Flt3 agonist enhances immunogenicity of arenavirus vector-based simian immunodeficiency virus vaccine in macaques

Arenaviral vaccine vectors encoding simian immunodeficiency virus (SIV) immunogens are capable of inducing efficacious humoral and cellular immune responses in nonhuman primates. Several studies have evaluated the use of immune modulators to further enhance vaccine-induced T-cell responses. The hematopoietic growth factor Flt3L drives the expansion of various bone marrow progenitor populations, and administration of Flt3L was shown to promote expansion of dendritic cell populations in spleen and blood, which are targets of arenaviral vectors. Therefore, we evaluated the potential of Flt3 signaling to enhance the immunogenicity of arenaviral vaccines encoding SIV immunogens (SIVSME543 Gag, Env, and Pol) in rhesus macaques, with a rhesus-specific engineered Flt3L-Fc fusion protein. In healthy animals, administration of Flt3L-Fc led to a 10- to 100-fold increase in type 1 dendritic cells 7 days after dosing, with no antidrug antibody (ADA) generation after repeated dosing. We observed that administration of Flt3L-Fc fusion protein 7 days before arenaviral vaccine increased the frequency and activation of innate immune cells and enhanced T-cell activation with no treatment-related adverse events. Flt3L-Fc administration induced early innate immune activation, leading to a significant enhancement in magnitude, breadth, and polyfunctionality of vaccine-induced T-cell responses. The Flt3L-Fc enhancement in vaccine immunogenicity was comparable to a combination with αCTLA-4 and supports the use of safe and effective variants of Flt3L to augment therapeutic vaccine-induced T-cell responses.IMPORTANCEInduction of a robust human immunodeficiency virus (HIV)-specific CD4+ and CD8+ T-cell response through therapeutic vaccination is considered essential for HIV cure. Arenaviral vaccine vectors encoding simian immunodeficiency virus (SIV) immunogens have demonstrated strong immunogenicity and efficacy in nonhuman primates. Here, we demonstrate that the immunogenicity of arenaviral vectors encoding SIV immunogens can be enhanced by administration of Flt3L-Fc fusion protein 7 days before vaccination. Flt3L-Fc-mediated increase in dendritic cells led to robust improvements in vaccine-induced T- and B-cell responses compared with vaccine alone, and Flt3L-Fc dosing was not associated with any treatment-related adverse events. Importantly, immune modulation by either Flt3L-Fc or αCTLA-4 led to comparable enhancement in vaccine response. These results indicate that the addition of Flt3L-Fc fusion protein before vaccine administration can significantly enhance vaccine immunogenicity. Thus, safe and effective Flt3L variants could be utilized as part of a combination therapy for HIV cure.

Preclinical evaluation of two phylogenetically distant arenavirus vectors for the development of novel immunotherapeutic combination strategies for cancer treatment

BACKGROUND

Engineered arenavirus vectors have recently been developed to leverage the body's immune system in the fight against chronic viral infections and cancer. Vectors based on Pichinde virus (artPICV) and lymphocytic choriomeningitis virus (artLCMV) encoding a non-oncogenic fusion protein of human papillomavirus (HPV)16 E6 and E7 are currently being tested in patients with HPV16+ cancer, showing a favorable safety and tolerability profile and unprecedented expansion of tumor-specific CD8+ T cells. Although the strong antigen-specific immune response elicited by artLCMV vectors has been demonstrated in several preclinical models, PICV-based vectors are much less characterized.

METHODS

To advance our understanding of the immunobiology of these two vectors, we analyzed and compared their individual properties in preclinical in vivo and in vitro systems. Immunogenicity and antitumor effect of intratumoral or intravenous administration of both vectors, as well as combination with NKG2A blockade, were evaluated in naïve or TC-1 mouse tumor models. Flow cytometry, Nanostring, and histology analysis were performed to characterize the tumor microenvironment (TME) and T-cell infiltrate following treatment.

RESULTS

Despite being phylogenetically distant, both vectors shared many properties, including preferential infection and activation of professional antigen-presenting cells, and induction of potent tumor-specific CD8+ T-cell responses. Systemic as well as localized treatment induced a proinflammatory shift in the TME, promoting the infiltration of inducible T cell costimulator (ICOS)+CD8+ T cells capable of mediating tumor regression and prolonging survival in a TC-1 mouse tumor model. Still, there was evidence of immunosuppression built-up over time, and increased expression of H2-T23 (ligand for NKG2A T cell inhibitory receptor) following treatment was identified as a potential contributing factor. NKG2A blockade improved the antitumor efficacy of artARENA vectors, suggesting a promising new combination approach. This demonstrates how detailed characterization of arenavirus vector-induced immune responses and TME modulation can inform novel combination therapies.

CONCLUSIONS

The artARENA platform represents a strong therapeutic vaccine approach for the treatment of cancer. The induced antitumor immune response builds the backbone for novel combination therapies, which warrant further investigation.

Efficacy of LCMV-based cancer immunotherapies is unleashed by intratumoral injections of polyI:C

BACKGROUND

Lymphocytic choriomeningitis virus (LCMV) belongs to the Arenavirus family known for inducing strong cytotoxic T-cell responses in both mice and humans. LCMV has been engineered for the development of cancer immunotherapies, currently undergoing evaluation in phase I/II clinical trials. Initial findings have demonstrated safety and an exceptional ability to activate and expand tumor-specific T lymphocytes. Combination strategies to maximize the antitumor effectiveness of LCMV-based immunotherapies are being explored.

