Deletion is neither sufficient nor necessary for the induction of peripheral tolerance in mature CD8+ T cells

Tumor resident memory CD8 T cells and concomitant tumor immunity develop independently of CD4 help

Tissue resident memory (Trm) CD8 T cells infiltrating tumors represent an enriched population of tumor antigen-specific T cells, and their presence is associated with improved outcomes in patients. Using genetically engineered mouse pancreatic tumor models we demonstrate that tumor implantation generates a Trm niche that is dependent on direct antigen presentation by cancer cells. However, we observe that initial CCR7-mediated localization of CD8 T cells to tumor draining lymph nodes is required to subsequently generate CD103+ CD8 T cells in tumors. We observe that the formation of CD103+ CD8 T cells in tumors is dependent on CD40L but independent of CD4 T cells, and using mixed chimeras we show that CD8 T cells can provide their own CD40L to permit CD103+ CD8 T cell differentiation. Finally, we show that CD40L is required to provide systemic protection against secondary tumors. These data suggest that CD103+ CD8 T cell formation in tumors can occur independent of the two-factor authentication provided by CD4 T cells and highlight CD103+ CD8 T cells as a distinct differentiation decision from CD4-dependent central memory.

Male Lower Urinary Tract Dysfunction: An Underrepresented Endpoint in Toxicology Research

Lower urinary tract dysfunction (LUTD) is nearly ubiquitous in men of advancing age and exerts substantial physical, mental, social, and financial costs to society. While a large body of research is focused on the molecular, genetic, and epigenetic underpinnings of the disease, little research has been dedicated to the influence of environmental chemicals on disease initiation, progression, or severity. Despite a few recent studies indicating a potential developmental origin of male LUTD linked to chemical exposures in the womb, it remains a grossly understudied endpoint in toxicology research. Therefore, we direct this review to toxicologists who are considering male LUTD as a new aspect of chemical toxicity studies. We focus on the LUTD disease process in men, as well as in the male mouse as a leading research model. To introduce the disease process, we describe the physiology of the male lower urinary tract and the cellular composition of lower urinary tract tissues. We discuss known and suspected mechanisms of male LUTD and examples of environmental chemicals acting through these mechanisms to contribute to LUTD. We also describe mouse models of LUTD and endpoints to diagnose, characterize, and quantify LUTD in men and mice.

Perfect adaptation of CD8+ T cell responses to constant antigen input over a wide range of affinities is overcome by costimulation

Reduced T cell responses by contrast antigen stimulation can be rescued by signals from costimulatory receptors.

Robust antigen-specific CD8 T cell tolerance to a model prostate cancer neoantigen

Immunotherapy has shown limited success in prostate cancer; this may be partially explained by its immunosuppressive tumor microenvironment (TME). Although androgen-deprivation therapy (ADT), the most common treatment for prostate cancer, initially promotes a robust T cell infiltrate, T cell responses are later attenuated. Based on the castration-sensitive Myc-CaP model, we developed an antigen-specific system to study CD8 T cell tolerance to prostate tumors. This model is unique in that CD8 T cells recognize a bona-fide tumor antigen (Her-2/neu), rather than an overexpressed xenogenic antigen like chicken ovalbumin or influenza hemagglutinin. Using this novel model, we demonstrate robust tolerance that is not alleviated by TLR agonists or ADT. This model may serve as a novel and useful tool to further interrogate methods by which to augment anti-tumor cancer immune responses to prostate cancer.

Significance

Prostate cancer is a leading cause of cancer-related death in men worldwide, with an estimated 33,000 deaths projected in the U.S. in 2020. Although primary (localized) tumors can be cured by surgery or radiation, approximately 40% of patients eventually develop recurrent disease. While initially responsive to androgen-deprivation, many patients with recurrent prostate cancer eventually progress to a more advanced disease state known as metastatic castration-resistant prostate cancer (mCRPC); this is the lethal phenotype. These studies describe a novel androgen-responsive murine cell line that expresses a bona-fide tumor antigen (Her-2/neu). Pre-clinical work with this model shows robust and antigen-specific CD8 T cell tolerance, providing a novel preclinical model to study CD8 T cell tolerance to prostate tumors.

