A conserved isoleucine in the binding pocket of RIG-I controls immune tolerance to mitochondrial RNA

RIG-I is a cytosolic receptor of viral RNA essential for the immune response to numerous RNA viruses. Accordingly, RIG-I must sensitively detect viral RNA yet tolerate abundant self-RNA species. The basic binding cleft and an aromatic amino acid of the RIG-I C-terminal domain(CTD) mediate high-affinity recognition of 5'triphosphorylated and 5'base-paired RNA(dsRNA). Here, we found that, while 5'unmodified hydroxyl(OH)-dsRNA demonstrated residual activation potential, 5'-monophosphate(5'p)-termini, present on most cellular RNAs, prevented RIG-I activation. Determination of CTD/dsRNA co-crystal structures and mutant activation studies revealed that the evolutionarily conserved I875 within the CTD sterically inhibits 5'p-dsRNA binding. RIG-I(I875A) was activated by both synthetic 5'p-dsRNA and endogenous long dsRNA within the polyA-rich fraction of total cellular RNA. RIG-I(I875A) specifically interacted with long, polyA-bearing, mitochondrial(mt) RNA, and depletion of mtRNA from total RNA abolished its activation. Altogether, our study demonstrates that avoidance of 5'p-RNA recognition is crucial to prevent mtRNA-triggered RIG-I-mediated autoinflammation.

Tumor-derived GDF-15 blocks LFA-1 dependent T cell recruitment and suppresses responses to anti-PD-1 treatment

Immune checkpoint blockade therapy is beneficial and even curative for some cancer patients. However, the majority don't respond to immune therapy. Across different tumor types, pre-existing T cell infiltrates predict response to checkpoint-based immunotherapy. Based on in vitro pharmacological studies, mouse models and analyses of human melanoma patients, we show that the cytokine GDF-15 impairs LFA-1/β2-integrin-mediated adhesion of T cells to activated endothelial cells, which is a pre-requisite of T cell extravasation. In melanoma patients, GDF-15 serum levels strongly correlate with failure of PD-1-based immune checkpoint blockade therapy. Neutralization of GDF-15 improves both T cell trafficking and therapy efficiency in murine tumor models. Thus GDF-15, beside its known role in cancer-related anorexia and cachexia, emerges as a regulator of T cell extravasation into the tumor microenvironment, which provides an even stronger rationale for therapeutic anti-GDF-15 antibody development.

Abstract 6118: Tumor-derived GDF-15 promotes immune escape of tumors by functional alteration of the myeloid compartment

Background: Growth and differentiation factor 15 (GDF-15), a divergent member of the TGF-β protein superfamily, shows low physiological baseline expression. GDF-15 is, however, strongly upregulated during pregnancy. It is further induced in stressed and damaged tissues, where it limits immune infiltration and inflammation. In solid tumors, GDF-15 was shown to be a key inhibitor of T-cell infiltration. While this might already explain the strong correlation between GDF-15 overexpression and poor survival with or without checkpoint-based immunotherapy, effects of GDF-15 on dendritic cells and monocytes may further shape the tumor microenvironment.

Methods: To analyze the impact of GDF-15 in murine tumor models, GDF-15 was either deleted by CRISPR/CAS9 gene editing or neutralized by administration of a blocking antibody. Effects on tumor growth were recorded and the composition of the tumor microenvironment was characterized by flow cytometry. More detailed insight into tumor-immune interactions was obtained via the CrownBio Mouse I/O RNA-Seq Panel. Specific effects on polarization of innate and on antigen-specific priming of adaptive immune cells were confirmed in cellular assays in vitro.

Results: Tumor-derived GDF-15 modulates the tumor microenvironment by inhibiting infiltration and activation of myeloid cells. GDF-15 thereby impairs the induction of antitumoral immune responses. Deletion of GDF-15 enhances infiltration of innate cells into immune-excluded tumors, supports the priming of naïve T cells by dendritic cells and generates a pro-inflammatory tumor microenvironment. In vitro, GDF-15 inhibits DC maturation and synapse formation, thus preventing successful T-cell activation. Moreover, GDF-15 interferes with M1 polarization of macrophages.

