Immune response of healthy horses to DNA constructs formulated with a cationic lipid transfection reagent

Background

Deoxyribonucleic acid (DNA) vaccines are used for experimental immunotherapy of equine melanoma. The injection of complexed linear DNA encoding interleukin (IL)-12/IL-18 induced partial tumour remission in a clinical study including 27 grey horses. To date, the detailed mechanism of the anti-tumour effect of this treatment is unknown.

Results

In the present study, the clinical and cellular responses of 24 healthy horses were monitored over 72 h after simultaneous intradermal and intramuscular application of equine IL-12/IL-18 DNA (complexed with a transfection reagent) or comparative substances (transfection reagent only, nonsense DNA, nonsense DNA depleted of CG).

Although the strongest effect was observed in horses treated with expressing DNA, horses in all groups treated with DNA showed systemic responses. In these horses treated with DNA, rectal temperatures were elevated after treatment and serum amyloid A increased. Total leukocyte and neutrophil counts increased, while lymphocyte numbers decreased. The secretion of tumour necrosis factor alpha (TNFα) and interferon gamma (IFNγ) from peripheral mononuclear blood cells ex vivo increased after treatments with DNA, while IL-10 secretion decreased. Horses treated with DNA had significantly higher myeloid cell numbers and chemokine (C-X-C motif) ligand (CXCL)-10 expression in skin samples at the intradermal injection sites compared to horses treated with transfection reagent only, suggesting an inflammatory response to DNA treatment.

In horses treated with expressing DNA, however, local CXCL-10 expression was highest and immunohistochemistry revealed more intradermal IL-12-positive cells when compared to the other treatment groups.

In contrast to non-grey horses, grey horses showed fewer effects of DNA treatments on blood lymphocyte counts, TNFα secretion and myeloid cell infiltration in the dermis.

Conclusion

Treatment with complexed linear DNA constructs induced an inflammatory response independent of the coding sequence and of CG motif content. Expressing IL-12/IL-18 DNA locally induces expression of the downstream mediator CXCL-10.

The grey horses included appeared to display an attenuated immune response to DNA treatment, although grey horses bearing melanoma responded to this treatment with moderate tumour remission in a preceding study. Whether the different immunological reactivity compared to other horses may contributes to the melanoma susceptibility of grey horses remains to be elucidated.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0452-3) contains supplementary material, which is available to authorized users.

Design and Structural Requirements of the Potent and Safe TLR-9 Agonistic Immunomodulator MGN1703

Single-stranded oligodeoxynucleotides (ODN), containing nonmethylated cytosine–guanine motifs (CpG ODN), are recognized by the innate immune system as “danger signals.” CpG ODN are efficacious immunomodulators but require phosphorothioate (PT) or other backbone modifications for metabolic stability, which cause toxicities in mice and primates. We therefore designed a covalently closed DNA molecule (dSLIM^®) where two single-stranded loops containing CG motifs are connected through a double-stranded stem in the absence of any nonnatural DNA component. The most promising immunomodulator, MGN1703, comprises two loops of 30 nucleotides containing three CG motifs each, and a connecting stem stem of 28 base pairs. MGN1703 stimulates cytokine secretion [interferon (IFN)-α, IFN-γ, interleukin (IL)-12, IL-6, and IL-2] and activates immune cells by increased expression of CD80, CD40, human leukocyte antigen (HLA)-DR and ICAM-1. Efficacy of immunomodulation strictly depends on the descriptive dumbbell shape and size of the molecule. Variations in stem length and loop size lead to reduced potency of the respective members of the dSLIM^® class. In a representative mouse model, toxicities from injections of high amounts of a CpG ODN-PT and of MGN1703 were evaluated. The CpG ODN-PT group showed severe organ damage, whereas no such or other pathologies were found in the MGN1703 group. Oncological clinical trials of MGN1703 already confirmed our design.

