You start with 1.0 × 10⁷ splenic B cells from an immunized mouse; 0.2% of these B cells are specific for the injected antigen. Fusion conditions yield hybridomas from 0.5% of the total B cells (i.e., 0.5% of B cells successfully fuse to a myeloma). Estimate the number of antigen-specific hybridomas you expect to obtain after fusion (before any screening losses). Show your calculation.

• A. Approximately 20,000 antigen-specific hybridomas, because all antigen-specific B cells survive and each becomes ten hybridomas through spontaneous division during the fusion procedure.
• B. Approximately 2 antigen-specific hybridomas, since most specific B cells will die immediately after fusion attempts and only a trivial fraction survive to form hybridomas.
• C. Approximately 100 antigen-specific hybridomas.
• D. Approximately 50,000 antigen-specific hybridomas, because fusion multiplies the antigen-specific pool by the total myeloma number regardless of fusion efficiency.

Answer: (C)