Conclusion: GDF-15 secretion helps tumors to generate a microenvironment that is poorly infiltrated by immune cells. GDF-15 further polarizes myeloid cells towards a tumor-promoting, anti-inflammatory phenotype. By inducing a more pro-inflammatory tumor phenotype, anti-GDF-15 antibodies may synergize with other immunotherapeutic agents. A clinical trial combining anti-GDF-15 (CTL002) with anti-PD-1 (NCT04725474) is ongoing.

Citation Format: Markus Haake, Beatrice Haack, Sabrina Genßler, Julia Weigandt, Marlene Auer, Vincent Thiemann, Wahid M. Haq, Melanie Haag, Florian Wedekink, Birgitt Fischer, Kathrin Klar, Matthias Wölfl, Christine Schuberth-Wagner, Jorg Wischhusen. Tumor-derived GDF-15 promotes immune escape of tumors by functional alteration of the myeloid compartment [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 6118.

Abstract P06-01: A phase I, first-in-human clinical trial of the GDF-15 neutralizing antibody CTL-002 in subjects with advanced stage solid tumors (Acronym: GDFATHER)

Background: Growth and differentiation factor 15 (GDF-15) is a TGF-β superfamily member physiologically expressed mainly in placenta and linked to feto-maternal tolerance. Under pathophysiologic conditions, prevention of excessive immune cell infiltration during tissue damage and cachexia induction have been ascribed to GDF-15. A recent study [Haake et al. AACR2020; Abstract #5597] elucidated a mechanism by which GDF-15 inhibits LFA-1 activation on CD8+ T cells, thus interfering with effector T cell recruitment to tissues. Importantly, several cancer entities secrete high levels of GDF-15, correlating with poor prognosis and reduced overall survival [reviewed in Front Immunol 2020 May 19;11:951]. To block this effect the GDF-15 neutralizing antibody CTL-002 was generated. In preclinical models CTL-002 demonstrated potent effector T cell shifting into tumor tissue by neutralizing GDF-15 and enhancing response to checkpoint inhibitor therapy. Methods: This is a phase 1, first-in-human (FIH), two-part, open-label clinical trial of intravenous (IV) administration of CTL-002 given as monotherapy and in combination with an anti-PD-1 antibody in subjects with advanced-stage, relapsed/refractory solid tumors who relapsed on or were refractory to a prior anti-PD-1/PD-L1 therapy. Eligible subjects have exhausted all available approved standard treatments, including prior anti-PD1/-PD-L1 treatment, and present with a biopsy-accessible tumor for serial biopsy taking. The trial is termed GDFATHER, for “GDF-15 Antibody-mediaTed Effector cell Relocation”. Main endpoints are safety of CTL-002 monotherapy and CTL-002 combination with an anti-PD-1 antibody, pharmacokinetics, pharmacodynamics (e.g., degree of GDF-15 neutralization achieved and change in immune-cell number and composition in the tumor tissue) as well as preliminary clinical efficacy (tumor mass reduction; anticachexia effect). In part A of the trial (dose escalation) up to 24 subjects will receive escalating doses of CTL-002 IV (0.3 – 20 mg/kg) in a „mono-followed-by-combination“-design with CTL-002 given as monotherapy and followed by combination with an anti-PD-1 checkpoint inhibitor. In part B (expansion) up to 5 cohorts with up to 25 subjects per cohort with defined tumor entities expected to be GDF-15 dependent will be treated to determine the recommended phase 2 dose (RP2D) and further evaluate safety and preliminary efficacy of CTL-002 monotherapy and the combination. The study was initiated in December 2020 and enrolled the first patient on Dec 09, 2020. Cohort 4 is ongoing at time of submission (07/2021) and so far no DLT has occurred. Updated safety, biomarker and response assessments will be reported. The ClinicalTrials.gov Identifier is NCT04725474.

