of CD8(+) T cells from tolerant animals prevent naive syngeneic rats from developing pathologic Th2 immune responses. These observations indicate that CD8(+) T cells are endowed with regulatory functions in neonatal tolerance and mediate active suppression. Moreover, neonatal tolerance induced the expansion of CD8(+)CD45RC(high) T cells and the emergence of a high percentage of IFN-gamma-synthesizing CD8(+) T cells, which probably reflects the implication of regulatory Tc1 cells. Thus, in vivo induction of neonatal tolerance suppresses Th2 autoimmune responses via generation of a CD8(+) cell-mediated regulatory response.     

Development of infectious tolerance after donor-specific transfusion and rat heart transplantation

Regulatory cells developed after donor-specific transfusion (DST)-induced acceptance of a LEW heart transplanted into a DA rat. Both DST and the cardiac transplant were necessary to generate the regulatory cells. This donor-specific tolerance can then be transferred into a new DA recipient by adoptive transfer of lymphocytes from the DST-treated long term survivor (LTS) in a dose-dependent manner. The effectiveness of tolerance did not diminish over five generations of adoptive transfer, thus supporting its infectious nature. Although both spleen and lymph node cells were equally effective, graft-infiltrating lymphocytes were more potent. A high level of indirect CTL activity and MLC proliferation were observed in lymphocytes from LTS. In vivo tracking of adoptively transferred CFSE-labeled splenocytes from LTS showed equivalent FACS proliferation and a higher percentage of graft-infiltrating lymphocytes 7 days after heart transplantation, compared with adoptively transferred naive splenocytes. Adoptive transfer of CD8(+)-depleted LTS splenocytes resulted in 100% subsequent LEW allograft acceptance; whereas CD4(+) depletion decreased acceptance to 40%, and depletion of both CD4 and CD8 resulted in 0% acceptance. When positively selected CD4(+) or CD8(+) cells were adoptively transferred, 100% or 62.5% of LEW cardiac allografts survived, respectively. In conclusion, DST alone promotes a donor-specific infectious tolerance of a heart graft that can be adoptively transferred to subsequent naive allograft recipients despite the undiminished in vitro immunological response to donor Ag. Although both CD4(+) and CD8(+) populations are responsible for the regulatory mechanism in DST-induced tolerance, the CD4(+) population appears to dominate.     

A novel functional CTL avidity/activity compartmentalization to the site of mucosal immunization contributes to protection of macaques against simian/human immunodeficiency viral depletion of mucosal CD4+ T cells

The presence of high-avidity CTLs in the right compartment can greatly affect clearance of a virus infection (for example, AIDS viral infection of and dissemination from mucosa). Comparing mucosal vs systemic immunization, we observed a novel compartmentalization of CTL avidity and proportion of functionally active Ag-specific CD8(+) T cells to tissues proximal to sites of immunization. Whereas both s.c. and intrarectal routes of immunization induced tetramer(+) cells in the spleen and gut, the mucosal vaccine induced a higher percentage of functioning IFN-gamma(+) Ag-specific CD8(+) T cells in the gut mucosa in mice. Translating to the CD8(+) CTL avidity distribution in rhesus macaques, intrarectal vaccination induced more high-avidity mucosal CTL than s.c. vaccination and protection of mucosal CD4(+) T cells from AIDS viral depletion, whereas systemic immunization induced higher avidity IFN-gamma-secreting cells in the draining lymph nodes but no protection of mucosal CD4(+) T cells, after mucosal challenge with pathogenic simian/human immunodeficiency virus. Mucosal CD4(+) T cell loss is an early critical step in AIDS pathogenesis. The preservation of CD4(+) T cells in colonic lamina propria and the reduction of virus in the intestine correlated better with high-avidity mucosal CTL induced by the mucosal AIDS vaccine. This preferential localization of high-avidity CTL may explain previous differences in vaccination results and may guide future vaccination strategy.     

