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PDF file - 308K, Phenotypic fidelity of transferred T cell subsets.

PDF file - 111K, CpG/H11 vaccination but not CpG alone induces the expression of CD137 on FoxP3pos Tregs.

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PDF file - 139K, Reconstitution of endogenous CD8 T cells post-transplant.

While immunotherapies based on single recombinant cytokines such as IL12 and IL21 have shown great promise in preclinical models of solid tumors, clinical translation has proven challenging due to limited mechanisms of action, narrow therapeutic windows upon systemic administration, and short half-lives resulting in poor pharmacokinetics and distribution. Thus, there is a need for tumor-localized cytokine therapies capable of driving sustained efficacy with a wide therapeutic window. SENTI-101 is a cell-based immunotherapy comprising allogeneic bone marrow-derived mesenchymal stromal cells (BM-MSCs) genetically modified to express IL12 and IL21. Consistent with prior studies, we demonstrated that SENTI-101 innately homes to disseminated tumors in the peritoneal cavity and induces durable anti-tumor responses and immune memory in various preclinical models of peritoneal tumors. In this study, we investigated the mechanisms of action of SENTI-101. Our results demonstrate that the IL12 and IL21 combination elicits pleiotropic and complementary effects that drive a multi-modal immune response across various steps of the cancer immunity cycle. Treatment of preclinical murine models of peritoneal tumors (e.g., CT26 and B16F10) with SENTI-101 significantly increased the local production of IFNg by more than 40-fold (p Overall, our preclinical studies show that SENTI-101 modulates the tumor immune landscape via multiple complementary modes of action, resulting in long-term anti-tumor immunity. Furthermore, this work demonstrates the therapeutic potential of tumor-localized cell therapies armed with gene circuits expressing combinatorial immune effectors to trigger a multi-factorial anti-tumor response. Citation Format: Alba Gonzalez, Frances D. Liu, Archana Nagaraja, Alyssa Mullenix, Russell M. Gordley, Daniel O. Frimannsson, Anissa Benabbas, Chen-Ting Lee, Tiffany A. Truong, Allison Quach, Mengxi Tian, Rowena Martinez, Rishi Savur, Alyssa Perry-McNamara, Don-Hong Wang, Ori Maller, Dharini Iyer, Ashita Magal, Sravani Mangalampalli, Christina J. Huynh, Carmina C. Blanco, Jack T. Lin, Brian S. Garrison, Philip Lee, Timothy K. Lu, Gary Lee. SENTI-101, a novel genetically modified allogeneic cell product expressing IL12 and IL21, elicits a tumor-localized, robust, and multimodal immune response in preclinical models of solid tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4246.

Adoptive immunotherapy with antitumor T cells is a promising novel approach for the treatment of cancer. However, T-cell therapy may be limited by the cotransfer of regulatory T cells (Treg). Here, we explored this hypothesis by using 2 cell surface markers, CD44 and CD137, to isolate antitumor CD4 T cells while excluding Tregs. In a murine model of B-cell lymphoma, only CD137negCD44hi CD4 T cells infiltrated tumor sites and provided protection. Conversely, the population of CD137posCD44hi CD4 T cells consisted primarily of activated Tregs. Notably, this CD137pos Treg population persisted following adoptive transfer and maintained expression of FoxP3 as well as CD137. Moreover, in vitro these CD137pos cells suppressed the proliferation of effector cells in a contact-dependent manner, and in vivo adding the CD137posCD44hi CD4 cells to CD137negCD44hi CD4 cells suppressed the antitumor immune response. Thus, CD137 expression on CD4 T cells defined a population of activated Tregs that greatly limited antitumor immune responses. Consistent with observations in the murine model, human lymphoma biopsies also contained a population of CD137pos CD4 T cells that were predominantly CD25posFoxP3pos Tregs. In conclusion, our findings identify 2 surface markers that can be used to facilitate the enrichment of antitumor CD4 T cells while depleting an inhibitory Treg population. Cancer Res; 72(5); 1239–47. ©2012 AACR.

