Study of Dexpramipexole Chronic Sinusitis With Nasal Polyps and Eosinophilia

Inclusion Criteria: * Male or female \>18 or \<70 years of age * Willing to practice effective contraception during the study and be willing and able to continue contraception for 1 month (females) or 3 months (males) after the last dose of study treatment * Confirmed diagnosis of chronic sinusitis with nasal polyps * Documented history of nasal eosinophilia * Documented peripheral absolute eosinophil count \>300 cells/μL * Bilateral total polyp score of \>4 * Sino-nasal outcome test (SNOT-22) score of \>7 * Using an intranasal corticosteroid spray or irrigation (\< 1000 μg/day beclomethasone or equivalent) Exclusion Criteria: * Acute sinusitis, concurrent nasal infection, or subjects who have had a nasal or upper respiratory tract infection within 2 weeks prior to baseline * CT scan suggestive of allergic fungal rhinosinusitis * Nasal septal deviation that would occlude at least one nostril * Nasal surgery (including polypectomy) within 6 months prior to baseline * History of more than 5 sinonasal surgeries requiring general anesthesia * History of more than 2 sinonasal surgeries that changed the lateral wall of the nose * History of cystic fibrosis, primary ciliary's dysfunction or Kartagener's syndrome * History of diagnosis with a parasitic infection * Hospitalization or emergency treatment for the treatment of asthma two or more times in the 12 months prior to baseline * Hospitalization for an acute asthmatic attack within 4 weeks prior to baseline * Forced expiratory volume (FEV1) of \<60% of predicted normal range * Treatment with a systemic corticosteroid or intra-polyp corticosteroid within 8 weeks prior to baseline or anticipated need for systemic corticosteroids during the study treatment period * Utilization of rescue oral corticosteroids for asthma or chronic sinusitis exacerbation more than one time within the past 1 year * Treatment with an investigational drug in the previous 30 days or 5-half-lives, whichever is longer * Treatment with a monoclonal antibody therapy including omalizumab (Xolair®), within 5-half-lives * Treatment with zileuton (Zyflo®) within 4 weeks of baseline * Treatment with pramipexole (Mirapex®) within 4 weeks of baseline * History of malignancy, including solid tumors and hematologic malignancies (except basal cell and squamous cell cancers of the skin that have been completely excised and cured) * History of human immunodeficiency virus (HIV) or hepatitis B or C * History of unstable or severe cardiac, hepatic, or renal disease, or other medically significant illness * Medical or other condition likely to interfere with subject's ability to undergo study procedures, adhere to visit schedule or comply with study requirements * Absolute neutrophil count \<2000 cells/μL at screening, or any documented history of neutropenia * Total IgE \>1500 IU/ml at any visit prior to baseline * Renal dysfunction, defined as an estimated glomerular filtration rate (eGFR) of ≤80 mg/dL at screening (estimation of creatinine clearance using the MDRD formula) * History of long QT syndrome or arrhythmia * Prolongation of QT/QTc interval (e.g., repeated demonstration of a QT/QTc interval \>450 ms) at screening or pre-dose on day 1 * Clinically important abnormalities in resting ECG that may interfere with the interpretation of QTc interval changes at screening or pre-dose on day 1, including any of the following: * PR interval \>210 ms; * QRS \>110 ms; * Heart rate \<45 bpm or \>100 bpm (average of 3 assessments). * Pregnant women or women breastfeeding