Abstract LB105: In vivo CAR T therapy: targeted in vivo gene delivery of a CAR using a CD8-specific fusogen results in tumor eradication

CAR T cells are highly effective at inducing remissions in patients with refractory B cell malignancies. The ex vivo process used to manufacture these therapies limits patient access and exposes T cells to non-physiologic conditions in culture. Viral vectors are efficient at genetically modifying T cells and are used in the ex vivo manufacture of most CAR T cell products but lack target-cell specificity. Here we describe how viral envelope glycoproteins, termed fusogens, engineered to target the CD8 co-receptor can efficiently and specifically deliver a chimeric antigen receptor (CAR) to human T cells in vivo that support target cell killing and tumor eradication. Modification of viral envelope proteins to include antibody-based binding domains (CD8 binders) can produce fusogen-viral vector compositions that deliver genetic payloads to CD8 T cells with therapeutic effect (1, 2). Screening CD8-targeted binders identified fusogens with a range of on-target cell transduction efficiencies and off-target cell line specificities. CD8-targeted fusogens with the highest efficiency were comparable to VSVg-pseudotyped lentiviruses at transducing CD8 T cells, but unlike VSVg showed CD8 T cell specific transduction. Interestingly, CD8-targeted fusogens were superior to VSVg-pseudotyped lentivirus at transducing non-activated human T cells. In vivo fusogen-mediated delivery showed efficient and specific CD8 T cell transduction and expression of a GFP reporter gene. Second-generation CARs containing a CD19 binding domain and a 41BB costimulatory domain delivered by targeted fusogen demonstrated CD8 specific expression and functional activity against non-malignant B cells and CD19+ Nalm6 leukemia cells. To demonstrate targeted fusogen-mediated in vivo CAR delivery and activity, we established Nalm6 xenografts in mice into which unmodified activated human PBMCs were infused. Activated human PBMCs alone were unable to control tumor growth. A single intravenous delivery of a CD8 fusogen containing a second-generation CD19 CAR transgene across a range of functional titer doses resulted in the generation of CD8 CAR Ts that eradicated the CD19+ tumor xenografts. A high percentage of T cells demonstrated CAR expression after fusogen delivery with clear specificity for the CD8+ cells. Importantly, the fusogen was able to generate a functional CAR response regardless of prior activation status of the T cells. Targeted in vivo delivery of CAR into T cell subsets may represent a novel therapeutic approach for human B cell malignancies. The ability to specifically deliver a CAR gene to a T cell in vivo would be transformative in terms of patient access and is likely to generate a qualitatively superior therapeutic T cell. References: 1) Bender, R. R. et al. PLOS Pathogens 12, e1005641 (2016). 2) Agarwal, S. et al. OncoImmunology 8, 1-8 (2019).

Citation Format: Akinola Emmanuel, Patty Cruite, Hanane Ennajdaoui, Carmela Passaro, Paige Baldwin, Victoria Duback, Anna Liang, Jess Elman, Samantha Crocker, Shirisha Amatya, Caspian Harding, Allyse Mazarelli, Sergey Lyubinetsky, Vidur Patel, Avani Parikh, Kelan Hlavaty, Jason Rodriguez, Lauren Pepper, Albert Ruzo, Salvatore Iovino, Kutlu Elpek, Michael Laska, Trevor McGill, Donna Dambach, Terry Fry, Jagesh Shah. In vivo CAR T therapy: targeted in vivo gene delivery of a CAR using a CD8-specific fusogen results in tumor eradication [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB105.

ICOS agonism by JTX-2011 (vopratelimab) requires initial T cell priming and Fc cross-linking for optimal T cell activation and anti-tumor immunity in preclinical models