METHODS

We assessed the antitumor therapeutic effects of intratumoral administration of polyinosinic:polycytidylic acid (poly(I:C)) and systemic vaccination using an LCMV-vector expressing non-oncogenic versions of the E6 and E7 antigens of human papillomavirus 16 (artLCMV-E7E6) in a bilateral model engrafting TC-1/A9 cells. This cell line, derived from the parental TC-1, exhibits low MHC class I expression and is highly immune-resistant. The mechanisms underlying the combination's efficacy were investigated through bulk RNA-seq, flow cytometry analyses of the tumor microenvironment, selective depletions using antibodies and clodronate liposomes, Batf3 deficient mice, and in vivo bioluminescence experiments. Finally, we assessed the antitumor effectiveness of the combination of artLCMV-E7E6 with BO-112, a GMP-grade poly(I:C) formulated in polyethyleneimine, currently under evaluation in clinical trials.

RESULTS

Intratumoral injection of poly(I:C) enhanced the antitumor efficacy of artLCMV-E7E6 in both injected and non-injected tumor lesions. The combined treatment resulted in a significant delay in tumor growth and often complete eradication of several tumor lesions, leading to significantly improved survival compared with monotherapies. While intratumoral administration of poly(I:C) did not impact LCMV vector biodistribution or transgene expression, it significantly modified leucocyte infiltrates within the tumor microenvironment and amplified systemic efficacy through proinflammatory cytokines/chemokines such as CCL3, CCL5, CXCL10, TNF, IFNα, and IL12p70. Upregulation of MHC on tumor cells and a reconfiguration of the gene expression programs related to tumor vasculature, leucocyte migration, and the activation profile of tumor-infiltrating CD8+ T lymphocytes were observed. Indeed, the antitumor effect relied on the functions of CD8+ T lymphocytes and macrophages. The synergistic efficacy of the combination was further confirmed when BO-112 was included.

CONCLUSION

Intratumoral injection of poly(I:C) sensitizes MHClow tumors to the antitumor effects of artLCMV-E7E6, resulting in a potent therapeutic synergy.

Alternating Arenavirus Vector Immunization Generates Robust Polyfunctional Genotype Cross-Reactive Hepatitis B Virus-Specific CD8 T-Cell Responses and High Anti-Hepatitis B Surface Antigen Titers

Hepatitis B Virus (HBV) is a major driver of infectious disease mortality. Curative therapies are needed and ideally should induce CD8 T cell-mediated clearance of infected hepatocytes plus anti-hepatitis B surface antigen (HBsAg) antibodies (anti-HBs) to neutralize residual virus. We developed a novel therapeutic vaccine using non-replicating arenavirus vectors. Antigens were screened for genotype conservation and magnitude and genotype reactivity of T cell response, then cloned into Pichinde virus (PICV) vectors (recombinant PICV, GS-2829) and lymphocytic choriomeningitis virus (LCMV) vectors (replication-incompetent, GS-6779). Alternating immunizations with GS-2829 and GS-6779 induced high-magnitude HBV T cell responses, and high anti-HBs titers. Dose schedule optimization in macaques achieved strong polyfunctional CD8 T cell responses against core, HBsAg, and polymerase and high titer anti-HBs. In AAV-HBV mice, GS-2829 and GS-6779 were efficacious in animals with low pre-treatment serum HBsAg. Based on these results, GS-2829 and GS-6779 could become a central component of cure regimens.

A replicating LCMV-based vaccine for the treatment of solid tumors

Harnessing the immune system to eradicate tumors requires identification and targeting of tumor antigens, including tumor-specific neoantigens and tumor-associated self-antigens. Tumor-associated antigens are subject to existing immune tolerance, which must be overcome by immunotherapies. Despite many novel immunotherapies reaching clinical trials, inducing self-antigen-specific immune responses remains challenging. Here, we systematically investigate viral-vector-based cancer vaccines encoding a tumor-associated self-antigen (TRP2) for the treatment of established melanomas in preclinical mouse models, alone or in combination with adoptive T cell therapy. We reveal that, unlike foreign antigens, tumor-associated antigens require replication of lymphocytic choriomeningitis virus (LCMV)-based vectors to break tolerance and induce effective antigen-specific CD8+ T cell responses. Immunization with a replicating LCMV vector leads to complete tumor rejection when combined with adoptive TRP2-specific T cell transfer. Importantly, immunization with replicating vectors leads to extended antigen persistence in secondary lymphoid organs, resulting in efficient T cell priming, which renders previously "cold" tumors open to immune infiltration and reprograms the tumor microenvironment to "hot." Our findings have important implications for the design of next-generation immunotherapies targeting solid cancers utilizing viral vectors and adoptive cell transfer.

Immunogenic arenavirus vector SIV vaccine reduces setpoint viral load in SIV-challenged rhesus monkeys

HIV affects more than 38 million people worldwide. Although HIV can be effectively treated by lifelong combination antiretroviral therapy, only a handful of patients have been cured. Therapeutic vaccines that induce robust de novo immune responses targeting HIV proteins and latent reservoirs will likely be integral for functional HIV cure. Our study shows that immunization of naïve rhesus macaques with arenavirus-derived vaccine vectors encoding simian immunodeficiency virus (SIVSME543 Gag, Env, and Pol) immunogens is safe, immunogenic, and efficacious. Immunization induced robust SIV-specific CD8+ and CD4+ T-cell responses with expanded cellular breadth, polyfunctionality, and Env-binding antibodies with antibody-dependent cellular cytotoxicity. Vaccinated animals had significant reductions in median SIV viral load (1.45-log10 copies/mL) after SIVMAC251 challenge compared with placebo. Peak viral control correlated with the breadth of Gag-specific T cells and tier 1 neutralizing antibodies. These results support clinical investigation of arenavirus-based vectors as a central component of therapeutic vaccination for HIV cure.

