Which vector is used introduce a functional ADA cDNA into the lymphocytes?

Explanation

To answer the question of which vector is used to introduce functional ADA cDNA into lymphocytes, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding ADA and its Importance**:
- ADA stands for adenosine deaminase, an enzyme crucial for the immune system. A deficiency in ADA can lead to severe combined immunodeficiency (SCID).

2. **Identifying the Target Cells**:
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