Immunotherapy checkpoint inhibitors, such as antibodies targeting PD-1 and CTLA-4, have demonstrated the potential of harnessing the immune system to treat cancer. However, despite encouraging results particularly with respect to survival, only a minority of patients benefit from these therapies. In clinical studies aimed at understanding changes in the immune system following immunotherapy treatment, ICOS (Inducible T cell CO-Stimulator) was shown to be significantly up-regulated on CD4+ T cells and this was associated with clinical activity, indicating that ICOS stimulatory activity may be beneficial in the treatment of solid tumors. In this report, we describe the generation of specific, species cross-reactive, agonist antibodies to ICOS, including the humanized clinical candidate, JTX-2011 (vopratelimab). Preclinical studies suggest that the ICOS stimulating antibodies require Fc receptor cross-linking for optimal agonistic activity. Notably, the ICOS antibodies do not exhibit superagonist properties but rather require T cell receptor (TCR)-mediated upregulation of ICOS for agonist activity. Treatment with the ICOS antibodies results in robust anti-tumor benefit and long-term protection in preclinical syngeneic mouse tumor models. Additional benefit is observed when the ICOS antibodies are administered in combination with anti-PD-1 and anti-CTLA-4 therapies. Based on the preclinical data, JTX-2011 is currently being developed in the clinical setting for the treatment of solid tumors.

Abstract 6604: Drug responsive domain regulation of IL15-engineered T cells provides pharmacological control over antigen-independent cell expansion

Engineered T cell therapies have been remarkably successful in the treatment of B cell malignancies, yet lack of control over these “living drugs” can lead to significant toxicities or limited efficacy. One particular challenge is the achievement of durable anti-tumor responses because the reduction of tumor burden results in reduced antigen stimulation and therefore reduced antigen-dependent T cell expansion. Interleukin-15 (IL15) drives T and NK cell expansion and persistence in an antigen-independent manner, however unregulated expression of this cytokine may compromise the safety and efficacy of cellular immunotherapy. To address these issues, we engineered T cells with a pharmacologically controllable, membrane-bound IL15 that supports antigen-independent T cell expansion and has the potential to reduce the safety risks associated with continuous exposure to soluble IL15. Our approach utilizes Drug Responsive Domains (DRDs) which are fully human protein domains that are inherently unstable in the cell but are reversibly stabilized when bound to specific FDA-approved drugs. Fusion of a DRD to a protein of interest confers drug-dependent, reversible regulation of protein expression and function. We developed a DRD based on the carbonic anhydrase 2 (CA2) protein, which is stabilized in the presence of the FDA-approved drug acetazolamide (ACZ). Upon gene transfer of membrane-bound IL15 fused to a CA2 DRD, regulated IL15 expression on T cells was detected only in the presence of ACZ. In the absence of ACZ, the level of IL15 detected on the surface of gene-modified T cells is not substantially different from the level detected on untransduced T cells. ACZ treatment of gene-modified T cells increases surface IL15 expression in a dose-dependent manner. We observed prolonged survival and up to 15-fold expansion of IL15-CA2 DRD-transduced T cells in the absence of supplemental cytokines or antigen stimulation. In contrast, vehicle-treated IL15-CA2 DRD modified T cells and untransduced T cells did not survive or expand in vitro. Importantly, both IL15-CA2-transduced T cells and unengineered, co-infused NK cells survived and persisted significantly more in vivo in ACZ-treated but not vehicle-treated non-tumor-bearing NSG mice. Our results demonstrate that a novel membrane-bound IL15-CA2 fusion protein coupled with ACZ treatment induces antigen-independent T cell expansion and augments bystander NK cell persistence. Regulatable IL15 expression has significant implications for both T and NK cell therapies by providing more durable cell expansion and cytolytic activity in vivo, and thus the potential to significantly reduce cell dosing while maintaining clinical efficacy in patients.

Citation Format: Steven Shamah, Kutlu Elpek, Tucker Ezell, Michelle Fleury, Michael Gallo, Jennifer Gori, Scott Heller, Mara Inniss, Meghan Langley, Grace Olinger, Celeste Richardson, Karen Tran, Dhruv Sethi, Dexue Sun, Vipin Suri. Drug responsive domain regulation of IL15-engineered T cells provides pharmacological control over antigen-independent cell expansion [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 6604.