Abstract 5747: A novel combination therapy of arenavirus vectors and PD1-IL2v strongly potentiates tumor specific T cell responses resulting in synergistic anti-tumor efficacy

It is undisputed that CD8 T cells play a critical role in controlling tumor growth and killing tumor cells, and that tumor specific T cells are essential for clinical responses to immune checkpoint inhibitors. Yet, the induction and maintenance of functional tumor antigen specific T cell responses represent still one of the greatest challenges in cancer immunotherapy.

Therapeutic cancer vaccines based on engineered arenavirus vectors have been shown preclinically to overcome self-tolerance to tumor associated antigens (TAA) and mount unprecedented T cell responses, both, in preclinical tumor models as well as HPV16+ cancer patients in an ongoing Phase 1/2 trial. The novel PD-1 targeted IL-2 variant (PD1-IL2v) was created to maximize the potency of IL-2R activation of effector T cells while overcoming the toxicities of wildtype IL-2. Cis binding of PD1-IL2v to PD-1 and IL-2Rβγ on the same cell was recently shown to promote differentiation of stem-like CD8 T cells into better effectors and was therefore identified as an ideal compound for combination therapies with arenavirus vectors. Combination of vectors encoding tumor associated foreign or self-antigens with PD1-IL2v lead to a massive, up to 60-fold, increase of peripheral tumor specific CD8 T cell numbers compared to vector treatment alone. Notably, frequency of peripheral regulatory T cells was not enhanced by this combination. The massive increase of TAA specific CD8 T cells was associated with synergistic anti-tumor efficacy in two independent tumor models, resulting in longer survival times and up to 60% complete responders. Complete tumor clearance resulted in a stable memory T cell population and protection against tumor re-challenge. Ongoing studies will address modifications of the tumor microenvironment and further characterization of tumor infiltrating T cells upon combination therapy.

These preclinical data establish the combination of arenavirus vectors and PD1-IL2v as a promising next generation cancer immunotherapy.

Citation Format: Judith Strauss, Diana Reckendorfer, Kimberly Pojar, Laura Codarri Deak, Valeria Nicolini, Roger Sutmuller, Christian Klein, Pablo Umaña, Klaus K. Orlinger, Henning Lauterbach. A novel combination therapy of arenavirus vectors and PD1-IL2v strongly potentiates tumor specific T cell responses resulting in synergistic anti-tumor efficacy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5747.

Preclinical development of a first-in-class vaccine encoding HER2, Brachyury and CD40L for antibody enhanced tumor eradication

The induction of antiviral innate immunity by systemic immunization with live virus can be employed to positively impact the response to therapeutic vaccination. We previously demonstrated that systemic immunization with a non-replicating MVA encoding CD40 ligand (CD40L) enhances innate immune cell activation and function, and triggers potent antitumor CD8⁺ T cell responses in different murine tumor models. Antitumor efficacy was increased when combined with tumor targeting antibodies. Here we report the development of TAEK-VAC-HerBy (TVH), a first-in-class human tumor antibody enhanced killing (TAEK) vaccine based on the non-replicating MVA-BN viral vector. It encodes the membrane bound form of human CD40L, HER2 and the transcription factor Brachyury. TVH is designed for therapeutic use in HER2- or Brachyury-expressing cancer patients in combination with tumor targeting antibodies. To preclude possible oncogenic activities in infected cells and to prevent binding of vaccine-encoded HER2 by monoclonal antibodies trastuzumab and pertuzumab, genetic modifications of HER2 were introduced in the vaccine. Brachyury was genetically modified to prevent nuclear localization of the protein thereby inhibiting its transcriptional activity. CD40L encoded in TVH enhanced human leukocyte activation and cytokine secretion in vitro. Lastly, TVH intravenous administration to non-human primates was proven immunogenic and safe in a repeat-dose toxicity study. Nonclinical data presented here highlight TVH as a first-in-class immunotherapeutic vaccine platform currently under clinical investigation.

Abstract 4198: Evaluation of a cancer immunotherapy with engineered arenavirus vectors and 4-1BB agonists in a preclinical tumor model

T cells play a central role in immune responses against cancer. Within the tumor, however, T cells are exposed to a plethora of inactivating factors causing various degrees of dysfunction, changes in metabolism and a generally reduced cellular fitness, eventually leading to tumor progression. To prevent or delay the onset of exhaustion and instead augment effector functions and persistence of functional T cells, costimulatory factors and cytokines are needed. Targeting 4-1BB (CD137), a member of the tumor necrosis factor receptor superfamily, has been shown to represent a promising strategy for inducing an activating signal in CD8+ T cells, resulting in increased pro-inflammatory cytokine secretion, cytotoxic function, and survival. Engineered arenavirus vectors based on lymphocytic choriomeningitis virus (LCMV) or Pichinde virus (PICV) have been shown previously to induce massive infiltration of tumor antigen specific CD8+ T cells into the tumor in several preclinical cancer models. To investigate whether enhanced co-stimulation via 4-1BB further improves T cell responses and/or tumor control, combination therapies with replicating LCMV based vectors (artLCMV) and 4-1BB agonists were explored. A single intravenous treatment of artLCMV encoding the tumor associated antigens (TAA) gp70 or Trp2 in B16.F10 tumor bearing mice induced TAA specific CD8+ T cells in both the periphery and the tumor, resulting in tumor growth delay and some complete responses. Combining artLCMV with agonistic anti-4-1BB significantly improved tumor control and increased the number of complete responders. Analysis of tumor infiltrating lymphocytes revealed higher absolute numbers of TAA specific CD8+ T cells in the combination group compared to the artLCMV alone group. Analyses of the TAA specific cells revealed that more cells expressed granzyme B, Ki67 and Bcl-XL when co-stimulated with anti-4-1BB compared to the group treated with artLCMV alone. Importantly, encoding 4-1BBL in addition to a TAA in artLCMV revealed similar outcomes as just summarized for the combination with agonistic antibodies. Overall, these experiments confirmed the strong antigenicity and T cell inducing capacity of the engineered arenavirus platform, leading to efficient tumor control in a stringent mouse model. Combination with 4-1BB agonists, either in form of antibodies or encoded within the vector genome, was shown to further augment TAA-specific T cell responses within the tumor, leading to better tumor growth control and a higher rate of complete responders.