Influences of age and sex on leukocytes of healthy horses and their ex vivo cytokine release

Leukocytes and their functional capacities are used extensively as biomarkers in immunological research. Commonly employed indicators concerning leukocytes are as follows: number, composition in blood, response to discrete stimuli, cytokine release, and morphometric characteristics. In order to employ leukocytes as biomarkers for disease and therapeutic monitoring, physiological variations and influencing factors on the parameters measured have to be considered. The aim of this report was to describe the ranges of selected leukocyte parameters in a sample of healthy horses and to analyse whether age, sex, breed, and sampling time point (time of day) influence peripheral blood leukocyte composition, cell morphology and release of cytokines ex vivo. Flow cytometric comparative characterisation of cell size and complexity in 24 healthy horses revealed significant variance. Similarly, basal release of selected cytokines by blood mononuclear cells also showed high variability [TNFα (65-16,624pg/ml), IFNγ (4-80U/ml), IL-4 (0-5069pg/ml), IL-10 (49-1862pg/ml), and IL-17 (4-1244U/ml)]. Each animal's age influenced leukocyte composition, cell morphology and cytokine release (TNFα, IL-4, IL-10) ex vivo. Geldings showed smaller monocytes and higher spontaneous production of IL-10 when compared to the mares included. The stimulation to spontaneous release ratios of TNFα, IL-4 and IL-17 differed in Warmblood and Thoroughbred types. Sampling time influenced leukocyte composition and cell morphology. In summary, many animal factors - age being the dominant one - should be considered for studies involving the analysis of equine leukocytes. In addition, high inter-individual variances argue for individual baseline measurements.

Maintenance therapy with the TLR-9 agonist MGN1703 in the phase II IMPACT study of metastatic colorectal cancer patients: A subgroup with improved overall survival

680

Background: Patients with mCRC and disease control after induction with first-line chemotherapy +/- bevacizumab were included in the double-blind placebo-controlled phase II IMPACT trial, aiming to assess the clinical efficacy, safety, and immunological effects of the immunomodulator MGN1703, a potent TLR9 agonist, given at the dose of 60 mg subcutaneously twice weekly as switch maintenance after first line induction therapy in mCRC. Methods: The trial was prematurely closed after randomization of 59 patients. The final analysis showed a superior effect of MGN1703 compared to placebo with hazard ratios (HR) for the primary endpoint PFS on maintenance of 0.55 (p=0.041) and 0.56 (p=0.070) by local investigator assessment or independent radiological review, respectively. Exploratory PFS analyses of pretreatment characteristics identified patients with normalized CEA, objective response, and the presence of activated NKT cells at the end of induction chemotherapy to benefit the most from maintenance with MGN1703. We analysed the impact of these factors on the secondary endpoint overall survival (OS). Results: At time of final study analysis, OS data were not mature. Only 35% of MGN1703 patients had an event, as opposed to 50% of placebo patients. The HR for OS of whole study population was 0.63 (median 22.6 vs. 15.1 months, p=NS). The subgroup of patients randomized into the study with confirmed RECIST response had a HR of 0.40 (median 24.5 vs. 15.1 months, p=NS), suggesting this may be the population with greater benefit. HR for patients with normalized CEA or with activated NKT cells were 0.69 and 0.43, respectively. Based on this evidence, in the phase III IMPALA study patients with objective response after standard induction therapy are randomized to standard treatment or switch maintenance with MGN1703. CEA and activated NKT cells are stratification factors for the study and will be prospectively assessed. Conclusions: The pretreatment characteristics predictive of a PFS benefit in the IMPACT study seem to retain their value also in exploratory analyses for OS. This information has been used to design the phase III IMPALA study, currently recruiting patients. Clinical trial information: NCT01208194.

Abstract 2565: Conformation overrides base sequence - insights from a novel class TLR-9 agonists

Introduction

DNA-based TLR-9 agonists are potent activators of immune cell populations and the immune system. Preclinical and ongoing clinical studies support the use of TLR-9 agonists as immunomodulators and/or adjuvants, and proof their anti-tumor effect by enhancing both the humoral and cellular responses. From the 4 classes of known activators with distinct immunomodulation profiles all members except one comprise of linear DNA molecules. The exception is dSLIM®, the active ingredient of MGN1703 in several clinical trials. dSLIM® establishes a new class of TLR-9 agonists, represented by covalently closed dumbbell-like DNA molecules consisting entirely of natural DNA with two single-stranded CG-containing loops separated by a double-stranded stem.

