Protein disulphide isomerase (PDI) is protective against amyotrophic lateral sclerosis (ALS)-related mutant Fused in Sarcoma (FUS) in in vitro models

Mutations in Fused in Sarcoma (FUS) are present in familial and sporadic cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). FUS is localised in the nucleus where it has important functions in DNA repair. However, in ALS/FTD, mutant FUS mislocalises from the nucleus to the cytoplasm where it forms inclusions, a key pathological hallmark of neurodegeneration. Mutant FUS also inhibits protein import into the nucleus, resulting in defects in nucleocytoplasmic transport. Fragmentation of the neuronal Golgi apparatus, induction of endoplasmic reticulum (ER) stress, and inhibition of ER-Golgi trafficking are also associated with mutant FUS misfolding in ALS. Protein disulphide isomerase (PDI) is an ER chaperone previously shown to be protective against misfolding associated with mutant superoxide dismutase 1 (SOD1) and TAR DNA-binding protein-43 (TDP-43) in cellular and zebrafish models. However, a protective role against mutant FUS in ALS has not been previously described. In this study, we demonstrate that PDI is protective against mutant FUS. In neuronal cell line and primary cultures, PDI restores defects in nuclear import, prevents the formation of mutant FUS inclusions, inhibits Golgi fragmentation, ER stress, ER-Golgi transport defects, and apoptosis. These findings imply that PDI is a new therapeutic target in FUS-associated ALS.

Activation of antigen-exposed iMC-DCs at the "right place" and "right time" promotes potent anti-tumor immunity

To better control the “licensing” of pro-Th1 dendritic cells (DCs), Spencer and colleagues have developed a synthetic ligand-inducible chimeric receptor, iMyD88/CD40 (iMC), incorporating synergistic Toll-like receptor (TLR) and costimulatory signaling elements, permitting DC regulation in vivo within the context of an immunological synapse. This novel technology results in potent anti-cancer activity.

Engineering Tolerance toward Allogeneic CAR-T Cells by Regulation of MHC Surface Expression with Human Herpes Virus-8 Proteins

Allogeneic, off-the-shelf (OTS) chimeric antigen receptor (CAR) cell therapies have the potential to reduce manufacturing costs and variability while providing broader accessibility to cancer patients and those with other diseases. However, host-versus-graft reactivity can limit the durability and efficacy of OTS cell therapies requiring new strategies to evade adaptive and innate-immune responses. Human herpes virus-8 (HHV8) maintains infection, in part, by evading host T and natural killer (NK) cell attack. The viral K3 gene encodes a membrane-tethered E3 ubiquitin ligase that discretely targets major histocompatibility complex (MHC) class I components, whereas K5 encodes a similar E3 ligase with broader specificity, including MHC-II and the MHC-like MHC class I polypeptide-related sequence A (MIC-A)- and sequence B (MIC-B)-activating ligands of NK cells. We created γ-retroviruses encoding K3 and/or K5 transgenes that efficiently transduce primary human T cells. Expression of K3 or K5 resulted in dramatic downregulation of MHC-IA (human leukocyte antigen [HLA]-A, -B, and -C) and MHC class II (HLA-DR) cell-surface expression. K3 expression was sufficient for T cells to resist exogenously loaded peptide-MHC-specific cytotoxicity, as well as recognition in one-way allogeneic mixed lymphocyte reactions. Further, in immunodeficient mice engrafted with allogeneic T cells, K3-transduced T cells selectively expanded in vivo. Ectopic K5 expression in MHC class I^-, MIC-A⁺/B⁺ K562 cells also reduced targeting by primary NK cells. Coexpression of K3 in prostate stem cell antigen (PSCA)-directed, inducible MyD88/CD40 (iMC)-enhanced CAR-T cells did not impact cytotoxicity, T cell growth, or cytokine production against HPAC pancreatic tumor target cells, whereas K5-expressing cells showed a modest reduction in interleukin (IL)-2 production without effect on cytotoxicity. Together, these results support application of these E3 ligases to advance development of OTS CAR-T cell products.

Abstract 2193: Small molecule inducible MyD88/CD40 (iMC) in CAR-T cells can repolarize M2 macrophage to an anti-tumor M1 phenotype

Background: Effective chimeric antigen receptor (CAR) T cell therapy against solid tumors must overcome a hostile, tumor microenvironment that includes tumor-associated macrophages (TAM). Pancreatic adenocarcinomas (PDAC) are commonly infiltrated with TAMs polarized to a tumor-promoting M2 phenotype rather than a T cell-stimulatory and tumor-inhibitory M1 phenotype. The GoCAR platform combines an inducible MyD88/CD40 (iMC) costimulation protein with a 1st generation CAR. Our previously published results demonstrated that iMC costimulation, activated by the small molecule dimerizer, rimiducid (Rim), enhanced CAR-T proliferation and anti-tumor efficacy. Here, we examined the extrinsic effects of iMC signaling on CAR-T cell immune-activating ligands, cytokine production and their ability to polarize M2 macrophage to an anti-tumor phenotype.

Methods: Macrophages were prepared from peripheral blood monocytes of four or more random blood donors from the Gulf Coast Regional Blood Center (Houston, TX) and differentiated in vitro to an M2 phenotype with TGF-β and IL-10, or an M1 phenotype (as a positive control). GoCAR-T cells targeting prostate stem cell antigen (PSCA) were prepared by retroviral transduction from the autologous donors. To test the effects of iMC activation on macrophage polarization, contact-dependent or independent (i.e., separation of cell populations with transwell inserts) coculture assays were performed with and without activation of iMC with 1 nM Rim and/or surface-bound PSCA. Anti-tumor cytotoxicity was measured by coculture with PSCA+ Panc1-GFP cells.

Results: CAR activation by PSCA antigen recognition or iMC activation with Rim decreased CD163, an M2 macrophage marker, and increased CD80, expressed on M1 macrophage. Full activation of the GoCAR-T cells with both Rim and the target antigen fully repolarized M2 macrophage to an M1 marked phenotype (CD163lowCD80high). This repolarization could be directed partially in the absence of cell-cell contact by diffusion of soluble factors through Transwell membranes. M2 macrophages repolarized by conditioning media from activated GoCAR-T cells also exhibited the functionality of M1 macrophages and acquired cytotoxicity against tumor cells. Furthermore, cultures of conditioned macrophages and limiting dilutions of GoCAR-T cells demonstrated a cooperative enhancement of the cytotoxicity of PSCA GoCAR-T cells toward Panc-1 targets. This cooperation was more effective for GoCAR-T cells than CD28- or 4-1BB-enhanced 2nd generation PSCA CAR-T cells.

Conclusions: These results predict that GoCAR-T activation with Rim will convert TAMs within a solid tumor microenvironment from T cell inhibitors to tumor-caustic agents.

Citation Format: Xiaohong Wang, Konrad Gabrusiewicz, David M. Spencer, Aaron E. Foster, J. Henri Bayle. Small molecule inducible MyD88/CD40 (iMC) in CAR-T cells can repolarize M2 macrophage to an anti-tumor M1 phenotype [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 2193.

Two-Dimensional Regulation of CAR-T Cell Therapy with Orthogonal Switches

Use of chimeric antigen receptors (CARs) as the basis of targeted adoptive T cell therapies has enabled dramatic efficacy against multiple hematopoietic malignancies, but potency against bulky and solid tumors has lagged, potentially due to insufficient CAR-T cell expansion and persistence. To improve CAR-T cell efficacy, we utilized a potent activation switch based on rimiducid-inducible MyD88 and CD40 (iMC)-signaling elements. To offset potential toxicity risks by this enhanced CAR, an orthogonally regulated, rapamycin-induced, caspase-9-based safety switch (iRC9) was developed to allow in vivo elimination of CAR-T cells. iMC costimulation induced by systemic rimiducid administration enhanced CAR-T cell proliferation, cytokine secretion, and antitumor efficacy in both in vitro assays and xenograft tumor models. Conversely, rapamycin-mediated iRC9 dimerization rapidly induced apoptosis in a dose-dependent fashion as an approach to mitigate therapy-related toxicity. This novel, regulatable dual-switch system may promote greater CAR-T cell expansion and prolonged persistence in a drug-dependent manner while providing a safety switch to mitigate toxicity concerns.

