The goal of this (monocentric, randomised, placebo-controlled single-blinded; phase 2) clinical trial is to test the hypothesis that DNase 1 administration leads to a reduction in systemic immune response measured in patients after acute ischaemic stroke compared to control treatment.

Participants will receive intravenous DNase 1 (500 µg/kg) or placebo (NaCl 0.9%) twice within 24±6 hours after symptom onset (last seen well). Blood samples will be taken at baseline, day 1 and 3. Personal visits will occur on baseline, day 1, 3 and discharge date. A telephone interview will be conducted on day 30±3.

Inclusion Criteria:

• Patients with suspected acute ischemic stroke with symptom onset (last-seen-well) until Investigational drug application of less than 12 hours.
• Consent to participate in the study.
• Age ≥ 18 years.
• NIHSS ≥10 at admission.

Exclusion Criteria:

• Presence of any of the following conditions: Sinus or cerebral venous thrombosis, intracerebral haemorrhage, subarachnoid haemorrhage on qualified imaging (cCT with CT-A or MRI with MR-A). However, petechial haemorrhagic transformations of the index infarct and cerebral microhaemorrhages may be included.
• Active malignant tumour disease in the last 6 months.
• Current known immunosuppression due to immunomodulatory medication with immunosuppressive dose or underlying immunosuppressive disease (e.g. HIV).
• Acute fulminant infectious disease in the last 7 days (fever > 38.5°C or suspected by the Investigator).
• Breastfeeding or pregnant woman, women of childbearing age without known use of contraceptives with positive urine or serum beta-human choriogonadotropin test.
• Ischemic stroke or myocardial infarction in the previous 30 days.
• Surgery in the previous 30 days, except minor dermatological or gynaecological surgery without anaesthesia and wound healing disorders and patients with thrombectomy.
• Estimated or known weight > 100 kg.
• Known allergies or intolerance to dornase alfa (Pulmozyme) or recombinant protein products derived from Chinese hamster ovary cells.
• Thrombocytopenia, leukocyte count <1500/μl.
• Known participation in another clinical trial investigating a drug and/or medical product in the last 7 days before study inclusion.
• Severe renal insufficiency with GFR≤29 ml/min/ 1.73m³ and/or renal insufficiency requiring dialysis.