Project Updates The Stimulator of Interferon Genes (STING) pathway has been implicated as a key mechanism by which the host innate immune system “senses” cancer. Recent evidence implicates the pattern-recognition receptor DEAD-box polypeptide 41 (DDX41) as a critical component of the STING pathway. This is of particular interest because, not only has the role of DDX41 not been well described in the STING response to cancer, but hereditary mutations in DDX41 have been recently described to predispose patients to blood cancers. My aims for this proposal are to test the integrity of the STING pathway in mice with Ddx41 mutations and to determine whether these Ddx41 mutations result in blunted anti-tumor immunity.

To investigate these aims, I am utilizing mice with either a knockout (Ddx41-/- ) or point mutation (Ddx41R525H/R525H) in the Ddx41 gene. We have determined that homozygosity for either the knockout or point mutation in Ddx41 is embryonically lethal and thus mice with heterozygous deficiency are being used. Using Western blot, we have demonstrated that Ddx41+/- mice have an approximately 50% decrease in expressed Ddx41 protein compared to littermate controls. In vitro, stimulation of bone marrow derived dendritic cells (BMDCs) for 6 hours with a known STING agonist (tumor DNA with lipofectamine) demonstrated that expression of downstream STING cytokines (IFN-β, TNF-α and IL-6), as measured by qPCR, was decreased in Ddx41+/- mice compared to littermate controls. In contrast, stimulation of BMDCs with DMXAA, known to bind directly to the STING receptor, resulted in equivalent expression of STING pathway cytokines. Interestingly, intravenous (in vivo) administration of DMXAA resulted in increased STING pathway cytokine production (IFN-β, TNF-α and IL-6) in Ddx41+/- mice compared to littermate controls. Innate immune cell subsets (conventional dendritic cells, macrophages, NK cells) and adaptive immune cell subsets (CD4+ and CD8+ T cells) had similar frequencies within Ddx41+/- mice and littermate control splenocytes. Interestingly, an increased rate of tumor growth was noted following subcutaneous injection of immunogenic cell lines (MC38.SIY, MC57.SIY, C1498.SIY) in Ddx41+/- mice compared to littermate controls. Thus, in contrast to the initial hypothesis that Ddx41 deficiency would result in decreased STING pathway activity, it appears that decreased Ddx41 expression may result in decreased STING activity and enhanced tumor control.

Future directions: I am currently investigating the mechanism by which Ddx41 deficiency may lead to enhanced tumor control, and plan to submit a manuscript later this year detailing these findings. Studies are focusing on the tumor microenvironment and upregulation of immune evasion pathways in Ddx41+/- mice compared to littermate controls. We are also developing a conditional knockout mouse, so that complete deficiency of Ddx41 can be investigated. Finally, using mice predisposed to leukemia development, I am investigating how Ddx41 haploinsufficiency leads to hereditary hematologic malignancies.

Publications/Presentations

1. Curran E, Mattingly J, Godley L, Kline J. Role of Ddx41 in the Stimulator of Interferon Genes (STING) Pathway, Clinical Lymphoma, Myeloma and Leukemia. 2017, 17(S2):S395. (Poster presentation at annual meeting of the Society of Hematologic Oncology annual meeting)

2. Curran E, Larson RA: Acute lymphoblastic leukemia, in Boyiadzis MM (ed): Cancer Immunotherapy in Clinical Practice, 2017

3. Curran E, Godfrey J, Kline J. Mechanisms of immune tolerance in leukemia and lymphoma. Trends in Immunology, 2017, 38(7):513-525. PMID:28511816.

Funding: I am currently supported by an institutional K12 grant (CA139160), “Developing an Oncology Workforce for the 21st Century” (7/1/16-6/30/18) and am applying for K08 funding based on this work, as well as additional work on the STING pathway. As an extension of this work, I am further investigating the role of Ddx41 in hematologic malignancies in particular, and was awarded a Gilead Sciences Research Scholars Program in Hematology/Oncology award (6/8/17- 6/7/19) to support ongoing studies.