Late-Stage Tumor Regression after PD-L1 Blockade Plus a Concurrent OX40 Agonist

The protective capability of tumor antigen-specific T cells is regulated by costimulatory and inhibitory signals. Current approaches in cancer immunotherapy seek to restore the function of unresponsive T cells by blocking inhibitory pathways. In contrast, providing exogenous costimulatory signals to T cells also enhances antitumor functionality. By combining these two clinical approaches, we demonstrate the synergy of targeting PD-L1 together with the costimulatory molecule OX40, to enhance antitumor immunity. Concurrently blocking PD-L1 and providing a costimulatory agonist to OX40 increased the presence and functionality of tumor antigen-specific CD8⁺ T cells with simultaneous enhancement of T-helper type 1 (Th1)-skewed CD4⁺ T cells. This shift was functionally supported by increased glucose metabolism of antigen-specific CD8⁺ T cells and the acquisition of granzyme B by regulatory T cells. Together, this mechanism promoted tumor regression of late-stage tumors beyond that achieved by either blockade as monotherapy. These findings indicate that targeting both T-cell intrinsic (OX40) and extrinsic (PD-L1) regulatory molecules increases the bioenergetic potential of T cells, thereby expanding functional and tumor antigen-specific T cells.

Immunotherapy Expands and Maintains the Function of High-Affinity Tumor-Infiltrating CD8 T Cells In Situ

Cancer cells harbor high-affinity tumor-associated Ags capable of eliciting potent antitumor T cell responses, yet detecting these polyclonal T cells is challenging. Therefore, surrogate markers of T cell activation such as CD69, CD44, and programmed death-1 (PD-1) have been used. We report in this study that in mice, expression of activation markers including PD-1 is insufficient in the tumor microenvironment to identify tumor Ag-specific T cells. Using the Nur77GFP T cell affinity reporter mouse, we highlight that PD-1 expression can be induced independent of TCR ligation within the tumor. Given this, we characterized the utility of the Nur77GFP model system in elucidating mechanisms of action of immunotherapies independent of PD-1 expression. Coexpression of Nur77GFP and OX40 identifies a polyclonal population of high-affinity tumor-associated Ag-specific CD8(+) T cells, which produce more IFN-γ in situ than OX40 negative and doubles in quantity with anti-OX40 and anti-CTLA4 mAb therapy but not with anti-PD-1 or programmed death ligand-1. Moreover, expansion of these high-affinity CD8 T cells prolongs survival of tumor-bearing animals. Upon chronic stimulation in tumors and after adoptive cell therapy, CD8 TCR signaling and Nur77GFP induction is impaired, and tumors progress. However, this can be reversed and overall survival significantly enhanced after adoptive cell therapy with agonist OX40 immunotherapy. Therefore, we propose that OX40 agonist immunotherapy can maintain functional TCR signaling of chronically stimulated tumor-resident CD8 T cells, thereby increasing the frequency of cytotoxic, high-affinity, tumor-associated Ag-specific cells.

How do I steer this thing? Using dendritic cell targeted vaccination to more effectively guide the antitumor immune response with combination immunotherapy

Mounting an immune response sufficient to eradicate a tumor is the goal of modern immunotherapy. Single agent therapies with checkpoint inhibitors or costimulatory molecule agonists are effective only for a small portion of all treated patients. Combined therapy, e.g., CTLA-4 and PD-1 checkpoint blockade, is a more effective treatment modality, but in preclinical studies OX40 agonism with CTLA-4 blockade using monoclonal antibodies (aOX40/aCTLA-4) failed to induce tumor regression of larger, more established tumors. We hypothesized that administration of a vaccine with a tumor-associated antigen targeted to the appropriate antigen presenting cell could make combined aOX40/aCTLA-4 therapy more effective. We administered an antibody-based vaccine targeting HER2 to the DEC-205 endocytic receptor on cross-presenting dendritic cells (anti-DEC-205/HER2; aDEC-205/HER2) and a potent adjuvant (poly (I:C)) to assist with maturation, along with aOX40/aCTLA-4 therapy. This therapy induced complete regression of established tumors and a pronounced infiltration of effector CD8 and CD4 T cells, with no effect on regulatory T cell infiltration compared to aOX40/aCTLA-4 alone. To be maximally effective, this therapy required expression of both OX40 and CTLA-4 on CD8 T cells. These data indicate that vaccination targeting cross-presenting dendritic cells with a tumor-associated antigen is a highly effective immunization strategy that can overcome some of the limitations of current systemic immunotherapeutic approaches that lack defined tumor-directed antigenic targets.