Phase I trial of antigen-targeted autologous dendritic cell-based vaccine with in vivo activation of inducible CD40 for advanced prostate cancer

This phase I trial reports the safety and activity of BPX101, a second-generation antigen-targeted autologous antigen presenting cell (APC) vaccine in men with metastatic castration-resistant prostate cancer (mCRPC). To manufacture BPX101, APCs collected in a single leukapheresis were transduced with adenoviral vector Ad5f35 encoding inducible human (ih)-CD40, followed by incubation with protein PA001, which contains the extracellular domain of human prostate-specific membrane antigen. The ih-CD40 represents a modified chimeric version of the dendritic cell (DC) co-stimulatory molecule, CD40, which responds to a bioinert membrane-permeable activating dimerizer drug, rimiducid (AP1903), permitting temporally controlled, lymphoid-localized, DC-specific activation. Eighteen men with progressive mCRPC following ≤1 prior chemotherapy regimen were enrolled to evaluate three doses of BPX101 (4 × 106, 12.5 × 106 and 25 × 106 cells) administered intradermally every 2-4 weeks followed by rimiducid (0.4 mg/kg) intravenous (IV) infusion 24 h after each BPX101 dose. There were no dose-limiting toxicities. Immune upregulation as well as anti-tumor activity was observed with PSA declines, objective tumor regressions and robust efficacy of post-trial therapy. This novel antigen-targeted and in vivo activated immunotherapy platform may warrant further development as monotherapy and as a component of rational combinations.

Inducible Activation of MyD88 and CD40 in CAR T Cells Results in Controllable and Potent Antitumor Activity in Preclinical Solid Tumor Models

Adoptive immunotherapy with T cells expressing chimeric antigen receptors (CAR) has had limited success for solid tumors in early-phase clinical studies. We reasoned that introducing into CAR T cells an inducible costimulatory (iCO) molecule consisting of a chemical inducer of dimerization (CID)-binding domain and the MyD88 and CD40 signaling domains would improve and control CAR T-cell activation. In the presence of CID, T cells expressing HER2-CARζ and a MyD88/CD40-based iCO molecule (HER2ζ.iCO T cells) had superior T-cell proliferation, cytokine production, and ability to sequentially kill targets in vitro relative to HER2ζ.iCO T cells without CID and T cells expressing HER2-CAR.CD28ζ. HER2ζ.iCO T cells with CID also significantly improved survival in vivo in two xenograft models. Repeat injections of CID were able to further increase the antitumor activity of HER2ζ.iCO T cells in vivo Thus, expressing MyD88/CD40-based iCO molecules in CAR T cells has the potential to improve the efficacy of CAR T-cell therapy approaches for solid tumors.Significance: Inducible activation of MyD88 and CD40 in CAR T cells with a small-molecule drug not only enhances their effector function, resulting in potent antitumor activity in preclinical solid tumors, but also enables their remote control post infusion. Cancer Discov; 7(11); 1306-19. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 1201.

Regulated Expansion and Survival of Chimeric Antigen Receptor-Modified T Cells Using Small Molecule-Dependent Inducible MyD88/CD40

Anti-tumor efficacy of T cells engineered to express chimeric antigen receptors (CARs) is dependent on their specificity, survival, and in vivo expansion following adoptive transfer. Toll-like receptor (TLR) and CD40 signaling in T cells can improve persistence and drive proliferation of antigen-specific CD4⁺ and CD8⁺ T cells following pathogen challenge or in graft-versus-host disease (GvHD) settings, suggesting that these costimulatory pathways may be co-opted to improve CAR-T cell persistence and function. Here, we present a novel strategy to activate TLR and CD40 signaling in human T cells using inducible MyD88/CD40 (iMC), which can be triggered in vivo via the synthetic dimerizing ligand, rimiducid, to provide potent costimulation to CAR-modified T cells. Importantly, the concurrent activation of iMC (with rimiducid) and CAR (by antigen recognition) is required for interleukin (IL)-2 production and robust CAR-T cell expansion and may provide a user-controlled mechanism to amplify CAR-T cell levels in vivo and augment anti-tumor efficacy.

Abstract LB-184: Dual-switchGoCAR-T cells: small molecule-regulated “GO” and “STOP” switches to target solid cancer in vivo

Background:

While chimeric antigen receptor (CAR)-T immunotherapies have shown remarkable efficacy against leukemias and lymphomas, improved CAR-T efficacy and persistence are needed to overcome solid tumors, without compromising safety. Here, we present two independently regulated molecular switches that can elicit specific and rapid induction of cellular responses upon exposure to their cognate ligands. Cell activation is controlled by the homodimerizer rimiducid that triggers signaling cascades downstream of MyD88 and CD40 via an engineered chimeric protein termed iMC. A rapamycin-controlled pro-apoptotic switch, iRC9, is co-expressed, which induces dimerization of the caspase-9 domain to mitigate possible toxicity from excessive CAR-T function. When combined with a first generation CAR, these molecular switches allow for specific and efficient regulation of engineered T cells.

Methods & Results:

T cells were activated and co-transduced with the HER2 GoCAR (SFG-iMC.2A-CAR.ζ) and RapaCIDe (SFG-iRC9.2A-ΔCD19) vectors to generate “Dual-switch GoCAR-T” cells. Combined transduction of RapaCIDe and HER2 GoCAR vectors into T cells did not adversely affect the antitumor efficacy of the GoCAR-T cells, which eliminated OE19 esophageal tumor cells in a 7-day coculture assay at a 1:20 effector to target ratio (3.9±4.3% OE19-eGFPFluc cells remained in GoCAR-modified cultures vs. 1.1±0.1% for the dual-switch GoCAR), and promoted T cell expansion (53.4±9.4% CAR+ for GoCAR vs. 44.6±13.2% for the dual-switch). When challenged in an OE19 tumor-bearing mouse model, rimiducid stimulation of the dual-switch GoCAR-T cells enhanced tumor killing and T cell expansion.

Deployment of the off-switch induced fast (½ Vmax ~ 8 hours) and efficient elimination of T cells (Dual-switch GoCAR-T = 94.1% AnnV+/PI+ vs. GoCAR-T = 5.1%) in a caspase-3 activation assay with real-time (IncuCyte) monitoring as well as AnnV/PI detection by flow cytometry. In vivo assessment of the RapaCIDe switch was performed via eGFPluciferase (eGFPfluc)-labeled RapaCIDe-T cells in NSG mice. Rapamycin, but not rimiducid, treatment efficiently eliminated RapaCIDe-T cells within 24 hours, which is similar to the rate observed by the clinically validated rimiducid-regulated CaspaCIDe switch.

Summary:

Dual-switch GoCAR-T, a novel platform comprising a first-generation CAR combined with regulated costimulation and apoptotic signaling elements, effectively controlled tumor growth and T cell expansion and elimination in vitro and in vivo. This dual-switch technology provides a user-controlled system for managing persistence and safety of tumor antigen-specific CAR-T cells.

Citation Format: MyLinh T. Duong, Matthew R. Collinson-Pautz, Eva Morschl, Mary E. Brandt, Ming Zhang, Kevin W. Slawin, Aaron E. Foster, J. Henri Bayle, David M. Spencer. Dual-switchGoCAR-T cells: small molecule-regulated “GO” and “STOP” switches to target solid cancer in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-184. doi:10.1158/1538-7445.AM2017-LB-184

Exposure to sequestered self-antigens in vivo is not sufficient for the induction of autoimmune diabetes

Although the role of T cells in autoimmunity has been explored for many years, the mechanisms leading to the initial priming of an autoimmune T cell response remain enigmatic. The 'hit and run' model suggests that self-antigens released upon cell death can provide the initial signal for a self-sustaining autoimmune response. Using a novel transgenic mouse model where we could induce the release of self-antigens via caspase-dependent apoptosis. We tracked the fate of CD8+ T cells specific for the self-antigen. Our studies demonstrated that antigens released from apoptotic cells were cross-presented by CD11c+ cells in the draining lymph node. This cross-presentation led to proliferation of self-antigen specific T cells, followed by a transient ability to produce IFN-γ, but did not lead to the development of autoimmune diabetes. Using this model we examined the consequences on T cell immunity when apoptosis was combined with dendritic cell maturation signals, an autoimmune susceptible genetic background, and the deletion of Tregs. The results of our study demonstrate that autoimmune diabetes cannot be initiated by the presentation of antigens released from apoptotic cells in vivo even in the presence of factors known to promote autoimmunity.

