A Study of the Safety, Tolerability, Pharmacokinetics and Efficacy of Treatment With AP1189 in Patients With iMN and Severe Proteinuria

Inclusion Criteria: * Written informed consent has been obtained prior to initiating any study-specific procedures * Male and female subjects, 18 to 85 years of age diagnosed with iMN within 6 months prior to inclusion * Diagnosed as anti-PLA2-Receptor positive by local laboratory within 6 months prior to inclusion * Severe proteinuria defined by a U-protein/creatinine ratio \>3.0 g/g and/or U-albumin/creatinine ratio \>2.0 g/g and a P-albumin below the lower normal limit * eGFR \> 30 ml/min/1.73m2 * Treated with ACE- inhibitors or angiotensin II receptor blocker for a minimum of 1 months with a stable systemic arterial blood pressure OR treatment with ACE inhibitors and/or angiotensin receptor blocker was excluded or discontinued due to hypotension, intolerance or other side effect Only Denmark and Norway: * Females of child-bearing potential using reliable means of contraception or are post-menopausal * Females of childbearing potential with negative pregnancy test at screening and baseline Only Sweden: * Post-menopausal women or women who are surgically sterilized. Exclusion Criteria: * Participation in any other study involving investigational drug(s) during the study and within 4 weeks prior to study entry * Clinicial findings that in the opinion of the investigator would suggest condition(s) other than iMN as a major cause of severe proteinuria * Major surgery within 8 weeks prior to screening or planned surgery within 1 month following randomization * Blood pressure with systolic pressure above 160 mmHg and/or diastolic pressure above 100 mmHg despite antihypertensive treatment will in all cases be considered "uncontrolled" * Treated with systemic corticosteroids, or other immune suppressive, or immune modulating compounds within 4 weeks prior to screening and during the entire treatment period and until the final visit * Treated with rituximab within 12 months of screening * Evidence of active malignant disease * Uncontrolled disease states, such as asthma, psoriasis, or inflammatory bowel disease where flares are commonly treated with oral or parenteral corticosteroids * Evidence of serious uncontrolled concomitant cardiovascular, nervous system, pulmonary, renal, hepatic, endocrine or gastrointestinal disease * Pregnant women or nursing mothers * History of alcohol, drug, or chemical abuse within the 6 months prior to screening * Any condition that in the view of the investigator would suggest that the patient is unable to comply with study protocol and procedures Only Sweden: * Females of child-bearing potential.