Citation Format: Judith Strauss, Marilies Scheinost, Theresa Kleissner, Diana Reckendorfer, Kimberly Pojar, Mohamed Habbeddine, Sarah Ahmadi-Erber, Daniela Deutschmann, Sarah Schmidt, Josipa Raguz, Igor Matushansky, Christoph Lampert, Klaus K. Orlinger, Henning Lauterbach. Evaluation of a cancer immunotherapy with engineered arenavirus vectors and 4-1BB agonists in a preclinical tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4198.

Abstract 2048: In vitro and in vivo characterization of non-oncolytic engineered arenavirus vectors for cancer immunotherapy

Cytotoxic CD8+ T cells are paramount for effective cancer immunotherapy. We engineered two distantly related arenaviruses, lymphocytic choriomeningitis virus (LCMV) and Pichinde virus (PICV), encoding the same non-oncogenic HPV16 E7E6 fusion protein to effectively mount and maintain tumor specific CD8+ T cell responses. The designated vectors, HB-201 (LCMV) and HB-202 (PICV), are currently in an ongoing Phase I/II open labelled clinical trial of HB-201 single vector therapy and HB-202/HB-201 alternating two-vector therapy in patients with treatment-refractory HPV16+ cancers (NCT04180215). To characterize the immunogenic properties of both vectors, we designed a comprehensive set of preclinical and translational experiments utilizing human PBMCs, artificial APCs and HPV16 E6 and E7 specific reporter T cells. This was done in conjunction with a preclinical model for HPV16 associated cancer (TC-1). HB-201 (LCMV) and HB-202 (PICV) surrogate vectors encoding GFP readily infected human monocytes, plasmacytoid dendritic, and conventional dendritic cells. In addition, HB-201 and HB-202 vectors successfully induced antigen presentation of E7 and E6 epitopes as evidenced by TCR reporter cells. Innate immune cell activation and cytokine responses to HB-202 were slightly lower compared to HB-201, findings which are consistent with different memory profiles of E7 specific CD8+ T cells in non-tumor bearing mice. In a therapeutic setting of the TC-1 tumor model, both vectors were comparably effective, showing major infiltration of CD8+ T cells into the tumor microenvironment, tumor growth delay and a significantly prolonged survival already after a single administration. In this data set we have confirmed the strong immunogenicity of the engineered arenavirus platform leading to efficient tumor control in a relevant mouse model for HPV16+ cancers, which further supports the clinical development of our novel arenavirus platform.

Citation Format: Josipa Raguz, Theresa Kleissner, Sandra Rosskopf, Mohamed Habbeddine, Katharina Lechner, Valentin Just, Donna Edwards, Igor Matushansky, Christoph Lampert, Klaus K. Orlinger, Henning Lauterbach. In vitro and in vivo characterization of non-oncolytic engineered arenavirus vectors for cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2048.

Abstract 3284: HB-201 and HB-202, an arenavirus-based immunotherapy, induces tumor T cell infiltration in patients with HNSCC and other HPV16+ tumors

Background: Human Papillomavirus 16 (HPV16) is the most common etiologic agent of HPV-associated cancers. Treatment options are limited for patients with HPV16+ recurrent or metastatic cancers. HPV16 E7 and E6 oncogenes constitute attractive immunotherapeutic targets. HB-201 and HB-202 are live-attenuated replicating vectors based on LCMV and PICV arenaviruses, respectively, that express the same non-oncogenic HPV16 E7E6 fusion protein for induction of tumor specific T cell responses.

Methods: A Phase I/II open labelled clinical trial of HB-201 single vector therapy and HB-202/HB-201 alternating two-vector therapy in patients with treatment-refractory HPV16+ cancers is currently ongoing (NCT04180215). To assess circulating E6/E7 specific T cell responses, IFN-γ enzyme-linked immunospot (ELISpot) and intracellular cytokine staining were performed on pre- and post-treatment peripheral blood mononuclear cells (PBMCs). Evaluation of T cell infiltration and PD-L1 status in tumor bed was performed on paired tissue biopsies from a subset of patients by multiplex immunofluorescence.

Results: Single vector therapy (HB-201) and alternating two-vector therapy (HB-202/HB-201) rapidly induce high E6/E7 specific T cell levels, reaching up to ~40% of the circulating CD8+ T cell pool. Alternating two-vector therapy seems to maintain E6/E7 specific T cell responses better in continuous dosing compared to single vector therapy. Furthermore, we demonstrate tumor tissue T cell infiltration in more than 50% of patient samples analyzed. Currently, in depth sequencing of paired biopsies is underway to characterize the tumor microenvironment in response to HB-201 and HB-202/HB-201 treatment.

