A Phase I/II Study of Intratumoral Injection of SD-101

Inclusion Criteria * Biopsy-confirmed low-grade B-cell lymphoma, specifically, follicular grade 1 or 2, or 3A marginal zone or small lymphocytic lymphoma; patients must have relapsed from or are refractory to prior therapy * Patients must have at least one site of disease that is accessible for intratumoral injection of SD-101 and of ipilimumab (diameter ≥ 10mm), percutaneously * Tumor specimens must be available for immunological studies either from a previous biopsy or a new biopsy obtained before the initiation of the study * Patients must have measurable disease other than the injection site or biopsy site * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 \[corresponds to Karnofsky Performance Status (KPS) of ≥ 70\] * White blood cell count (WBC) ≥ 2000/µL (2 x 10\^9/L) * Absolute neutrophil count (ANC) ≥ 1000/µL (0.5 x 10\^9/L) * Platelets ≥ 75 x 10\^3/µL (75 x 10\^9/L) * Hemoglobin ≥ 8 g/dL (may be transfused) * Creatinine ≤ 2.0 x upper limit of normal (ULN) * Aspartate aminotransferase (AST)/alanine aminotransferase (ALT) ≤ 2.5 x ULN for subjects without liver metastasis; ≤ 5 times for liver metastases * Bilirubin ≤ 2.0 x ULN (except for subjects with Gilbert's Syndrome, who must have a total bilirubin of less than 3.0 mg/dL) * No active or chronic infection with human immunodeficiency virus (HIV), Hepatitis B, or Hepatitis C * Must be at least 4 weeks since treatment with standard or investigational chemotherapy, biochemotherapy, surgery, radiation, cytokine therapy, and 8 weeks since any monoclonal antibodies or immunotherapy, and recovered from any clinically significant toxicity experienced during treatment * Patients of reproductive potential must agree to use an effective (\> 90% reliability) form of contraception during the study and for 6 months following the last study drug administration * Women of reproductive potential must have negative urine pregnancy test * Life expectancy greater than 4 months * Able to comply with the treatment schedule * Ability to understand and the willingness to sign a written informed consent document Exclusion Criteria * Pre-existing autoimmune or antibody mediated disease including systemic lupus erythematosus, rheumatoid arthritis, multiple sclerosis, Sjogren's syndrome, autoimmune thrombocytopenia, Addison's disease, but excluding the presence of auto-antibodies without clinical autoimmune disease * History of inflammatory bowel disease (eg, Crohn's disease or ulcerative colitis), celiac disease, or other chronic gastrointestinal conditions associated with diarrhea, or current acute colitis of any origin * Any history of diverticulitis, or evidence of diverticulitis at baseline, including evidence limited to computed tomography (CT) scan only (note diverticulosis is not an exclusion criterion) * Severe psoriasis * Active thyroiditis * History of uveitis * Known history of HIV; patients with Acquired Immunodeficiency Syndrome (AIDS) are excluded * Patients with active infection or with a fever \> 38.5 degrees C within 3 days prior to the first scheduled treatment * Central nervous system (CNS) lymphoma * Prior malignancy (active within 5 years of screening) except basal cell or completely excised non-invasive squamous cell carcinoma of the skin, or in situ squamous cell carcinoma of the cervix * History of allergic reactions attributed to compounds of similar composition to SD-101 or ipilimumab (anti-cytotoxic T-lymphocyte-associated protein 4 \[CTLA4\] antibodies) * Current anticoagulant therapy (EXCEPTION acetylsalicylic acid ≤ 325 mg per day allowed) * Treatment with an immunosuppressive regimen of corticosteroids or other immunosuppressive medication (eg, methotrexate, rapamycin) within 30 days of study treatment; note patients with adrenal insufficiency may take up to 5 mg of prednisone or equivalent daily; topical and inhaled corticosteroids in standard doses are allowed * Significant cardiovascular disease \[ie, New York Heart Association (NYHA) class 3 congestive heart failure; myocardial infarction with the past 6 months; unstable angina; coronary angioplasty with the past 6 months; uncontrolled atrial or ventricular cardiac arrhythmias\] * Pregnant or lactating * Any other medical history, including laboratory results, deemed by the investigator to be likely to interfere with their participation in the study, or to interfere with the interpretation of the results.