Combination OX40 agonism/CTLA-4 blockade with HER2 vaccination reverses T-cell anergy and promotes survival in tumor-bearing mice

Immunotherapy is gathering momentum as a primary therapy for cancer patients. However, monotherapies have limited efficacy in improving outcomes and benefit only a subset of patients. Combination therapies targeting multiple pathways can augment an immune response to improve survival further. Here, we demonstrate that dual aOX40 (anti-CD134)/aCTLA-4 (anti-cytotoxic T-lymphocyte-associated protein 4) immunotherapy generated a potent antigen-specific CD8 T-cell response, enhancing expansion, effector function, and memory T-cell persistence. Importantly, OX40 and CTLA-4 expression on CD8 T cells was critical for promoting their maximal expansion following combination therapy. Animals treated with combination therapy and vaccination using anti-DEC-205 (dendritic and epithelial cells, 205 kDa)-HER2 (human epidermal growth factor receptor 2) had significantly improved survival in a mammary carcinoma model. Vaccination with combination therapy uniquely restricted Th2-cytokine production by CD4 cells, relative to combination therapy alone, and enhanced IFNγ production by CD8 and CD4 cells. We observed an increase in MIP-1α (macrophage inflammatory protein-1α)/CCL3 [chemokine (C-C motif) ligand 3], MIP-1β/CCL4, RANTES (regulated on activation, normal T-cell expressed and excreted)/CCL5, and GM-CSF production by CD8 and CD4 T cells following treatment. Furthermore, this therapy was associated with extensive tumor destruction and T-cell infiltration into the tumor. Notably, in a spontaneous model of prostate adenocarcinoma, vaccination with combination therapy reversed anergy and enhanced the expansion and function of CD8 T cells recognizing a tumor-associated antigen. Collectively, these data demonstrate that the addition of a vaccine with combined aOX40/aCTLA-4 immunotherapy augmented antitumor CD8 T-cell function while limiting Th2 polarization in CD4 cells and improved overall survival.

Characterization of autoimmune inflammation induced prostate stem cell expansion

BACKGROUND

The presence of inflammation in prostate cancer (PCa) and benign prostate hyperplasia (BPH) has been well described but the cellular mechanisms by which inflammation modulates the prostate are currently unclear. Prostate stem cells (PSC) not only maintain prostate homeostasis but also are considered to be the cell of origin of PCa and an important contributor to BPH. However, the impact of inflammation on PSC is not well understood. Therefore, we initiated studies to evaluate the effect of inflammation on PSC.

METHOD

Ovalbumin specific CD8(+) T cells were intravenously delivered to intact and castrated prostate ovalbumin expressing transgenic-3 (POET-3) mice to induce inflammation. Lin (CD45/CD31)(-) Sca1(+) CD49f(+) cells (LSC) and progenitor cells within LSC were determined by flow cytometry. Sorted LSC were subjected to a prostate sphere forming assay to evaluate PSC clonal propagation, proliferation, immediate differentiation, and self-renewal ability. Density of individual spheres was measured by a cantilever-based resonator weighing system. Morphology and characterization of prostate spheres was determined by hematoxylin and eosin (H&E) staining and immunohistochemistry (IHC). Finally, immediate PSC differentiation in sphere formation was determined by immunofluorescence for epithelial cytokeratin markers cytokeratin (CK) 5 and CK8.