MyD88/CD40 Genetic Adjuvant Function in Cutaneous Atypical Antigen-Presenting Cells Contributes to DNA Vaccine Immunogenicity

Therapeutic DNA-based vaccines aim to prime an adaptive host immune response against tumor-associated antigens, eliminating cancer cells primarily through CD8+ cytotoxic T cell-mediated destruction. To be optimally effective, immunological adjuvants are required for the activation of tumor-specific CD8+ T cells responses by DNA vaccination. Here, we describe enhanced anti-tumor efficacy of an in vivo electroporation-delivered DNA vaccine by inclusion of a genetically encoded chimeric MyD88/CD40 (MC) adjuvant, which integrates both innate and adaptive immune signaling pathways. When incorporated into a DNA vaccine, signaling by the MC adjuvant increased antigen-specific CD8+ T cells and promoted elimination of pre-established tumors. Interestingly, MC-enhanced vaccine efficacy did not require direct-expression of either antigen or adjuvant by local antigen-presenting cells, but rather our data supports a key role for MC function in "atypical" antigen-presenting cells of skin. In particular, MC adjuvant-modified keratinocytes increased inflammatory cytokine secretion, upregulated surface MHC class I, and were able to increase in vitro and in vivo priming of antigen-specific CD8+ T cells. Furthermore, in the absence of critical CD8α+/CD103+ cross-priming dendritic cells, MC was still able to promote immune priming in vivo, albeit at a reduced level. Altogether, our data support a mechanism by which MC signaling activates an inflammatory phenotype in atypical antigen-presenting cells within the cutaneous vaccination site, leading to an enhanced CD8+ T cell response against DNA vaccine-encoded antigens, through both CD8α+/CD103+ dendritic cell-dependent and independent pathways.

Abstract LB-084: Go-TCR™: Inducible MyD88/CD40 (iMC) enhances proliferation and survival of tumor-specific TCR-modified T cells, increasing anti-tumor efficacy

Introduction: Use of tumor antigen-specific T cell receptors (TCRs) to refocus T cell killing has shown tantalizing clinical efficacy; however, durable responses have been limited by poor T cell persistence and expansion in vivo. Also, MHC class I downregulation in tumors further reduces therapeutic efficacy. Therefore, we co-expressed in human T cells a small molecule dimerizer (rimiducid)-dependent “activation switch”, called inducible MyD88/CD40 (iMC), along with tumor-targeted TCRs to regulate T cell expansion and activation, while affecting upregulation of MHC class I on tumors.

Methods: Human T cells were CD3/CD28-activated and transduced with αβTCR-encoding γ-retroviruses recognizing either the CT antigen, PRAME (HLA-A*02:01/SLLQHLIGL), or the B-cell-specific transcriptional co-activator, Bob1/OBF-1 (HLA-B*07:02/APAPTAVVL). Parallel “Go-TCR” vectors co-expressed iMC, comprising MyD88 and CD40 signaling domains along with rimiducid-binding FKBP12-V36. Proliferation, cytokine production and cytotoxicity of modified T cells was assessed using peptide-pulsed T2 cells (PRAME only) or against PRAME+/Bob1+, HLA-A2+ -B7+ U266 myeloma cells +/- 10 nM rimiducid. MHC class I induction was measured using transwell assays and flow cytometry. In vitro tumor killing was analyzed by T cell and tumor coculture assays at various effector to target ratios over a 7-day period. Finally, in vivo efficacy was determined using immune-deficient NSG mice engrafted i.v. with U266 cells and treated i.v. with 1×107 transduced T cells. iMC was activated in vivo by weekly i.p. rimiducid injections (1-5 mg/kg). Tumor size and T cell expansion was measured using in vivo BLI imaging and flow cytometry.

Results: All vectors efficiently (∼85%) transduced activated T cells and showed antigen-specific IFN-γ production and cytotoxicity against peptide-pulsed T2 cells and/or PRAME+Bob1+ U266 cells. However, both iMC signaling and TCR ligation of PRAME peptide-pulsed T2 Cells were required for IL-2 production. Coculture assays with U266 cells showed that tumor elimination, IL-2 secretion and robust (∼ 50-fold) T cell proliferation (vs TCR signaling alone) was optimized with concurrent rimiducid-driven iMC activation in both “Go-PRAME” and “Go-Bob1” constructs. Further, iMC activation produced TCR-independent IFN-γ that increased (∼100-fold) MHC class I expression on tumor cells. In NSG mice engrafted with U266 tumors, iMC-PRAME TCR-modified T cells persisted for at least 81 days post-injection and prevented tumor growth, unlike other T cell groups. Importantly, weekly rimiducid injection dramatically expanded iMC-PRAME TCR-expressing T cell numbers by ∼1000-fold on day 81 post-injection vs T cells expressing only the PRAME TCR (p < 0.001).

Summary: The novel rimiducid-regulated “Go” switch, iMC, greatly augments activation and expansion of TCR-engineered T cells while sensitizing tumors to T cells via cytokine-induced MHC class I upregulation. iMC-enhanced TCRs are prototypes of novel “Go-TCR” engineered T cell therapies that increase efficacy, safety and durability of adoptive T cell therapies.

Citation Format: David M. Spencer, Tsvetelina P. Hoang, Aaron Foster, Tania Rodriguez, David Torres, An Lu, Jeannette Crisostomo, Lorenz Jahn, Mirjam H.M. Heemskerk. Go-TCR™: Inducible MyD88/CD40 (iMC) enhances proliferation and survival of tumor-specific TCR-modified T cells, increasing anti-tumor efficacy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-084.

Inducible MyD88/CD40 to allow rimiducid-dependent activation for control of proliferation and survival of chimeric antigen receptor (CAR) T cells targeting prostate stem cell antigen (PSCA)

206

Background: PSCA is a cell surface antigen that is overexpressed in a majority of metastatic prostate, transitional cell and pancreatic carcinomas. We describe a novel T cell costimulation switch, inducible MyD88/CD40 (iMC), activated by a small molecule, rimiducid, to enhance survival, proliferation and anti-tumor activity of CAR-T cells targeting PSCA. Methods: T cells were transduced with a retrovirus encoding tandem rimiducid-binding domains,cloned in-frame with MyD88 and CD40 signaling elements and first generation CARs (CAR.ζ) targeting PSCA (SFG-iMC-2A-PSCA.ζ). iMC activation was assessed with and without rimiducid treatment of T cells. Coactivation via iMC and CAR was tested in coculture assays with or without rimiducid using various PSCA+tumor cells, e.g. Capan-1 and HPAC pancreatic adenocarcinoma. Efficacy of iMC-modified CAR-T cells in vivo was assessed using an NSG mouse tumor model. Results: T cells transduced with iMC-PSCA.ζ produced cytokines (e.g., IFN-γ and IL-6) in response to rimiducid; however, IL-2 was only produced when both iMC and CAR were activated simultaneously by rimiducid and tumor antigen. Treatment of NSG mice bearing large (> 200 mm3) HPAC tumors with a single i.v. dose of 1x107 iMC-PSCA.ζ cells resulted in complete tumor elimination in 10/10 mice including both rimiducid-treated and untreated animals, compared to mice receiving non-transduced T cells (p = 0.0003). Weekly rimiducid administration dramatically increased CAR-T cell numbers, resulting in a 23-fold expansion of iMC-PSCA.ζ-modified T cells in the spleen compared to mice not receiving rimiducid four weeks after infusion (p = 0.02). In a dose-titration study, rimiducid administration was required for tumor control, and led to 565- and 948-fold T cell expansion at the tumor site, respectively, when lower numbers (1.25x106 or 6.25x105, respectively) of iMC-PSCA.ζ-modified T cells were given. Conclusions: GoCAR-T cells targeting PSCA, which contain an inducible MyD88/CD40 activation switch, may be an effective adoptive cell therapy for patients with pancreatic, prostate, bladder, and other cancers that overexpress PSCA.

Abstract A057: Uni-CIDeCAR-T cells: MyD88/CD40-enhanced, Ab-directed CAR incorporating the CaspaCIDe® safety switch

Background: While chimeric antigen receptor (CAR)-T immunotherapies are remarkably effective against a subset of leukemias and lymphomas, three current hurdles for broad deployment include lack of regulation once administered to the patient, modest efficacy against solid tumors, and the necessity to make separate GMP vectors for each tumor target.

Methods: We developed two methods that utilize chemical induction of protein dimerization (CID) to regulate the activity of engineered T cells containing a CAR of broad utility. “Uni-iC9CAR” combines Bellicum's caspase-9-based, rimiducid-inducible safety switch, CaspaCIDe, with a first generation CD16/FCGR3A–CAR. Antigen receptor specificity relies on the interaction of the Fc-binding domain of CD16 with various tumor-targeted antibodies. In the “Uni-GoCAR” strategy, signaling domains from MyD88 and CD40 are fused to two copies of FKBPv36 to generate iMC, which is co-expressed with the CD16-based CAR. In each strategy, the same dimerizer, rimiducid, binds to FKBPv36 with sub-nanomolar affinity to cause the activation of signaling molecules with distinct functions and outcomes. Lastly, we generated the “Uni-CIDeCAR” vector that combines the iCaspase-9 and CD16-CAR activities from Uni-iC9CAR with augmented ligand-independent MyD88/CD40 costimulation to generate a potent universal CAR with a rapid and effective suicide gene, activated by the normally bio-inert ligand, rimiducid.

