Surviving animals produced by nuclear transfer are healthy. There, is a substantial loss of individual before and after birth some of the cloned animals display abnormalities. Abnormlities such as increased birth weight. Dna methylation and histone modification of the original donor cell is inappropriate maintained in the cells of the recipient animals. INVIVO: The direct delivery of the therapeutic gene into the target cells of a particular tissue. Genes are changed in cells when the cells are still in the body. These include liver, muscle, skin, spleen, lung, brain and blood cells. Carried out by viral and non viral vector system EXVIVO: Cells are modified outside the body and then transplanted back in again. SCID is a inherited immune disorder associated with T-lymphocyte and B-lymphocytes dysfunction. Gene encodes for adenosine deaminase. The patients of SCID(lacking ADA) suffer from infectious diseases and die at an young age.