Scott H. Robbins

Design of a novel integration-deficient lentivector technology that incorporates genetic and posttranslational elements to target human dendritic cells.

As sentinels of the immune system, dendritic cells (DCs) play an essential role in regulating cellular immune responses. One of the main challenges of developing DC-targeted therapies includes the delivery of antigen to DCs in order to promote the activation of antigen-specific effector CD8 T cells. With the goal of creating antigen-directed immunotherapeutics that can be safely administered directly to patients, Immune Design has developed a platform of novel integration-deficient lentiviral vectors that target and deliver antigen-encoding nucleic acids to human DCs. This platform, termed ID-VP02, utilizes a novel genetic variant of a Sindbis virus envelope glycoprotein with posttranslational carbohydrate modifications in combination with Vpx, a SIVmac viral accessory protein, to achieve efficient targeting and transduction of human DCs. In addition, ID-VP02 incorporates safety features in its design that include two redundant mechanisms to render ID-VP02 integration-deficient. Here, we describe the characteristics that allow ID-VP02 to specifically transduce human DCs, and the advances that ID-VP02 brings to conventional third-generation lentiviral vector design as well as demonstrate upstream production yields that will enable manufacturing feasibility studies to be conducted.

A novel HSV-2 subunit vaccine induces GLA-dependent CD4 and CD8 T cell responses and protective immunity in mice and guinea pigs.

BACKGROUND/OBJECTIVES There is currently no licensed prophylactic or therapeutic vaccine for HSV-2 infection. METHODS We developed a novel preclinical vaccine candidate, G103, consisting of three recombinantly expressed HSV-2 proteins (gD and the UL19 and UL25 gene products) adjuvanted with the potent synthetic TLR4 agonist glucopyranosyl lipid A (GLA) formulated in stable emulsion. The vaccine was tested for immunogenicity and efficacy in pre-clinical models for preventative and therapeutic vaccination. RESULTS Vaccination of mice with G103 elicited antigen-specific binding and neutralizing antibody responses, as well as robust CD4 and CD8 effector and memory T cells. The T cell responses were further boosted by subsequent challenge with live virus. Prophylactic immunization completely protected against lethal intravaginal HSV-2 infection in mice, with only transient replication of virus in the genital mucosa and sterilizing immunity in dorsal root ganglia. Supporting the use of G103 therapeutically, the vaccine expanded both CD4 and CD8 T cells induced in mice by previous infection with HSV-2. In the guinea pig model of recurrent HSV-2 infection, therapeutic immunization with G103 was approximately 50% effective in reducing the number of lesions per animal as well as the overall lesions score. CONCLUSIONS Taken together, the data show that G103 is a viable candidate for development of a novel prophylactic and therapeutic HSV-2 vaccine.

Virological and preclinical characterization of a dendritic cell targeting, integration-deficient lentiviral vector for cancer immunotherapy.

Dendritic cells (DCs) are essential antigen-presenting cells for the initiation of cytotoxic T-cell responses and therefore attractive targets for cancer immunotherapy. We have developed an integration-deficient lentiviral vector termed ID-VP02 that is designed to deliver antigen-encoding nucleic acids selectively to human DCs in vivo. ID-VP02 utilizes a genetically and glycobiologically engineered Sindbis virus glycoprotein to target human DCs through the C-type lectin DC-SIGN (CD209) and also binds to the homologue murine receptor SIGNR1. Specificity of ID-VP02 for antigen-presenting cells in the mouse was confirmed through biodistribution studies showing that following subcutaneous administration, transgene expression was only detectable at the injection site and the draining lymph node. A single immunization with ID-VP02 induced a high level of antigen-specific, polyfunctional effector and memory CD8 T-cell responses that fully protected against vaccinia virus challenge. Upon homologous readministration, ID-VP02 induced a level of high-quality secondary effector and memory cells characterized by stable polyfunctionality and expression of IL-7R&agr;. Importantly, a single injection of ID-VP02 also induced robust cytotoxic responses against an endogenous rejection antigen of CT26 colon carcinoma cells and conferred both prophylactic and therapeutic antitumor efficacy. ID-VP02 is the first lentiviral vector which combines integration deficiency with DC targeting and is currently being investigated in a phase I trial in cancer patients.

