Incidence of somatically mutated V_Htranscripts in lymphocyte cocultures is dependent primarily on the source of B cells.

Accumulation of somatic mutation was assessed by sequential hybridization as described.7,14-16 The results are presented as the percentage of V_H transcripts that have acquired 1 or more mutations in either of two 21–base-pair (bp) target sequences.7,14 15 In the Figure, h indicates healthy subject; p, BMT patient, (−), T cells replaced by CD40 ligand and L cells. Closed circles indicate sources of transcripts selected for sequence analysis (see also Figure 4).