Conclusion: In this updated dataset, we show that HB-201 and HB-202/HB-201, rapidly induce unprecedented E6/E7 specific T cell levels in circulation following a single dose. Furthermore, these data are seen in conjunction with a pronounced increase of post-treatment CD8+ T cells in tumor, suggesting E6/E7 specific T cell infiltration. Our arenavirus vectors expressing the E7E6 fusion antigen demonstrate an attractive and safe therapy for patients with treatment refractory HPV16+ cancers. The ability of replicating arenavirus vectors to incorporate a broad range of antigens and the potent T cell inducing capacity provide a strong rationale to apply this novel therapy to other cancers.

Citation Format: Donna Edwards, Michael Schwendinger, Kia Katchar, Katia Schlienger, Klaus Orlinger, Igor Matushansky, Henning Lauterbach. HB-201 and HB-202, an arenavirus-based immunotherapy, induces tumor T cell infiltration in patients with HNSCC and other HPV16+ tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3284.

Development and Characterization of a Novel Non-Lytic Cancer Immunotherapy Using a Recombinant Arenavirus Vector Platform

Engineered viral vectors represent a promising strategy to trigger antigen-specific antitumor T cell responses. Arenaviruses have been widely studied because of their ability to elicit potent and protective T cell responses. Here, we provide an overview of a novel intravenously administered, replication-competent, non-lytic arenavirus-based vector technology that delivers tumor antigens to induce antigen-specific anti-cancer T cell responses. Preclinical studies in mice and cell culture experiments with human peripheral blood mononuclear cells demonstrate that arenavirus vectors preferentially infect antigen-presenting cells. This, in conjunction with a non-lytic functional activation of the infected antigen-presenting cells, leads to a robust antigen-specific CD8⁺ T cell response. T cell migration to, and infiltration of, the tumor microenvironment has been demonstrated in various preclinical tumor models with vectors encoding self- and non-self-antigens. The available data also suggest that arenavirus-based vector therapy can induce immunological memory protecting from tumor rechallenge. Based on promising preclinical data, a phase 1/2 clinical trial was initiated and is currently ongoing to test the activity and safety of arenavirus vectors, HB-201 and HB-202, created using lymphocytic choriomeningitis virus and Pichinde virus, respectively. Both vectors have been engineered to deliver non-oncogenic versions of the human papilloma virus 16 (HPV16) antigens E7 and E6 and will be injected intravenously with or without an initial intratumoral dose. This dose escalation/expansion study is being conducted in patients with recurrent or metastatic HPV16+ cancers. Promising preliminary data from this ongoing clinical study have been reported. Immunogenicity data from several patients demonstrate that a single injection of HB-201 or HB-202 monotherapy is highly immunogenic, as evidenced by an increase in inflammatory cytokines/chemokines and the expansion of antigen-specific CD8⁺ T cell responses. This response can be further enhanced by alternating injections of HB-202 and HB-201, which has resulted in frequencies of circulating HPV16 E7/E6-specific CD8⁺ T cells of up to 40% of the total CD8⁺ T cell compartment in peripheral blood in analyses to date. Treatment with intravenous administration also resulted in a disease control rate of 73% among 11 evaluable patients with head and neck cancer dosed every three weeks, including 2 patients with a partial response.

Type I interferon mediated induction of somatostatin leads to suppression of ghrelin and appetite thereby promoting viral immunity in mice

Loss of appetite (anorexia) is a typical behavioral response to infectious diseases that often reduces body weight. Also, anorexia can be observed in cancer and trauma patients, causing poor quality of life and reduced prospects of positive therapeutic outcomes. Although anorexia is an acute symptom, its initiation and endocrine regulation during antiviral immune responses are poorly understood. During viral infections, plasmacytoid dendritic cells (pDCs) produce abundant type I interferon (IFN-I) to initiate first-line defense mechanisms. Here, by targeted ablation of pDCs and various in vitro and in vivo mouse models of viral infection and inflammation, we identified that IFN-I is a significant driver of somatostatin (SST). Consequently, SST suppressed the hunger hormone ghrelin that led to severe metabolic changes, anorexia, and rapid body weight loss. Furthermore, during vaccination with Modified Vaccinia Ankara virus (MVA), the SST-mediated suppression of ghrelin was critical to viral immune response, as ghrelin restrained the production of early cytokines by natural killer (NK) cells and pDCs, and impaired the clonal expansion of CD8⁺ T cells. Thus, the hormonal modulation of ghrelin through SST and the cytokine IFN-I is fundamental for optimal antiviral immunity, which comes at the expense of calorie intake.

Abstract LB049: Preliminary analysis of immunogenicity of HB-201 and HB-202, an arenavirus-based cancer immunotherapy, in patients with advanced HPV16-positive cancers