RESULT

Data presented here demonstrate a significant expansion of the proliferative (BrdU(+) ) LSC population, including CK5(+) , p63(+) , CK18(+) cells, as well as intermediate cells (CK5(+) /CK8(+) ) in inflamed prostates. Histological images reveal that PSC from inflamed prostates produce significantly larger spheres, indicating that the enhanced proliferation observed in LSC is sustained in vitro in the absence of inflammatory mediators. In addition, cultures from inflamed PSC yielded increased number of tubule-like spheres. These tube-like spheres grown from PSCs isolated from inflamed mice exhibited stratification of a CK8(+) luminal-like layer and a CK5(+) basal-like layer. Notably, the numbers of spheres formed by inflamed and non-inflamed PSC were equal, suggesting that even though proliferation is enhanced by inflammation, the homeostatic level of PSC is maintained.

CONCLUSION

Induction of inflammation promotes PSC expansion and immediate differentiation through highly proliferative progenitor cells while the homeostasis of PSC is maintained.

Combined targeting of costimulatory (OX40) and coinhibitory (CTLA-4) pathways elicits potent effector T cells capable of driving robust antitumor immunity

Ligation of the TNF receptor family costimulatory molecule OX40 (CD134) with an agonist anti-OX40 monoclonal antibody (mAb) enhances antitumor immunity by augmenting T-cell differentiation as well as turning off the suppressive activity of the FoxP3(+)CD4(+) regulatory T cells (Treg). In addition, antibody-mediated blockade of the checkpoint inhibitor CTLA-4 releases the "brakes" on T cells to augment tumor immunotherapy. However, monotherapy with these agents has limited therapeutic benefit particularly against poorly immunogenic murine tumors. Therefore, we examined whether the administration of agonist anti-OX40 therapy in the presence of CTLA-4 blockade would enhance tumor immunotherapy. Combined anti-OX40/anti-CTLA-4 immunotherapy significantly enhanced tumor regression and the survival of tumor-bearing hosts in a CD4 and CD8 T cell-dependent manner. Mechanistic studies revealed that the combination immunotherapy directed the expansion of effector T-bet(high)/Eomes(high) granzyme B(+) CD8 T cells. Dual immunotherapy also induced distinct populations of Th1 [interleukin (IL)-2, IFN-γ], and, surprisingly, Th2 (IL-4, IL-5, and IL-13) CD4 T cells exhibiting increased T-bet and Gata-3 expression. Furthermore, IL-4 blockade inhibited the Th2 response, while maintaining the Th1 CD4 and effector CD8 T cells that enhanced tumor-free survival. These data demonstrate that refining the global T-cell response during combination immunotherapy can further enhance the therapeutic efficacy of these agents.

CD134/CD137 dual costimulation-elicited IFN-γ maximizes effector T-cell function but limits Treg expansion

T cell tolerance to tumor antigens represents a major hurdle in generating tumor immunity. Combined administration of agonistic monoclonal antibodies to the costimulatory receptors CD134 plus CD137 can program T cells responding to tolerogenic antigen to undergo expansion and effector T cell differentiation, and also elicits tumor immunity. Nevertheless, CD134 and CD137 agonists can also engage inhibitory immune components. To understand how immune stimulatory versus inhibitory components are regulated during CD134 plus CD137 dual costimulation, the current study utilized a model where dual costimulation programs T cells encountering a highly tolerogenic self-antigen to undergo effector differentiation. IFN-γ was found to play a pivotal role in maximizing the function of effector T cells while simultaneously limiting the expansion of CD4⁺CD25⁺Foxp3⁺ Tregs. In antigen-responding effector T cells, IFN-γ operates via a direct cell-intrinsic mechanism to cooperate with IL-2 to program maximal expression of granzyme B. Simultaneously, IFN-γ limits expression of the IL-2 receptor alpha chain (CD25) and IL-2 signaling through a mechanism that does not involve T-bet-mediated repression of IL-2. IFN-γ also limited CD25 and Foxp3 expression on bystanding CD4⁺Foxp3⁺ Tregs, and limited the potential of these Tregs to expand. These effects could not be explained by the ability of IFN-γ to limit IL-2 availability. Taken together, during dual costimulation IFN-γ interacts with IL-2 through distinct mechanisms to program maximal expression of effector molecules in antigen-responding T cells while simultaneously limiting Treg expansion.

