In a series of 24 patients with chronic T-lymphoid disorders [13 T-prolymphocytic leukaemia (T-PLL) and 11
Sezary syndrome] we have studied (i) chromosome 17p abnormalities and p53 allele deletion by fluorescence in situ hybridization; (ii) mutation in the exons of the p53 gene by direct
DNA sequencing; and (iii) p53
protein expression by immunocytochemistry and, in some cases, also by flow cytometry with DO-1, a
monoclonal antibody to the p53
protein. The study revealed p53 deletion and accumulation of p53
protein in the absence of mutation in the exons that included the hot-spots and differs from that described in B-prolymphocytic leukaemia. Seven T-PLL and five
Sezary syndrome patients had p53 overexpression, and five T-PLL and nine
Sezary syndrome patients showed p53 deletion. Although the majority of cases with p53 accumulation had p53 deletion, the proportion of cells with the deletion did not correlate with the proportion of cells positive for p53 expression. Two cases of T-PLL showed strong p53 expression in the absence of p53 deletion, and one case of
Sezary syndrome with p53 deletion in 97% of cells did not express p53. These findings suggest that a non-mutational mechanism exists for the accumulation of p53
protein in these T-cell disorders. The oncogenic effect of the accumulating wild-type
protein has been reported in other
malignancies. Whether haploidy resulting from p53 deletion contributes to this mechanism has yet to be determined. Alternatively, the frequent loss of the p53 gene could be associated with the deletion of an adjacent gene, which could be involved in the pathogenesis of these diseases.