Results: Both Uni-GoCAR and Uni-iC9CAR constructs demonstrated rapid, effective and durable, rituximab-dependent antitumor activity when expressed in human T cells and mixed with Raji B cells as early as 7 days after T cell co-culture at a 1:1 ratio. Additionally, rimiducid induced robust cytokine production, including IL-2 and IL-6, and proliferation in T cells transduced with the Uni-GoCAR vector, which expresses the iMC activation switch. In contrast, co-expression of iC9 in the Uni-iC9CAR vector demonstrated robust rimiducid-dependent T cell apoptosis, thus providing a valuable safety mechanism for clinical applications. Finally, in the enhanced, but regulated, Uni-CIDeCAR vector, iC9 maintains safety in a CD16-CAR that is functionally enhanced by rimiducid-independent, basal MC activity.

Conclusion: We report an improved “universal” CAR-T technology that employs a CD16-based CAR (described by Kudo et al (14) Cancer Res) coupled with Bellicum's costimulatory and safety switches to effectively target tumor cells while providing a broad clinical safety net.

Citation Format: MyLinh T. Duong, Matthew R. Collinson-Pautz, Aaron E. Foster, J. Henri Bayle, David M. Spencer. Uni-CIDeCAR-T cells: MyD88/CD40-enhanced, Ab-directed CAR incorporating the CaspaCIDe® safety switch. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A057.

Regulated apoptosis of genetically modified hematopoietic stem and progenitor cells via an inducible caspase-9 suicide gene in rhesus macaques

The high risk of insertional oncogenesis reported in clinical trials using integrating retroviral vectors to genetically modify hematopoietic stem and progenitor cells (HSPCs) requires the development of safety strategies to minimize risks associated with novel cell and gene therapies. The ability to ablate genetically modified cells in vivo is desirable, should an abnormal clone emerge. Inclusion of "suicide genes" in vectors to facilitate targeted ablation of vector-containing abnormal clones in vivo is one potential safety approach. We tested whether the inclusion of the "inducible Caspase-9" (iCasp9) suicide gene in a gamma-retroviral vector facilitated efficient elimination of vector-containing HSPCs and their hematopoietic progeny in vivo long-term, in an autologous non-human primate transplantation model. Following stable engraftment of iCasp9 expressing hematopoietic cells in rhesus macaques, administration of AP1903, a chemical inducer of dimerization able to activate iCasp9, specifically eliminated vector-containing cells in all hematopoietic lineages long-term, suggesting activity at the HSPC level. Between 75% and 94% of vector-containing cells were eliminated by well-tolerated AP1903 dosing, but lack of complete ablation was linked to lower iCasp9 expression in residual cells. Further investigation of resistance mechanisms demonstrated upregulation of Bcl-2 in hematopoietic cell lines transduced with the vector and resistant to AP1903 ablation. These results demonstrate both the potential and the limitations of safety approaches using iCasp9 to HSPC-targeted gene therapy settings, in a model with great relevance to clinical development.

Development of an inducible caspase-9 safety switch for pluripotent stem cell-based therapies

Induced pluripotent stem cell (iPSC) therapies offer a promising path for patient-specific regenerative medicine. However, tumor formation from residual undifferentiated iPSC or transformation of iPSC or their derivatives is a risk. Inclusion of a suicide gene is one approach to risk mitigation. We introduced a dimerizable-“inducible caspase-9” (iCasp9) suicide gene into mouse iPSC (miPSC) and rhesus iPSC (RhiPSC) via a lentivirus, driving expression from either a cytomegalovirus (CMV), elongation factor-1 α (EF1α) or pluripotency-specific EOS-C(3+) promoter. Exposure of the iPSC to the synthetic chemical dimerizer, AP1903, in vitro induced effective apoptosis in EF1α-iCasp9-expressing (EF1α)-iPSC, with less effective killing of EOS-C(3+)-iPSC and CMV-iPSC, proportional to transgene expression in these cells. AP1903 treatment of EF1α-iCasp9 miPSC in vitro delayed or prevented teratomas. AP1903 administration following subcutaneous or intravenous delivery of EF1α-iPSC resulted in delayed teratoma progression but did not ablate tumors. EF1α-iCasp9 expression was downregulated during in vitro and in vivo differentiation due to DNA methylation at CpG islands within the promoter, and methylation, and thus decreased expression, could be reversed by 5-azacytidine treatment. The level and stability of suicide gene expression will be important for the development of suicide gene strategies in iPSC regenerative medicine.

The expression of HMGB1 on microparticles from Jurkat and HL-60 cells undergoing apoptosis in vitro

HMGB1 is a highly conserved nuclear protein that displays important biological activities inside as well as outside the cell and serves as a prototypic alarmin to activate innate immunity. The translocation of HMGB1 from inside to outside the cell occurs with cell activation as well as cell death, including apoptosis. Apoptosis is also a setting for the release of cellular microparticles (MPs), which are small membrane-bound vesicles that represent an important source of extracellular nuclear molecules. To investigate whether HMGB1 released from cells during apoptosis is also present on MPs, we determined the presence of HMGB1 on particles released from Jurkat and HL-60 cells induced to undergo apoptosis in vitro by treatment with either etoposide or staurosporine; MPs released from cells undergoing necrosis by freeze-thaw were also characterized. As shown by both Western blot analysis and flow cytometry, MPs from apoptotic cells contain HMGB1, with binding by antibodies indicating an accessible location in the particle structure. These results indicate that HMGB1, like other nuclear molecules, can translocate into MPs during apoptosis and demonstrate another biochemical form of this molecule that may be immunologically active.

Tobacco mosaic virus efficiently targets DC uptake, activation and antigen-specific T cell responses in vivo

Over the past 20 years, dendritic cells (DCs) have been utilized to activate immune responses capable of eliminating cancer cells. Currently, ex vivo DC priming has been the mainstay of DC cancer immunotherapies. However, cell-based treatment modalities are inherently flawed due to a lack of standardization, specialized facilities and personnel, and cost. Therefore, direct modes of DC manipulation, circumventing the need for ex vivo culture, must be investigated. To facilitate the development of next-generation, in vivo targeted DC vaccines, we characterized the DC interaction and activation potential of the Tobacco Mosaic virus (TMV), a plant virus that enjoys a relative ease of production and the ability to deliver protein payloads via surface conjugation. In this study we show that TMV is readily taken up by mouse bone marrow-derived DCs, in vitro. Footpad injection of fluorophore-labeled TMV reveals preferential uptake by draining lymph node resident DCs in vivo. Uptake leads to activation, as measured by the upregulation of key DC surface markers. When peptide antigen-conjugated TMV is injected into the footpad of mice, DC-mediated uptake and activation leads to robust antigen-specific CD8(+) T cell responses, as measured by antigen-specific tetramer analysis. Remarkably, TMV priming induced a greater magnitude T cell response than Adenovirus (Ad) priming. Finally, TMV is capable of boosting either Ad-induced or TMV-induced antigen-specific T cell responses, demonstrating that TMV, uniquely, does not induce neutralizing self-immunity. Overall, this study elucidates the in vivo DC delivery and activation properties of TMV and indicates its potential as a vaccine vector in stand alone or prime-boost strategies.

FGFR1-WNT-TGF-β signaling in prostate cancer mouse models recapitulates human reactive stroma

The reactive stroma surrounding tumor lesions performs critical roles ranging from supporting tumor cell proliferation to inducing tumorigenesis and metastasis. Therefore, it is critical to understand the cellular components and signaling control mechanisms that underlie the etiology of reactive stroma. Previous studies have individually implicated fibroblast growth factor receptor 1 (FGFR1) and canonical WNT/β-catenin signaling in prostate cancer progression and the initiation and maintenance of a reactive stroma; however, both pathways are frequently found to be coactivated in cancer tissue. Using autochthonous transgenic mouse models for inducible FGFR1 (JOCK1) and prostate-specific and ubiquitously expressed inducible β-catenin (Pro-Cat and Ubi-Cat, respectively) and bigenic crosses between these lines (Pro-Cat × JOCK1 and Ubi-Cat × JOCK1), we describe WNT-induced synergistic acceleration of FGFR1-driven adenocarcinoma, associated with a pronounced fibroblastic reactive stroma activation surrounding prostatic intraepithelial neoplasia (mPIN) lesions found both in in situ and reconstitution assays. Both mouse and human reactive stroma exhibited increased transforming growth factor-β (TGF-β) signaling adjacent to pathologic lesions likely contributing to invasion. Furthermore, elevated stromal TGF-β signaling was associated with higher Gleason scores in archived human biopsies, mirroring murine patterns. Our findings establish the importance of the FGFR1-WNT-TGF-β signaling axes as driving forces behind reactive stroma in aggressive prostate adenocarcinomas, deepening their relevance as therapeutic targets.