Results

By cytokine secretion and cellular activation of relevant cells in human PBMC we show that CG-motifs - such as in ODN2006, a class B TLR9 agonist - if incorporated in dSLIM® conformation reveal an improved immunomodulatory potential compared to their corresponding linear CpG oligonucleotides. Increased cytokine secretion encompasses the central anti-cancer cytokine IFN-alpha, the potent angiostatic cytokine IP-10, or IFN-gamma the key activator of NK-, NKT-, and cytotoxic T-cell responses. After 24-48h exposure to dSLIM® TLR-9 agonists, also activation surface markers of relevant cell subpopulations of PBMC are up-regulated including CD80 of pDCs, CD86 of B-cells, CD86 and CD169 of monocytes, CD69 of NK, NKT as well as T cells. Consequently, dSLIM® triggers an explicit specific cytotoxicity against Jurkat target cells while ODN2006 is without significant effect in this readout. All these effects are considered important and relevant cancer-fighting features of dSLIM®.

Conclusions

Differences in immunomodulation profiles between classes of TLR-9 agonists appear to be more closely related to their conformation than their individual nucleotide sequences. We show individual loop sequences in dSLIM® that differentiate the immunomodulation profile of molecules only to a moderate extent. Inherent to the dumbbell-like structure of dSLIM® TLR-9 agonists is their potential to dimerize loop-binding TLR-9 molecules in the membrane of immune-competent cells. Thereby, dSLIM® TLR-9 agonists most probably not only bind and activate but also cluster TLR-9 molecules thereby changing the TLR-9 triggered immune response in a qualitative way. Stabilizing chemical modifications in linear CpG ODN also impact the immunomodulatory profile of TLR-9 agonists and are discussed.

Citation Format: Kerstin Kapp, Christiane Kleuss, Matthias Schroff, Burghardt Wittig. Conformation overrides base sequence - insights from a novel class TLR-9 agonists. [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 2565. doi:10.1158/1538-7445.AM2014-2565

Maintenance treatment with the immunomodulator MGN1703, a Toll-like receptor 9 (TLR9) agonist, in patients with metastatic colorectal carcinoma and disease control after chemotherapy: a randomised, double-blind, placebo-controlled trial

PURPOSE

This phase II study evaluated the synthetic DNA-based immunomodulator and Toll-like receptor 9 agonist MGN1703 as maintenance treatment in metastatic colorectal carcinoma (mCRC).

METHODS

Fifty-nine patients with mCRC and disease control after standard first-line chemotherapy were randomised to MGN1703 60 mg (N = 43) or placebo (N = 16).

RESULTS

The hazard ratio (HR) for the primary endpoint [progression-free survival (PFS) from the start of maintenance] was 0.56 (95 % CI 0.29-1.08; P = 0.07) and 0.55 (95 % CI 0.3-1.0; P = 0.04) by independent and investigator review, respectively. MGN1703 significantly improved PFS measured from the start of induction therapy versus placebo on independent (HR 0.49; 95 % CI 0.26-0.94; P = 0.03) and investigator review (HR 0.50; 95 % CI 0.31-1.02; P = 0.02). Overall survival (OS) data remain immature (HR 95 %; 95 % CI 0.3-1.5; P = 0.29) with 28/43 patients alive after a medium follow-up of >17 months. Retrospective subgroup analysis showed a significant effect of MGN1703 on PFS versus placebo in patients with greater than median tumour size reduction and normalised carcinoembryonic antigen concentrations following induction therapy, and in patients with elevated activated NKT cells ≥3.08 %. Adverse events were mild to moderate and limited to injection-site reactions or linked to general immune system activation.

CONCLUSIONS

MGN1703 maintenance treatment was well tolerated and appears to induce durable and prolonged PFS and disease control in a subgroup of patients with mCRC following induction therapy. Activated NKT cells may be a predictive biomarker for selecting patients likely to benefit more from MGN1703.