Dual anti-OX40/IL-2 therapy augments tumor immunotherapy via IL-2R-mediated regulation of OX40 expression

The provision of T cell co-stimulation via members of the TNFR super-family, including OX40 (CD134) and 4-1BB (CD137), provides critical signals that promote T cell survival and differentiation. Recent studies have demonstrated that ligation of OX40 can augment T cell-mediated anti-tumor immunity in pre-clinical models and more importantly, OX40 agonists are under clinical development for cancer immunotherapy. OX40 is of particular interest as a therapeutic target as it is not expressed on naïve T cells but rather, is transiently up-regulated following TCR stimulation. Although TCR engagement is necessary for inducing OX40 expression, the downstream signals that regulate OX40 itself remain unclear. In this study, we demonstrate that OX40 expression is regulated through a TCR and common gamma chain cytokine-dependent signaling cascade that requires JAK3-mediated activation of the downstream transcription factors STAT3 and STAT5. Furthermore, combined treatment with an agonist anti-OX40 mAb and IL-2 augmented tumor immunotherapy against multiple tumor types. Dual therapy was also able to restore the function of anergic tumor-reactive CD8 T cells in mice with long-term well-established (>5 wks) tumors, leading to increased survival of the tumor-bearing hosts. Together, these data reveal the ability of TCR/common gamma chain cytokine signaling to regulate OX40 expression and demonstrate a novel means of augmenting cancer immunotherapy by providing dual anti-OX40/common gamma chain cytokine-directed therapy.

An inducible model of abacterial prostatitis induces antigen specific inflammatory and proliferative changes in the murine prostate

BACKGROUND

Prostatitis is a poorly understood disease and increasing evidence suggests inflammation is involved in other prostatic diseases including prostate cancer.

METHODS

The ability of pre-activated CD8 T cells to induce prostatitis was examined by adoptive transfer of prostate antigen specific CD8 T cells into POET-3 mice or POET-3/Luc/Pten(-/+) mice. Characterization of the inflammatory response was determined by examining leukocyte infiltration by histological analysis, flow cytometry and by evaluating cytokine and chemokine levels in prostate tissue. The impact of inflammation on the prostate was evaluated by monitoring epithelial cell proliferation over time.

RESULTS

Initiation of inflammation by ovalbumin specific CD8⁺ T cells (OT-I cells) resulted in development of acute prostatitis in the anterior, dorsolateral and ventral prostate of POET-3 and POET-3/Luc/Pten(-/+) mice. Acute prostatitis was characterized by recruitment of adoptively transferred OT-I cells and importantly, autologous CD4⁺ and CD8⁺ T cells, myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg). In concert with leukocyte infiltration elevated levels of pro-inflammatory cytokines and chemokines were observed. Inflammation also resulted in marked epithelial cell proliferation that was sustained up to 80 days post adoptive transfer of OT-I cells.

CONCLUSIONS

The POET-3 model represents a novel mouse model to study both acute and chronic prostate inflammation in an antigen-specific system. Further, the POET-3 mouse model can be crossed with other genetic models of disease such as the C57/Luc/Pten(-/-) model of prostate cancer, allowing the impact of prostatitis on other prostatic diseases to be evaluated.

Ligation of the OX40 co-stimulatory receptor reverses self-Ag and tumor-induced CD8 T-cell anergy in vivo

Tumor-specific CD8 T-cell peripheral tolerance occurs through clonal deletion, suppression, and the induction of anergy and can limit the generation of anti-tumor immunity. Several groups have demonstrated that prostate cancer can render tumor-specific CD8 T cells anergic, suggesting reversing tumor-induced anergy may greatly augment anti-tumor immunity. Recent work has demonstrated that signaling through the OX40 (CD134) co-stimulatory receptor, a member of the TNFR super-family, can augment CD4 and CD8 T-cell expansion, differentiation, and the generation of memory cells. However, whether OX40 ligation can reverse CD8 T-cell anergy, and more specifically, tumor-induced CD8 T-cell anergy, remains unclear. In the current study, we demonstrate that OX40 ligation can reverse CD8 T-cell anergy to a prostate-specific self-Ag in non-tumor-bearing hosts. Furthermore, OX40 engagement reversed tumor-specific CD8 T-cell anergy and restored the proliferative capacity of tumor-reactive CD8 T cells, which attenuated tumor growth and enhanced the survival of tumor-bearing hosts. These data demonstrate that OX40 ligation can rescue the function of anergic self- or tumor-reactive CD8 T cells in vivo and suggests that OX40-mediated therapy may provide a novel means of boosting anti-tumor immunity by restoring the responsiveness of previously anergic tumor-specific CD8 T cells.

