Multiple myeloma: plasma cell immunophenotype and monitoring of minimal residual disease after induction therapy and autologous hematopoietic stem cell transplantation

Background. Minimal residual disease (MRD) is the presence of a tumor clone in the bone marrow that can prevent remission during treatment. The immunophenotype of MM cells may be different, so it is necessary to understand the spectrum of markers that allow differentiating abnormal plasma cells (PCs). Monitoring MRD can influence the choice of patient management tactics.

Aim. Analysis of the immunophenotype of myeloma cells and assessment of the frequency of MRD during treatment.

Materials and methods. The study included 56 MM patients, the average age was 55 years. Induction chemotherapy was carried out according to the VRD scheme (including lenalidomide, bortezomib, and dexamethasone), autologous hematopoietic stem cell transplantation (auto-HSCT). The MOB status was assessed by multicolored flow cytometry using a Becton Dickinson FACSCanto II cytofluorimeter (Becton Diskinson, USA), Kaluza Analysis v. 2.1 (Beckman Coulter, Inc., USA). Monoclonal antibodies of clusters of differentiation (CD) were used: CD45, CD19, CD27, CD56, CD28, CD38, CD117, CD19, CD81, immunoglobulin light chains κ / λ, nuclear dye 7-aminoactinomycin D (Becton Diskinson, USA).

Results. The most common MM immunophenotype was aberrant in the absence of CD19 and CD27, reduced expression of CD38, and abnormal presence of CD56 was noted. There is aberrancy in CD27 / CD117 / CD81. Most often, the immunophenotype of PCs corresponded to CD19^–CD45^–CD56⁺, noted in 46.4 % of cases. The frequency of MRD negativity after induction therapy is 35.7 %, after auto-HSCT – 56.7 %. A 1.3-fold decrease in the number of PCs in the bone marrow after auto-HSCT was established. Conversion after auto-HSCT of MRD positive cases (before transplantation of PCs more than 0.01 %, but less than 0.1 %) was detected in 53 % of patients.

Conclusion. The MRD status in MM is assessed based on the aberrant expression of the main and additional plasma cell markers. At the stage of induction therapy and after auto-HSCT, the MRD status differs and there is a conversion of MRD-positive cases to negative ones. Monitoring MRD can be useful for choosing the tactics of managing patients with MM.