What is the purpose of HAT medium in monoclonal antibody production?

• A. Fusion of the two cell types
• B. Restricting the growth of myeloma cells
• C. Restricting the growth of spleen cells
• D. Restricting antibody production to the IgM class

Answer: (B)

HAT medium is used to select hybridomas after fusing spleen cells with myeloma cells. The key idea is that aminopterin blocks de novo purine synthesis, so cells must salvage purines through HGPRT to survive. Myeloma cells used for fusion are HGPRT-deficient, so they cannot salvage and die in HAT. Spleen cells provide HGPRT but are not immortal and will eventually die off. Only the fused hybrids inherit both immortality (from the myeloma) and HGPRT salvage capability (from the spleen), allowing them to survive and proliferate in HAT. In short, HAT medium purposefully restricts the growth of the unfused myeloma cells, enriching for the desired hybridomas that can produce monoclonal antibodies.