B‐cell chronic lymphocytic leukaemia with CD8 expression: report of 10 cases and immunochemical analysis of the CD8 antigen

Abstract

We report 10 cases of B-cell chronic lymphocytic leukaemia (B-CLL) with expression of the T-cell antigen CD8. The majority of patients had typical B-cell CLL with stable and non-progressive stage A(O) disease except for more common expression of lambda light chain and CD25. Two patients had progressive disease and required therapy, one with atypical morphological and phenotypic features. The incidence of CD8 expression was approximately 0.5% of B-CLL patients from our institutions. Immunoprecipitation of the CD8 antigen from four of these B-CLLs showed identity to the CD8 antigen expressed on T cells with precipitation of CD8alpha bands of molecular weight approximately 34 kD. In view of the known intracellular signalling mechanism of CD8 using the tyrosine kinase p56-lck, we studied p56-lck expression by Western blot and found lack of consistent expression of the CD8 surface antigen, with most lacking p56-lck. Our report indicates that CD8 expression in B-CLL is probably underrecognized but is not a marker of disease progression. The CD8 on the B-CLL surface is immunochemically identical to the antigen on T cells, but is not accompanied by its usual signalling mechanism of p56-lck tyrosine kinase and therefore is unlikely to be a functionally active receptor.

Chronic Lymphocytic Leukemia with Aberrant CD8 Expression and Atypical Morphology: A Case Report and Review

“…Some reports suggested that CD8 expression was associated with a favorable prognosis either in terms of lack of progression or good response to treatment [4][5][6][7][8][9][10][11][12]; however, other reports suggested CD8 as a marker of aggressive disease [13,14]. Our patient showed an indolent clinical course.…”

“…The cytoplasmic domain of CD8 recruits the T-cell specific tyrosine kinase, p56lck, to the TCR-CD8-MHC signalling complex triggering downstream signalling for T-cell activation [16]. A previous study showed that p56lck was absent in three of four cases of CD8+ CLL, suggesting a non-functional CD8 in CLL cells [9]. In our patient, the CLL population clearly expressed CD8, but lacked the T-lineage defining antigens of CD3 and CD7.…”

“…These CLL cells resembled T cells in reactive processes. Only one other case of CD8+ B-CLL with atypical morphology was reported in the literature [9]. As there were no descriptions of morphological features in most reports, further study is required to determine whether CD8 expression is commonly associated with atypical morphology of CLL.…”

“…Aberrant expression of CD8 in CLL is rare but has been reported previously. The retrospective studies revealed a frequency of 0.5-3% for the aberrant expression of CD8 in CLL [6,9]. CD8 expression was also found in other types of B-cell neoplasms, though even more rarely than in CLL.…”

“…Most are reports of single cases or small case series. It is not clear whether CD8 expression is associated with disease progression [4][5][6][7][8][9][10][11][12].…”