Prognostic Significance of Molecular Remission Determined by Highly Specific PCR after Dose-Reduced Allogeneic Stem Cell Transplantation (SCT) in Patients with Multiple Myeloma.

Achieving molecular remission after standard allogeneic stem cell transplantation in multiple myeloma is associated with long term freedom of disease and possible cure. We recently reported a high rate of complete remission after an auto-allo tandem approach using fludarabine (150 mg/m²), melphalan (140 mg/m²) and anti-thymocyte globulin (ATG: 3 x 10–20mg/kg) three months after a cytoreductive autograft (melphalan 200 mg/m²). To determine the incidence of molecular remission we tried to develop allele-specific oligonucleotides (ASO) based upon the clonal rearrangement of immunoglobulin heavy chain genes and ASO - polymerase chain reaction (ASO-PCR) for each patient who achieved complete remission with negative immunofixation after SCT (n=27). The specificity of the ASO-PCR was tested using patient and control DNA. Patient DNA isolated from bone marrow (BM) samples obtained at diagnosis and after allografting at variable time points was used for further molecular analysis. For nine patients we were able to generate specific primers and MRD diagnostics have been performed for a median of two years after SCT. Molecular remission was strictly defined by the absence of any PCR-positivity. In 6 patients nested PCR remained negative after a median follow up of 22 months (range 10–24). Only one of these patients relapsed with extramedullary disease (14 months) still being PCR-negative in his bone marrow. In contrast, all those patients with complete remission but positive PCR (n=3) relapsed (at 11, 14 and 16 months after SCT, respectively) thus underlining the importance of achieving molecular remission after allo-SCT. We suppose that quantitative real-time PCR might be a useful tool to closely monitor MRD kinetics post allo-transplantation in order to verify efficiency of various treatment regimens, e.g. donor lymphocyte infusions.