Abstract LB-013: CAR-Ts armored with small molecule-regulated IL12 or CD40L cassettes for enhanced activity against solid tumors

Adoptive cell therapy with chimeric antigen receptor (CAR) modified T cells has demonstrated remarkable clinical efficacy in the treatment of certain B cell malignancies, and more recently in multiple myeloma. However, CAR-T therapy has been less successful in treating solid tumors due to multiple obstacles, including the lack of robust CAR-T cell expansion, the immunosuppressive tumor microenvironment, and tumor escape due to the loss of targeted antigen. Engineering CAR-T cells to produce immunomodulatory factors such as Interleukin 12 (IL12) and Cluster of Differentiation 40 Ligand (CD40L) has been shown to enhance functional activity by driving T cell expansion, conferring resistance to immunosuppression, improving antigen presentation, and inducing antigen spread. However, the clinical utility of both IL12 and activators of the CD40 signaling pathway have been limited by systemic toxicity associated with their potent pharmacological activities. Providing precise tuning of the timing and level of expression of these immunomodulatory factors in CAR-T cells could significantly enhance safety and therapeutic efficacy, in particular against solid tumor malignancies. We describe here the implementation of ligand-controlled regulation of IL12 and CD40L in vitro and in vivo in engineered primary human T cells via the use of destabilizing domain (DD) technology. DDs are small protein domains that are misfolded and inherently unstable in the cell, but which can be reversibly stabilized by the binding of approved pharmacologic agents. This conditional stability of DDs can be readily conferred to any protein of interest by fusing it to the DD, thus providing fine-tuned, exogenous regulation of protein expression and function. We have identified mutations in several human protein substrates, including phosphodiesterase 5 (PDE5), dihydrofolate reductase (DHFR), and estrogen receptor (ER), which convey DD activity and can be regulated by FDA-approved drugs. We show that transduction of human T cells with either DD-IL12 or DD-CD40L fusion constructs yields low expression levels in the basal state and a rapid, dose-dependent induction of IL12 or CD40L protein in the presence of the corresponding stabilizing ligand. Moreover, kinetically precise, on-demand production of either factor from CAR-T cells can be achieved in mice by oral dosing of stabilizing drugs. A CD19 CAR-T Nalm6 mouse model has been established that measures potent CAR-T expansion and enhanced anti-tumor efficacy with armored immunomodulatory constructs. Studies are underway in this model, as well as in solid tumor models, to test for enhanced CAR-T activity via drug-induced activation of IL12 and CD40L towards the development of next generation cell therapies with more favorable efficacy and safety profiles.

Citation Format: Michelle Ols, Michael Schebesta, Emily Brideau, Kutlu Elpek, Michelle Fleury, Jennifer Gori, Scott Heller, Dan Jun Li, Benjamin Primack, Christopher Reardon, Dhruv Sethi, Alex Storer, Dexue Sun, Karen Tran, Elizabeth Weisman, Michael Briskin, Celeste Richardson, Vipin Suri, Steven Shamah. CAR-Ts armored with small molecule-regulated IL12 or CD40L cassettes for enhanced activity against solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-013.

Abstract A220: Destabilizing domain technology facilitates exogenous regulation of IL15 and IL12 for adaptive T-cell therapy

Cytokines are messenger molecules that act as regulators of innate and adaptive immunity by propagating cell-cell immune signaling. Several cytokines have been approved for the treatment of metastatic renal cell cancer, advanced melanoma, and hairy cell leukemia (HCL) and can be particularly effective when combined with adoptive cell therapy. However, systemic delivery or constitutive expression of cytokines even at moderate levels can potentially lead to significant toxicity. These hurdles to enabling cytokine-enhanced adoptive cell therapy motivated us to implement destabilizing domain (DD) technology for regulating cytokines in chimeric antigen receptor (CAR) reprogrammed T-cells. The ability of CAR-T-cells to traffic to tumor sites enables localized co-delivery of cytokines for enhanced CAR-T-cell antitumor activity while improving safety. Obsidian Therapeutics’ DD technology enables titratable and reversible regulation of a protein of interest with FDA-approved small-molecule drugs in a time- and dose-dependent manner. Protein-fused DDs are misfolded in the absence of a stabilizing small-molecule ligand and are rapidly degraded by the proteasome. However, the addition of ligand restores the folding, stability, and function of the DD-protein fusion. We have generated IL-12 and membrane-bound IL15-IL15Ra (mbIL15) fused to DDs such as FK506 binding protein (FKBP), Escherichia coli dihydrofolate reductase (ecDHFR), as well as human protein substrates (huDDs) with clinically approved ligands. DD-IL12 and DD-mbIL15 fusions displayed ligand-dependent regulation of cytokine secretion or cell surface expression, respectively, in cell lines and primary human T-cells. We then tested DD regulation of IL12 or mbIL15 in vivo by injecting T-cells engineered with cytokine-fused DDs into NSG mice, followed by oral administration of vehicle or corresponding ligand. Vehicle-treated mice displayed low level expression of the respective cytokines, whereas ligand treatment robustly induced the expression of target cytokine within 4-6 hours after treatment. Cytokine expression returned to baseline levels 24 hours following ligand administration. These data demonstrate the feasibility of exogenous control over transgene-derived protein expression in primary human T-cells for the development of next-generation CAR-T-cell products with enhanced efficacy and more favorable safety profiles.

