ABERRATIONS OF THE B-CELL RECEPTOR B29 (CD79B) GENE IN CHRONIC LYMPHOCYTIC-LEUKEMIA

Leukemic B cells in chronic lymphocytic leukemia (B-CLL) typically exh ibit low or undetectable surface Ig. Because the B29 (CD79b and Ig bet a) and mb-1 (CD79a and Ig alpha) gene products are required for surfac e Ig display in the B-cell receptor complex (BCR), we analyzed the exp ression of these genes in B-CLL cells. The majority (83%) of the rando mly selected B-CLL patient samples analyzed exhibited low or undetecta ble surface BCR measured by mu heavy chain and B29 expression, Levels of mb-1 mRNA in these B-CLL samples with low surface BCR were similar to those in normal B cells. Among those with decreased surface express ion, B29 mRNA was not detected in half of these B-CLL samples. The rem aining B-CLL samples with diminished surface BCR contained normal leve ls of B29 mRNA. Further analysis of cDNA clones from the majority of t hese latter samples contained point mutations, insertions, or deletion s that were largely located in the B29 transmembrane and cytoplasmic d omains. These results indicate the occurrence of somatic mutations pre dicted to affect B29 expression and/or function in the majority of B-C LL and suggest that these aberrations underlie the diminished surface BCR display and loss of BCR signaling characteristic of this leukemia, (C) 1997 by The American Society of Hematology.