ASET study: Long-term follow-up data of patients with metastatic renal cell carcinoma treated with MGN1601

LBA399

Background: The cell-based therapeutic cancer vaccine MGN1601 is a fixed combination of allogeneic tumor cells modified via MIDGE vectors to express IL-7, GM-CSF, CD80, and CD154 plus the immunomodulator dSLIM. In the ASET trial heavily pretreated patients with metastatic renal cell carcinoma (mRCC) were enrolled to assess safety, immunological effects, and clinical efficacy of MGN1601. Methods: The ASET study was a multicenter, single-arm phase 1/2 study. The treatment phase consisted of 8 intradermal vaccinations over 12 weeks. Following evaluation, patients with at least disease stabilization entered an extension phase (EP, 5 vaccinations over 120 weeks). Overall, 19 patients were included and received at least one MGN1601 injection (ITT); the majority (N=17) had ≥3 lines of previous therapy. Results: Of 19 patients, 10 (55%) completed the treatment phase per-protocol (PP); 9 patients discontinued the study due to disease progression (PD) or rapid deterioration. Overall, 110 adverse events were documented (grade 1-2: 80.9%) of which only 10 (9.1%) were drug-related. No drug-related serious adverse event was reported. PBMCs from patients increased cytokine secretion after re-stimulation with standard antigens, confirming an improved cellular immune function. Two patients achieved disease control (PR, SD) after 12 treatment weeks and continued in the extension phase: One patient had PD after 60 weeks, the other remains in sustained partial remission after completion of the EP. Median overall survival (OS) was 24.8 weeks in the ITT population and 115.3 weeks in the PP population. Univariate analysis of pre-treatment characteristics revealed absolute lymphocyte counts, neutrophil to lymphocyte ratios, platelets, MSKCC score, and liver metastasis as putative predictive factors of longer overall survival. Conclusions: MGN1601 administration was safe and showed promising OS in a population of heavily pretreated RCC patients who could receive therapy over 12 weeks (PP population). These results warrant further evaluation in a larger, controlled clinical trial. Baseline biomarkers and factors may allow identifying patients more likely to benefit from this innovative vaccination approach. Clinical trial information: NCT01265368.

Preclinical study on combined chemo- and nonviral gene therapy for sensitization of melanoma using a human TNF-alpha expressing MIDGE DNA vector

Nonviral gene therapy represents a realistic option for clinical application in cancer treatment. This preclinical study demonstrates the advantage of using the small-size MIDGE(®) DNA vector for improved transgene expression and therapeutic application. This is caused by significant increase in transcription efficiency, but not by increased intracellular vector copy numbers or gene transfer efficiency. We used the MIDGE-hTNF-alpha vector for high-level expression of hTNF-alpha in vitro and in vivo for a combined gene therapy and vindesine treatment in human melanoma models. The MIDGE vector mediated high-level hTNF-alpha expression leads to sensitization of melanoma cells towards vindesine. The increased efficacy of this combination is mediated by remarkable acceleration and increase of initiator caspase 8 and 9 and effector caspase 3 and 7 activation. In the therapeutic approach, the nonviral intratumoral in vivo jet-injection gene transfer of MIDGE-hTNF-alpha in combination with vindesine causes melanoma growth inhibition in association with increased apoptosis in A375 cell line or patient derived human melanoma xenotransplant (PDX) models. This study represents a proof-of-concept for an anticipated phase I clinical gene therapy trial, in which the MIDGE-hTNF-alpha vector will be used for efficient combined chemo- and nonviral gene therapy of malignant melanoma.

