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

Options

A. lambda phase
B. Ti plasmid
C. Retrovirus
D. pBR 322

Answer

To answer the question regarding which vector is commonly used for introducing a DNA fragment in human lymphocytes, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Options**: The options provided are Lambda phage, Ti plasmid, retrovirus, and PVR322.

2. **Understand the Function of Each Vector**:
- **Lambda Phage**: This is a bacteriophage used primarily in bacterial systems for cloning DNA.
- **Ti Plasmid**: This is a plasmid from the bacterium Agrobacterium tumefaciens, mainly used in plant genetic engineering.
- **Retrovirus**: This is a type of virus that has RNA as its genetic material and can convert RNA into DNA using the enzyme reverse transcriptase. It is commonly used in gene therapy.
- **PVR322**: This is a plasmid vector used in various cloning experiments but is not specifically known for use in human lymphocytes.

3. **Evaluate the Most Suitable Vector**: Among the options, the retrovirus is specifically designed to introduce genetic material into human cells, including lymphocytes. It is particularly useful in gene therapy applications, such as treating severe combined immunodeficiency (SCID).

4. **Conclusion**: Based on the characteristics of each vector, the retrovirus is the most appropriate choice for introducing a DNA fragment into human lymphocytes.

### Final Answer:
The correct option is **retrovirus**.