Citation Format: Karen Tran, Kutlu Elpek, Tucker Ezell, Scott Heller, Mara Inniss, Abhishek Kulkarni, Dan Jun Li, Grace Olinger, Michelle Ols, Christopher Reardon, Dexue Sun, Tariq Kassum, Michael Briskin, Celeste Richardson, Vipin Suri, Steven Shamah, Michael Gilman. Destabilizing domain technology facilitates exogenous regulation of IL15 and IL12 for adaptive T-cell therapy [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A220.

Abstract 3580: Enhancing adoptive cell therapies through exogenous regulation

Adoptive cell therapy with chimeric antigen receptor (CAR) modified T cells has demonstrated remarkable clinical efficacy in the treatment of certain B cell malignancies and more recently in multiple myeloma. However, in solid tumors, CAR-T therapy has been far less successful, likely due to the lack of robust CAR-T cell expansion, the immunosuppressive microenvironment, and clonal heterogeneity within these tumors. The trafficking of CAR-T cells to tumor sites provides an opportunity for selective delivery of cargo that can enhance CAR-T cell activity at the site of the tumor. Interleukin-12 (IL12) and membrane tethered interleukin-15 (mbIL15) have previously been shown to enhance CAR-T activity, yet the unregulated expression of either compromises safety and/or efficacy. The Obsidian Therapeutics platform equips engineered immune cells with new functionalities whose activity can be regulated via the administration of FDA-approved small-molecule drugs, putting dosing control back in the hands of the treating physician. We utilize small, fully human protein sequences called destabilizing domains (DDs) that confer reversible destabilization to a fused target protein. In the absence of ligand the fusion protein is degraded, whereas the presence of small molecule ligand restores expression and functionality. Furthermore, stabilization is titratable with small molecule ligand dose, providing finely tuned control over target protein expression and function. We have applied our technology to create DD-IL12 and DD-mbIL15 “cassettes” that provide exogenous regulation of cytokine activity when transduced into CAR-Ts for enhanced cellular function. We describe here the successful implementation of the DD technology in engineered primary human T cells and show small-molecule ligand controlled regulation of DD-IL12 and DD-mbIL15 protein expression in vivo in mouse models. These data demonstrate the feasibility of exogenous control over protein expression in primary human T cells for the development of next-generation CAR-T cell products with enhanced efficacy and more favorable safety profiles.

Citation Format: Celeste Richardson, Kutlu Elpek, Michelle Ols, Tariq Kassum, Steve Shamah. Enhancing adoptive cell therapies through exogenous regulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3580.

Abstract SY03-02: Preclinical assessment of JTX-2011, an agonist antibody targeting ICOS, supports evaluation in ICONIC clinical trial

ICOS (the inducible T-cell co-stimulator) is a co-stimulatory molecule expressed on the surface of T cells and a member of the CD28 family, which includes clinically validated targets of cancer immunotherapies, such as PD-1 and CTLA-4. Clinical data identified ICOS as a potentially key molecule in providing optimal antitumor benefit following anti-CTLA-4 therapy. We have developed a species cross-reactive humanized IgG1 agonist antibody, JTX-2011, that binds ICOS and is designed to induce an antitumor immune response. Our preclinical data suggest that JTX-2011 functions through a dual mechanism of action, by stimulating T effector cells (Teff) and depleting intratumoral T regulatory cells (Tregs). The ICOS antibody is efficacious as a single agent in mouse syngeneic tumor models and demonstrates enhanced activity when administered in combination with anti-PD-1. Single-agent activity in the preclinical models appears to correlate with ICOS expression, with greater efficacy observed in tumor models that exhibit a higher percentage of ICOS-expressing immune cell infiltrate. An integrated expression analysis of human tumors identified non-small cell lung cancer (NSCLC) and head and neck squamous cell carcinoma (HNSCC) as indications with higher percentages of ICOS-expressing cell infiltrate. Preclinical studies performed in rodent and monkeys evaluated safety, pharmacokinetics, and pharmacodynamics of JTX-2011 to inform the first in-human study. The ICONIC phase I/II clinical trial is currently ongoing for evaluation of JTX-2011 alone or in combination with the anti-PD-1 antibody Nivolumab in patients with advanced solid tumors and incorporates a patient enrichment strategy design based on the preclinical and translational findings.

