A Retrospective Study of Alemtuzumab Level, T Cell Chimerism and Graft Versus Host Disease Using Intermediate Dose Alemtuzumab for Matched Related and Matched Unrelated Reduced Intensity Transplantation.
Authors: Charlton Andrew , Spence Laura , Bigley Venetia , Groves Natasha , Hale Geoff , Pagan Sarah , Turner Brie E , Jones Gail , Jackson Graham H , Dickinson Anne M , Collin Matthew 
Published: October 2019

Abstract
Abstract 3333
Poster Board III-221
Alemtuzumab (CAMPATH 1H) is a well established agent for effecting in vivo T cell depletion and prevention of GVHD in reduced intensity transplants. Many studies indicate that full dose alemtuzumab (100mg in 5 daily doses of 20mg) induces profound immunodeficiency, almost completely ablating GVHD in Fludarabine and Melphalan (FM) matched related donor (MRD) and matched unrelated donor (MUD) transplants. In contrast, FM conditioning alone exposes patients to a high burden of acute and chronic GVHD. Accordingly, many transplant centres have adopted policies of intermediate alemtuzumab dosing of 50mg or less. While the pharmacokinetics, rate of T cell engraftment and incidence of GVHD are well described using full dose alemtuzumab, much less is known about the in vivo action of alemtuzumab at intermediate doses.

Methods
We report our experience of alemtuzumab at 30mg (day -2) for MRD and 60mg (30mg day -4 and day -2) for MUD transplants, which was adopted as standard GVHD prophylaxis for FM transplantation at our centre in 2006. We avoided giving alemtuzumab on day -1, since there is a steep drop in alemtuzumab level in the first 24 hours after infusion and the timing of stem cell infusion may vary considerably, especially with unrelated donor grafts. From May 2006 to May 2009, 24 patients received MRD and 27 patients received MUD transplants. Post transplant serum samples were available from 19 MRD transplants and 15 MUD transplants at day +1. In addition, day +3 samples were identified from 10 patients previously transplanted with 100mg alemtuzumab, 10 MUD receiving 60mg and 10 MRD transplants receiving 30mg. All patients gave consent for clinical follow up and post transplant serum sampling for research purposes, according to protocols approved by the local research ethics committee of Northumberland and North Tyneside. Alemtuzumab concentration was measured by a validated flow cytometry assay, as previously described.

Results
The mean (SEM) alemtuzumab concentration (micrograms/ml) on day +1 was 2.9 (0.3) after 30mg and 4.6 (0.6) after 60mg (t test p<0.01). On day +3 the levels were 2.4 (0.2); 4.0 (0.6); 8.4 (1.9) after 30mg, 60mg and historical controls of 100mg, respectively (p<0.05 between each dosing level). There were significant inverse correlations between patient surface area and alemtuzumab concentration by linear regression for both 30mg (r2 0.51 p<0.01) and 60mg dosing (r2 0.18 p<0.05). A trend for lower alemtuzumab with increasing cell dose was also observed, although this may be related indirectly to patient weight. All patients achieved >95% myeloid engraftment by day 100. Median (range) T cell engraftment was variable and significantly higher after MUD transplants: 70% (9-99%) than MRD transplants: 21% (5-85%; Mann Witney p <0.05). T cell chimerism was inversely correlated with alemtuzumab level in MRD transplants by linear regression (r2 0.37; p <0.05) but this trend was not apparent in MUD transplants. The incidence of acute GVHD was also greater after MUD transplantation at 47% (grade I or II) compared with 11% (grade I only) for MRD recipients. There was no significant relationship between GVHD grade and alemtuzumab level in either group. There were 2/24 non-relapse deaths after MRD and 3/27 following MUD transplantation; none were due to GVHD. The incidence of chronic GVHD is currently being evaluated.

Conclusion
This analysis demonstrates predictable dose and surface-area relationships with alemtuzumab level in patients receiving FM conditioning. It also reveals that significantly less than 100mg alemtuzumab confers reliable GVHD prophylaxis in both MRD and MUD recipients, although at least twice the level of alemtuzumab is required to achieve comparable GVHD control in MUD transplants. Finally, it is notable that T cell chimerism at day 100 is directly related to alemtuzumab level at day +1 in MRD transplants. We conclude that optimisation of immune reconstitution and GVHD control using alemtuzumab in vivo depends upon due consideration of both recipient and donor factors, notably the size of the recipient and the origin of the graft.

Disclosures
Groves: BioAnaLab: Employment. Hale:BioAnaLab: Employment, Equity Ownership.