A Study of TAK-664 in People With Primary Immunodeficiency Diseases Who Have Not Yet Been Treated With Immunoglobulins

Primary immunodeficiency disease (or PIDD) is a group of conditions in which the immune system does not work properly. Some people with PIDD do not make enough antibodies. Antibodies are proteins that help to either protect the body from infections or fight infections. The main type of antibodies that helps protect the body from infection is IgG. People who do not make enough IgG often need medical treatment that gives the body those antibodies. This treatment is called IgG replacement therapy. It can be given through a vein (intravenous or IV) or under the skin (subcutaneous SC). TAK-664 is approved worldwide for SC IG replacement therapy. The study wants to learn more about TAK-664 given to people with PIDD who have not yet been treated with IG (called 'treatment-naïve'). The main aim of the study is to check if giving TAK-664 daily for 5 days, and then once more 3 days later (Day 8), can raise IgG to the target level and keep IgG there. Another aim of the study is to learn if TAK-664 given once a week can keep the IgG at the target levels during the study. The study also wants to find out how much the IgG levels raise and learn how many infections occur and how they are treated.