Citation Format: Jennifer S. Michaelson, Christopher Harvey, Kutlu Elpek, Ellen Duong, Lindsey Shallberg, Matthew Wallace, Robert Mabry, Jenny Shu, Amit Deshpande, Tong Zi, Stephen Sazinsky, Joshua Apgar, Barbara Mounho-Zamora, Michael Briskin, Elizabeth Trehu, Jason Reeves, Heather Hirsch, Sriram Sathyanarayanan, Deborah Law. Preclinical assessment of JTX-2011, an agonist antibody targeting ICOS, supports evaluation in ICONIC clinical trial [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 SY03-02. doi:10.1158/1538-7445.AM2017-SY03-02

Abstract A059: Efficacy of anti-ICOS agonist monoclonal antibodies in preclinical tumor models provides a rationale for clinical development as cancer immunotherapeutics

ICOS (inducible co-stimulator molecule) is a T cell encoded member of the extended B7/CD28 superfamily that is up-regulated upon early T cell activation. Previous studies have shown that higher ICOS expression on circulating T cells, post treatment with ipilimumab, is associated with better clinical outcome. In complementary pre-clinical studies, efficacy observed with a whole cell vaccine consisting of ICOS-L expressing B16 melanoma (IVAX) suggests that agonism of this pathway could provide therapeutic benefit in the cancer setting.

In accordance with these observations, we generated a panel of anti-ICOS monoclonal antibodies with in vitro agonist properties. A lead series of mAbs were shown to be efficacious as monotherapies in syngeneic tumors models with enhanced tumor inhibition observed in combination with anti-PD1. Mechanistic studies demonstrate that tumor regression is associated with enhanced ratios of cytotoxic CD8/regulatory T (Tregs) cells and that this change is related to preferential reduction in ICOS high Tregs in the tumor microenvironment.

These data provided the rationale for development of a high affinity humanized agonist monoclonal antibody to be tested in both mono therapy and in combination with other T cell checkpoints. Our lead anti-ICOS antibody is currently in IND-enabling studies and will be tested for activity in solid tumor indications.

Citation Format: Kutlu Elpek, Christopher Harvey, Ellen Duong, Tyler Simpson, Jenny Shu, Lindsey Shallberg, Matt Wallace, Sriram Sathy, Robert Mabry, Jennifer Michaelson, Michael Briskin. Efficacy of anti-ICOS agonist monoclonal antibodies in preclinical tumor models provides a rationale for clinical development as cancer immunotherapeutics. [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 A059.

In vivo discovery of immunotherapy targets in the tumour microenvironment

Recent clinical trials showed that targeting of inhibitory receptors on T cells induces durable responses in a subset of cancer patients, despite advanced disease. However, the regulatory switches controlling T-cell function in immunosuppressive tumours are not well understood. Here we show that such inhibitory mechanisms can be systematically discovered in the tumour microenvironment. We devised an in vivo pooled short hairpin RNA (shRNA) screen in which shRNAs targeting negative regulators became highly enriched in murine tumours by releasing a block on T-cell proliferation upon tumour antigen recognition. Such shRNAs were identified by deep sequencing of the shRNA cassette from T cells infiltrating tumour or control tissues. One of the target genes was Ppp2r2d, a regulatory subunit of the PP2A phosphatase family. In tumours, Ppp2r2d knockdown inhibited T-cell apoptosis and enhanced T-cell proliferation as well as cytokine production. Key regulators of immune function can therefore be discovered in relevant tissue microenvironments.