The signaling pathways utilized by naïve and experienced effector CD4 T cells during activation and proliferation were evaluated. While inhibition of either mTOR or MAPK alone was able to inhibit naïve T cell proliferation, both mTOR and MAPK (ERK) pathway inhibition was required to efficiently block experienced, effector CD4 T cell proliferation. This was demonstrated both in vitro, and in vivo by treating mice with collagen-induced arthritis using mTOR and/or ERK inhibitors. The combination of mTOR and ERK inhibition prevented or treated disease more efficiently than either agent alone. These data illustrate the different requirements of naïve and experienced effector CD4 T cells in the use of the mTOR and MAPK pathways in proliferation, and suggest that therapies targeting both the mTOR and MAPK pathways may be more effective than targeting either pathway alone in the treatment of CD4 T cell-mediated autoimmunity.

GRAIL (gene related to anergy in lymphocytes, also known as RNF128), an ubiquitin-protein ligase (E3), utilizes a unique single transmembrane protein with a split function motif, and is an important gatekeeper of T cell unresponsiveness. While it may play a role in other CD4 T cell functions including activation, survival, and differentiation, GRAIL is most well characterized as a negative regulator of TCR responsiveness and cytokine production. Here, we review the recent literature on this remarkable E3 in the regulation of human and mouse CD4 T cell unresponsiveness.

Despite the success of passive immunotherapy with monoclonal antibodies (mAbs), many lymphoma patients eventually relapse. Induction of an adaptive immune response may elicit active and long-lasting antitumor immunity, thereby preventing or delaying recurrence. Immunomodulating mAbs directed against immune cell targets can be used to enhance the immune response to achieve efficient antitumor immunity. Anti-CD137 agonistic mAb has demonstrated antitumor efficacy in various tumor models and has now entered clinical trials for the treatment of solid tumors. Here, we investigate the therapeutic potential of anti-CD137 mAb in lymphoma. We found that human primary lymphoma tumors are infiltrated with CD137+ T cells. We therefore hypothesized that lymphoma would be susceptible to treatment with anti-CD137 agonistic mAb. Using a mouse model, we demonstrate that anti-CD137 therapy has potent antilymphoma activity in vivo. The antitumor effect of anti-CD137 therapy was mediated by both natural killer (NK) and CD8 T cells and induced long-lasting immunity. Moreover, the antitumor activity of anti-CD137 mAb could be further enhanced by depletion of regulatory T cell (Tregs). These results support the evaluation of anti-CD137 therapy in clinical trials for patients with lymphoma.

Ubiquitination of eukaryotic proteins regulates a broad range of cellular processes, including T cell activation and tolerance. We have previously demonstrated that GRAIL (gene related to anergy in lymphocytes), a transmembrane RING finger ubiquitin E3 ligase, initially described as induced during the induction of CD4 T cell anergy, is also expressed in resting CD4 T cells. In this study, we show that GRAIL can down-modulate the expression of CD83 (previously described as a cell surface marker for mature dendritic cells) on CD4 T cells. GRAIL-mediated down-modulation of CD83 is dependent on an intact GRAIL extracellular protease-associated domain and an enzymatically active cytosolic RING domain, and proceeds via the ubiquitin-dependent 26S proteosome pathway. Ubiquitin modification of lysine residues K168 and K183, but not K192, in the cytoplasmic domain of CD83 was shown to be necessary for GRAIL-mediated degradation of CD83. Reduced CD83 surface expression levels were seen both on anergized CD4 T cells and following GRAIL expression by retroviral transduction, whereas GRAIL knock-down by RNA interference in CD4 T cells resulted in elevated CD83 levels. Furthermore, CD83 expression on CD4 T cells contributes to T cell activation as a costimulatory molecule. This study supports the novel mechanism of ubiquitination by GRAIL, identifies CD83 as a substrate of GRAIL, and ascribes a role for CD83 in CD4 T cell activation.

