Objective: Primary systemic AL amyloidosis arises from immunoglobulin light chains produced by plasma cell dyscrasia. To prospectively investigate the production of M-protein and plasma cells in bone marrow before and after chemotherapy, we performed flow cytometry and analysis of serum free light chains (FLCs).
Patients and methods: Fifty-nine patients with primary systemic AL amyloidosis (mean age, 59.9+/-8.8 years) were enrolled in this study, and of these 31 were serially studied before and after chemotherapy. Complete hematological remission was defined as normalization of the FLC kappa/lambda ratio.
Results: MPC-1(-)CD45(-) (p<0.05) and MPC-1(+)CD45(-)CD49e(-) (p<0.005) were significantly higher, and MPC-1(-)-CD45(+) (p<0.05), MPC-1(+)CD45(+)CD49e(-) (p<0.0001) and MPC-1(+)CD45(+)CD49e(+) (p<0.0005) were significantly lower in the patients with AL amyloidosis than in controls. There was a significantly positive correlation between the serum predominant FLC/serum creatinine ratio and MPC-1(+)CD45(-)CD49e(-) (p<0.05). After chemotherapies, such as high-dose melphalan with autologous stem cell support, 20 of 31 patients with AL amyloidosis achieved complete hematological remission. There were no significant differences in any subtype of plasma cells before treatment between the remission and non-remission groups, but in the former group MPC-1(+)CD45(-)CD49e(-) and MPC-1(-)CD45(+) were significantly decreased and increased after chemotherapy compared with before, respectively.
Conclusion: Abnormal plasma cells in the bone marrow, particularly the MPC-1(+)CD45(-)CD49e(-) subset, may be important as a follow-up marker before and after chemotherapy in primary systemic AL amyloidosis. These cells maintain low levels as long as no relapse occurs.