Tumor recognition and self-recognition induce distinct transcriptional profiles in antigen-specific CD4 T cells

Tumors express a wide variety of both mutated and nonmutated Ags. Whether these tumor Ags are broadly recognized as self or foreign by the immune system is currently unclear. Using an autochthonous prostate cancer model in which hemagglutinin (HA) is specifically expressed in the tumor (ProHA x TRAMP mice), as well as an analogous model wherein HA is expressed in normal tissues as a model self-Ag (C3HA(high)), we examined the transcriptional profile of CD4 T cells undergoing Ag-specific division. Consistent with our previous data, transfer of Ag-specific CD4 T cells into C3HA(high) resulted in a functionally inactivated CD4 T cell profile. Conversely, adoptive transfer of an identical CD4 T cell population into ProHA x TRAMP mice resulted in the induction of a regulatory phenotype of the T cell (Treg) both at the transcriptional and functional level. Interestingly, this Treg skewing was a property of even early-stage tumors, suggesting Treg induction as an important tolerance mechanism during tumor development.

Transforming growth factor-beta-mediated signaling in T lymphocytes impacts on prostate-specific immunity and early prostate tumor progression

T cells are in general tolerant of prostate-specific tumor antigens. That prostate tumor tissue makes transforming growth factor-beta (TGFbeta) is thought to play a role in the induction of T-cell tolerance within the host and to contribute to tumor progression itself. Here we sought to investigate the influence of TGFbeta signaling on prostate antigen-specific T-cell responses as well as prostate tumorogenesis in an autochthonous murine model of the disease. The response of naive and activated ovalbumin (OVA) antigen-specific T cells, which had been rendered incapable of responding to TGFbeta through T-cell-specific transgenic expression of a dominant-negative variant of the TGFbeta receptor II (dnTGFRII), was analyzed after adoptive transfer into prostate OVA-expressing transgenic (POET) mice. The role of TGFbeta signaling in endogenous T cells in mice, which spontaneously form tumors, was also assessed by monitoring prostate tumor formation and progression in F1 progeny of productive matings between transgenic adenocarcinoma of the mouse prostate (TRAMP) and dnTGFRII mice. TGFbeta-resistant CD8(+) T cells proliferated more and produced IFNgamma more readily after OVA stimulation in vitro. OVA-specific T cells did not damage the prostate gland of POET mice irrespective of TGFbeta responsiveness. However, ex vivo activation facilitated entry of TGFbeta-insensitive T cells into the prostate and was associated with prostate tissue damage. Early tumor progression was delayed in TRAMP mice that carried endogenous TGFbeta-insensitive T cells. Together, these results suggest that TGFbeta-signaling represses CD8(+) T-cell responses to a prostate-specific antigen. TGFbeta-mediated repression of T-cell function may include production of IFNgamma, which is known to contribute to tumor immunosurveillance.

Direct presentation of a melanocyte-associated antigen in peripheral lymph nodes induces cytotoxic CD8+ T cells

