Molecular Monitoring of Residual Disease in Patients with Mantle Cell Lymphoma and CLL after Allogeneic Bone Marrow Transplantation Post Reduced Intensity Conditioning.
Authors: Schüler Frank , Hirt Carsten , Kiefer Thomas , Dolken Gottfried 
Published: April 2020

Abstract
To control circulating lymphoma cells after allogeneic transplantation in order to induce or manipulate graft-versus-lymphoma (GvL) reactivity in case of relapse, molecular monitoring of circulating lymphoma cells was carried out by quantitative real-time PCR for clone-specific IgH(CDR3) sequences on six patients (CLL n=3; mantle cell lymphoma (MCL) n=2; variant hairy cell leukaemia (vHCL) n=1). All patients were considered as high risk for recurrence or relapse because of age, refractory disease, failure after autografting or poor performance status. They had at least one or more high-risk features that precluded the application of a standard myeloablative conditioning regimen. Therefore, they were treated with allogeneic blood stem cell transplantation (BSCT) from unrelated donors after toxicity-reduced conditioning with treosulfan and fludarabine. Molecular relapse was defined as an increase of circulating lymphoma cells by more than three orders of magnitude in the absence of symptoms or signs of clinical relapse.
In the three patients with CLL and one MCL patient leukemic cells disappeared from peripheral blood and bone marrow within the first six months after transplant as demonstrated by quantitative PCR. Only short periods of acute GvHD were observed and successfully treated. In 2/6 patients (one with vHCL and one with MCL) a molecular relapse was detected one month (MCL) and 6 months (vHCL) after transplant. A 3-log increase of circulating lymphoma cells was observed within about 20 days (MCL) and 3 months (vHCL) starting from &lt;1 lymphoma cell/500,000 cells to about 1,000 lymphoma cells/100,000 cells. Rapid reduction and withdrawal of immunosuppressive therapy combined with the infusion of the monoclonal antibody rituximab led to the disappearance of circulating lymphoma cells in both patients. It has to be emphasized that in both patients with documented molecular relapse rituximab alone or in combination with chemotherapy has not led to a stable CR or molecular remission before allogeneic BSCT. The disappearance of recurrent lymphoma cells in both patients correlated well with the development of acute GvHD. This fact demonstrates the curing potency of GvL. Serial molecular monitoring at short-term intervals provided the additional important information that further therapeutic interventions, c.f. infusion of donor lymphocytes, were not necessary. All patients monitored are still in continuous complete clinical and molecular remission for almost three years.
Clinical relapse of malignant B cell lymphoma after allogeneic BSCT can be successfully treated by immune therapeutic intervention, e.g. reduction and rapid withdrawal of immunosuppression and infusions of peripheral blood lymphocytes from the original blood stem cell donor by establishing graft versus lymphoma (GvL) reactions. In addition, B-cell specific monoclonal antibodies seem to be very helpful for treating relapses. These therapeutic interventions may be even more effective when introduced before clinical relapse, possibly already at molecular relapse detected by quantitative real time PCR. Therefore, molecular monitoring by quantitative real-time PCR carried out at ≤ 3 months intervals may further improve transplant results and the long-term outcome of patients treated within clinical studies.