Background: Human Papillomavirus 16 (HPV16) is linked to most HPV-associated cancers such as cervical, head and neck, vaginal and anal cancers. Treatment options are limited for patients with HPV16+ recurrent or metastatic cancers. The generation and maintenance of the HPV16+ malignant state requires the stable expression of HPV16-specific E7 and E6 oncogenes, which therefore constitute attractive targets for immunotherapy. HB-201 and HB-202 are both replicating live-attenuated vectors based on arenaviruses LCMV and PICV, respectively, expressing the same non-oncogenic HPV16 E7E6 fusion protein for induction of tumor specific T-cell responses. In preclinical models, administration of HB-201 alone and sequential administration of HB-202 followed by HB-201 was safe and demonstrated potent immunogenicity by induction of E7 and E6 -specific CD8+ T cell responses and efficient tumor control of HPV+ TC-1 tumors. Methods: A first-in-human, Phase I/II open-labelled clinical trial of HB-201 single vector therapy and HB-201 & HB-202 two-vector therapy in patients with treatment-refractory HPV16+ cancers is currently ongoing (NCT04180215). Here, we present first immunogenicity results from the dose escalation phase I of this study. The phase I of the trial is designed to evaluate different dose levels and dosing schedules of HB-201 as a single-vector therapy or as an alternating two-vector therapy together with HB-202. Peripheral blood mononuclear cells (PBMCs) were collected before and after treatment from all patients. PBMCs from a subset of patients were examined for HPV16-specific T cell responses measured by IFN-γ enzyme-linked immunospot. Paired tissue biopsy and serum samples were also collected and being currently evaluated for histology and pharmacokinetics. Results: We demonstrated induction of a directly ex vivo (i.e. no expansion) detectable HPV16-specific T-cell response in PBMCs from patients receiving a single dose of HB-201 or HB-202. Additional exploratory analysis will be available at the time of the meeting. Conclusion: These preliminary data demonstrate for the first time with arenavirus vectors, the induction of HPV16-specific T cells in cancer patients following a single injection of HB-201 or HB-202. Arenavirus vectors expressing E7E6 may constitute a new potential therapy for patients with treatment refractory HPV16+ cancers. Clinical data will be presented in an upcoming scientific meeting. Additional schedules, alternating two-vector therapy with HB-201/HB-202, and combination with anti-PD-1 mAbs are being explored in additional cohorts.

Citation Format: Kia Katchar, Michael Schwendinger, Diane DaSilva, Henning Lauterbach, Klaus Orlinger, Xiaoping Qing, Daniel Pinschewer, Igor Matushansky. Preliminary analysis of immunogenicity of HB-201 and HB-202, an arenavirus-based cancer immunotherapy, in patients with advanced HPV16-positive cancers [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 LB049.

Intratumoral virotherapy with 4-1BBL armed modified vaccinia Ankara eradicates solid tumors and promotes protective immune memory

Background Human cancers are extraordinarily heterogeneous in terms of tumor antigen expression, immune infiltration and composition. A common feature, however, is the host′s inability to mount potent immune responses that prevent tumor growth effectively. Often, naturally primed CD8⁺ T cells against solid tumors lack adequate stimulation and efficient tumor tissue penetration due to an immune hostile tumor microenvironment.

Methods To address these shortcomings, we cloned tumor-associated antigens (TAA) and the immune-stimulatory ligand 4-1BBL into the genome of modified vaccinia Ankara (MVA) for intratumoral virotherapy.

Results Local treatment with MVA-TAA-4-1BBL resulted in control of established tumors. Intratumoral injection of MVA localized mainly to the tumor with minimal leakage to the tumor-draining lymph node. In situ infection by MVA-TAA-4-1BBL triggered profound changes in the tumor microenvironment, including the induction of multiple proinflammatory molecules and immunogenic cell death. These changes led to the reactivation and expansion of antigen-experienced, tumor-specific cytotoxic CD8⁺ T cells that were essential for the therapeutic antitumor effect. Strikingly, we report the induction of a systemic antitumor immune response including tumor antigen spread by local MVA-TAA-4-1BBL treatment which controlled tumor growth at distant, untreated lesions and protected against local and systemic tumor rechallenge. In all cases, 4-1BBL adjuvanted MVA was superior to MVA.

Conclusion Intratumoral 4-1BBL-armed MVA immunotherapy induced a profound reactivation and expansion of potent tumor-specific CD8⁺ T cells as well as favorable proinflammatory changes in the tumor microenvironment, leading to elimination of tumors and protective immunological memory.

Live-attenuated lymphocytic choriomeningitis virus-based vaccines for active immunotherapy of HPV16-positive cancer

Infection with human papillomavirus (HPV) is associated with a variety of cancer types and limited therapy options. Therapeutic cancer vaccines targeting the HPV16 oncoproteins E6 and E7 have recently been extensively explored as a promising immunotherapy approach to drive durable antitumor T cell immunity and induce effective tumor control. With the goal to achieve potent and lasting antitumor T cell responses, we generated a novel lymphocytic choriomeningitis virus (LCMV)-based vaccine, TT1-E7E6, targeting HPV16 E6 and E7. This replication-competent vector was stably attenuated using a three-segmented viral genome packaging strategy. Compared to wild-type LCMV, TT1-E7E6 demonstrated significantly reduced viremia and CNS immunopathology. Intravenous vaccination of mice with TT1-E7E6 induced robust expansion of HPV16-specific CD8⁺ T cells producing IFN-γ, TNF-α and IL-2. In the HPV16 E6 and E7-expressing TC-1 tumor model, mice immunized with TT1-E7E6 showed significantly delayed tumor growth or complete tumor clearance accompanied with prolonged survival. Tumor control by TT1-E7E6 was also achieved in established large-sized tumors in this model. Furthermore, a combination of TT1-E7E6 with anti-PD-1 therapy led to enhanced antitumor efficacy with complete tumor regression in the majority of tumor-bearing mice that were resistant to anti-PD-1 treatment alone. TT1-E7E6 vector itself did not exhibit oncolytic properties in TC-1 cells, while the antitumor effect was associated with the accumulation of HPV16-specific CD8⁺ T cells with reduced PD-1 expression in the tumor tissues. Together, our results suggest that TT1-E7E6 is a promising therapeutic vaccine for HPV-positive cancers.