In this study, we demonstrate that the E3 ubiquitin ligase gene related to anergy in lymphocytes (GRAIL) is expressed in quiescent naive mouse and human CD4 T cells and has a functional role in inhibiting naive T cell proliferation. Following TCR engagement, CD28 costimulation results in the expression of IL-2 whose signaling through its receptor activates the Akt-mammalian target of rapamycin (mTOR) pathway. Activation of mTOR allows selective mRNA translation, including the epistatic regulator of GRAIL, Otubain-1 (Otub1), whose expression results in the degradation of GRAIL and allows T cell proliferation. The activation of mTOR appears to be the critical component of IL-2R signaling regulating GRAIL expression. CTLA4-Ig treatment blocks CD28 costimulation and resultant IL-2 expression, whereas rapamycin and anti-IL-2 treatment block mTOR activation downstream of IL-2R signaling. Thus, all three of these biotherapeutics inhibit mTOR-dependent translation of mRNA transcripts, resulting in blockade of Otub1 expression, maintenance of GRAIL, and inhibition of CD4 T cell proliferation. These observations provide a mechanistic pathway sequentially linking CD28 costimulation, IL-2R signaling, and mTOR activation as important requirements for naive CD4 T cell proliferation through the regulation of Otub1 and GRAIL expression. Our findings also extend the role of GRAIL beyond anergy induction and maintenance, suggesting that endogenous GRAIL regulates general cell cycle and proliferation of primary naive CD4 T cells.

Activation of naive T lymphocytes is regulated through a series of discrete checkpoints that maintain unresponsiveness to self. During this multistep process, costimulatory interactions act as inducible signals that allow APCs to selectively mobilize T cells against foreign Ags. In this study, we provide evidence that the anergy-associated E3 ubiquitin ligase GRAIL (gene related to anergy in lymphocytes) regulates expression of the costimulatory molecule CD40L on CD4 T cells. Using its luminal protease-associated domain, GRAIL binds to the luminal/extracellular portion of CD40L and facilitates transfer of ubiquitin molecules from the intracellular GRAIL RING (really interesting new gene) finger to the small cytosolic portion of CD40L. Down-regulation of CD40L occurred following ectopic expression of GRAIL in naive T cells from CD40−/− mice, and expression of GRAIL in bone marrow chimeric mice was associated with diminished lymphoid follicle formation. These data provide a model for intrinsic T cell regulation of costimulatory molecules and a molecular framework for the initiation of clonal T cell anergy.

Autoimmune hepatitis (AIH) is mediated by a T-cell attack upon liver parenchyma. Susceptibility to the development of AIH is genetically determined. While particular MHC haplotypes are known risk factors, it has been widely speculated that autoimmune liver damage can be regulated by additional genetic loci unlinked to MHC. However, evidence for the existence of such loci in humans is scant. We examined the contribution of the MHC in a murine model of autoimmune hepatocellular injury. BALB/c mice lacking the immunoregulatory cytokine transforming growth factor-beta1 (TGF-beta1) rapidly develop autoimmune T-helper 1-mediated necroinflammatory liver disease. Susceptibility to liver damage is strictly regulated by genetic background. Whereas TGF-beta1-deficient mice on the BALB/c background develop necroinflammatory liver disease, TGF-beta1-deficient mice on the 129/CF-1 genetic background do not. We asked whether MHC locus haplotype is the principal determinant of genetic susceptibility to liver disease in this model system. BALB/c mice harbor the H-2d haplotype. We used a 'haplotype swapping' approach to generate H-2b or H-2k congenic BALB-background TGF-beta1-deficient mice. In addition, F1 (BALB/c x 129/CF-1)-TGF-beta1-deficient mice were generated. As determined by plasma transaminase levels and histopathology, severe necroinflammatory liver disease developed in all BALB-background TGF-beta1-deficient mice, regardless of H-2 haplotype, but developed neither in 129/CF-1-TGF-beta1-deficient mice nor in F1 (BALB/c x 129/CF-1)-TGF-beta1-deficient mice. Thus, H-2d is neither necessary nor sufficient for the development of necroinflammatory liver disease in BALB-background TGF-beta1-deficient mice. This constitutes the first direct evidence that susceptibility to autoimmune hepatocellular damage, at least in mice, can be determined by genetic loci distinct from the MHC.

