Discrete subpopulations, defined by CD45 isoforms, coexist within the leukaemic cells of B-chronic lymphocytic leukaemia patients

The expression of CD45 isoforms by B-CLL leukaemic lymphocytes has been analysed by 2 colour flow cytometry and vectorial iodination. The cytometry has demonstrated the presence of cells with different CD45 phenotypes which vary in the relative expression of the CD45RA and CD45RO determinants. Discrete populations have been detected which can coexist within an individual patient. One of these populations which is CD45RO-negative consists of cells expressing only the 230 kD isoform, in the others the smaller isoforms are expressed, the appearance of the CD45RO determinant of 180 kD being accompanied by the appearance of the 190 kD isoform. The relative proportion of cell populations is stable within patients but can be altered by phorbol ester which enhances CD45RO expression and diminishes CD45RA expression. The populations may be partially resolved by the density gradient fractionation.