The transcriptional landscape of αβ T cell differentiation

αβT cell differentiation from thymic precursors is a complex process, explored here with the breadth of ImmGen expression datasets, analyzing how differentiation of thymic precursors gives rise to transcriptomes. After surprisingly gradual changes though early T commitment, transit through the CD4⁺CD8⁺ stage involves a shutdown or rare breadth, and correlating tightly with MYC. MHC-driven selection promotes a large-scale transcriptional reactivation. We identify distinct signatures that mark cells destined for positive selection versus apoptotic deletion. Differential expression of surprisingly few genes accompany CD4 or CD8 commitment, a similarity that carries through to peripheral T cells and their activation, revealed by mass cytometry phosphoproteomics. The novel transcripts identified as candidate mediators of key transitions help define the “known unknown” of thymocyte differentiation.

Transcriptional profiling of steady-state and inflamed lymph node stroma reveals potential hematopoietic-stromal cross-talk pathways and suggests an active role for stroma during ongoing immune responses. (176.22)

Lymph node stromal cells (LNSCs) closely regulate immunity and self-tolerance, yet key aspects of their biology remain poorly illuminated. Little is known about what factors these cells produce beyond a short list of critical molecules, or how these subsets respond to inflammation. Comparative transcriptomic analyses of steady-state murine LNSC subsets revealed expression of important immune mediators and growth factors. Further, pairwise analyses of ligand and cognate receptor expression by hematopoietic and stromal subsets suggested a complex web of cross-talk. Transcriptional profiling of steady-state LNSC subsets also suggested a readiness of these cells to respond to inflammatory and infectious triggers. Accordingly, fibroblastic reticular cells (FRCs), blood endothelial cells (BECs), and lymphatic endothelial cells (LECs) isolated from inflamed lymph nodes upregulated expression of numerous genes involved in the acute phase response, immune cell recruitment, and the MHC II antigen processing and presentation pathway, among others. Flow cytometric analysis demonstrated elevated levels of surface MHC II on FRCs, BECs, and LECs isolated from skin-draining lymph nodes 18 hours after the onset of inflammation. LNSC subsets from inflamed lymph nodes also produced the antimicrobial molecule lipocalin 2. Together these data offer insight into the transcriptional identities of murine LNSC subsets, while suggesting that they may be active players during ongoing inflammation.

Integrin alpha-7+ pericytes are a novel, immunologically relevant lymph node stromal subset found in mice and humans (47.6)

Within lymph nodes, non-hematopoietic stromal cells attract, arrange, and promote the survival of naïve T cells, while deleting self-reactive T cells in a non-redundant fashion. Despite these important functions, subsets are poorly characterized. One major subset (gp38-CD31- double negative, termed DN) comprises 10-15% of stroma, with transcript for relevant peripheral tissue-restricted antigens (PTAs) and Aire, yet nothing was known of their lineage, localization, phenotype, or capacity to interact with leukocytes. We addressed this through in-depth transcriptomic, protein and functional analyses of DN stroma, in comparison to 5 other stromal subsets. DNs express CCL19, CCL21, CXCL13, CXCL9, CXCL10 and other chemokines, with high levels of Flt3L, BAFF, CSF-1, TGFb family members and lymphangiogenic growth factors. Phylogenetic analysis showed DNs were similar to but distinct from fibroblastic reticular cells, with a unique integrin profile, higher contractility in culture, and a lack of IL-7 expression. In situ, we found a unique surface protein, integrin α7, which identified DNs as lymph node pericytes in the cortex and medulla. Strikingly, DNs strongly alter PTA transcription following inflammation without increasing surface expression of MHC molecules. We subsequently identified DN cells in human lymph nodes. These data identify DNs as a unique, immunologically relevant subset of fibroblastic, contractile pericytes, which we term integrin α7+ pericytes (IAPs).

