Allogeneic Stem Cell Transplantation for Mantle Cell Lymphoma Can Achieve Durable Remission and Myeloablative Conditioning Is Associated with Inferior Survival: An Australasian Bone Marrow Transplant Recipient Registry Study
Authors: Di Ciaccio Pietro R , Ritchie David , Kennedy Glen A , Milliken Sam , Purtill Duncan , Gottlieb David , Perera Travis , Yeung David T , Larsen Stephen R , Doocey Richard , Greenwood Matthew , Durrant Simon , Watson Anne-Marie , Butler Andrew , Khot Amit , Curley Cameron , Hamad Nada 
Published: February 2021

Introduction
Mantle cell lymphoma (MCL) is a mature B lymphoproliferative disorder with a frequently aggressive clinical course. Although the response rates in patients eligible for conventional chemoimmunotherapy are high, relapses are virtually inevitable, with a median overall survival (OS) of three to five years.
For some patients allogeneic stem haematopoietic cell transplantation (alloHCT) is a potential therapeutic option. AlloHCT for MCL has been associated with long term overall survival (OS) of around 40%, with high rates of non-relapse mortality (NRM) of 20-40% and relapse rates of 20-30% (Urbano-Ispizua et al., Biol Blood Marrow Transplant 2015;21:1746, Robinson et al., Leukemia 2015;29:464). Whilst there is evidence of a graft-versus-lymphoma effect in MCL, it has not been shown to translate into improved OS. We performed a retrospective national registry study to examine alloHCT practice and outcomes for MCL in Australia and New Zealand in the modern era.
Methods
Data was collected through the Australasian Bone Marrow Transplant Recipient Registry (ABMTRR) for patients receiving an alloHCT for MCL between January 2009 and December 2019. This time range was chosen to capture the era of widespread rituximab use. Survival, relapse and toxicities of alloHCT were investigated, as well as transplant trends over time. Survival was analysed using the Kaplan-Meier method, with comparisons between the transplant periods 2009-2014 and 2015-2019 performed using the log-rank test. Cox proportional hazards regression was performed to determine significant risk factors for transplant outcome. The following risk factors were analysed for impact on outcomes: age, transplant before 2015, previous autologous HCT (autoHCT), remission status at transplant, use of myeloablative conditioning (MAC), haploidentical donor and use of T cell depletion (TCD).
Results
A total of 86 patients were included in the analysis. The median age was 56 (range 39-71). There was a male predominance with only 12% female patients. At the time of transplant, 51% were in complete remission, 26% had a partial response and 20% had stable or progressive disease (data missing in 3%). Sixty-seven percent had undergone previous autoHCT. The majority of donors were HLA-matched siblings (51%), followed by HLA-matched-unrelated (42%) and haploidentical (7%). Myeloablative conditioning was utilised in 14%, and T-cell depletion (TCD) in 24%. The median times to neutrophil engraftment (&gt;0.5x109/L) and platelet engraftment (&gt;20x109/L) were 16 and 20 days respectively.
NRM at 1 and 5 years was 23% (95% confidence interval [95%CI] 10-39%) and 30% (95%CI 15-48%) respectively. The 100-day cumulative incidence of grade II to IV acute GVHD was 29%. The 3-year cumulative incidence of chronic GVHD was 27%.
The median duration of follow up was 4.17 years (range 0-9.6 years). Median OS was 4.2 years, with an estimated 5-year OS of 47% (95%CI 35-58%) and 10-year OS of 23% (95%CI 8-43%) (figure 1). Five-year relapse free survival (RFS) was 38% (95%CI 26-50%) (figure 2). The cumulative incidence of relapse (CIR) was 20% at 1 year and 33% at 4 years, with a flattening of the curve after this point (figure 3).
On multivariate analysis (MVA), the use of myeloablative conditioning (MAC) was associated with inferior RFS (hazard ratio 2.33; 95%CI 1.05-5.17; p=0.038) and OS (hazard ratio 3.11; 95%CI 1.39-7.00; p=0.006) (figure 4). No risk factors on MVA impacted NRM or CIR. Chronic GVHD was not associated with RFS or CIR.
An average of nine alloHCTs were performed each year. There was an increase in the proportion of haploidentical transplants between 2009-2014 and 2015-2019 (4% to 10%). There was no significant change over time in OS, RFS or NRM, or in the use of MAC or TCD.
Conclusion
There has been no significant change in the rates of alloHCT for MCL in Australia and New Zealand over the past decade. Trends show an increasing utilisation of haploidentical donors. Overall outcomes were comparable to those previously published with favourable OS and durable remissions seen in a subset of patients. MAC was associated with inferior OS and RFS, however the cause for this is unclear given the lack of association with NRM or CIR. Ongoing reporting of alloHCT outcomes in MCL is important given the emerging role of novel therapies, such as Bruton tyrosine kinase inhibitors, bispecific T cells and CAR-T cell therapy.
Figure 1

Disclosures
Di Ciaccio: Jansen: Honoraria, Other: travel and accomodation grant. Greenwood:MSD: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Servier: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Hamad:Novartis: Honoraria; Abbvie: Honoraria.