Cyclophosphamide (CPA) and ifosfamide (IFA) are oxazaphosphorine anticancer prodrugs metabolized by two alternative cytochrome P450 (P450) pathways, drug activation by 4-hydroxylation and drug inactivation by N-dechloroethylation, which generates the neurotoxic and nephrotoxic byproduct chloroacetaldehyde. CPA and IFA metabolism catalyzed by P450s 2B1, 2B4, 2B5, and seven site-specific 2B1 mutants was studied in a reconstituted Escherichia coli expression system to identify residues that contribute to the unique activities and substrate specificities of these enzymes. The catalytic efficiency of CPA 4-hydroxylation by rat P450 2B1 was 10- to 35-fold higher than that of rabbit P450 2B4 or 2B5. With IFA, approximately 50% of metabolism proceeded via N-dechloroethylation for 2B1 and 2B4, whereas CPA N-dechloroethylation corresponded to only approximately 3% of total metabolism (2B1) or was absent (2B4, 2B5). Improved catalytic efficiency of CPA and IFA 4-hydroxylation was obtained upon substitution of 2B1 Ile-114 by Val, and replacement of Val-363 by Leu or Ile selectively suppressed CPA N-dechloroethylationor=90%. P450 2B1-V367A, containing the Ala replacement found in 2B5, exhibited only approximately 10% of wild-type 2B1 activity for both substrates. Canine P450 2B11, which has Val-114, Leu-363, and Val-367, was therefore predicted to be a regioselective CPA 4-hydroxylase with high catalytic efficiency. Indeed, P450 2B11 was 7- to 8-fold more active as a CPA and IFA 4-hydroxylase than 2B1, exhibited a highly desirable low K(m) (80-160 microM), and catalyzed no CPA N-dechloroethylation. These findings provide insight into the role of specific P450 2B residues in oxazaphosphorine metabolism and pave the way for gene therapeutic applications using P450 enzymes with improved catalytic activity toward these anticancer prodrug substrates.

The etiology of autoimmune liver disease is poorly understood. BALB/c mice deficient in the immunoregulatory cytokine TGF-β1 spontaneously develop necroinflammatory liver disease, but the immune basis for the development of this pathology has not been demonstrated. Here, we show that BALB/c-TGF-β1−/− mice exhibit abnormal expansion in hepatic mononuclear cells (MNCs) compared with wild-type littermate control mice, particularly in the T cell and macrophage lineages. To test whether lymphocytes of the adaptive immune system are required for the spontaneous development of necroinflammatory liver disease, BALB/c-TGF-β1−/− mice were rendered deficient in B and T cells by crossing them with BALB/c-recombinase-activating gene 1−/− mice. BALB/c-TGF-β1−/−/recombinase-activating gene 1−/− double-knockout mice showed extended survival and did not develop necroinflammatory liver disease. The cytolytic activity of BALB/c-TGF-β1−/− hepatic lymphocytes was assessed using an in vitro CTL assay. CTL activity was much higher in BALB/c-TGF-β1−/− hepatic MNCs compared with littermate control hepatic MNCs and was particularly pronounced in the CD4+ T cell subset. Experimental depletion of CD4+ T cells in young BALB/c-TGF-β1−/− mice prevented the subsequent development of necroinflammatory liver disease, indicating that CD4+ T cells are essential for disease pathogenesis in vivo. These data definitively establish an immune-mediated etiology for necroinflammatory liver disease in BALB/c-TGF-β1−/− mice and demonstrate the importance of CD4+ T cells in disease pathogenesis in vivo. Furthermore, TGF-β1 has a critical role in homeostatic regulation of the hepatic immune system, inhibiting the development or expansion of hepatic cytolytic CD4+ T cells.

