Synergy of Unrelated Donor and Full Intensity Conditioning Breaks the Control of Graft Versus Host Disease By Alemtuzumab
Authors: Laverick Olivia , Publicover Amy , Jardine Laura , Green Kile , Potter Alan , Jackson Graham H , Collin Matthew 
Published: October 2019

Abstract
Many variables influence the risk of graft versus host disease following hematopoietic stem cell transplantation. Comparison between preparative regimens is hampered by the use of many different combinations of chemotherapy and radiotherapy, varying intensity of conditioning, use of T cell depletion and donors who are either siblings or unrelated volunteers. Many reduced intensity regimens also incorporate enhanced GVHD prophylaxis with in vivo T cell depletion. Here we describe a cohort of patients prepared in a modular fashion with either reduced or full intensity conditioning combined with a uniform GVHD prophylaxis regimen for all transplants with sibling donors (alemtuzumab 30mg) and for all with unrelated donors (UD; alemtuzumab 60mg). Thus it was possible to dissect independently the effect of conditioning intensity and sibling or UD type upon GVHD risk in this settig of in vivo T cell depletion.
Patients and analysis: the study was a retrospective analysis of 258 sequential transplants performed in adults with hematological malignancy between September 2005 and September 2013 at a single UK institution. Reduced intensity conditioning (n = 221) included fludarabine 150mg/m2 plus melphalan 140mg/m2 or fludarabine 150mg/m2 plus busulfan 9.6mg/kg. Full intensity transplants (n = 37) received 12Gy TBI plus melphalan 140mg/m2, 12Gy TBI plus cyclophosphamide 120mg/kg, or busulfan 16mg/kg plus cyclophosphamide 120mg/kg. All patients with sibling donors received 30mg alemtuzumab and those with UD received a 60mg of alemtuzumab. UD matching was similar in both reduced intensity and full intensity cohorts (92.2% and 86.5% 10/10 matches, respectively) but patients receiving reduced intensity were older than those receiving full intensity conditioning (median age 51 vs 31; p < 0.001). Outcome was analyzed according to EBMT guidelines. Relapse, non-relapse mortality and cGVHD were treated as competing risks and analysed as cumulative incidence.
Outcome: the incidence of acute GVHD grades I-IV was comparable between reduced intensity and full intensity sibling transplants (45% vs 45%; p = NS) indicating a lack of effect of conditioning intensity upon GVHD risk in this setting. There was a slight increase in the risk of GVHD between reduced intensity UD compared with reduced intensity sibling donor transplants (57% vs 45%; p = NS) but a marked synergistic increase between UD transplants performed with full intensity compared with reduced intensity conditioning (100% vs 57%; p = < 0.001). The incidence of grades III-IV acute GVHD was also higher in full intensity UD transplants (16%) compared with reduced intensity UD transplants (5%). The incidence of chronic GVHD was also highest in full intensity UD transplants but both conditioning intensity and UD contributed in an additive manner: the rate of chronic GVHD progressed from 33% to 44% in reduced intensity and full intensity sibling transplants respectively and from 57% to 75% for reduced and full intensity UD transplants, respectively. Two year overall survival was comparable in all groups, ranging from 55% to 70%. In keeping with the higher rates of acute GVHD in full intensity transplants performed with UD, this group experienced the lowest relapse risk (15% vs 29% for all the other groups combined; p = 0.04) but the highest non-relapse mortality, reaching 41% at 2 years compared with 28% for all the other groups combined (p = 0.08).
Conclusion: these results show that alemtuzumab provides good protection from acute GVHD in reduced intensity transplantation from sibling and UD. In sibling transplants given identical GVHD prophylaxis, full intensity conditioning does not increase the risk of GVHD. In contrast, a slight increase in GVHD risk with UD transplants seen with reduced intensity conditioning, is amplified in a synergistic manner by full intensity conditioning. This is associated with a high non-relapse mortality, even though the median age of full intensity patients is more than 20 years younger than those receiving reduced intensity conditioning.

Disclosures
No relevant conflicts of interest to declare.