Notch and TGFβ form a reciprocal positive regulatory loop that suppresses murine prostate basal stem/progenitor cell activity

The role of Notch signaling in the maintenance of adult murine prostate epithelial homeostasis remains unclear. We found that Notch ligands are mainly expressed within the basal cell lineage, while active Notch signaling is detected in both the prostate basal and luminal cell lineages. Disrupting the canonical Notch effector Rbp-j impairs the differentiation of prostate basal stem cells and increases their proliferation in vitro and in vivo, but does not affect luminal cell biology. Conversely, ectopic Notch activation in adult prostates results in a decrease in basal cell number and luminal cell hyperproliferation. TGFβ dominates over Notch signaling and overrides Notch ablation-induced proliferation of prostate basal cells. However, Notch confers sensitivity and positive feedback by upregulating a plethora of TGFβ signaling components including TgfβR1. These findings reveal crucial roles of the self-enforced positive reciprocal regulatory loop between TGFβ and Notch in maintaining prostate basal stem cell dormancy.

Targeted expression of Escherichia coli purine nucleoside phosphorylase and Fludara® for prostate cancer therapy

BACKGROUND

Previous studies have shown that Herpes Simplex Virus thymidine kinase (HSV-tk)/ganciclovir (GCV) comprised the most commonly used suicide gene therapy for prostate cancer, with modest results being obtained. However, novel suicide genes, such as Escherichia coli purine nucleoside phosphorylase (PNP), have been utilized to demonstrate more potent tumor killing and an enhanced bystander effect on local, non-expressing cells compared to HSV-tk.

METHODS

PNP/fludarabine (Fludara®; fludarabine phosphate; Berlex Labs, Richmond, CA, USA) was deliveried by prostate-specific, rat probasin-based promoter, ARR2PB. After infection of various cell lines with ADV.ARR(2) PB-PNP and administration of androgen analog, R1881, expression of PNP mRNA was detected; in vivo, the antitumor effect of the ARR(2) PB-PNP/Fludara system was monitored and analyzed, as well as animal survival.

RESULTS

After in vitro infection with ADV.ARR(2) PB-PNP (multiplicity of infection  =  10), LNCaP cells were more sensitive to a lower concentration Fludara (LD(50) , approximately 0.1 µg/ml) in the presence of R1881. Furthermore, robust bystander effects after R1881/Fludara treatment were observed in LNCaP cells after infection with bicistronic vector ADV.ARR2PB/PNP-IRES-EGFP in contrast to a much weaker effect in cells treated with ADV.CMV-HSV-tk/GCV. In vivo, tumor size in the ADV.ARR2PB-PNP/Fludara treatment group was dramatically smaller than in the control groups, and the mice treated with our system had a significantly prolonged survival, with three of eight mice surviving up to the 160-day termination point, as well as no systemic toxicity.

CONCLUSIONS

The ARR(2) PB-PNP/Fludara system induced massive tumor cell death and a prolonged life span without systemic cytotoxicity; therefore, it might be a more attractive strategy for suicide gene therapy of prostate cancer.

Abstract 1568: Developing a novel in vivo electroporation-based DNA vaccine utilizing a small molecule regulated immune switch

Dendritic cell (DC) vaccines are a rapidly progressing area of translational research intended for developing new cancer treatment modalities. Although ex vivo DC-based vaccines have been extensively studied and clinically tested for the treatment of cancer, they are inherently limited by short DC lifespan after activation, labor-intensive production (requiring ex vivo manipulation of autologous cells), high cost and consequent limited accessibility to the patient. Therefore, we have attempted to develop portable, regulatable adjuvants that could be targeted to DCs and activated in situ. Development by our lab of an inducible variant of the costimulatory molecule, CD40 (iCD40), and a composite, inducible MyD88/CD40 (iMC) adjuvant, that also incorporates the universal Toll like receptor adapter, MyD88, have been shown to increase the potency and lifespan of DC vaccines. These inducible receptors act as in vivo DC “switches” that lead to the priming and robust expansion of antigen (Ag)-specific T-cells capable of eliminating pre-established tumors in mice. Despite the success of these DC “switch” systems, practicality and scalability of patient-tailored ex vivo DC vaccines remains a major hindrance to their widespread applicability. Therefore, the future of DC vaccines lies in the development of “off-the-shelf” methodologies, such as viral or non-viral vectors that can deliver adjuvants along with tumor antigens. DNA vaccines are attractive for this purpose owing to their elegant simplicity, ease of production, and lack of anti-vector immune responses. In order to successfully vaccinate patients with DNA, one must be able to deliver plasmid encoding therapeutic genes to target cells efficiently. In vivo electroporation is a relatively new technology just starting to be tested in clinical trials, and provides a safe, simple, and effective means by which to administer DNA vaccines. Data from our preliminary studies of the electroporative delivery of plasmids encoding the model antigen β-galactosidase (LacZ) in mice suggests that LacZ-specific T-cell responses are induced, and that upon tumor challenge, mice receiving prophylaxis via electroporation had slower tumor growth kinetics when compared to controls. Together, this preliminary data supports the notion that DNA vaccination with tumor Ag by electroporation may be a simple and effective “off-the-shelf” cancer vaccine strategy. Additionally, this vaccination strategy may be enhanced by the addition of the iMC adjuvant. Therefore, further investigation of intradermal electroporation is warranted by these findings, to better characterize the induced immune responses and better optimize vaccination

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1568. doi:1538-7445.AM2012-1568

Abstract 1564: Partial immunovesiculectomy by Th-1 dendritic cell vaccination: Implications for immunotherapy of solid tumors

The efficient and specific manner by which the mammalian immune system identifies and eradicates target antigen has stood as a testament to both its power and potential to similarly eradicate neoplastic self. In spite of this undeniable potential, the recalcitrance of the immune system to directed manipulation has been formidable, and the manner by which self-directed cellular (Th-1) immunity might be reproducibly promulgated has not yet been elucidated. Recent basic advances in the understanding of dendritic cell (DC) maturation, Th-1 polarization, T-cell homing, and plasmacytoid DC biology might allow promulgation of self-directed cellular immunity provided that all important aspects of such promulgation have been identified and are properly implemented. To investigate this hypothesis, seminal vesicle (SV), was chosen as a model organ system in the wild type mouse. In this system, SV serves as a proxy tumor from an immunological perspective: antigenically distinguishable from other organ systems yet comprised entirely of self tissue antigens and stringently protected from immunological recognition by mechanisms of central and peripheral tolerance. Equivalent class I and class II antigenic environments were provided to spleen-derived DC by electroporation with SV mRNA and incubation with SV lysate. DC were matured with a full complement of inflammatory cytokines. DC were applied i.p. in the vicinity of the SV so as to have access to the specific lymphatics that drain the area. Plasmacytoid recruitment and IFN-γ secretion was induced by local i.p. administration of particulate imiquimod. Two months post-vaccination, SV and other organs were harvested and examined for pathological changes by H&E staining. Ipsilateral SV was reduced in size as much as 75% in comparison to contralateral SV. Active inflammatory responses were ongoing as evidenced by mixed lineage inflammatory infiltrates comprising lymphocytes, neutrophils, eosinophils, macrophages, and multinucleated giant cells. Remnant SV physiologic structures were infiltrated by fibrous connective tissue and scar. Antigen-specific tissue destruction was shown to be dependent upon local TLR-7 adjuvantation with imiquimod as well as the activation of lymphocyte subsets. Antigenically similar tissues demonstrated normal histopathology. Subsequent experiments using the TRAMP-C2 prostate cancer cell line demonstrated the ability of Th-1 DC vaccination to recognize and eradicate neoplastic self as demonstrated by Kaplan-Meier survival analysis. The data demonstrate that provision and maintenance of the appropriate signals are sufficient to mediate durable self-directed Th-1 immunity against peripheral-self. The data further suggest a plausible role for DC vaccination as a front line therapy for the treatment of some neoplasias in the future.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1564. doi:1538-7445.AM2012-1564

Abstract 3287: Intra- and intercellular Wnt pathway induction synergistically accelerates FGFR1-mediated prostate tumorigenesis

