BCR and plasma cell myeloma: As the FVIII B cell tetramer did not bind to Cell Trace Violet (CTV) labeled myeloma cells expressing an invariant BCR (54) and incubation with a large molar excess of monomeric FVIII prior to addition of the tetramer resulted in the loss of detection of tetramer+ hybridomas expressing a BCR specific to FVIII (Figure 2A), these results demonstrate that binding of the FVIII B cell tetramer is BCR specific.