Comparative analysis of melphalan <i>versus</i> busulphan T‐cell deplete conditioning using alemtuzumab in unrelated donor stem cell transplantation for acute myeloid leukaemia

For most patients with intermediate or high-risk acute myeloid leukaemia (AML), allogeneic stem cell transplantation (allo-HSCT) offers the best chance of cure (Döhner et al, 2017). Reduced intensity conditioning (RIC) protocols, with greater emphasis on a graft-versus-leukaemia effect, allow allo-HSCT in older patients and those with co-morbidities (Sengsayadeth et al, 2015). The morbidity and mortality associated with acute and chronic graft-versus-host disease (aGVHD, cGVHD, respectively) has been reduced by in vivo T-cell depletion (TCD) (Soiffer et al, 2011; Walker et al, 2016) but there is limited evidence for optimal allo-HSCT protocols in AML (Bacigalupo et al, 2009; Jethava et al, 2017). We conducted a multi-centre retrospective analysis of two reduced toxicity alemtuzumab-based T-cell deplete protocols in common use in the United Kingdom for unrelated donor allo-HSCT in patients with AML: fludarabine-melphalan (FMC) and fludarabine-busulfan (FBC). We identified 117 patients from University College London Hospital (UCLH) (employing FMC), Royal Free London Hospital (RFH)(employing FMC) and Kings College Hospital, London (KCH) (employing FBC) receiving matched unrelated TCD-HSCT for AML in complete remission (CR) [defined as per (Cheson et al, 2003)] between January 2005 and December 2014. Patient demographic data are shown in Table 1. Chimerism, GvHD and graft failure were assessed using published and/or standard methods with further details of transplant conditioning regimens, immunosuppression and statistical methods provided in Data S1. The primary endpoint was overall survival (OS), measured from day 0 to death from any cause. Secondary endpoints included cumulative incidence of relapse (CIR); relapse-free survival (RFS), measured from day 0 to first relapse or death; non-relapse mortality (NRM) measured from day 0 to death without relapse. The overall median age of the whole cohort (n = 117) was 55 years (range 19–68). The 5-year OS for the whole cohort was 48% (Fig 1A) with no significant difference between FMC (n = 70; 5-year OS 46%) and FBC n = 47; 5-year OS 52%, P = 0·2) (Fig 1B). Patients receiving FBC were younger (P = 0·04), more likely to have a fully matched (10/10) donor (P = 0·03) and received a lower dose of alemtuzumab (P < 0·001). No other significant differences between the two groups were observed. Median follow-up for patients alive at the end of the study was 37 months (range 11·2–97·5) for FMC (n = 27) and 42 months (range 4·6–106) with FBC (n = 33) regimen (P = 0·40). Patients aged ≥60 years had a poorer 5-year OS of 38% vs. 55% (<60 years) (P = 0·03; Fig 1C). Patients with a mismatched unrelated donor (MMUD) had inferior 5-year OS of 29% compared with 60% with 10/10 human leucocyte antigen (HLA)-matched unrelated donor (MUD) (P = 0·009; Fig 1D), with both these variables retained significance on adjusted Cox regression (Table SI). Patients <60 years age who underwent 10/10 HLA-matched MUD HSCT had an excellent 5-year OS of 73%, with no difference noted between the two regimens (P = 0·14). There was no significant difference in OS/RFS for other variables measured including cytogenetic risk group and FLT3-internal tandem duplication (ITD) (Fig 1E,F, Table SII). Overall NRM at 1 and 5 years was 20% and 25% respectively and not different between the two regimens (Fig 1G). Five-year NRM was higher for older patients (42% vs. 15%; P = 0·001; Fig 1H), in those with extensive versus limited cGVHD (43% vs. 5%, P = 0·0006; Fig 1I) and those using MMUD vs. 10/10 MUD (36% vs. 18% respectively; P = 0·03; Table SII). The 5-year RFS was 45% across the whole cohort with similar results between the 2 regimens (P = 0·68; Fig 1J). CIR was 16% and 30% at 1 and 5 years respectively, with no significant difference observed between the two regimens (Fig 1K). Five-year CIR was increased in male recipients (38% male vs. 18% female; P = 0·02) and patients with normal karyotype FLT3-ITD mutated (FLT3ITD) versus wild type (FLT3WT) (52% vs. 25% respectively; P = 0·02). CIR was reduced in patients with cGVHD (all grades) (P = 0·02), most notably with extensive cGHVD (P = 0·006; Fig 1L, Table SI) but this did not translate into differences in OS (P = 0·39). The FMC cohort was more likely to develop grade 1 acute and limited cGVHD events compared to the FBC cohort (P < 0·001); while the incidence of grade 3-4 aGVHD and extensive cGVHD was similar in both cohorts (Table SIII). Interestingly, CIR was significantly lower in patients with a more strictly defined full donor T-cell chimerism (>97% CD3 FDC) (P = 0·03) but no such differences were observed using standard FDC (>95%) definition versus other chimerism groups (Table SIV). At the completion of the study, 33 patients had relapsed (FMC = 17, FBC = 16). Median survival following disease relapse was longer in the FBC versus FMC group (240 days vs. 52 days; P = 0·0002) corresponding to a 2-year post-relapse OS of 10% vs. 0%, probably related to the differences in intensity of post-relapse salvage treatment rather than conditioning protocol itself. Details of the treatments and response at relapse are provided in Data S1. Ten patients received pre-emptive donor lymphocyte infusion (DLI) for mixed T-cell chimerism (50–95% donor) or very mixed (>50% recipient) chimerism in the absence of relapse (FMC, n = 8; FBC, n = 2), with 2 of them achieving >95% donor chimerism. All five patients with very mixed chimerism converted to predominantly donor chimerism. Nine of 10 patients receiving DLI remained alive and in remission at the end of the study, with only one patient developing cGVHD (skin and ophthalmic), and one dying of relapse. This retrospective study presents long-term