Cancer growth and metastasis requires proliferation, cell migration, and stromal remodeling, functions also found during organogenesis and wound repair. The fibroblast growth factor (FGF) and canonical Wnt/β-catenin signaling pathways are two pathways central to these functions. FGFs and their receptors (FGFRs) are expressed in most tissues and play pivotal roles in development, wound healing and neovascularization, and are also upregulated in many solid cancers, including prostate, mammary, renal, kidney, bladder, and testicular tumors. We previously demonstrated in the JOCK1 (juxtaposition of CID and kinase) prostate cancer (PCa) mouse model that chemically induced dimerization (CID) of FGFR1 signaling in the prostate is sufficient for tumor initiation and early tumor maintenance and prolonged (42 weeks) FGFR1 activation results in PCa with distant metastasis. The Wnt pathway is also vital for proper embryogenesis and homeostasis of adult tissues by regulating stem cell self-renewal, pluripotency, and differentiation in several tissues, including colon, hair shaft, and chondrocyte stem/progenitor cells. The uncontrolled activation of this important stem pathway is also associated with various cancers, including colon, breast and prostate. Recently, we have discovered that induced crosslinking of the Wnt co-receptor LRP5 is sufficient to induce canonical Wnt signaling and nuclear localization of β-catenin. We subsequently developed two novel mouse models where Wnt can be specifically activated in the prostate epithelium, Pro-Cat (prostate-targeted inducible β-catenin), or in virtually every tissue sub-layer, Ubi-Cat (ubiquitously expressed inducible β-catenin). Consistent with previous literature, induced Pro-Cat mice never progressed beyond prostatic hyperplasia, however, after a year of pathway induction, 2 out of 6 Ubi-Cat mice developed adenocarcinoma, indicating a yet unexplored role for stromal Wnt signaling in tumorigenesis. In order to delineate possible crosstalk and synergism between FGF and Wnt pathways, we bred JOCK1 mice unto Pro-Cat and Ubi-Cat transgenic lines. Both Pro-Cat/JOCK1 and Ubi-Cat/JOCK1 mice developed widespread hyperplasia, high-grade PIN and adenocarcinoma with an extensive reactive stroma by 24 weeks of CID injections. Fascinatingly, Pro-Cat/JOCK1 mice do not continue to progress beyond the timeline established by JOCK1 induction alone whereas Ubi-Cat/JOCK1 mice continue to progress to advanced transitional sarcomatoid lesions. These results suggest that intracellular crosstalk between Wnt and FGFR1 in the epithelia is sufficient to accelerate tumor initiation, however accelerated progression requires intercellular crosstalk between the stroma and the epithelia. Additional experiments necessary to definitively implicate the stroma in accelerated tumorigenesis are underway and will be discussed.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3287. doi:1538-7445.AM2012-3287

Rational truncation of an RNA aptamer to prostate-specific membrane antigen using computational structural modeling

RNA aptamers represent an emerging class of pharmaceuticals with great potential for targeted cancer diagnostics and therapy. Several RNA aptamers that bind cancer cell-surface antigens with high affinity and specificity have been described. However, their clinical potential has yet to be realized. A significant obstacle to the clinical adoption of RNA aptamers is the high cost of manufacturing long RNA sequences through chemical synthesis. Therapeutic aptamers are often truncated postselection by using a trial-and-error process, which is time consuming and inefficient. Here, we used a "rational truncation" approach guided by RNA structural prediction and protein/RNA docking algorithms that enabled us to substantially truncateA9, an RNA aptamer to prostate-specific membrane antigen (PSMA),with great potential for targeted therapeutics. This truncated PSMA aptamer (A9L; 41mer) retains binding activity, functionality, and is amenable to large-scale chemical synthesis for future clinical applications. In addition, the modeled RNA tertiary structure and protein/RNA docking predictions revealed key nucleotides within the aptamer critical for binding to PSMA and inhibiting its enzymatic activity. Finally, this work highlights the utility of existing RNA structural prediction and protein docking techniques that may be generally applicable to developing RNA aptamers optimized for therapeutic use.

Activation of Wnt signaling by chemically induced dimerization of LRP5 disrupts cellular homeostasis

Wnt signaling is crucial for a variety of biological processes, including body axis formation, planar polarity, stem cell maintenance and cellular differentiation. Therefore, targeted manipulation of Wnt signaling in vivo would be extremely useful. By applying chemical inducer of dimerization (CID) technology, we were able to modify the Wnt co-receptor, low-density lipoprotein (LDL)-receptor-related protein 5 (LRP5), to generate the synthetic ligand inducible Wnt switch, iLRP5. We show that iLRP5 oligomerization results in its localization to disheveled-containing punctate structures and sequestration of scaffold protein Axin, leading to robust β-catenin-mediated signaling. Moreover, we identify a novel LRP5 cytoplasmic domain critical for its intracellular localization and casein kinase 1-dependent β-catenin signaling. Finally, by utilizing iLRP5 as a Wnt signaling switch, we generated the Ubiquitous Activator of β-catenin (Ubi-Cat) transgenic mouse line. The Ubi-Cat line allows for nearly ubiquitous expression of iLRP5 under control of the H-2K^b promoter. Activation of iLRP5 in isolated prostate basal epithelial stem cells resulted in expansion of p63⁺ cells and development of hyperplasia in reconstituted murine prostate grafts. Independently, iLRP5 induction in adult prostate stroma enhanced prostate tissue regeneration. Moreover, induction of iLRP5 in male Ubi-Cat mice resulted in prostate tumor progression over several months from prostate hyperplasia to adenocarcinoma. We also investigated iLRP5 activation in Ubi-Cat-derived mammary cells, observing that prolonged activation results in mammary tumor formation. Thus, in two distinct experimental mouse models, activation of iLRP5 results in disruption of tissue homeostasis, demonstrating the utility of iLRP5 as a novel research tool for determining the outcome of Wnt activation in a precise spatially and temporally determined fashion.

Inducible apoptosis as a safety switch for adoptive cell therapy

BACKGROUND

Cellular therapies could play a role in cancer treatment and regenerative medicine if it were possible to quickly eliminate the infused cells in case of adverse events. We devised an inducible T-cell safety switch that is based on the fusion of human caspase 9 to a modified human FK-binding protein, allowing conditional dimerization. When exposed to a synthetic dimerizing drug, the inducible caspase 9 (iCasp9) becomes activated and leads to the rapid death of cells expressing this construct.

METHODS

We tested the activity of our safety switch by introducing the gene into donor T cells given to enhance immune reconstitution in recipients of haploidentical stem-cell transplants. Patients received AP1903, an otherwise bioinert small-molecule dimerizing drug, if graft-versus-host disease (GVHD) developed. We measured the effects of AP1903 on GVHD and on the function and persistence of the cells containing the iCasp9 safety switch.

RESULTS

Five patients between the ages of 3 and 17 years who had undergone stem-cell transplantation for relapsed acute leukemia were treated with the genetically modified T cells. The cells were detected in peripheral blood from all five patients and increased in number over time, despite their constitutive transgene expression. A single dose of dimerizing drug, given to four patients in whom GVHD developed, eliminated more than 90% of the modified T cells within 30 minutes after administration and ended the GVHD without recurrence.

CONCLUSIONS

The iCasp9 cell-suicide system may increase the safety of cellular therapies and expand their clinical applications. (Funded by the National Heart, Lung, and Blood Institute and the National Cancer Institute; ClinicalTrials.gov number, NCT00710892.).

Wnt and Notch pathways have interrelated opposing roles on prostate progenitor cell proliferation and differentiation

Tissue stem cells are capable of both self-renewal and differentiation to maintain a constant stem cell population and give rise to the plurality of cells within a tissue. Wnt signaling has been previously identified as a key mediator for the maintenance of tissue stem cells; however, possible cross-regulation with other developmentally critical signaling pathways involved in adult tissue homeostasis, such as Notch, is not well understood. By using an in vitro prostate stem cell colony ("prostasphere") formation assay and in vivo prostate reconstitution experiments, we demonstrate that Wnt pathway induction on Sca-1(+) CD49f(+) basal/stem cells (B/SCs) promotes expansion of the basal epithelial compartment with noticeable increases in "triple positive" (cytokeratin [CK] 5(+), CK8(+), p63(+)) prostate progenitor cells, concomitant with upregulation of known Wnt target genes involved in cell-cycle induction. Moreover, Wnt induction affects expression of epithelial-to-mesenchymal transition signature genes, suggesting a possible mechanism for priming B/SC to act as potential tumor-initiating cells. Interestingly, induction of Wnt signaling in B/SCs results in downregulation of Notch1 transcripts, consistent with its postulated antiproliferative role in prostate cells. In contrast, induction of Notch signaling in prostate progenitors inhibits their proliferation and disrupts prostasphere formation. In vivo prostate reconstitution assays further demonstrate that induction of Notch in B/SCs disrupts proper acini formation in cells expressing the activated Notch1 allele, Notch-1 intracellular domain. These data emphasize the importance of Wnt/Notch cross-regulation in adult stem cell biology and suggest that Wnt signaling controls the proliferation and/or maintenance of epithelial progenitors via modulation of Notch signaling.