GITR ligand fusion protein agonist enhances the tumor antigen–specific CD8 T-cell response and leads to long-lasting memory

BackgroundThe expansion of antigen-specific CD8 T cells is important in generating an effective and long-lasting immune response to tumors and viruses. Glucocorticoid-induced tumor necrosis factor receptor family-related receptor (GITR) is a co-stimulatory receptor that binds the GITR ligand (GITRL). Agonism of GITR can produce important signals that drive expansion of effector T cell populations.MethodsWe explored two separate murine tumor models, CT26 and TC-1, for responsiveness to GITR Ligand Fusion Protein(GITRL-FP) monotherapy. In TC-1, GITRL-FP was also combined with concurrent administration of an E7-SLP vaccine. We evaluated tumor growth inhibition by tumor volume measurements as well as changes in CD8 T cell populations and function including cytokine production using flow cytometry. Additionally, we interrogated how these therapies resulted in tumor antigen-specific responses using MHC-I dextramer staining and antigen-specific restimulations.ResultsIn this study, we demonstrate that a GITR ligand fusion protein (GITRL-FP) is an effective modulator of antigen-specific CD8 T cells. In a CT26 mouse tumor model, GITRL-FP promoted expansion of antigen-specific T cells, depletion of regulatory T cells (Tregs), and generation of long-lasting CD8 T cell memory. This memory expansion was dependent on the dose of GITRL-FP and resulted in complete tumor clearance and protection from tumor rechallenge. In contrast, in TC-1 tumor–bearing mice, GITRL-FP monotherapy could not prime an antigen-specific CD8 T cell response and was unable to deplete Tregs. However, when combined with a vaccine targeting E7, treatment with GITRL-FP resulted in an augmentation of the vaccine-induced antigen-specific CD8 T cells, the depletion of Tregs, and a potent antitumor immune response. In both model systems, GITR levels on antigen-specific CD8 T cells were higher than on all other CD8 T cells, and GITRL-FP interacted directly with primed antigen-specific CD8 T cells.ConclusionsWhen taken together, our results demonstrate that the delivery of GITRL-FP as a therapeutic can promote anti-tumor responses in the presence of tumor-specific CD8 T cells. These findings support further study into combination partners for GITRL-FP that may augment CD8 T-cell priming as well as provide hypotheses that can be tested in human clinical trials exploring GITR agonists including GITRL-FP.

Development of a replication-competent lentivirus assay for dendritic cell-targeting lentiviral vectors

It is a current regulatory requirement to demonstrate absence of detectable replication-competent lentivirus (RCL) in lentiviral vector products prior to use in clinical trials. Immune Design previously described an HIV-1-based integration-deficient lentiviral vector for use in cancer immunotherapy (VP02). VP02 is enveloped with E1001, a modified Sindbis virus glycoprotein which targets dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) expressed on dendritic cells in vivo. Vector enveloped with E1001 does not transduce T-cell lines used in standard HIV-1-based RCL assays, making current RCL testing formats unsuitable for testing VP02. We therefore developed a novel assay to test for RCL in clinical lots of VP02. This assay, which utilizes a murine leukemia positive control virus and a 293F cell line expressing the E1001 receptor DC-SIGN, meets a series of evaluation criteria defined in collaboration with US regulatory authorities and demonstrates the ability of the assay format to amplify and detect a hypothetical RCL derived from VP02 vector components. This assay was qualified and used to test six independent GMP production lots of VP02, in which no RCL was detected. We propose that the evaluation criteria used to rationally design this novel method should be considered when developing an RCL assay for any lentiviral vector.

A Rev-Independent gag/pol Eliminates Detectable psi-gag Recombination in Lentiviral Vectors

Abstract Lentiviral vectors (LVs) are being developed for clinical use in humans for applications including gene therapy and immunotherapy. A safety concern for use of LVs in humans is the generation of replication-competent lentivirus (RCL), which may arise due to recombination between the split genomes of third-generation LVs. Although no RCL has been detected to date, design optimizations that minimize recombination events between split genome vectors would provide an added safety benefit that may further reduce the risk of RCL formation. Here we describe design elements introduced to the gag/pol plasmid with the intention of eliminating psi-gag recombination between the vector genome and gag/pol. These design changes, consisting of codon optimization of the gag/pol sequence and the deletion of the Rev-responsive element, abrogate the requirement for Rev in expression of Gag protein, thus the resulting gag/pol construct being Rev independent (RI gag/pol). We show that generating vector using the RI gag/pol construct has no effect on particle production or transduction titers. The RI and wild-type gag/pol vectors function equivalently as antigen-specific immunotherapy, potently inducing antigen-specific CD8 T cells that protect against challenge with vaccinia virus. Most importantly, the designed RI gag/pol eliminated detectable psi-gag recombination. Interestingly, we detected recombination between the vector genome and gag/pol from regions without sequence homology. Our findings imply that although unpredictable recombination events may still occur, the RI gag/pol design is sufficient to prevent psi-gag recombination.

