Study Purpose: This study is testing a new way to treat a condition called SCID-X1. SCID-X1 is a type of Severe Combined Immunodeficiency, where the body's defense system can't fight off illnesses well. The study uses a special process called gene transfer to help fix this problem.

What is Gene Transfer? Gene transfer involves changing a person's cells to help them work better. In this study, cells from a patient's bone marrow (a part of the body where blood cells are made) are changed using a special tool called a lentiviral vector. After this, the modified cells are put back into the patient's body.

Key Points:

• The study lasts 2 years, with 15 years of follow-up checks.
• Participants must be 5 years old or younger, diagnosed with SCID-X1, and have no matching donor.
• Participants can't have severe infections or other major health issues.

Benefits and Risks: The goal is to improve the body's ability to fight infections. However, there may be risks like infections or other side effects from the procedure. Participants will be carefully monitored to ensure safety.