A composite MyD88/CD40 switch synergistically activates mouse and human dendritic cells for enhanced antitumor efficacy

The in vivo therapeutic efficacy of DC-based cancer vaccines is limited by suboptimal DC maturation protocols. Although delivery of TLR adjuvants systemically boosts DC-based cancer vaccine efficacy, it could also increase toxicity. Here, we have engineered a drug-inducible, composite activation receptor for DCs (referred to herein as DC-CAR) comprising the TLR adaptor MyD88, the CD40 cytoplasmic region, and 2 ligand-binding FKBP12 domains. Administration of a lipid-permeant dimerizing ligand (AP1903) induced oligomerization and activation of this fusion protein, which we termed iMyD88/CD40. AP1903 administration to vaccinated mice enabled prolonged and targeted activation of iMyD88/CD40-modified DCs. Compared with conventionally matured DCs, AP1903-activated iMyD88/CD40-DCs had increased activation of proinflammatory MAPKs. AP1903-activated iMyD88/CD40-transduced human or mouse DCs also produced higher levels of Th1 cytokines, showed improved migration in vivo, and enhanced both antigen-specific CD8+ T cell responses and innate NK cell responses. Furthermore, treatment with AP1903 in vaccinated mice led to robust antitumor immunity against preestablished E.G7-OVA lymphomas and aggressive B16.F10 tumors. Thus, the iMyD88/CD40 unified "switch" effectively and safely replaced exogenous adjuvant cocktails, allowing remote and sustained DC activation in vivo. DC "licensing" through iMyD88/CD40 may represent a mechanism by which to exploit the natural synergy between the TLR and CD40 signaling pathways in DCs using a single small molecule drug and could augment the efficacy of antitumor DC-based vaccines.

The phosphatase SRC homology region 2 domain-containing phosphatase-1 is an intrinsic central regulator of dendritic cell function

Dendritic cells (DCs) initiate proinflammatory or regulatory T cell responses, depending on their activation state. Despite extensive knowledge of DC-activating signals, the understanding of DC inhibitory signals is relatively limited. We show that Src homology region 2 domain-containing phosphatase-1 (SHP-1) is an important inhibitor of DC signaling, targeting multiple activation pathways. Downstream of TLR4, SHP-1 showed increased interaction with several proteins including IL-1R-associated kinase-4, and modulated LPS signaling by inhibiting NF-κB, AP-1, ERK, and JNK activity, while enhancing p38 activity. In addition, SHP-1 inhibited prosurvival signaling through AKT activation. Furthermore, SHP-1 inhibited CCR7 protein expression. Inhibiting SHP-1 in DCs enhanced proinflammatory cytokines, IL-6, IL-12, and IL-1β production, promoted survival, and increased DC migration to draining lymph nodes. Administration of SHP-1-inhibited DCs in vivo induced expansion of Ag-specific cytotoxic T cells and inhibited Foxp3(+) regulatory T cell induction, resulting in an enhanced immune response against pre-established mouse melanoma and prostate tumors. Taken together, these data demonstrate that SHP-1 is an intrinsic global regulator of DC function, controlling many facets of T cell-mediated immune responses.

Death switch for gene therapy: application to erythropoietin transgene expression

The effectiveness of the caspase-9-based artificial "death switch" as a safety measure for gene therapy based on the erythropoietin (Epo) hormone was tested in vitro and in vivo using the chemical inducer of dimerization, AP20187. Plasmids encoding the dimeric murine Epo, the tetracycline-controlled transactivator and inducible caspase 9 (ptet-mEpoD, ptet-tTAk and pSH1/Sn-E-Fv'-Fvls-casp9-E, respectively) were used in this study. AP20187 induced apoptosis of iCasp9-modified C2C12 myoblasts. In vivo, two groups of male C57BI/6 mice, 8-12 weeks old, were injected intramuscularly with 5 microg/50 g ptet-mEpoD and 0.5 microg/50 g ptet-tTAk. There were 20 animals in group 1 and 36 animals in group 2. Animals from group 2 were also injected with the 6 microg/50 g iCasp9 plasmid. Seventy percent of the animals showed an increase in hematocrit of more than 65% for more than 15 weeks. AP20187 administration significantly reduced hematocrit and plasma Epo levels in 30% of the animals belonging to group 2. TUNEL-positive cells were detected in the muscle of at least 50% of the animals treated with AP20187. Doxycycline administration was efficient in controlling Epo secretion in both groups. We conclude that inducible caspase 9 did not interfere with gene transfer, gene expression or tetracycline control and may be used as a safety mechanism for gene therapy. However, more studies are necessary to improve the efficacy of this technique, for example, the use of lentivirus vector.

Abstract 4761: The iCD40. MyD88 combo-vector: A new platform for enhanced DC tumor immunotherapy

Introduction: Given the pre-eminent role of dendritic cells (DCs) as antigen-presenting cells, their exploitation as natural adjuvants in vaccination protocols for the treatment of various malignancies and infectious diseases is not surprising. Nevertheless, inadequate or unsustained activation has likely limited response rates in clinical trials. We previously reported a potent synthetic dimerizer drug-inducible CD40 (iCD40) receptor that permits temporally controlled DC-specific activation within the context of an immunological synapse (Hanks et al, Nat Med, 2005). We showed that when combined with Toll-like Receptor (TLR) adjuvants, iCD40-modified DCs (iCD40-DCs) have enhanced survival, co-stimulatory marker expression, migration, IL-12 production, antigen (Ag)-specific T cell stimulatory capacity and anti-tumor responses (Lapteva et al, Cancer Res, 2007). A phase I/II clinical trial based on iCD40-DCs to treat castration-resistant, metastatic prostate cancer began enrolling patients in August 2009.

Procedures: To simplify this approach, we have developed a unified, inducible DC switch, called “iCD40. MyD88”, which combines signaling elements from costimulatory molecule, CD40, and TLR adapter, MyD88, fused to tandem FK506-binding binding proteins (FKBP12v36). Activation is initiated in vitro or in vivo by lipid-permeable dimerizing ligands (i.e. AP1903 or AP20187).

Results: Both murine and human iCD40. MyD88-DCs secrete high (ng) levels of IL-12 and maturation markers in a ligand-dependent fashion without the need for exogenous adjuvants. iCD40. MyD88 activation is associated with synergistic activation of IKKα/β and p38. Moreover, tumor-bearing mice treated with antigen-pulsed, iCD40. MyD88-DCs show a potent anti-tumor immune response, consistent with expansion of antigen-specific CTLs in vivo. Bicistronic vectors combining iCD40. MyD88 along with tumor-associated antigens are underway.

Conclusion: This “combo-switch” permits potent, targeted activation of antigen-pulsed DCs in vivo, leading to improved anti-tumor immunity with a high likelihood for reduced side effects. Production of a single vector that combines a potent DC switch with tumor antigen is the first requisite step leading to economically viable, “off-the-shelf”, vaccine therapies for cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4761.

Emerging vaccine therapy approaches for prostate cancer

Prostate cancer vaccines attempt to induce clinically relevant, cancer-specific systemic immune responses in patients with prostate cancer and represent a new class of targeted, nontoxic therapies. With a growing array of vaccine technologies in preclinical or clinical development, autologous antigen-presenting cell vaccines loaded with the antigen, prostate acid phosphatase, and poxvirus vaccines targeting prostate-specific antigen have recently demonstrated a significant survival benefit in randomized trials of patients with metastatic castration-resistant prostate cancer, whereas others have failed to demonstrate any benefit. The combination of vaccines with chemotherapy, radiotherapy, and other biologic agents is also being evaluated. Efforts to optimize vaccine approaches and select ideal patient populations need to continue to build on these early successes.

Lipid raft-targeted Akt promotes axonal branching and growth cone expansion via mTOR and Rac1, respectively

The molecular mechanisms by which extracellular guidance cues regulate axonal morphology are not fully understood. Recent findings suggest that increased activity of the protein kinase Akt promotes dendritic branching and elongation in hippocampal neurons. We tested whether expression of constitutively active Akt (CA-Akt) in primary sensory neurons would promote axonal branching and whether targeting CA-Akt to lipid rafts, common sites of Akt function, would differentially regulate axonal morphology. Biolistic transduction of sensory neurons induced a rapid expression of CA-Akt, resulting in increased axonal branching, cell hypertrophy, and growth cone expansion. Additionally, we found that targeting of CA-Akt to lipid rafts significantly potentiated growth cone expansion compared with expression of CA-Akt throughout the neuron. Because lipid rafts are concentrated within the growth cone, this finding suggests that signaling of expansion is likely regulated locally. We found that CA-Akt-mediated growth cone expansion, but not axonal branching, was attenuated by coexpression of dominant-negative Rac1. In contrast, blockade of mammalian target of rapamycin (mTOR) prevented axonal branching and hypertrophy in response to CA-Akt, but not growth cone expansion. These data indicate that Akt activity can regulate growth cone expansion via localized Rac1 signaling and regulate axonal branching and soma size via activation of mTOR.

