Absence of cytotoxic molecules in CD8-and/or CD56-positive adult T-cell leukaemia/lymphoma

Adult T-cell leukaemia/lymphoma (ATLL) cells usually exhibit a CD4(+) (help er/inducer) phenotype (CD4(+)/8(-)/56(-)), and only a minority of tumours e xpress the CD8 (cytotoxic/suppressor) or CD56 (natural killer [NK]-associat ed) antigene. TIA-1 is a cytotoxic granule-associated protein expressed in NK cells and cytotoxic T lymphocytes (CTLs). Granzyme B, perforin and Fas l igand (FasL) are also expressed in activated CTLs and NK cells. To clarify the cytotoxic potential of ATLL cells, immunohistochemistry was performed i n CD8(+) and/or CD56(+) ATLL cells, using anti-TIA-1, anti-granzyme B, anti -perforin and anti-Fast antibodies. We studied nine cases of CD8(+) and/or CD56+ ATLt, all of which exhibited monoclonal integration of human T-cell l eukaemia virus type 1 (HTLV-1) proviral DNA. Four cases exhibited a CD8(+)/ CD56(-) phenotype, four others had a CD8(-)/CD56(+) phenotype, and one was CD8(+)/CD56(+). All but one case also expressed the surface antigens CD3, T CR alpha beta, and CD4. Expression of granzyme B and TIA-I were demonstrate d in three and two cases, respectively, but none expressed perforin or Fast . In the control study, 10 cases with typical CD3(+)/4(+)/8(-)/56(-) ATLL d emonstrated no expression of those cytotoxic-associated proteins. Our findi ngs suggest that CD8 and/or CD56 positivity probably confer(s) no cytotoxic function on ATLL cells, and it is possible that CD8 and CD56 may be simply aberrant surface markers in ATLL.