Abstract 4058: TheraT - a highly versatile arenavirus based vector platform for intravenous and intratumoral cancer immunotherapy

The unprecedented success of checkpoint blockade therapies clearly demonstrates the power of the immune system to fight cancer. Yet, only a minority of cancer patients respond with long-term control of the tumor or even cure, necessitating the development of other treatment modalities. Hookipa Pharma developed a novel attenuated, replication-competent viral vector platform (TheraT) that induces powerful cytotoxic T lymphocyte responses against foreign and self-antigens. In a preclinical model for human papilloma virus 16 (HPV16) associated cancer (TC-1), we evaluated immunogenicity and efficacy upon systemic and intratumoral application of TheraT vectors based on the arenaviruses lymphocytic choriomeningitis virus (LCMV) and pichinde virus (PICV). Both HB-201 (LCMV) and HB-202 (PICV) product candidates encode a non-oncogenic but highly antigenic E6/E7 fusion protein from HPV16. Independent of the route of administration, single administration of HB-201 or HB-202 induced potent peripheral E7-specific CD8+ T cell responses and led to efficient tumor growth control. Survival of TheraT treated animals was significantly longer compared to buffer treated animals. Similarly, single systemic as well as intratumoral application of HB-201 or HB-202 induced major infiltration of CD8+ T cells into the tumor microenvironment. Combination of intravenous HB-201 and anti-PD1 was well tolerated but did not further enhance efficacy in this model, implicating the presence of other immune evasion factors. In conclusion, replication-attenuated TheraT is safe, highly immunogenic and shows excellent therapeutic efficacy after single intravenous and intratumoral application. These data underline the potential and versatility of this novel vector platform. Mechanistic studies in various mouse tumor models are underway. Phase 1/2 clinical trial initiation of HB-201 monotherapy is planned for end of 2019 and preparations for an IND filing for a combination trial of HB-201 and HB-202 in H1 2020 have been initiated.

Citation Format: Josipa Raguz, Sarah Schmidt, Theresa Kleisner, Manuel Zerbs, Goran Bekic, Sonja Feher, Daniel Oeler, Felix Stemeseder, Ursula Berka, Bettina Kiefmann, Sophie Schulha, Igor Matushansky, Henning Lauterbach, Klaus Orlinger. TheraT - a highly versatile arenavirus based vector platform for intravenous and intratumoral cancer immunotherapy [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 4058.

Abstract 1468: Synergistic cancer immunotherapy combination of MVA-CD40L with tumor targeting antibodies or checkpoint blockade to achieve strong antitumor immune responses against large, established tumors

Virus-based vaccines and appropriate costimulation potently enhance antigen-specific T cell immunity against cancer. In the present study, we exploit both innate and adaptive immune responses triggered by recombinant modified vaccinia virus Ankara (rMVA) encoding costimulatory CD40L against large, established tumors in different combinatory settings. Therapeutic treatment with rMVA-CD40L resulted in the control or eradication of solid tumors in several unrelated tumor models. The expansion of non-exhausted, tumor-specific cytotoxic CD8+ T cells was essential for the therapeutic activity and was partially dependent on CD8α+ cross-presenting dendritic cells. Combination of rMVA-CD40L with PD-1 checkpoint blockade further enhanced the therapeutic activity of MVA virotherapy in colorectal carcinoma. In addition, rMVA-CD40L combined with antibodies targeting Tumor-Associated Antigens (TAA) resulted in increased therapeutic antitumor efficacy against two unrelated tumor models. We describe a translationally relevant therapeutic synergy between viral vaccination and CD40L costimulation. We show strengthened antitumor immune responses when both rMVA-CD40L-induced innate and adaptive immune mechanisms are exploited by combining immunotherapeutic regimes, such as checkpoint blockade and TAA targeting antibodies. This novel immunotherapeutic approach could translate into clinical cancer therapies where ADCC competent TAA targeting antibodies PD-1 checkpoint blockade are employed.

Citation Format: Jose Medina-Echeverz, Maria Hinterberger, Raphael Giessel, Barbara Bathke, Ronny Kassub, Giovanna Fiore, Paul Chaplin, Hubertus Hochrein, Henning Lauterbach. Synergistic cancer immunotherapy combination of MVA-CD40L with tumor targeting antibodies or checkpoint blockade to achieve strong antitumor immune responses against large, established 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 1468.

Abstract 727: A novel rMVA combination immunotherapy triggers potent innate and adaptive immune responses against established tumors

Virus-based vaccines and appropriate costimulation enhance potent antigen-specific T cell immunity against cancer. However, the tumor microenvironment exerts intrinsic and extrinsic mechanisms to evade tumor destruction. In the present study we exploit both innate and adaptive immune responses triggered by a novel recombinant modified vaccinia virus Ankara (rMVA) encoding costimulatory CD40L against solid tumors in combination regimes to overcome tumor-induced resistance to immunotherapy. Therapeutic treatment with rMVA-CD40L resulted in strong antitumor effects in unrelated established tumor models. Tumor infiltration was composed of non-exhausted, antigen-specific CD8+ T cells with proliferative capacity after rMVA-CD40L immunization. Strikingly, this antitumor effect was not entirely dependent on cross-presenting CD8α+ DC -induced CD8+ T cell expansion, as experiments with MVA encoding for T. gondii profilin (TLR11 ligand) and using Batf3-/- tumor bearers depicted. Indeed, rMVA-CD40L-induced tumor control did not depend on cytosolic DNA sensor STING. Interestingly, rMVA-CD40L induced strong NK cell activation and thereby potent Antibody Dependent Cell Cytotoxicity (ADCC) against Tumor-Associated Antigen (TAA) targeting antibodies. Hence, the combination of TAA targeting antibodies and rMVA-CD40L resulted in increased therapeutic antitumor efficacy. We describe a novel and translationally relevant therapeutic synergy between viral vaccination and CD40L costimulation. We connect CD40 ligation to cross-presenting CD8α+ DC -mediated expansion of non-exhausted CD8+ T cells in the tumor microenvironment. Taking advantage from intrinsic MVA-induced NK cell activation and further improved NK cell function by CD40 ligation, we show strengthened antitumor immune responses when both rMVA-CD40L-induced innate and adaptive immune mechanisms are exploited by combining immunotherapeutic regimes. This finding has a direct potential impact in clinical trials where TAA targeting antibodies are currently under evaluation.