Maintenance with the TLR-9 agonist MGN1703 versus placebo in patients with advanced colorectal carcincoma (mCRC): A randomized phase II trial (IMPACT)

3643

Background: Standard induction chemotherapy for mCRC is often discontinued in patients responding to the treatment. MGN1703, a synthetic DNA-based immunomodulator, acts as TLR-9 agonist. This trial has been conducted to assess clinical efficacy, safety, and immunogenicity of MGN1703 as maintenance therapy vs placebo. Methods: The IMPACT trial is an international, multicenter, randomized (2:1) double-blind placebo-controlled phase 2 trial in mCRC patients with disease control (CR, PR, SD) after 4.5 to 6 months of 1st-line induction chemotherapy with FOLFOX/XELOX or FOLFIRI +/- bevacizumab. Results: 59 patients have been randomized (43 MGN1703, 16 placebo). Median PFS from start of maintenance was not different with 2.8 vs 2.7 months, however the HR was 0.56 (CI 95%: 0.29-1.08; p=0.069) in favor of MGN1703, due to a small favorable subgroup with long-term PFS (20% vs 0% at 9 months; p=0.006). Total PFS from beginning of induction chemotherapy including maintenance was significantly improved: HR 0.49 (CI 95%: 0.25-0.94), p=0.029. After a median follow-up of 13 months 66% of patients are still alive (67% vs 62%), therefore survival data are still preliminary (HR 0.79; CI 95%: 0.3-2.1) and will be mature at the meeting. Activation of cellular immune function as indicated by significant increase of CD14+CD169+monocytes was observed in all but one of the MGN1703 treated patients, while absent in all placebo patients. Treatment was well tolerated: 46.5% vs 31.3% of patients (MGN1703 vs placebo) had any drug-related adverse events (AE) and 20.9% vs 18.8% had AE with grade 3 or 4 (including hypertension, ileus, sepsis, sensory polyneuropathy, nausea/vomiting for MGN1703 and pain, popular exanthema for placebo). Conclusions: MGN1703 maintenance seems to prolong PFS in a subgroup of patients with disease control after induction chemotherapy vs placebo, and is associated with relative mild toxicity. This in an early signal in a selected and very limited patient population which supports further investigation. Predictive biomarkers are under evaluation to identify a potential subgroup which might have benefit from this TLR-9 MGN1703 maintenance. Clinical trial information: NCT01208194.

Identification of biomarkers for overall survival of patients with metastatic renal cell carcinoma treated with MGN1601

468

Background: The cell-based therapeutic cancer vaccine MGN1601 consists of two active pharmaceutical ingredients in fixed combination. Fourfold gene-modified, allogeneic tumor cells expressing IL-7, GM-CSF, CD80, and CD154 through MIDGE gene expression vectors are combined with the DNA-based immunomodulator dSLIMas a TLR-9 agonist. In the phase I-II clinical trial (ASET trial) heavily pre-treated patients with metastatic renal cell carcinoma (mRCC) were enrolled. Methods: TheASET study has been conducted as a multicenter, open, single-arm phase I-II study. The treatment phase (TP) consisted of 8 intradermal vaccinations, administered within 12 weeks. We analysed known mRCC prognostic factors for their predictive value, i.e. safety laboratory and immunological parameters, quality of life, local reactions and other patients’ characteristics. Results: 19 patients from the ASET study, who received at least one vaccination (ITT population), were included in the biomarker evaluation. The median overall survival (mOS) in the ITT population is currently 25 weeks. mOS of patients who discontinued TP prematurely was only 10 weeks. However, mOS of those patients who completed at least TP is not yet mature for statistical calculation (NR), but is currently estimated as 69 weeks, resulting in a highly significant difference (10 weeks vs. NR, p < 0.001). Patients with an absolute lymphocyte counts (ALC) at baseline of ≥1,000/μL had increased overall survival (mOS NR vs. 16 weeks, p = 0.013), if compared to those with an ALC <1,000/μL. Neutrophil lymphocyte ratios (NLR) at baseline of >3, bone and liver metastasis, high MSKCC score were identified as risk factors associated with lower overall survival. ALC ≥1,000/μL after three MGN1601 vaccinations (week 5) was even more significantly associated with increased overall survival (mOS NR vs. 17 weeks, p = 0.007). The NLR and quality of life improvement at week 5 as well as local reactions at injection sites seem to correlate with OS. Conclusions: MGN1601 shows promising efficacy in late stage mRCC patients. The identified parameters should be further investigated as potential biomarkers for efficacy. Clinical trial information: NCT01265368.