B-CELL CHRONIC LYMPHOCYTIC-LEUKEMIA WITH CD8 EXPRESSION - REPORT OF 10 CASES AND IMMUNOCHEMICAL ANALYSIS OF THE CD8 ANTIGEN

We report 10 cases of B-cell chronic lymphocytic leukaemia (B-CLL) wit h expression of the T-cell antigen CD8. The majority of patients had t ypical B-cell CLL with stable and non-progressive stage A(O) disease e xcept for more common expression of lambda light chain and CD25. Two p atients had progressive disease and required therapy, one with atypica l morphological and phenotypic features. The incidence of CD8 expressi on was approximately 0.5% of B-CLL patients from our institutions. Imm unoprecipitation of the CD8 antigen from four of these B-CLLs showed i dentity to the CD8 antigen expressed on T cells with precipitation of CD8 alpha bands of molecular weight similar to 34 kD. In view of the k nown intracellular signalling mechanism of CD8 using the tyrosine kina se p56-lck, we studied p56-lck expression by Western blot and found la ck of consistent expression of the CD8 surface antigen, with most lack ing p56-lck. Our report indicates that CD8 expression in B-CLL is prob ably underrecognized but is not a marker of disease progression. The C D8 on the B-CLL surface is immunochemically identical to the antigen o n T cells, but is not accompanied by its usual signalling mechanism of p56-lck tyrosine kinase and therefore is unlikely to be a functionall y active receptor.