Citation Format: Jose Medina-Echeverz, Maria Hinterberger, Marco Testori, Marlene Geiger, Raphael Giessel, Paul Chaplin, Hubertus Hochrein, Henning Lauterbach. A novel rMVA combination immunotherapy triggers potent innate and adaptive immune responses against established tumors [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 727.

CD70 encoded by modified vaccinia virus Ankara enhances CD8 T-cell-dependent protective immunity in MHC class II-deficient mice

The immunological outcome of infections and vaccinations is largely determined during the initial first days in which antigen-presenting cells instruct T cells to expand and differentiate into effector and memory cells. Besides the essential stimulation of the T-cell receptor complex a plethora of co-stimulatory signals not only ensures a proper T-cell activation but also instils phenotypic and functional characteristics in the T cells appropriate to fight off the invading pathogen. The tumour necrosis factor receptor/ligand pair CD27/CD70 gained a lot of attention because of its key role in regulating T-cell activation, survival, differentiation and maintenance, especially in the course of viral infections and cancer. We sought to investigate the role of CD70 co-stimulation for immune responses induced by the vaccine vector modified vaccinia virus Ankara-Bavarian Nordic^® (MVA-BN^® ). Short-term blockade of CD70 diminished systemic CD8 T-cell effector and memory responses in mice. The dependence on CD70 became even more apparent in the lungs of MHC class II-deficient mice. Importantly, genetically encoded CD70 in MVA-BN^® not only increased CD8 T-cell responses in wild-type mice but also substituted for CD4 T-cell help. MHC class II-deficient mice that were immunized with recombinant MVA-CD70 were fully protected against a lethal virus infection, whereas MVA-BN^® -immunized mice failed to control the virus. These data are in line with CD70 playing an important role for vaccine-induced CD8 T-cell responses and prove the potency of integrating co-stimulatory molecules into the MVA-BN^® backbone.

NLRC4 Inflammasome-Driven Immunogenicity of a Recombinant MVA Mucosal Vaccine Encoding Flagellin

Bacterial flagellin enhances innate and adaptive immune responses and is considered a promising adjuvant for the development of vaccines against infectious diseases and cancer. Antigen-presenting cells recognize flagellin with the extracellular TLR5 and the intracellular NLRC4 inflammasome-mediated pathway. The detailed cooperation of these innate pathways in the induction of the adaptive immune response following intranasal (i.n.) administration of a recombinant modified vaccinia virus Ankara (rMVA) vaccine encoding flagellin (rMVA-flagellin) is not known. rMVA-flagellin induced enhanced secretion of mucosal IL-1β and TNF-α resulting in elevated CTL and IgG2c antibody responses. Importantly, mucosal IgA responses were also significantly enhanced in both bronchoalveolar (BAL) and intestinal lavages accompanied by the increased migration of CD8⁺ T cells to the mesenteric lymph nodes (MLN). Nlrc4^−/− rMVA-flagellin-immunized mice failed to enhance pulmonary CTL responses, IgG2c was lower, and IgA levels in the BAL or intestinal lavages were similar as those of control mice. Our results show the favorable adjuvant effect of rMVA-flagellin in the lung as well as the intestinal mucosa following i.n. administration with NLRC4 as the essential driver of this promising mucosal vaccine concept.

Genetic Adjuvantation of Recombinant MVA with CD40L Potentiates CD8 T Cell Mediated Immunity

Modified vaccinia Ankara (MVA) is a safe and promising viral vaccine vector that is currently investigated in several clinical and pre-clinical trials. In contrast to inactivated or sub-unit vaccines, MVA is able to induce strong humoral as well as cellular immune responses. In order to further improve its CD8 T cell inducing capacity, we genetically adjuvanted MVA with the coding sequence of murine CD40L, a member of the tumor necrosis factor superfamily. Immunization of mice with this new vector led to strongly enhanced primary and memory CD8 T cell responses. Concordant with the enhanced CD8 T cell response, we could detect stronger activation of dendritic cells and higher systemic levels of innate cytokines (including IL-12p70) early after immunization. Interestingly, acquisition of memory characteristics (i.e., IL-7R expression) was accelerated after immunization with MVA-CD40L in comparison to non-adjuvanted MVA. Furthermore, the generated cytotoxic T-lymphocytes (CTLs) also showed improved functionality as demonstrated by intracellular cytokine staining and in vivo killing activity. Importantly, the superior CTL response after a single MVA-CD40L immunization was able to protect B cell deficient mice against a fatal infection with ectromelia virus. Taken together, we show that genetic adjuvantation of MVA can change strength, quality, and functionality of innate and adaptive immune responses. These data should facilitate a rational vaccine design with a focus on rapid induction of large numbers of CD8 T cells able to protect against specific diseases.