Injection of soluble antigen into the anterior chamber of the eye induces expansion and functional unresponsiveness of antigen-specific CD8+ T cells

The injection of soluble Ag into the anterior chamber (a.c.) of the eye induces systemic tolerance, termed a.c.-associated immune deviation (ACAID), characterized by Ag-specific inhibition of delayed-type hypersensitivity responses and a reduction in complement-fixing Abs. Recently, we have shown that CD8(+) CTL responses are also inhibited in ACAID. In this study, we have used an adoptive transfer approach to follow the fate of Ag-specific CD8(+) TCR transgenic (OT-I) T cells in vivo during the induction and expression of ACAID. C57BL/6 (B6) recipients of OT-I splenocytes that were injected with chicken OVA in the a.c. displayed reduced OVA-specific delayed-type hypersensitivity and CTL responses, compared with those of mice given OVA in the subconjunctiva or an irrelevant Ag human IgG in the a.c. OT-I T cells increased 9-fold in the submandibular lymph nodes and 3-fold in the spleen following an a.c. injection with OVA, indicating that expansion rather than deletion of Ag-specific CD8(+) T cells was induced by this treatment. OT-I T cells expanded equivalently upon administration of OVA in CFA to mice previously given OVA in the a.c. or subconjunctiva. However, the lytic activity attributed to OT-I T cells was reduced on a per-cell basis in mice previously given OVA in the a.c. We conclude that tolerance of CTL responses in mice given Ag via the a.c. results from unresponsiveness of Ag-specific CD8(+) T cells.     

Autoimmunity to DNA and nucleosomes in binary tetracycline-regulated polyomavirus T-Ag transgenic mice

The mechanism(s) responsible for autoimmunity to DNA and nucleosomes in SLE is largely unknown. We have demonstrated that nucleosome-polyomavirus T-Ag complexes, formed in context of productive polyomavirus infection, activate dsDNA-specific B cells and nucleosome-specific CD4(+) T cells. To investigate whether de novo expressed T-Ag is able to terminate nucleosome-specific T cell tolerance and to maintain anti-dsDNA Ab production in nonautoimmune mice, we developed two binary transgenic mouse variants in which expression of SV40 large T-Ag is controlled by tetracycline, MUP tTA/T-Ag (tet-off), and CMV rtTA/T-Ag (tet-on) mice. Data demonstrate that MUP tTA/T-Ag mice, but not CMV rtTA/T-Ag mice, are tightly controlling T-Ag expression. In MUP tTA/T-Ag transgenic mice, postnatal T-Ag expression activated CD8(+) T cells but not DNA-specific B cells, while immunization with T-Ag and nucleosome-T-Ag-complexes before T-Ag expression resulted in elevated and remarkably stable titers of anti-T-Ag and anti-dsDNA Abs and activation of T-Ag-specific CD4(+) T cells. Immunization of nonexpressing MUP tTA/T-Ag mice resulted in transient anti-T-Ag and anti-dsDNA Abs. This system reveals that a de novo expressed DNA-binding quasi-autoantigen maintain anti-dsDNA Abs and CD4(+) T cell activation once initiated by immunization, demonstrating direct impact of a single in vivo expressed molecule on sustained autoimmunity to DNA and nucleosomes.     

CTL-dependent and -independent antitumor immunity is determined by the tumor not the vaccine

Previously, we compared the efficiency of direct injection with an adenovirus (Ad) expressing human gp100 (hgp100) to immunization with dendritic cells (DC) loaded with the same vector ex vivo. The DC vaccine provided the greatest protection against challenge with B16F10 melanoma, and antitumor immunity was found to be CD8(+) T cell-independent. In the current study, we sought to determine whether lack of CD8(+) T cell-mediated antitumor immunity was a function of the vaccine platform or the tumor line. Both Ad and DC/Ad vaccines elicited CD8(+) CTL reactive against hgp100 and provided protection against B16F10 engineered to express hgp100 demonstrating that both vaccination platforms can effectively generate protective CD8(+) T cell-mediated immunity. The hgp100-induced CTL cross-reacted with murine gp100 (mgp100) and lysed B16F10 cells pulsed with mgp100 peptide indicating that the resistance of B16F10 cells to CTL elicited by hgp100 vaccination may be due to a defect in processing of the endogenous mgp100. Indeed, introduction of the TAP-1 cDNA into B16F10 rendered the cells sensitive to lysis by gp100-specific CTL. Furthermore, gp100-immunized mice were protected from challenge with B16F10-TAP1 cells through a mechanism dependent upon CD8(+) T cells. These results demonstrate that tumor phenotype, not the vaccination platform, ultimately determines CD8(+) or CD4(+) T cell-mediated tumor clearance.