All patients will receive the investigational medicinal product BP-SCIG 20%, solution for subcutaneous administration, manufactured by BIOPHARMA PLASMA LLC. A loading dose of IMP may be required (at the Investigator's decision): at least 0.2-0.5 g/kg (1.0-2.5 mL/kg) of body weight. This dose is distributed across several days, with a maximum daily dose of 0.1 to 0.15 g/kg. After achieving a steady-state (minimal) level of IgG, maintenance doses are administered at repeated intervals (approximately once a week) to achieve a cumulative monthly dose of 0.4-0.8 g/kg.