Paths of FGFR-driven tumorigenesis

Fibroblast growth factor receptors (FGFRs) comprise a subfamily of receptor tyrosine kinases (RTKs) that are master regulators of a broad spectrum of cellular and developmental processes, including apoptosis, proliferation, migration and angiogenesis. Due to their broad impact, FGFRs and other RTKs are highly regulated and normally only basally active. Deregulation of FGFR signaling by activating mutations or ligand/receptor overexpression could allow these receptors to become constitutively active, leading to cancer development, including both hematopoietic and solid tumors, such as breast, bladder and prostate carcinomas. In this review, we focus on potential modes of FGFR-mediated tumorigenesis, in particular, the role of FGFR1 during prostate cancer progression.

Pleiotropic biological activities of alternatively spliced TMPRSS2/ERG fusion gene transcripts

TMPRSS2/ERG gene fusions are found in the majority of prostate cancers; however, there is significant heterogeneity in the 5' region of the alternatively spliced fusion gene transcripts. We have found that there is also significant heterogeneity within the coding exons as well. There is variable inclusion of a 72-bp exon and other novel alternatively spliced isoforms. To assess the biological significance of these alternatively spliced transcripts, we expressed various transcripts in primary prostatic epithelial cells (PrEC) and in an immortalized PrEC line, PNT1a. The fusion gene transcripts promoted proliferation, invasion, and motility with variable activities that depended on the structure of the 5' region encoding the TMPRSS2/ERG fusion and the presence of the 72-bp exon. Cotransfection of different isoforms further enhanced biological activity, mimicking the situation in vivo, in which multiple isoforms are expressed. Finally, knockdown of the fusion gene in VCaP cells resulted in inhibition of proliferation in vitro and tumor progression in an in vivo orthotopic mice model. Our results indicate that TMPRSS2/ERG fusion isoforms have variable biological activities promoting tumor initiation and progression and are consistent with our previous clinical observations indicating that certain TMPRSS2/ERG fusion isoforms are significantly correlated with more aggressive disease.

Inducible FGFR-1 activation leads to irreversible prostate adenocarcinoma and an epithelial-to-mesenchymal transition

Fibroblast Growth Factor Receptor-1 (FGFR1) is commonly overexpressed in advanced prostate cancer (PCa). To investigate causality, we utilized an inducible FGFR1 (iFGFR1) prostate mouse model. Activation of iFGFR1 with chemical inducers of dimerization (CID) led to highly synchronous, step-wise progression to adenocarcinoma that is linked to an epithelial-to-mesenchymal transition (EMT). iFGFR1 inactivation by CID withdrawal led to full reversion of prostatic intraepithelial neoplasia, whereas PCa lesions became iFGFR1-independent. Gene expression profiling at distinct stages of tumor progression revealed an increase in EMT-associated Sox9 and changes in the Wnt signaling pathway, including Fzd4, which was validated in human PCa. The iFGFR1 model clearly implicates FGFR1 in PCa progression and demonstrates how CID-inducible models can help evaluate candidate molecules in tumor progression and maintenance.

Level of endothelial cell apoptosis required for a significant decrease in microvessel density

Endothelial cell apoptosis plays a critical role in the disruption of blood vessels mediated by natural inhibitors of angiogenesis and by anti-vascular drugs. However, the proportion of endothelial cells required to mediate a significant decrease in microvessel density is unknown. A system based on an inducible caspase (iCaspase-9) offers a unique opportunity to address this question. The dimerizer drug AP20187 induces apoptosis of human dermal microvascular endothelial cells stably transduced with iCaspase-9 (HDMEC-iCaspase-9), but not control cells (HDMEC-LXSN). Here, we generated blood vessels containing several HDMEC-iCaspase-9:HDMEC-LXSN ratios, and developed a mathematical modeling involving a system of differential equations to evaluate experimentally inaccessible ratios. A significant decrease in capillary sprouts was observed when at least 17% of the endothelial cells underwent apoptosis in vitro. Exposure to vascular endothelial growth factor (VEGF(165)) did not prevent apoptosis of HDMEC-iCaspase-9, but increased the apoptotic requirement for sprout disruption. In vivo experiments showed the requirement of at least 22% apoptotic endothelial cells for a significant decrease in microvascular density. The combined use of biological experimentation with mathematical modeling allowed us to conclude that apoptosis of a relatively small proportion of endothelial cells is sufficient to mediate a significant decrease in microvessel density.

Double-inducible gene activation system for caspase 3 and 9 in epidermis

Expression of genes with tight and precise temporal and spatial control is desired in a wide variety of applications ranging from cultured cells and transgenic animals to gene therapy. While current inducible systems, such as RU486 and chemical inducers of dimerization (CID), have improved earlier inducible models (Gossen et al., 1995, Science. 268:1766-1769; Wang et al., 1994, Proc Natl Acad Sci USA 91:8180-8184), no single system is perfect at present. One potential drawback of these systems is leakage of transgene expression, causing limitations of each system. We have developed an inducible model containing both RU486 and CID systems, which in addition to inducing caspase activation, has potential applicability specifically to other genes encoding proteins that require a dimerization event for activation. This Double-Inducible Gene Activation System generates two barriers for the target gene expression and protein activation thereby minimizing leakage.

Angiogenesis blockade as a new therapeutic approach to experimental colitis

BACKGROUND

Neoangiogenesis is a critical component of chronic inflammatory disorders. Inhibition of angiogenesis is an effective treatment in animal models of inflammation, but has not been tested in experimental colitis.

AIM

To investigate the effect of ATN-161, an anti-angiogenic compound, on the course of experimental murine colitis.

METHOD

Interleukin 10-deficient (IL10(-/-)) mice and wild-type mice were kept in ultra-barrier facilities (UBF) or conventional housing, and used for experimental conditions. Dextran sodium sulphate (DSS)-treated mice were used as a model of acute colitis. Mice were treated with ATN-161 or its scrambled peptide ATN-163. Mucosal neoangiogenesis and mean vascular density (MVD) were assessed by CD31 staining. A Disease Activity Index (DAI) was determined, and the severity of colitis was determined by a histological score. Colonic cytokine production was measured by ELISA, and lamina propria mononuclear cell proliferation by thymidine incorporation.

RESULT

MVD increased in parallel with disease progression in IL10(-/-) mice kept in conventional housing, but not in IL10(-/-) mice kept in UBF. Angiogenesis also occurred in DSS-treated animals. IL10(-/-) mice with established disease treated with ATN-161, but not with ATN-163, showed a significant and progressive decrease in DAI. The histological colitis score was significantly lower in ATN-161-treated mice than in scrambled peptide-treated mice. Inhibition of angiogenesis was confirmed by a significant decrease of MVD in ATN-161-treated mice than in ATN-163-treated mice. No therapeutic effects were observed in the DSS model of colitis. ATN-161 showed no direct immunomodulatory activity in vitro.

CONCLUSION

Active angiogenesis occurs in the gut of IL10(-/-) and DSS-treated colitic mice and parallels disease progression. ATN-161 effectively decreases angiogenesis as well as clinical severity and histological inflammation in IL10(-/-) mice but not in the DDS model of inflammatory bowel disease (IBD). The results provide the rational basis for considering anti-angiogenic strategies in the treatment of IBD in humans.

Conditional activation of FGFR1 in the prostate epithelium induces angiogenesis with concomitant differential regulation of Ang-1 and Ang-2

The expression of fibroblast growth factor receptor (FGFR)-1 correlates with angiogenesis and is associated with prostate cancer (CaP) progression. To more precisely define the molecular mechanisms whereby FGFR1 causes angiogenesis in the prostate we exploited a transgenic mouse model, JOCK-1, in which activation of a conditional FGFR1 allele in the prostate epithelium caused rapid angiogenesis and progressive hyperplasia. By labeling the vasculature in vivo and applying a novel method to measure the vasculature in three dimensions, we were able to observe a significant increase in vascular volume 1 week after FGFR1 activation. Although vessel volume and branching both continued to increase throughout a 6-week period of FGFR1 activation, importantly, we discovered that continued activation of FGFR1 was not required to maintain the new vasculature. Exploring the molecular mediators of the angiogenic phenotype, we observed consistent upregulation of HIF-1alpha, vascular endothelial growth factor (VEGF) and angiopoietin 2 (Ang-2), whereas expression of Ang-1 was lost. Further analysis revealed that loss of Ang-1 expression occurred in the basal epithelium, whereas the increase in Ang-2 expression occurred in the luminal epithelium. Reporter assays confirmed that the Ang-2 promoter was regulated by FGFR1 signaling and a small molecule inhibitor of FGFR activity, PD173074, could abrogate this response. These findings establish a method to follow spontaneous angiogenesis in a conditional autochthonous system, implicate the angiopoietins as downstream effectors of FGFR1 activation in vivo, and suggest that therapies targeting FGFR1 could be used to inhibit neovascularization during initiation and progression of CaP.