Non-Myeloablative Allogeneic Transplantation Resulting in Clinical and Molecular Remission with Low Non-Relapse Mortality (NRM) in Patients with Advanced Stage Mycosis Fungoides (MF) and Sézary Syndrome (SS)

Introduction: The majority of patients with refractory, advanced stage MF or SS have a life expectancy less than 5 years. Currently, there is no curative therapy and none of the available therapies provides a long-term remission. We have performed allogeneic transplant in 29 patients as a prospective clinical study using a novel non-myeloablative preparative regimen to provide prolonged disease control.

Patient and Transplant Regimen: This cohort included 11 patients with MF and 18 patients with SS. The median age was 62 years (range 20-75). These patients were heavily treated with a median number of prior systemic therapies of 5 (range 2-13). The median time from diagnosis to transplant was 33 months (range 9-147). Five patients had stage IIB disease and 24 patients (83%) had stage IV disease (21 with IVA and 3 with IVB). All 11 patients with MF had evidence of large cell transformation. All patients had active disease at the time of preparative regimen (skin: 100%, blood: 62%, lymph node: 62%). The patients received total skin electron beam therapy (TSEBT, 24-36 Gy) as part of preparative regimen for skin disease control, immediately followed by total lymphoid irradiation (TLI, 8 Gy) and rabbit anti-thymocyte globulin (ATG). All patients received G-CSF mobilized peripheral blood hematopoietic cells from either an HLA-matched related (n=11), HLA-matched unrelated (n=13) or HLA-mismatched unrelated (n=5) donor. Cyclosporine or tacrolimus and mycophenolate mofetil were used for GVHD prophylaxis. The entire protocol required only a 5-day inpatient stay during the infusion of ATG.

Results: As planned, all patients received their allograft infusion as outpatient. Patients tolerated the immediate post-transplant period extremely well. Fifteen patients required hospital admission within 100 days after transplant, with a median length of hospital stay of 4 days. The most common cause for admission was delayed ATG reaction. At day +90, full donor chimerism (donor CD3+ > 95%) was achieved in 10 patients (34%) and mixed chimerism was found in 14 patients (48%). Of these 14 patients, 9 of them subsequently achieved full donor chimerism and 1 had secondary graft rejection. Five patients (17%) had primary graft rejection (donor < 5%). Three of the 6 with graft rejection received a second transplant after experiencing disease progression. The incidence of GVHD in our study was considerably lower than reported in other studies using reduced intensity regimens. The cumulative incidence of grade II-IV acute GVHD was 21%. Five patients had grade II acute GVHD (4 skin, 1 GI) and 1 had fatal grade IV acute GVHD (GI). The cumulative incidence of extensive chronic GVHD at 1 and 2 years was 13% and 23%, respectively. One death was attributed to complications of chronic GVHD.

At 3-month post transplant, 19 patients achieved a complete response and 7 had a partial response (ORR 90%). Two patients experienced disease progression immediately after transplant, and 1 patient had stable disease. The median post-transplant follow-up for the entire cohort was 22.2 months and for the surviving patients was 24.5 months. The 2-year OS and PFS were 76% (95% CI, 54–88%) and 50% (95% CI, 28–68%), respectively. Among the surviving 21 patients, 81% (n=17) were in CR at last follow-up (16 with durable CR lasting >1 year). Of the 8 deaths in this study cohort, 3 were from NRM, each due to acute GVHD, complications related to chronic GVHD, or secondary malignancy (B-cell acute lymphoblastic leukemia). The 1-year cumulative NRM was 3%. High-throughput sequencing (HTS) of TCRß CDR3 was used for minimal residual disease (MRD) monitoring (Sci. Transl. Med.5:214ra171, 2013) (ImmunoSEQ, Adaptive Biotech). Of the 24 patients assessed, 11 patients (46%) achieved molecular remission in the blood after transplant. The median time to achieve molecular remission in the blood was 60 days (range 30-540). Of these 11 patients, 10 of them also achieved molecular remission in the skin. The 2-year OS and PFS for patients who achieved molecular remission were 86% (95% CI, 34–98%) and 71% (95% CI, 26–92%), respectively.

Conclusion: We have developed an effective novel preparatory regimen with low transplant related mortality for non-myeloablative allogeneic transplant in patients with advanced stage MF and SS. Using the utmost sensitive TCRß HTS method to assess MRD, we were able to demonstrate a potentially curative therapy with molecular remission in this patient population.