Question

During the production of hybridoma for monoclonal antibodies, the unfused myeloma cells fail to survive because

• A. It over-expresses dihydrofolate reductase
• B. Culture media contains aminopterin
• C. It over-expresses hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
• D. These cells lack mitochondria

Hint:

HAT Medium Selection:
Aminopterin $\rightarrow$ Blocks de novo nucleotide synthesis.
Myeloma $\rightarrow \text{HGPRT}^-$ (Dies). B cells $\rightarrow$ Finite lifespan (Dies). Hybridomas $\rightarrow$ Survive (B-cell $\text{HGPRT}^+$ + Myeloma immortality).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
HAT medium selective pressure forces hybridoma survival by blocking de novo nucleotide synthesis while requiring salvage pathway enzymes.
Key Formula or Approach:
\[ \text{Aminopterin blocks: } \text{Dihydrofolate Reductase (DHFR)} \implies \text{No De Novo Purine/Pyrimidine Synthesis} \]

Step 2: Detailed Explanation:
In the Köhler-Milstein hybridoma selection system:
1. Myeloma Fusion Partners: Are genetically deficient in HGPRT (Hypoxanthine-Guanine Phosphoribosyltransferase) and cannot use the salvage pathway for purine synthesis.
2. HAT Selective Medium: Contains Aminopterin, a folic acid analogue that irreversibly blocks dihydrofolate reductase (DHFR), shutting down the de novo nucleotide synthesis pathway completely.
3. Fate of Unfused Myeloma Cells: With the de novo pathway blocked by aminopterin and the salvage pathway disabled by lack of HGPRT, unfused myeloma cells fail to replicate DNA and die within days.

Step 3: Final Answer:
Therefore, unfused myeloma cells die because Culture media contains aminopterin, matching option (B).