Which of the following is commonly used as a vector for introducing a DNA fragment in human lymphocytes?

Usually, a retrovirus is used as a vector for introducing a DNA fragment in human cells. They have used as a vector in gene therapy to introduce the desired gene so as to replace the functioning of a defective gene

Ex: Severe Combined Immune Deficiency (SCID) is a disease caused due to a defect in the gene for the enzyme adenosine deaminase. In gene therapy against it, lymphocytes are extracted from the bone marrow of the patient. These are grown in a culture outside the body. A functional ADA rDNA, using a retroviral vector, is then introduced into these lymphocytes. These are reinjected into the patient's bone marrow.
λ-phage allows cloning of DNA fragments up to 23 kb lengths. Ti-plasmid is usually used for plants. pBR322 is an artificial cloning vector, usually used for bacteria.