Dendritic cells (DCs) can be matured by CD40 stimulation to upregulate their MHC class II/peptide complexes and costimulatory molecule surface expression to become adept at presenting antigen to and activating naive T lymphocytes. The use of anti-CD40 antibodies as adjuvants for DC-based therapy has been advanced. Little is known as to how DC biology in response to CD40 ligation differs between in vitro versus in vivo ligation. Therefore, the authors analyzed the expression kinetics of MHC class II (I-Ak)/HEL peptide "complex," total MHC class II, CD80, and CD86 on in vitro or in vivo CD40-stimulated DCs over a period of 5 days. MHC class II, "complex," and costimulatory molecule expression was elevated at 1 day in vitro and stayed high for the culture period, whereas in vivo expression of the cohort of molecules peaked earlier and then declined. When purified DCs were co-cultured in vitro with antigen-specific T cell hybridomas, the DCs had lower expression of total MHC class II and "complex," but did not reduce their CD80 and CD86 expression. The lower expression was dependent on cognate interaction as a non-antigen-specific T cell hybridoma was without effect. Blocking antigen-specific MHC class II/peptide-T cell receptor (TcR) complex interaction with antibody inhibited the reduction of MHC class II expression on CD40-stimulated DCs in vitro. Overall, their studies suggest distinct response of DCs to typical conditions that feature anti-CD40 monoclonal antibody (mAb)-activated DCs in vitro or in vivo.

Autoimmune hepatitis (AIH) in humans arises spontaneously in genetically susceptible individuals and is associated with the presence of Th1 cells in the liver. The understanding of AIH has advanced more slowly than that of other organ-specific autoimmune diseases, however, largely because of the lack of an appropriate animal model. We now describe a new mouse model characterized by spontaneous development of necroinflammatory hepatitis that is restricted by genetic background. Mice deficient in the immunomodulatory cytokine TGF-β1 were extensively back-bred to the BALB/c background. The BALB/c background dramatically modified the phenotype of TGF-β1−/− mice: specifically, BALB/c-TGF-β1−/− mice developed a lethal necroinflammatory hepatitis that was not observed in TGF-β1−/− mice on a different genetic background. BALB/c background TGF-β1−/− livers contained large numbers of activated CD4+ T cells that produced large quantities of IFN-γ, but little IL-4, identifying them as Th1 cells. BALB/c background TGF-β1−/−/IFN-γ−/− double knockout mice, generated by cross-breeding, did not develop necroinflammatory hepatitis, demonstrating that IFN-γ is mechanistically required for its pathogenesis. This represents the first murine model of hepatitis that develops spontaneously, is restricted by genetic background, and is dependent upon the Th1 cytokine IFN-γ, and that thus recapitulates these important aspects of AIH.