Citation Format: Ignacio Melero, Emiliano Calvo, Maria-Elisabeth Goebeler, Elena Garralda, Reinhard Dummer, María Rodríguez-Ruiz, María De Miguel, Cyrus Sayehli, Guzman Alonso Casal, Egle Ramelyte, Martin Schuler, Tanja Gromke, Miguel Sanmamed, Irene Moreno, Ralf Bargou, Maria Lostes, Julia-Tatjana Maul, Heike Richly, Petra Fettes, Kathrin Klar, Christine Schuberth-Wagner, Markus Haake, Joerg Wischhusen, Eugen Leo. A phase I, first-in-human clinical trial of the GDF-15 neutralizing antibody CTL-002 in subjects with advanced stage solid tumors (Acronym: GDFATHER) [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P06-01.

568 Tumor-derived GDF-15 prevents therapy success of checkpoint inhibitors by blocking T-lymphocyte recruitment

Background

Immune checkpoint blockade (ICB) can achieve durable responses in a subgroup of patients with metastatic cancer, only. Poor immune effector cell infiltration into the tumor microenvironment is a major obstacle to successful therapy. Growth and differentiation factor 15 (GDF-15) is a divergent member of the TGF-β superfamily and has been linked to feto-maternal tolerance, anorexia but recently also to potent local immunosuppression under physiologic and pathophysiologic conditions. GDF-15 is overexpressed in a wide variety of tumors and may be key factor produced by tumors to prevent effective immune cell infiltration into the tumor and to potently block checkpoint inhibitor activity.

Methods

Effects of recombinant GDF-15 and a proprietary GDF-15 neutralizing antibody (CTL-002) on immune cell trafficking and activation were analyzed by adhesion and interaction assays and in melanoma-bearing humanized mouse models. The impact of GDF-15 overexpression was tested in subcutaneously implanted, GDF-15-transgenic MC38 cells. Additionally, patient GDF-15 serum levels were correlated with immune infiltration and OS in cutaneous melanoma. Associations between GDF-15 serum levels, response to PD-1-based ICB and corresponding OS were assessed in two independent cohorts of melanoma patients.

Results

GDF-15 impairs adhesion of T and NK cells on activated endothelia. In HV18-MK bearing humanized mice, inhibition of GDF-15 strongly enhances infiltration of activated myeloid and lymphoid cells. In MC38 tumors, GDF-15 overexpression can abrogate tumor rejection upon anti-PD-1 therapy. 50% of the mice with GDF-15 overexpressing tumors were, however, rescued when anti-PD-1 was combined with anti-GDF-15 (CTL-002). Likewise, anti-GDF-15 improved responses to anti-CD40 + poly(I:C) in the same tumor model. Clinically, inverse correlations of GDF-15 levels with CD8+ T cell infiltration were shown for melanoma brain metastases. In two independent melanoma patient cohorts, low baseline serum GDF-15 levels predicted clinical response to anti-PD1 treatment and superior OS. Bivariate analysis including LDH indicates that GDF-15 is an independently predictor for poor survival in anti-PD-1 treated melanoma patients.

Conclusions

Tumor-derived GDF-15 blocks the infiltration of immune effector cells into tumor tissues. Neutralizing GDF-15 with CTL-002 restores the ability of immune cells to extravasate blood vessels and enter the tumor microenvironment in vivo. GDF-15 thus represents a promising target for cancer immunotherapy. Antibodies against GDF-15 may support treatments with anti-PD-1 and other immunotherapeutic agents. A clinical trial combining anti-GDF-15 (CTL002) with anti-PD-1 (NCT04725474, submitted Abstract ID 15073) is ongoing.

Ethics Approval

Use of patient samples for this study had been approved by the institutional ethics committee Tübingen (ethic vote 125/2015BO2). Use of surplus sera collected in the University of Zurich Hospital (USZ) Biobank during routine blood draws from consenting metastatic melanoma patients was performed according to IRB approval (KEK.Zh- 647/800) and followed the Declaration of Helsinki on Human Rights.

Consent

All patients had given written informed consent to have clinical data recorded by the Central Malignant Melanoma Registry (CMMR) database.

