PROJECT SUMMARY Non-Hodgkin lymphoma (NHL) is a heterogeneous group of diseases of mainly B-cell origin. NHL incidence is progressively increasing, making it the sixth most common cancer in the US, with over 70,000 estimated new cases in 2015. The NHLs range from indolent to aggressive cancer such as diffuse large B-cell lymphomas of activated B-cell-like type (ABC-DLBCL). Growing evidence links B cell lymphoma patients’ poor survival and immune suppression to persistent activation of signal transducer and activator of transcription 3 (STAT3). In ABC-DLBCL, genetic mutations augment Toll-like receptor 9 (TLR9)/MyD88 signaling, thereby leading to secretion of cytokines that induce STAT3 activation in lymphoma cells and in the tumor-associated immune cells, such as myeloid-derived suppressor cells (MDSCs). The autocrine and paracrine STAT3 activation in cancer cells and in the tumor-associated immune cells enhances lymphoma’s tumorigenic and tolerogenic potential. To overcome the challenge imposed by lack of pharmacological inhibitors of STAT3, we developed a strategy to deliver therapeutic siRNA specifically into myeloid and B cells, by physically linking siRNA to TLR9 ligands/agonists, CpG oligodeoxynucleotides (ODNs). We have demonstrated in multiple tumor models that local tumor treatment using CpG-STAT3siRNA silences STAT3, stimulating systemic antitumor immunity, in addition to inducing direct B-cell lymphoma tumor cell apoptosis and sensitivity to radiation therapy (RT). We propose to move CpG-STAT3siRNA to phase 1b clinical trials in NHL. In year 10 of the current SPORE, we included in the project a second generation STAT3 inhibitor: linking CpG to a high-affinity STAT3-DNA binding sequence called STAT3decoy ODN (dODN), which effectively competes STAT3 DNA binding. Compared to CpG-STAT3siRNA, CpG-STAT3dODN exhibits improved nuclease-resistance which allows for systemic administration and treatment of advanced, disseminated lymphomas. We anticipate that with the clinical testing of the first CpG-STAT3siRNA strategy together with RT in the local setting, and with the optimization of new CpG-STAT3dODN for systemic administration, the proposed studies will accelerate development of novel, effective and safe nucleotide-based immunotherapeutic strategies for targeting intracellular STAT3 in NHL and potentially other hematologic malignancies.