Flow cytometric immunophenotypic characteristics of plasma cell leukemia

The aim of this prospective study was to define the flow cytometric characteristics of simultaneously investigated bone marrow and peripheral blood plasma cells antigens expression in 36 plasma cell leukemia (PCL) patients. The immunophenotypic profile of plasma cells was determined with a panel of monoclonal antibodies. The antigen expression intensity was calculated as relative fluorescence intensity (RFI). Bone marrow plasma cells showed expression of particular antigens in the following proportion of cases: CD49d 100%, CD29 94%, CD54 93%, CD44 83%, CD56 60%, CD18 26%, CD11b 29%, CD11a 19%, CD117 27%, CD71 30%, CD126 100% and CD19 0%, while the expression of those antigens on peripheral blood plasma cells was present in the following percentage of patients: CD49d 100%, CD29 96%, CD54 93%, CD44 95%, CD56 56%, CD18 50%, CD11b 53%, CD11a 29%, CD117 26%, CD71 28%, CD126 100% and CD19 0%. The expression of CD54 was significantly higher than that of adhesion molecules belonging to the integrin b2 family: CD11a, CD18 and CD11b, on both bone marrow and peripheral blood cells (p < 0.01). Expression of CD18, CD11a and CD11b was differential between two cell compartments: lower on bone marrow and higher on peripheral blood cells. We found that plasma cells in the bone marrow of patients with plasma cell leukaemia showed significantly greater granularity and size than those in the peripheral blood (p = 0.0001 and p = 0.04, respectively). However, no differences in cell size or granularity were revealed between bone marrow plasma cells from patients with PCL and multiple myeloma. In conclusion, impaired expression of adhesion molecules such as CD11a/CD18 (LFA-1) or CD56 may explain hematogenic dissemination characterizing PCL. The following pattern of adhesion molecule expression according to the proportion of plasma cells expressing a given antigen in peripheral blood and bone marrow and arranged in diminishing order may be established: CD49d > CD44 > CD54 > CD29 > CD56 > CD18 > CD11b > CD11a. Immuno-phenotyping of plasma cells in PCL, as in multiple myeloma, might be useful in detecting minimal residual disease in cases with aberrant antigen expression and for selecting therapeutic agents towards specific membrane targets.