504 A phase I, first-in-human clinical trial of the GDF-15 neutralizing antibody CTL-002 in subjects with advanced stage solid tumors (Acronym: GDFATHER)

Background

Growth and differentiation factor 15 (GDF-15) is a TGF-β superfamily member physiologically expressed mainly in placenta and linked to feto-maternal tolerance. Under pathophysiologic conditions, prevention of excessive immune cell infiltration during tissue damage and cachexia induction have been ascribed to GDF-15. Recent research has though indicated a prominant role in modulation of the tumor microenvironment and the immune synapse, too1 2 indicating that GDF-15 may be a major tumor-derived immunosuppressant. Importantly, several cancer entities secrete high levels of GDF-15, correlating with poor prognosis and reduced overall survival [Front Immunol 2020 May 19;11:951]. To block this effect the GDF-15 neutralizing antibody CTL-002 was generated. In preclinical models CTL-002 demonstrated potent effector T cell shifting into tumor tissue by neutralizing GDF-15.

Methods

This is a phase 1, first-in-human (FIH), two-part, open-label clinical trial of intravenous (IV) administration of CTL-002 given as monotherapy and in combination with an anti-PD-1 antibody in subjects with advanced-stage, relapsed/refractory solid tumors who relapsed or were refractory to a prior anti-PD-1/PD-L1 therapy. Eligible subjects have exhausted all available approved standard treatments, including prior anti-PD1/-PD-L1 treatment, and present with a biopsy-accessible tumor for serial biopsy taking. The trial is termed GDFATHER, for ”GDF-15 Antibody-mediaTed Effector cell Relocation”.Main endpoints are safety of CTL-002 monotherapy and CTL-002 combination with an anti-PD-1 antibody, pharmacokinetics, pharmacodynamics (e.g. degree of GDF-15 neutralization achieved and change in immune-cell number and composition in the tumor tissue) as well as preliminary clinical efficacy (tumor mass reduction; anticachexia effect)In part A of the trial (dose escalation) up to 24 subjects will receive escalating doses of CTL-002 IV (0.3 – 20 mg/kg) in a ”mono-followed-by-combination”-design with CTL-002 given as monotherapy and followed by combination with an anti-PD-1 checkpoint inhibitor. In part B (expansion) up to 5 cohorts with up to 25 subjects per cohort with defined tumor entities expected to be GDF-15 dependent will be treated to determine the recommended phase 2 dose (RP2D) and further evaluate safety and preliminary efficacy of CTL-002 monotherapy and the combination.The study was initiated in December 2020 and enrolled the first patient on Dec 09, 2020. Cohort 4 is ongoing at time of submission (07/2021) and so far no DLT has occurred. Updated safety, biomarker and response assessments will be reported at the meeting. The ClinicalTrials.gov Identifier is NCT04725474. For more information please contact info@catalym.com.

Trial Registration

NCT04725474

References

Wischhusen J, Wistuba-Hamprecht K, Harter PN, Cheng P, Martens A, Gogolla F, Nonomura Y, Romer P, Koch SD, Haake M, Schuberth-Wagner C, Rudiger M, Leo E, Mittelbronn M, Levesque MP, Hackl H, Dummer R, Weide B. Identifying GDF-15 as potential novel immunotherapeutic target linked to immune cell exclusion in tumors and resistance to anti-PD-1 treatment [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 2161.

Hurt E, Thomas S, Mulgrew K, Blackmore S, Moynihan J, Cusdin F, Dodd R, Cariuk P, Sigurdardottir A, Brannigan E, Dobson C, Kumar R, Cobbold M. AZD8853: A novel antibody targeting GDF15 for immunotherapy refractory tumors [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 1828.

Ethics Approval

All participants gave informed consent prior to participation. EC approval by Gobierno de Navarra, Departamento de Salud, EC_2020/30, Dated: Oct 13, 2020 in Pamplona, Spain. Respective additional national lead EC approvals for Germany (Ethikkommission der Universität Würzburg, 203–20ff of Oct 26, 2020) and Switzerland (Kantonale Ethikkommission Zürich, 2020–02308 of Nov 24, 2020).

