Post-Transplant Immune Suppressive Therapy Is Not Necessary In Related and Unrelated Reduced Intensity Conditioning Stem Cell Transplantation Using Low Dose Alemtuzumab In Vivo T Cell Depletion Combined with Alemtuzumab-Mediated In Vitro T Cell Depletion of the Graft
Authors: Von Dem Borne P.A. , Halkes C.J.M. , Starrenburg C.W.J. , Marijt W.A.F. , Falkenburg J.H.F. 
Published: October 2019

Abstract
Abstract 2328

Introduction
T cell depletion with alemtuzumab administered in vivo to the patient reduces the risk of graft-versus-host disease (GVHD) and graft rejection following reduced intensity conditioning allogeneic stem cell transplantation (RIC SCT). However, high doses of alemtuzumab can result in delayed immune reconstitution, increased non relapse mortality (NRM) due to infections, and potential loss of graft versus tumor responses. Recently, the feasibility of T cell depletion with low dose in vivo alemtuzumab was demonstrated in HLA-identical related RIC SCT. Dose reduction of alemtuzumab to 30 mg combined with post-transplant immune suppressive therapy with cyclosporine tapered from 3 months after transplantation resulted in a low risk of GVHD, no increase in NRM and improved lymphocyte recovery (Chakraverty et al, Blood pre-published online June 29, 2010). Early immunotherapeutic intervention after SCT with donor lymphocytes may be hampered by the administration of post-transplant immune suppressive therapy. We investigated whether in RIC SCT using low dose in vivo alemtuzumab, post-transplant immune suppressive therapy can be replaced by alemtuzumab-mediated in vitro T cell depletion of the graft just prior to infusion (“Campath in the bag”).

Patient and donor characteristics
Between 2007 and 2009, 29 patients were transplanted with an unrelated donor, and 28 patients with a related donor using a RIC regimen consisting of fludarabine (50 mg/m2 p.o. day -10 to -5), busulphan (3.2 mg/kg i.v. day -6 and -5) and alemtuzumab (15 mg i.v. day -4 and -3), followed by infusion of the graft after in vitro incubation with 20 mg alemtuzumab. No additional immune suppressive therapy was used after SCT. Unrelated donors were matched for HLA-A, B, C, DR and DQ, three patient donor combinations had one HLA-DQ mismatch. Median patient age was 59 years (range 21–72). Remission status at the time of transplant was: 47% CR, 37% PR, 9% SD, 7% PD. Indications were diverse (19 AML, 16 myeloma, 6 CLL, 5 low grade NHL, 3 aggressive T-NHL, 2 aggressive B-NHL, 2 SAA, 1 CML, 1 myelofibrosis, 1 CMML, 1 ALL). The unrelated and related transplanted group were comparable regarding age, disease and remission status. The median Gratwohl transplantation risk score was 3 in the related group (range 1–5), and 5 in the unrelated group (range 3–6).

Results
All patients engrafted; platelet numbers of 50 × 109/L were reached after a median of 11 days (range 0–38 days), neutrophil numbers of 0.5 × 109/L were reached after a median of 18 days (range 0–161 days) post transplant. Two patients had secondary graft failure. In patients transplanted with a related donor, grade 1–2 and 3–4 acute GVHD was observed in 36% and 4% of evaluable patients, respectively, resolving in all patients without development of chronic GVHD. NRM was 0% at 3 months and 4% at 1 year. Overall survival was 100% at 3 months and 89% at 1 year. In patients transplanted with an unrelated donor more acute GVHD was observed (59% grade 1–2, 15% grade 3–4 of evaluable patients). 24% of evaluable patients developed chronic GVHD, which was limited in 75% and extensive in 25% of these patients. Chronic GVHD resolved in most patients, one patient has ongoing extensive chronic GVHD. NRM was 7% at 3 months and 24% at 1 year. Overall survival was 93% at 3 months and 55% at 1 year.

Conclusions
RIC SCT using low dose alemtuzumab in vivo T cell depletion combined with alemtuzumab-mediated in vitro T cell depletion of the graft without additional post-transplant immune suppressive therapy is feasible in patients transplanted with related and unrelated donors. Results are excellent in patients transplanted with related donors with low NRM and high overall survival. Although results are good in patients transplanted with unrelated donors considering the high Gratwohl score in this group, further improvement is being sought by increasing the efficiency of T cell depletion. This RIC SCT regimen without post-transplant immune suppressive therapy is an appropriate platform for early cellular immunotherapeutic interventions including donor lymphocyte infusion after SCT.

Disclosures:
No relevant conflicts of interest to declare.