The immunostimulatory cytokine interleukin-2 (IL-2) is a growth factor for a wide range of leukocytes, including T cells and natural killer (NK) cells. Considerable effort has been invested in using IL-2 as a therapeutic agent for a variety of immune disorders ranging from AIDS to cancer. However, adverse effects have limited its use in the clinic. On activated T cells, IL-2 signals through a quaternary 'high affinity' receptor complex consisting of IL-2, IL-2Rα (termed CD25), IL-2Rβ and IL-2Rγ. Naive T cells express only a low density of IL-2Rβ and IL-2Rγ, and are therefore relatively insensitive to IL-2, but acquire sensitivity after CD25 expression, which captures the cytokine and presents it to IL-2Rβ and IL-2Rγ. Here, using in vitro evolution, we eliminated the functional requirement of IL-2 for CD25 expression by engineering an IL-2 'superkine' (also called super-2) with increased binding affinity for IL-2Rβ. Crystal structures of the IL-2 superkine in free and receptor-bound forms showed that the evolved mutations are principally in the core of the cytokine, and molecular dynamics simulations indicated that the evolved mutations stabilized IL-2, reducing the flexibility of a helix in the IL-2Rβ binding site, into an optimized receptor-binding conformation resembling that when bound to CD25. The evolved mutations in the IL-2 superkine recapitulated the functional role of CD25 by eliciting potent phosphorylation of STAT5 and vigorous proliferation of T cells irrespective of CD25 expression. Compared to IL-2, the IL-2 superkine induced superior expansion of cytotoxic T cells, leading to improved antitumour responses in vivo, and elicited proportionally less expansion of T regulatory cells and reduced pulmonary oedema. Collectively, we show that in vitro evolution has mimicked the functional role of CD25 in enhancing IL-2 potency and regulating target cell specificity, which has implications for immunotherapy.

GRAIL (gene related to anergy in lymphocytes) is an ubiquitin-protein isopeptide ligase (E3) ubiquitin ligase necessary for the induction of CD4(+) T cell anergy in vivo. We have extended our previous studies to characterize the expression pattern of GRAIL in other murine CD4(+) T cell types with a described anergic phenotype. These studies revealed that GRAIL expression is increased in naturally occurring (thymically derived) CD4(+) CD25(+) T regulatory cells (mRNA levels 10-fold higher than naive CD25(-) T cells). Further investigation demonstrated that CD25(+) Foxp3(+) antigen-specific T cells were induced after a "tolerizing-administration" of antigen and that GRAIL expression correlated with the CD25(+) Foxp3(+) antigen-specific subset. Lastly, using retroviral transduction, we demonstrated that forced expression of GRAIL in a T cell line was sufficient for conversion of these cells to a regulatory phenotype in the absence of detectable Foxp3. These data demonstrate that GRAIL is differentially expressed in naturally occurring and peripherally induced CD25(+) T regulatory cells and that the expression of GRAIL is linked to their functional regulatory activity.

TGF-beta1 plays a critical role in restraining pathogenic Th1 autoimmune responses in vivo, but the mechanisms that mediate TGF-beta1's suppressive effects on CD4(+) T cell expression of IFN-gamma expression remain incompletely understood. To evaluate mechanisms by which TGF-beta1 inhibits IFN-gamma expression in CD4(+) T cells, we primed naive wild-type murine BALB/c CD4(+) T cells in vitro under Th1 development conditions in the presence or the absence of added TGF-beta1. We found that the presence of TGF-beta1 during priming of CD4(+) T cells suppressed both IFN-gamma expression during priming as well as the development of Th1 effector cells expressing IFN-gamma at a recall stimulation. TGF-beta1 inhibited the development of IFN-gamma-expressing cells in a dose-dependent fashion and in the absence of APC, indicating that TGF-beta1 can inhibit Th1 development by acting directly on the CD4(+) T cell. During priming, TGF-beta1 strongly inhibited the expression of both T-bet (T box expressed in T cells) and Stat4. We evaluated the importance of these two molecules in the suppression of IFN-gamma expression at the two phases of Th1 responses. Enforced expression of T-bet by retrovirus prevented TGF-beta1's inhibition of Th1 development, but did not prevent TGF-beta1's inhibition of IFN-gamma expression at priming. Conversely, enforced expression of Stat4 partly prevented TGF-beta1's inhibition of IFN-gamma expression during priming, but did not prevent TGF-beta1's inhibition of Th1 development. These data show that TGF-beta1 uses distinct mechanisms to inhibit IFN-gamma expression in CD4(+) T cells at priming and at recall.