Encounter of self-antigens in the periphery by mature T cells induces tolerance in the steady-state. Hence, it is not understood why the same peripheral antigens are also promiscuously expressed in the thymus to mediate central tolerance. Here, we analyzed CD8(+) T-cell tolerance to such an antigen constituted by ovalbumin under the control of the tyrosinase promoter. As expected, endogenous CD8(+) T-cell responses were altered in the periphery of transgenic mice, resulting from promiscuous expression of the self-antigen in mature medullary epithelial cells and deletion of high-affinity T cells in the thymus. In adoptive T-cell transfer experiments, we observed constitutive presentation of the self-antigen in peripheral lymph nodes. Notably, this self-antigen presentation induced persisting cytotoxic cells from high-affinity CD8(+) T-cell precursors. Lymph node resident melanoblasts expressing tyrosinase directly presented the self-antigen to CD8(+) T cells, independently of bone marrow-derived antigen-presenting cells. This peripheral priming was independent of the subcellular localization of the self-antigen, indicating that this mechanism may apply to other melanocyte-associated antigens. Hence, central tolerance by promiscuous expression of peripheral antigens is a mandatory, rather than a superfluous, mechanism to counteract the peripheral priming, at least for self-antigens that can be directly presented in lymph nodes. The peripheral priming by lymph node melanoblasts identified here may constitute an advantage for immunotherapies based on adoptive T-cell transfer.

Fas-mediated T cell deletion potentiates tumor antigen-specific tolerance in a mouse model of prostate cancer

A pivotal obstacle to cancer immunotherapy is peripheral T cell tolerance to tumor-associated antigens (TAAs). Tolerance induction among mature T cells in the periphery operates through a variety of mechanisms, including anergy and apoptosis. Although Fas-FasL-mediated apoptosis is a well-defined tolerance inducing mechanism, direct evidence of its interference with TAA-specific immunity in vivo is still lacking. In this report, we used the TRAMP mouse, which expresses SV40 large T antigen (Tag) preferentially in the prostate and develops prostate tumors, as a model system to address the role of Fas-mediated apoptosis in regulating peripheral T cell tolerance. Using RT-PCR and tetramer staining to quantify TAA-specific TCR-expressing cytolytic T lymphocytes (CTLs), we have shown the presence of TAA-specific CTLs at higher levels in TRAMP mice than in syngeneic C57Bl/6 mice. Tag-specific immunization led to the expansion of Tag-specific CTLs in C57Bl/6 mice, and to their elimination in TRAMP mice. Interestingly, in TRAMP mice with deficient Fas (Hybrid TRAMP-lpr/lpr), Tag-specific CTL elimination in response to Tag immunization did not take place. The results of cytolytic-function assays were consistent with induction and elimination patterns of TAA-specific CTLs and those of RT-PCR and tetramer staining. In conclusion, our data show that Fas-mediated TAA-specific CTL apoptosis contributes to T cell tolerance and suggest that such tolerance could be potentiated following TAA-specific immunization.

Rapid tolerization of virus-activated tumor-specific CD8+ T cells in prostate tumors of TRAMP mice

To study T cell responses to tumors in an autochthonous model, we expressed a CD8 T cell epitope SIYRYYGL (SIY) in the prostate of transgenic adenocarcinoma (TRAMP) mice (referred to as TRP-SIY), which spontaneously develop prostate cancer. Naïve SIY-specific CD8 T cells adoptively transferred into TRP-SIY mice became tolerized in the prostate draining lymph nodes. Vaccination of TRP-SIY mice intranasally with influenza virus that expresses the SIY epitope resulted in generation of SIY-specific effector T cells in the lung-draining lymph nodes. These effector T cells expressed TNFalpha and IFNgamma, eliminated SIY peptide-loaded target cells in vivo, and infiltrated prostate tumors, where they rapidly lost the ability to produce effector cytokines. A population of these T cells persisted in prostate tumors but not in lymphoid organs and could be induced to re-express effector functions following cytokine treatment in vitro. These findings suggest that T cells of a given clone can be activated and tolerized simultaneously in different microenvironments of the same host and that effector T cells are rapidly tolerized in the tumors. Our model provides a system to study T cell-tumor interactions in detail and to test the efficacy of cancer immunotherapeutic strategies.