outcomes for UK patients treated with two different T-cell depleting allo-HSCT protocols for AML in CR and demonstrates equivalent outcomes following treatment with FMC or FBC protocols. The OS rates observed in our study compare favourably to other published RIC and myeloablative protocols (Shimoni et al, 2006; Luger et al, 2012). Outcomes were particularly good for patients aged <60 years and those with a 10/10 HLA-matched donor due to a lower NRM, with no differences observed between the two regimens (P = 0·14). Of note, this patient population is different to the retrospective registry-based European Society for Blood and Marrow Transplantation study comparing fludarabine-busulfan (FB) versus fludarabine-melphalan (FM), in which patients who had received T-cell depleting agents were excluded from that analysis (Baron et al, 2015). While limitations of this analysis include the retrospective nature of the study, the differing approaches to chimerism monitoring and DLI; we believe that the observation of equivalent outcomes for both regimens is valid. The most relevant prognostic factors appear to be advanced patient age and degree of donor mismatch. Strategies to improve outcomes in these cohorts require a focus on decreasing NRM in the older age-group, donor selection and relapse prevention. Dr Rob S. Sellar conceived and designed the study, performed the research, analysed the data, wrote the manuscript, approved the final version and agreed to be accountable for all aspects of the work. This author can confirm that he has had full access to the data in the study and final responsibility for decision to submit for publication. Dr Varun Mehra performed the research, analysed the data, wrote the manuscript, approved the final version and agreed to be accountable for all aspects of the work. This author can also confirm that he has had full access to the data in the study and final responsibility for decision to submit for publication. Dr Thomas A. Fox contributed to data collection, approved the final version and agreed to be accountable for all aspects of the work. Dr Andrew Griggs contributed to design of the study, interpreting the results, revised the manuscript, approved the final version and agreed to be accountable for all aspects of the work. Dr Austin Kulasekararaj contributed to interpreting results, revising the manuscript, approving the final version and agreed to be accountable for all aspects of the work. Dr Anita Sarma contributed to data collection, interpreting results, revising the manuscript, approving the final version and agreed to be accountable for all aspects of the work. Dr Hugues de Lavallade contributed to revising the manuscript, approving the final version and agreed to be accountable for all aspects of the work. Dr Donal McLornan contributed to interpreting results, revising the manuscript, approving the final version and agreed to be accountable for all aspects of the work. Dr Kavita Raj contributed to revising the manuscript, approving the final version and agreed to be accountable for all aspects of the work. Prof Ghulam J Mufti contributed to clinical interpretation, revising the manuscript, approving the final version and agreed to be accountable for all aspects of the work. Prof Antonio Pagliuca contributed to clinical interpretation, revising the manuscript, approving the final version and agreed to be accountable for all aspects of the work. Prof Stephen Mackinnon provided clinical data, approving the final version and agreed to be accountable for all aspects of the work. Prof Ronjon Chakraverty provided clinical data, approved the final version and agreed to be accountable for all aspects of the work. Prof Adele K. Fielding provided clinical data, contributed to revising the manuscript, approved the final version and agreed to be accountable for all aspects of the work. Dr Ben Carpenter provided clinical data, contributed to revising the manuscript, approved the final version and agreed to be accountable for all aspects of the work. Dr Panagiotis D. Kottaridis contributed to revising the manuscript, approved the final version and agreed to be accountable for all aspects of the work. Prof Asim Khwaja contributed to interpreting results, revising the manuscript, approved the final version and agreed to be accountable for all aspects of the work. Dr Karl S. Peggs contributed to interpreting results, revising the manuscript, approved the final version and agreed to be accountable for all aspects of the work. Dr Kirsty J. Thomson reviewed clinical data, contributed to revising the manuscript, approved the final version and agreed to be accountable for all aspects of the work. Prof Emma C. Morris conceived and designed the study, reviewed clinical data, contributed to interpreting results, revising the manuscript, approved the final version, agreed to be accountable for all aspects of the work and has final responsibility for decision to submit for publication. Dr Victoria T. Potter conceived and designed the project, contributed to writing and revising the manuscript, approved the final version, agreed to be accountable for all aspects of the work and has final responsibility for decision to submit for publication. The authors declare no competing financial interests for this work. Fig S1. Schematic representation of FBC and FMC conditioning regimens. Table SI. Multivariate analysis of Overall Survival (OS), relapse frees survival (RFS), cumulative incidence of relapse (CIR) and non-relapse mortality (NRM). Table SII. Results of univariate analysis for overall survival (OS) and relapse free survival (RFS) (Cox Method). Table SIII. Comparison of GVHD events, Graft failure and Peripheral blood donor T-cell chimerism between FMC and FBC regimen. Table SIV. Univariate analysis for NRM and CIR (Gray Method). Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.