Long-term cytokine therapy with IL-15/IL-15Rα complexes leads to impaired NK cell function (131.11)

Immunotherapies targeting effector lymphocytes are promising approaches for the treatment of cancer and infectious diseases. One such approach employs IL-15/IL-15Rα complexes which are considerably more potent than IL-15 in expanding cytotoxic lymphocytes including NK and CD8 T cells. Recent studies demonstrated that short-term treatment with IL-15/IL-15Rα complexes is highly effective in driving a transient but substantial reduction in tumor burden via immune-mediated mechanisms whereas continuous cytokine therapy improves survival only modestly and fails to control tumor outgrowth. Given the limited efficacy of long-term therapy, we sought to investigate the impact of continuous in vivo stimulation with IL-15/IL-15Rα complexes on NK and CD8 T cells in tumor-free mice. Long-term treatment with IL-15/IL-15Rα complexes triggered massive expansion of NK and CD8 T cells. Strikingly, however, NK cells exhibited marked defects in activation, IFNγ production, degranulation, and cytotoxicity whereas CD8 T cells showed enhanced functional capacity. Additionally, continuous treatment generated a suppressive environment for transferred naïve NK and CD8 T cells and resulted in accumulation of CD11b+Gr1+ cells. The mechanistic basis for NK cell dysfunction upon chronic stimualation with IL-15/IL-15Ra complexes will be discussed. Our results have important clinical implications for the design of immunotherapies and vaccines using multiple doses of immunostimulatory agents.

Tumor cells engineered to codisplay on their surface 4-1BBL and LIGHT costimulatory proteins as a novel approach for cancer immunotherapy (144.24)

Tumor cells genetically modified to express immunomodulatory molecules as vaccine have shown efficacy against cancer. However, such vaccines are not only cost/labor and time intensive, but also have safety repercussions. As an alternative, we developed the ProtEx™ technology that involves modification of the cell membrane with biotin and engineering with proteins of interest chimeric with core streptavidin. We herein demonstrate that tumor cells can be engineered simultaneously with two SA-chimeric costimulatory ligands, SA-4-1BBL and SA-LIGHT. The choice of 4-1BBL and LIGHT were due to their immune activating pleiotropic functions and stimulatory effects on tumor stroma, respectively. Using TC-1 tumor cells as a transplantable cervical cancer mouse model, we demonstrated that these cells can be engineered simultaneously with both molecules. Vaccination with irradiated TC-1 cells engineered with both costimulatory proteins resulted in 100% efficacy in prophylactic and >57% efficacy in therapeutic TC-1 settings. In marked contrast, TC-1 cells displaying these molecules singly showed limited efficacy. Vaccine efficacy was associated with the generation of primary and memory T cell, IFN-γ, and Ab responses, and enhanced CD8+ T cell infiltration into the tumor. Engineering tumor cells in a rapid and effective manner to simultaneously display on their surface a collection of immunostimulatory molecules with distinct functions presents a novel approach for cancer immunotherapy.

SA-4-1BBL as an immune modulator and vehicle to deliver antigens into dendritic cells for effective cancer immunotherapy (144.25)

The success of TAAs-based vaccines may depend on the nature of adjuvants used. We recently generated a chimeric 4-1BBL with streptavidin (SA-4-1BBL) that exists as tetramers/oligomers with potent activity and can be used as a vehicle to deliver TAAs into dendritic cells constitutively expressing 4-1BB receptor. We demonstrated that SA-4-1BBL can be effectively conjugated to biotinylated ovalbumin (Ova) as a model antigen. Immunization with Ova conjugated to SA-4-1BBL resulted in increased Ova uptake and cross-presentation by DCs, that resulted in potent Ova specific proliferation of CD4+ (OT-II) and CD8+ (OT-I) T cells. The conjugate vaccine also generated significantly higher in vivo specific CTL responses to Ova and HPV E7 oncoprotein than nonconjugate vaccine. Importantly, a single vaccination with HPV E7 oncoprotein or survivin conjugated to SA-4-1BBL resulted in robust and superior efficacy than nonconjugate vaccine in the eradication of established E7 expressing TC-1 and survivin expressing 3LL tumors, respectively. Therapeutic efficacy was achieved in the absence of detectable toxicity and associated with increased CD4+ T and CD8+ T cell effector and memory responses and higher intratumoral CD8+ Teff/CD4+CD25+Foxp3+Treg ratio. In conclusion, potent immunomodulatory activities of SA-4-1BBL combined with its ability to serve as a vehicle to deliver TAAs to DCs further rationalizes the extensive evaluation for the development of therapeutic vaccines against cancer.