Transforming growth factor-beta1 (TGF-beta1) is a critical regulator of T cell responses in vivo. In vitro, TGF-beta1 can either enhance or inhibit T cell proliferative responses, but the relevant factors that determine the T cell response to TGF-beta1 remain obscure. Here, we present evidence that CD28 co-stimulation modifies the effects of TGF-beta1 on T cell proliferation. In the absence of CD28 co-stimulation, TGF-beta1 potently suppressed TCR-stimulated proliferation of naïve T cells. In the presence of CD28 co-stimulation, TGF-beta1 potently inhibited T cell apoptosis and enhanced TCR-stimulated proliferation. A similar effect of CD28 co-stimulation was not observed in memory/effector cells, whose proliferation was enhanced by TGF-beta1, whether co-stimulated or not. We examined the mechanism by which CD28 modulates naïve T cell responses to TGF-beta1. Since CD28 co-stimulation classically is a potent enhancer of interleukin (IL)-2 production, we anticipated observing high IL-2 production from naïve T cells stimulated with anti-CD3/anti-CD28 and TGF-beta1. Surprisingly, however, TGF-beta1 strongly inhibited production of IL-2 from naïve CD4(+) T cells, even when CD28 was engaged. Even though IL-2 levels were strongly suppressed by TGF-beta1 to trace levels, antibody neutralization studies showed that IL-2 is still a basic requirement for the proliferation of anti-CD3/anti-CD28/TGF-beta1-stimulated naïve T cells. These data show that CD28's modulation of T cell responses to TGF-beta1 is not via the production of high levels of IL-2, and suggest that engagement of CD28 may activate additional downstream pathways that modulate the responses of naïve T cells to TGF-beta1.

Dendritic cells (DCs) can be matured by CD40 stimulation to upregulate their MHC class II/peptide complexes and costimulatory molecule surface expression to become adept at presenting antigen to and activating naive T lymphocytes. The use of anti-CD40 antibodies as adjuvants for DC-based therapy has been advanced. Little is known as to how DC biology in response to CD40 ligation differs between in vitro versus in vivo ligation. Therefore, the authors analyzed the expression kinetics of MHC class II (I-Ak)/HEL peptide "complex," total MHC class II, CD80, and CD86 on in vitro or in vivo CD40-stimulated DCs over a period of 5 days. MHC class II, "complex," and costimulatory molecule expression was elevated at 1 day in vitro and stayed high for the culture period, whereas in vivo expression of the cohort of molecules peaked earlier and then declined. When purified DCs were co-cultured in vitro with antigen-specific T cell hybridomas, the DCs had lower expression of total MHC class II and "complex," but did not reduce their CD80 and CD86 expression. The lower expression was dependent on cognate interaction as a non-antigen-specific T cell hybridoma was without effect. Blocking antigen-specific MHC class II/peptide-T cell receptor (TcR) complex interaction with antibody inhibited the reduction of MHC class II expression on CD40-stimulated DCs in vitro. Overall, their studies suggest distinct response of DCs to typical conditions that feature anti-CD40 monoclonal antibody (mAb)-activated DCs in vitro or in vivo.

The question of whether cytokines can deliver ‘instructive’ signals through their interactions with the cytokine receptor extracellular domains remains an unsolved, but important question. While every cytokine receptor system to date exhibits some form of ligand-dependent oligomerization as a prerequisite for activation, it is unclear if the specific nuances of the recognition chemistry and extracellular domain-cytokine complex architecture play a role in modulating the specificity of signaling. Our group is exploring this questions in shared cytokine receptor systems such as Interferon, gp130/IL-12, and common gamma chain through an integration of structural studies to directly image the cytokine-receptor complexes, and engineering studies aimed at influencing signaling through introducing chemical and structural perturbations. In my talk I will present recent results from these studies bearing on the issue of ligand-based tuning of cytokine receptor signaling.