Abstract 2505: Therapeutic efficacy of the ZVex™ and GLAAS™ platforms in a B16-F10/hCAIX melanoma mouse model

ZVex™ and GLAAS™ are two dendritic-cell (DC) targeting platform technologies designed to enhance immune responses through the in vivo induction of antigen specific CD8 and CD4 T-cells, respectively. ZVex™ is a lentiviral vector pseudotyped with a modified Sindbis virus envelope engineered to deliver tumor antigen-encoding nucleic acids to dendritic cells in vivo. GLAAS™(Glucopyranosyl Lipid A Adjuvant System) activates DC by binding to the TLR-4 receptor and inducing strong Th1 type CD4 responses against co-delivered recombinant proteins. Currently both platform technologies are being investigated in phase I clinical trials in cancer patients. Human carbonic anhydrase 9 (hCAIX) is a tumor-associated transmembrane antigen that is over-expressed on various cancer cell types. We mapped hCAIX specific, multi-functional CD8 and CD4 T-cell epitopes within the extracellular and transmembrane regions of the protein for the mouse haplotype H-2b by intracellular cytokine staining. Mice lethally challenged s.c. on the flank with a B16-F10 tumor cell line expressing the hCAIX protein (designated BC.12) fully controlled large tumors (>100 mm2) when therapeutically immunized (subcutaneously at the base of tail) with ZVex™ encoding hCAIX or the recombinant hCAIX protein with GLAAS™ (either s.c. or i.m.). In both models, tumor control was dose-dependent. Additionally, the presence of a strong transmembrane H-2b restricted CD8 T-cell epitope was required for tumor control and regression. hCAIX-specific CD8 T-cell responses were detectable as far out as day 67 post challenge in mice displaying full regression of tumor. These results demonstrate proof of concept for ZVex™ and GLAAS™ platform technologies in an aggressive murine melanoma model. Citation Format: David J. Campbell, Rebecca S. Reeves, Patrick A. Flynn, Scott H. Robbins, Peter Berglund, Jan H. ter Meulen. Therapeutic efficacy of the ZVex™ and GLAAS™ platforms in a B16-F10/hCAIX melanoma mouse model. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2505. doi:10.1158/1538-7445.AM2015-2505

Abstract 702: DCVex(TM): A novel integration-deficient lentivector technology that incorporates genetic and post-translational elements to target dendritic cells

With the goal of creating antigen-directed immunotherapeutics that can be safely administered directly to patients, Immune Design has developed a platform of novel integration-deficient lentiviral vectors that target and deliver antigen-encoding nucleic acids to dendritic cells (DCs) in order to promote the activation of antigen-specific effector CD8 T cells. This platform, termed DCVex(TM), utilizes a novel genetic variant of a Sindbis virus envelope glycoprotein with post-translational carbohydrate modifications in combination with Vpx, a SIVmac viral accessory protein, to achieve efficient targeting and transduction of DCs. In addition, DCVex(TM) incorporates safety features in its design that include redundant mechanisms to render DCVex(TM) integration-deficient, as well as genetic modifications that eliminate psi-gag recombination between split genome components. The characteristics that allow DCVex(TM) to specifically transduce human DCs and the advances that DCVex(TM) brings to conventional third-generation lentiviral vector design demonstrate its potential as a vaccine designed to utilize DCs for cancer immunotherapy. Citation Format: Semih U. Tareen, Brenna Kelley-Clarke, Christopher J. Nicolai, Megan M. Slough, Chintan D. Vin, Neal Van Hoeven, Scott H. Robbins, Jan H. ter Meulen, Peter Berglund. DCVex(TM): A novel integration-deficient lentivector technology that incorporates genetic and post-translational elements to target dendritic cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 702. doi:10.1158/1538-7445.AM2014-702

Abstract 2817: DCVex(TM): A novel DC-targeted vector platform for cancer immunotherapy

Dendritic cells (DCs) are essential for the initiation of T cell responses and are therefore an attractive target for cancer immunotherapy. The DC vaccine, Provenge®, as well as a number of on-going clinical trials, have in principle validated this concept. However, the currently pursued strategy of ex vivo immunization of DCs is time-consuming and costly. We have developed a 3rd generation, integration-deficient lentivector platform, DCVex(TM), which is designed to deliver tumor antigen-encoding genes directly to DCs in vivo by targeting the DC-SIGN receptor. Mice immunized with DCVex(TM) vectors expressing a variety of model antigens developed strong, dose-dependent poly-functional and cytotoxic antigen-specific CD8 T cell responses, as assessed by intracellular cytokine staining and in vitro cytotoxic T lymphocyte assays. Repeated immunizations resulted in boosting of the T cell responses, indicating the absence of induction of inhibitory anti-vector immunity. Importantly, in stringent therapeutic tumor models (e.g., B16F10 footpad melanoma and CT26 lung metastasis models), immunization with tumor antigen-encoding vectors protected the majority of animals from death in a dose-dependent manner. These findings demonstrate the potential of DCVex(TM) as a novel cancer vaccine platform suitable for in vivo DC immunization. Citation Format: Tina C. Albershardt, Semih U. Tareen, Jared M. Odegard, David J. Campbell, Patrick Flynn, Scott H. Robbins, Peter Berglund, Jan H. ter Meulen. DCVex(TM): A novel DC-targeted vector platform for cancer immunotherapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2817. doi:10.1158/1538-7445.AM2014-2817