A phase I, first-in-human clinical trial of the GDF-15 neutralizing antibody CTL-002 in subjects with advanced-stage solid tumors (ACRONYM: GDFATHER)

TPS2658

Background: Growth and differentiation factor 15 (GDF-15) is a TGF-β superfamily member physiologically expressed mainly in placenta and linked to feto-maternal tolerance. Under pathophysiologic conditions, prevention of excessive immune cell infiltration during tissue damage and cachexia induction have been ascribed to GDF-15. A recent study [Haake et al. AACR2020; Abstract #5597] elucidated a mechanism by which GDF-15 inhibits LFA-1 activation on CD8+ T cells, thus interfering with effector T cell recruitment to tissues. Importantly, several cancer entities secrete high levels of GDF-15, correlating with poor prognosis and reduced overall survival [reviewed in Front Immunol 2020 May 19;11:951]. To block this effect the GDF-15 neutralizing antibody CTL-002 was generated. In preclinical models CTL-002 demonstrated potent effector T cell shifting into tumor tissue by neutralizing GDF-15. Methods: This is a phase 1, first-in-human (FIH), two-part, open-label clinical trial of intravenous (IV) administration of CTL-002 given as monotherapy and in combination with an anti-PD-1 antibody in subjects with advanced-stage, relapsed/refractory solid tumors who relapsed post or were refractory to a prior anti-PD-1/PD-L1 therapy. Eligible subjects have exhausted all available approved standard treatments. Further key eligibility criteria include having received at least one prior anti-PD1/-PD-L1 treatment and having relapsed on or after it or having been refractory to it, and presenting with a biopsy-accessible tumor for serial biopsy taking. The trial is termed GDFATHER, for “GDF-15 Antibody-mediaTed Effector cell Relocation”. Main endpoints are safety of CTL-002 monotherapy and CTL-002 combination with an anti-PD-1 antibody, pharmacokinetics, pharmacodynamics (e.g. degree of GDF-15 neutralization achieved and change in immune-cell number and composition in the tumor tissue) as well as preliminary clinical efficacy (tumor mass reduction; anticachexia effect) In part A of the trial (dose escalation) up to 24 subjects will receive escalating doses of CTL-002 IV (0.3 – 20 mg/kg) in a „mono-followed-by-combination“-design with CTL-002 given as monotherapy and followed by combination with an anti-PD-1 checkpoint inhibitor. In part B (expansion) up to 5 cohorts with up to 25 subjects per cohort with defined tumor entities expected to be GDF-15 dependent will be treated to determine the recommended phase 2 dose (RP2D) and further evaluate safety and preliminary efficacy of CTL-002 monotherapy and the combination. The study was initiated in December 2020 and enrolled the first patient on Dec 09, 2020. Cohort 1 has been completed without DLT and enrollment for cohort 2 began in February 2021. Clinical trial information: NCT04725474.

Tumor-derived GDF-15 to suppress t-lymphocyte recruitment to the tumor microenvironment resulting in resistance to ANTI-PD-1 treatment

e14532

Background: Growth and differentiation factor 15 (GDF-15) is a divergent member of the TGF-β superfamily with low to absent expression in healthy tissue. GDF-15 has been linked to feto-maternal immune tolerance, to prevention of excessive immune cell infiltration during tissue damage, and to anorexia. Various major tumor types secrete high levels of GDF-15. In cancer patients, elevated GDF-15 serum levels correlate with poor prognosis and reduced overall survival (OS). Methods: Impact of a proprietary GDF-15 neutralizing antibody (CTL-002) regarding T cell trafficking was analyzed by whole blood adhesion assays, a HV18-MK melanoma-bearing humanized mouse model and a GDF-15-transgenic MC38 model. Additionally, patient GDF-15 serum levels were correlated with clinical response and overall survival in oropharyngeal squamous cell carcinoma (OPSCC) and melanoma brain metastases. Results: In whole blood cell adhesion assays GDF-15 impairs adhesion of T and NK cells to activated endothelial cells. Neutralization of GDF-15 by CTL-002 rescued T cell adhesion. In HV18-MK-bearing humanized mice CTL-002 induced a strong increase in TIL numbers. Subset analysis revealed an overproportional enrichment of T cells, in particular CD8+ T cells. As immune cell exclusion is detrimental for checkpoint inhibitor (CPI) therapy, a GDF-15-transgenic MC38 model was tested for anti-PD-1 therapy efficacy. In GDF-15 overexpressing MC38 tumors response to anti PD-1 therapy was reduced by 90% compared to wtMC38 tumors. Combining aPD-1 with CTL-002 resulted in 50% of the mice rejecting their GDF-15 overexpressing tumors. Clinically, inverse correlations of GDF-15 levels with CD8+ T cell infiltration were shown for HPV+ OPSCC and for melanoma brain metastases. GDF-15 serum levels were significantly higher in HPV- than in HPV+ OPSCC patient (p < 0.0001). Low GDF-15 levels corresponded to longer OS in both HPV- and HPV+ OPSCC. In two independent melanoma patient cohorts treated with nivolumab or pembrolizumab low baseline serum GDF-15 levels were predictive for clinical response to anti-PD1 treatment and superior OS. Bivariate analysis including LDH indicates that GDF-15 independently predicts poor survival in aPD-1 treated melanoma patients. Conclusions: Taken together our in vitro and in vivo data show that elevated GDF-15 levels block T-cell infiltration into tumor tissues. Neutralizing GDF-15 with CTL-002 restores the ability of T cells to extravasate blood vessels and enter tumor tissue both in vitro and in vivo. In melanoma, patients with higher GDF-15 levels have significantly shorter survival and are less likely to respond to anti-PD1 therapy. GDF-15 may thus serve as a new predictive biomarker for anti-PD1 response, but most importantly also represents a novel target for cancer immunotherapy to improve tumor immune cell infiltration and response to anti-PD1 therapy.