Defects in the acquisition of CD8 T cell effector function after priming with tumor or soluble antigen can be overcome by the addition of an OX40 agonist

Several members of the TNFR superfamily, including OX40 (CD134), 4-1BB (CD137), and CD27 provide critical costimulatory signals that promote T cell survival and differentiation in vivo. Although several studies have demonstrated that OX40 engagement can enhance CD4 T cell responses, the mechanisms by which OX40-mediated signals augment CD8 T cell responses are still unclear. Previously, we and others have shown that OX40 engagement on Ag-specific CD8 T cells led to increased CD8 T cell expansion, survival, and the generation of greater numbers of long-lived memory cells. Currently, we demonstrate that provision of an OX40 agonist during the activation of naive CD8 T cells primed in vivo with either soluble or tumor-associated Ag significantly augments granzyme B expression and CD8 T cell cytolytic function through an IL-2-dependent mechanism. Furthermore, augmented CTL function required direct engagement of OX40 on the responding CD8 T cells and was associated with increased antitumor activity against established prostate tumors and enhanced the survival of tumor-bearing hosts. Thus, in the absence of danger signals, as is often the case in a tumor-bearing host, provision of an OX40 agonist can overcome defective CD8 T cell priming and lead to a functional antitumor response in vivo.

Transcriptional targeting of B cells for induction of peripheral CD8 T cell tolerance

Several mechanisms are in place to neutralize autoimmune CD8 T cells by tolerance induction. Developing self-specific CD8 T cells are eliminated in the thymus by Ag-presenting epithelial and dendritic cells (DCs). However, CD8 T cells escaping thymic central tolerance can also be inactivated by tolerance mechanisms in peripheral organs. In contrast to DCs, the role of B cells in generating CD8 T cell tolerance is not well-characterized. To investigate this question in more detail, we transcriptionally targeted Ag to B cells using B cell-specific retroviral vectors in vivo. Although Ag expression could be detected in B cells of thymus, lymph nodes, and spleen, B cells were unable to induce central tolerance of CD8 thymocytes. In contrast, in peripheral organs, we could identify clonal deletion and functional inhibition (anergy) of CD8 T cells as tolerance-inducing mechanisms. Although Ag expressed by B cells was acquired and cross-presented by DCs, B cells were also sufficient to tolerize CD8 T cells directly. These findings suggest exploitation of B cells for Ag-specific immunotherapy of CD8 T cell-mediated autoimmune diseases.

T cell tolerance to the skin: a central role for central tolerance

T cell tolerance to self-antigens is believed to be achieved in a two-step process. The first step, called central tolerance, takes place in the thymus. The second step takes place outside the thymus in secondary lymphoid organs. One may ask why two mechanisms are needed to insure T cell tolerance. These two mechanisms share redundant functions and dysfunctions, leading to T cell-mediated autoimmune syndromes. By reviewing the literature on relevant animal models for T cell tolerance and our own recent findings, we are providing evidences that only central tolerance is acting for the skin.

Urinary bladder epithelium antigen induces CD8+ T cell tolerance, activation, and autoimmune response

The effort to explore the specific autoimmune mechanisms of urinary bladder has long been hindered due to a lack of proper animal models. To better elucidate this issue, we developed a novel line of transgenic (Tg) mice, designated as URO-OVA mice, that express the model Ag OVA as a "self"-Ag on the bladder epithelium. URO-OVA mice are naturally tolerant to OVA and show no response to OVA stimulation. Adoptive transfer of naive OVA-specific T cells showed cell proliferation, activation, and infiltration but no bladder histopathology. In contrast, adoptive transfer of activated OVA-specific T cells induced OVA-mediated histological bladder inflammation. Increased mast cells and up-regulated mRNA expressions of TNF-alpha, nerve growth factor, and substance P precursor were also observed in the inflamed bladder. To further facilitate bladder autoimmunity study, we crossbred URO-OVA mice with OVA-specific CD8(+) TCR Tg mice (OT-I mice) to generate a dual Tg line URO-OVA/OT-I mice. The latter mice naturally acquire clonal deletion for autoreactive OT-I CD8(+) T cells (partial deletion in the thymus and severe deletion in the periphery). Despite this clonal deletion, URO-OVA/OT-I mice spontaneously develop autoimmune cystitis at 10 wk of age. Further studies demonstrated that the inflamed bladder contained infiltrating OT-I CD8(+) T cells that had escaped clonal deletion and gained effector functions before developing histological bladder inflammation. Taken together, we demonstrate for the first time that the bladder epithelium actively presents self-Ag to the immune system and induces CD8(+) T cell tolerance, activation, and autoimmune response.