Abstract 2093 Background: Adoptive immunotherapy is a promising novel approach to the treatment of cancer. However, clinical translation of adoptively transferred CD4 T cells is limited by cotransfer of an inhibitory population of regulatory CD4 T cells (Tregs). We identified a method of isolating viable antitumor CD4 T cells while excluding Tregs based on two surface markers—CD44 and CD137. Methods: We have developed a model for adoptive cell therapy of lymphoma whereby anti-tumor T cells are generated in vivo through vaccination with a CpG-loaded whole cell vaccine (CpG/H11). These vaccine-induced cells can protect from lethal tumor challenge when isolated and transferred into lethally irradiated, syngeneic recipient mice. We investigated the subsets of T cells involved in the anti-tumor response through a combination of in vitro and in vivo assays. Results: Adoptive transfer of CD137negCD44hi CD4 T cells, but not other sub-populations, provided protection from B cell lymphoma. We demonstrate that the population of CD137posCD44hi CD4 T cells consists primarily of activated Tregs. In vitro, these CD137pos cells suppressed the proliferation of effector cells in a contact-dependent manner. We observed that this CD137pos Treg population persisted following adoptive transfer and maintained expression of FoxP3 as well as CD137. Moreover, the addition of CD137posCD44hi CD4 cells to CD137negCD44hi CD4 cells suppressed the antitumor immune response. In the presence of CD137posCD44hi CD4 T cells, homing of other T cell populations to tumor sites was disrupted. These results suggest that CD137 expression on CD4 T cells defines a population of activated Tregs that prevent antitumor immune responses. Conclusions: Our findings identify two surface markers that can be used to facilitate the enrichment of anti-tumor CD4 T cells while depleting an inhibitory Treg population. This approach has direct applicability to clinical trials for patients with lymphoma. Disclosures: No relevant conflicts of interest to declare.

Abstract 722 Immunomodulating monoclonal antibodies (mAb) directed against immune cell targets can be used to enhance antitumor immune responses. CD137 (4-1BB) is a costimulatory molecule expressed on a variety of activated immune cells, including T and NK cells. Anti-CD137 agonistic mAb has demonstrated antitumor activity in various tumor models and has now entered clinical trials for the treatment of solid tumors (BMS-663513). Here, we investigate the therapeutic potential of anti-CD137 mAb in lymphoma. Using microarray gene expression data, we compared CD137 mRNA expression across 17 different types of cancer. We found that lymphoma tumor specimens significantly over-expressed CD137 mRNA compared to other tumors (p Using a murine model, we then investigated the anti-lymphoma activity of anti-CD137 agonistic mAb in vivo. BALB/c mice, bearing large and established A20 lymphoma tumors, were treated with anti-CD137 mAb or other immunomodulating mAbs (anti-OX40, anti-CTLA4, anti-GITR) for comparison. The mAbs were given i.p. on days 5 and 10 post tumor inoculation. Anti-CD137 mAb demonstrated potent anti-lymphoma activity in vivo, and appeared to be significantly superior to the other immunomodulating mAbs tested (Figure 1). The antitumor effect of anti-CD137 mAb was not due to direct targeting of the malignant cells as A20 tumor cells do not express CD137. Depletion experiments revealed that anti-CD137 therapy required both NK and CD8 T cells. Analysis of tumor-bearing mice showed that anti-CD137 therapy increased the number of CD8 T cells and reduced the number of Tregs at the tumor site. Anti-CD137 therapy also induced long-lasting antitumor immunity as cured mice harbored antitumor IFN-g producing memory CD8 T cells and were protected from tumor re-challenge more than 100 days after initial therapy. In conclusion, this study demonstrates for the first time that anti-CD137 agonistic mAb has potent antitumor activity in lymphoma. These results support the evaluation of anti-CD137 mAb in clinical trials for patients with lymphoma. Disclosures: No relevant conflicts of interest to declare.