Study to Investigate Efficacy, Safety and Pharmacokinetics of BT595 in Subjects With PID

Main Inclusion Criteria:

- Written informed consent/assent obtained from subjects/subjects' parent(s) or legally
acceptable representative indicating that they understand the purpose of and
procedures required for the study and are willing to participate in it.

- Male or female, aged 2 through 75 years.

- Diagnosis of PID with impaired antibody production, i.e.:

Diagnosis of common variable immunodeficiency (CVID) as defined by the European Society for
Immunodeficiencies (ESID)/Pan American Group for Immunodeficiency (PAGID) diagnostic
criteria.

Or

- X linked agammaglobulinemia (XLA) as defined by ESID/PAGID diagnostic criteria.

- Established replacement therapy with any intravenous immunoglobulin (IVIg) reference
preparation during the previous 6 months, including documentation of immunoglobulin G
(IgG) trough levels.

- Established replacement therapy with a single IVIg reference preparation for at least
3 months prior to treatment start with BT595 at a 3 or 4 week schedule with a constant
IVIg dose that did not change by ±20% of the mean dose, regular dosage intervals, and
at least 1 IgG trough level of ≥5 g/L during the previous 3 months.

Main Exclusion Criteria:

- Known intolerance to immunoglobulins or comparable substances (e.g., vaccination
reaction).

- Known intolerance to proteins of human origin or known allergic reactions to
components of the study product.

- Acquired medical conditions known to cause secondary immune deficiency, such as
chronic lymphatic leukemia, lymphoma, multiple myeloma, as well as protein losing
enteropathies and hypoalbuminemia.

- Recent febrile illness that precludes or delays participation.

- Active infection and receiving antibiotic therapy for the treatment of this infection
at the time of screening. Note: if the subject is deemed to be a screen failure due to
a nonserious active infection requiring antibiotic therapy, the subject may be
rescreened after the initial screening.

- Therapy with systemic steroids or other immunosuppressant drugs at the time of
enrollment (current daily use of corticosteroids, i.e., >10 mg prednisone
equivalent/day for >30 days. Intermittent corticosteroid use during the study is
allowable, if medically necessary).

- History of thrombotic events (including myocardial infarction, cerebral vascular
accident [including stroke], pulmonary embolism, and deep vein thrombosis) within the
6 months before treatment start with BT595 or the presence of significant risk factors
for thrombotic events.

- Therapy with live attenuated virus vaccines within 3 months before start of the study.

- Selective, absolute immunoglobulin A (IgA) deficiency or known antibodies to IgA.