Abstract 2161: Identifying GDF-15 as potential novel immunotherapeutic target linked to immune cell exclusion in tumors and resistance to anti-PD-1 treatment

Introduction:

Growth and differentiation factor 15 (GDF-15) is a TGF-β superfamily member mainly expressed in placenta and prostate of healthy individuals. GDF-15 has been linked to feto-maternal tolerance, prevention of excessive immune cell infiltration during tissue damage and to anorexia. In cancer patients, GDF-15 serum levels are frequently elevated and associated with poor prognosis, via so far mostly unknown mechanism(s). A recent study elucidated a mechanism by which GDF-15 inhibits LFA-1 activation on CD8+ T cells, thus interfering with T cell recruitment to tissues [Haake et al. AACR 2020; submitted]. To further delineate the role of GDF-15 in cancer in this study GDF-15 serum and tissue levels were analyzed and correlated with tumoral immune-cell infiltration and clinical anti-PD1 response.

Methods:

In-silico, TCGA-derived mRNA levels of GDF-15 were compared in cancer vs. normal tissue. Two independent melanoma patient cohorts (88 and 34 patients) treated with nivolumab or pembrolizumab were analyzed regarding baseline GDF-15 serum levels, correlation with clinical response and overall survival. Melanoma brain metastases from 80 patients were collected to assess and compare intratumoral GDF-15 levels vs. CD3+, CD8+ and Foxp3+ cell numbers by immunohistochemistry (IHC).

Results:

TCGA-based analyses demonstrated significantly elevated GDF-15 mRNA levels in tumor vs. surrounding normal tissue in various major cancer types such as e.g. colorectal, prostate, head & neck and melanoma. In the two independent, anti-PD1 treated melanoma patient cohorts baseline serum GDF-15 levels were predictive for superior overall survival and clinical response to anti-PD1 treatment (p&lt;0.0001 and p=0.0382, respectively). In melanoma biopsies an inverse correlation of GDF-15 levels (histoscore) with CD3+ (R=-0.26; p=0.016) and CD8+ T cells (R=-0.21; p=0.05), but no correlation with Foxp3+ T cells was shown.

Conclusion:

GDF-15 is elevated in serum and tumor tissue of various major cancer types. In melanoma, patients with higher GDF-15 levels have significantly shorter survival and are less likely to respond to anti-PD1 therapy. In addition, intratumoral GDF-15 levels in melanoma brain metastasis correlate inversely with CD3+ and CD8+ T cell infiltration. Consequently, GDF-15 may serve as a predictive biomarker for anti-PD1 response and potentially represent a novel target in the immunotherapy of cancer to improve tumor immune cell infiltration and anti-PD1 response.

