Treatment of genetic disorders by introducing proper genes into cells of the target organ, is called gene therapy.
Immunodeficiency diseases are mainly concerned with the derivatives of marrow cells. So they can be cured by bone marrow transplantation using gene augmentation therapy.  Example: SCID(Severe Combined Immunodeficiency).
Gene therapy, how it works?
Gene Replacement Therapy vs Corrective Gene Therapy
Gene Replacement Therapy
(Gene Augmentation)
Corrective Gene Therapy
  Random insertion of healthy counterpart of defective gene somewhere in genome so that its product could be available. Directing insertion of healthy gene at specific site to displace defective gene is required.
Suitable for recessive disorders  and for single gene mutations. Possible for dominant disorders.
No recombinant event required and non specific insertion will work so long as appropriate regulatory controls are provided for expression. Insertion at specific site would require some  form of induced recombinational event.
Approach is not useful for dominant nature disorders or where errant(defective) gene gives destructive or interfering substance. This approach would be ideal where errant gene produces destructive or interfering substance.
This approach is feasible today and has effect similar to transplantation approach only thing it bring done still at root level of the defect. Extensive study is still required to direct gene at correct position in the genome.

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