In a model of gene therapy for ADA deficiency, the genetically engineered lymphocytes of a patient…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In a model of gene therapy for ADA deficiency, the genetically engineered lymphocytes of a patient fall to half of their number every months. At the infusion the level is .
- What per cent is left after months?
- After how many months is the level ?
- After how many months is the level ?
Need a reminder? The key ideaShow
Gene therapy delivers a normal gene to take over the work of a non-functional one. The first clinical gene therapy, in 1990, was for a four-year-old girl with ADA deficiency, which is caused by the deletion of the gene for adenosine deaminase. Lymphocytes are grown outside the body, given a functional ADA cDNA by a retroviral vector, and returned. They are not immortal, so the infusions are repeated. Very low amounts of a germ can be found early by PCR, which copies the nucleic acid, and by ELISA, which uses antigen and antibody interaction.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Half-life: months. Start: .
Plan. Halve the level for each half-life.
Step 1. months. Two half-lives: , so .
Step 2. . One more half-life: . That is three half-lives, months.
Step 3. . Another half-life: . That is four half-lives, months.
Answer: ; months; months.
Check. The level after half-lives is per cent. For it is .
Watch out. The half-life is a made up value. In a real patient it depends on the cells and on the vector.
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