Citation Format: Jorg Wischhusen, Kilian Wistuba-Hamprecht, Patrick N. Harter, Phil Cheng, Alexander Martens, Falk Gogolla, Yumi Nonomura, Paula Romer, Sven D. Koch, Markus Haake, Christine Schuberth-Wagner, Manfred Rudiger, Eugen Leo, Michael Mittelbronn, Mitchell P. Levesque, Hubert Hackl, Reinhard Dummer, Benjamin Weide. Identifying GDF-15 as potential novel immunotherapeutic target linked to immune cell exclusion in tumors and resistance to anti-PD-1 treatment [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 2161.

RIG-I Activation Protects and Rescues from Lethal Influenza Virus Infection and Bacterial Superinfection

Influenza A virus infection causes substantial morbidity and mortality in seasonal epidemic outbreaks, and more efficient treatments are urgently needed. Innate immune sensing of viral nucleic acids stimulates antiviral immunity, including cell-autonomous antiviral defense mechanisms that restrict viral replication. RNA oligonucleotide ligands that potently activate the cytoplasmic helicase retinoic-acid-inducible gene I (RIG-I) are promising candidates for the development of new antiviral therapies. Here, we demonstrate in an Mx1-expressing mouse model of influenza A virus infection that a single intravenous injection of low-dose RIG-I ligand 5'-triphosphate RNA (3pRNA) completely protected mice from a lethal challenge with influenza A virus for at least 7 days. Furthermore, systemic administration of 3pRNA rescued mice with pre-established fulminant influenza infection and prevented the fatal effects of a streptococcal superinfection. Type I interferon, but not interferon-λ, was required for the therapeutic effect. Our results suggest that the use of RIG-I activating oligonucleotide ligands has the clinical potential to confine influenza epidemics when a strain-specific vaccine is not yet available and to reduce lethality of influenza in severely infected patients.

RIG-I activation induces the release of extracellular vesicles with antitumor activity

Activation of the innate immune receptor retinoic acid-inducible gene I (RIG-I) by its specific ligand 5'-triphosphate-RNA (3pRNA) triggers antitumor immunity predominantly via NK cell activation and direct apoptosis induction in tumor cells. However, how NK cells are mobilized to attack the tumor cells remains elusive. Here, we show that RIG-I activation induced the secretion of extracellular vesicles (EVs) from melanoma cells, which by themselves revealed antitumor activity in vitro and in vivo. RIG-I-induced EVs from melanoma cells exhibited an increased expression of the NKp30-ligand (BAG6, BAT3) on their surface triggering NK cell-mediated lysis of melanoma cells via activation of the cytotoxicity NK cell-receptor NKp30. Moreover, systemic administration of RIG-I-induced melanoma-EVs showed a potent antitumor activity in a melanoma mouse model in vivo. In conclusion, our data establish a new RIG-I-dependent pathway leading to NK cell-mediated tumor cell killing.

A Conserved Histidine in the RNA Sensor RIG-I Controls Immune Tolerance to N1-2'O-Methylated Self RNA

The cytosolic helicase retinoic acid-inducible gene-I (RIG-I) initiates immune responses to most RNA viruses by detecting viral 5'-triphosphorylated RNA (pppRNA). Although endogenous mRNA is also 5'-triphosphorylated, backbone modifications and the 5'-ppp-linked methylguanosine ((m7)G) cap prevent immunorecognition. Here we show that the methylation status of endogenous capped mRNA at the 5'-terminal nucleotide (N1) was crucial to prevent RIG-I activation. Moreover, we identified a single conserved amino acid (H830) in the RIG-I RNA binding pocket as the mediator of steric exclusion of N1-2'O-methylated RNA. H830A alteration (RIG-I(H830A)) restored binding of N1-2'O-methylated pppRNA. Consequently, endogenous mRNA activated the RIG-I(H830A) mutant but not wild-type RIG-I. Similarly, knockdown of the endogenous N1-2'O-methyltransferase led to considerable RIG-I stimulation in the absence of exogenous stimuli. Studies involving yellow-fever-virus-encoded 2'O-methyltransferase and RIG-I(H830A) revealed that viruses exploit this mechanism to escape RIG-I. Our data reveal a new role for cap N1-2'O-methylation in RIG-I tolerance of self-RNA.