Question: What is the birthdate of this prominent sufferer of severe combined immunodeficiency, referred to as the bubble boy, famous for living in a sterile environment?

Context paragraphs:
Severe combined immunodeficiency: Severe combined immunodeficiency, SCID, also known as alymphocytosis, Glanzmann–Riniker syndrome, severe mixed immunodeficiency syndrome, and thymic alymphoplasia, is a rare genetic disorder characterized by the disturbed development of functional T cells and B cells caused by numerous genetic mutations that result in heterogeneous clinical presentations.  SCID involves defective antibody response due to either direct involvement with B lymphocytes or through improper B lymphocyte activation due to non-functional T-helper cells. Consequently, both "arms" (B cells and T cells) of the adaptive immune system are impaired due to a defect in one of several possible genes.  SCID is the most severe form of primary immunodeficiencies, and there are now at least nine different known genes in which mutations lead to a form of SCID.  It is also known as the bubble boy disease and bubble baby disease because its victims are extremely vulnerable to infectious diseases and some of them, such as David Vetter, have become famous for living in a sterile environment.  SCID is the result of an immune system so highly compromised that it is considered almost absent.

David Vetter: David Phillip Vetter (September 21, 1971 – February 22, 1984) was a prominent sufferer of severe combined immunodeficiency (SCID), a hereditary disease which dramatically weakens the immune system.  Individuals born with SCID are abnormally susceptible to infections, and exposure to typically innocuous pathogens can be fatal.  Vetter was referred to as "David, the bubble boy" by the media.  Vetter's surname (last name) was not revealed to the general public until 10 years after his death in order to preserve his family's privacy.

Strimvelis: Strimvelis is the first "ex-vivo" stem cell gene therapy to treat patients with a very rare disease called ADA-SCID (Severe Combined Immunodeficiency due to Adenosine Deaminase deficiency), a rare disorder caused by the absence of an essential protein called adenosine deaminase (ADA), which is required for the production of lymphocytes.  Children born with ADA-SCID do not develop a healthy immune system so cannot fight off everyday infections, which results in severe and life-threatening illness.  Without prompt treatment, the disorder often proves fatal within the child’s first year of life.  ADA-SCID is estimated to occur in approximately 15 patients per year in Europe.

X-linked severe combined immunodeficiency: X-linked severe combined immunodeficiency (X-SCID) is an immunodeficiency disorder in which the body produces very few T cells and NK cells.  In the absence of T cell help, B cells become defective.  It is an x-linked recessive trait, stemming from a mutated (abnormal) version of the IL2-RG gene located at xq13.1 on the X-chromosome, which is shared between receptors for IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21.

Severe combined immunodeficiency (non-human): The severe combined immunodeficiency (SCID) is a severe immunodeficiency genetic disorder that is characterized by the complete inability of the adaptive immune system to mount, coordinate, and sustain an appropriate immune response, usually due to absent or atypical T and B lymphocytes.  In humans, SCID is colloquially known as "bubble boy" disease, as victims may require complete clinical isolation to prevent lethal infection from environmental microbes.

LIG4 syndrome: LIG4 syndrome (also known as Ligase IV syndrome) is an extremely rare condition caused by mutations in the DNA Ligase IV (LIG4) gene.  Some mutations in this gene are associated with a resistance against multiple myeloma and Severe Combined Immunodeficiency.  Severity of symptoms depends on the degree of reduced enzymatic activity of Ligase IV or gene expression.

Humanized mouse: A humanized mouse is a mouse carrying functioning human genes, cells, tissues, and/or organs.  Humanized mice are commonly used as small animal models in biological and medical research for human therapeutics.  Immunodeficient mice are often used as recipients for human cells or tissues, because they can relatively easily accept heterologous cells due to lack of host immunity.  Traditionally, the nude mouse and severe combined immunodeficiency (SCID) mouse have been used for this purpose, but recently the NOG mouse and the NSG mouse have been shown to engraft human cells and tissues more efficiently than other models.

Everything, Everything (novel): Everything, Everything is the debut young adult novel by American author Nicola Yoon, first published by Delacorte Books for Young Readers in 2015.  The novel centers around 18-year-old Madeline Whittier, who has severe combined immunodeficiency (SCID), also known as "bubble baby disease".  Due to her condition, Madeline is stuck inside her house in Los Angeles, where she lives with her mother and a physician who takes care of her.

Severe combined immunodeficient mice: Mice with severe combined immunodeficiency (SCIDs) are often used in the research of human disease.  Human immune cells are used to develop human lymphoid organs within these immunodeficient mice, and many different types of SCID mouse models have been developed.  These mice allow researchers to study the human immune system and human disease in a small animal model.

William French Anderson: William French Anderson (born December 31, 1936) is an American physician, geneticist and molecular biologist.  He is considered a pioneer of gene therapy.  He graduated from Harvard College in 1958 and from Harvard Medical School in 1963.  In 1990, he claimed to be the first person ever to succeed in gene therapy of a 4-year-old girl suffering from severe combined immunodeficiency (a disorder called "bubble boy disease").  His claims may have been exaggerated, albeit, he was not alone.  In 2006, he was convicted of sexual abuse of a minor and in 2007 was sentenced to 14 years in prison.

Supporting paragraphs: Severe combined immunodeficiency David Vetter
Answer: September 21, 1971