Low Dose Alemtuzumab (Campath 1H) Prior to Allogeneic Stem Cell Transplantation Is Associated with Low Incidence of Acute and Chronic GVHD but Protracted Immune Recovery.

Background: The administration of alemtuzumab (Campath 1H) as part of the conditioning regimen prior to allogeneic stem cell transplantation has been associated with a low incidence of acute and chronic GVHD. Initial studies employing doses of 100 mg have reported a high incidence of viral infections. Lower alemtuzumab doses combined with standard GVHD prophylaxis regimens (calcineurin inhibitor + MTX) have also resulted in a low incidence of acute GVHD in patients with CD52-positive malignancies. We investigated the effect of low-dose (40 mg) alemtuzumab on engraftment (VNTR chimerism studies), the incidence of acute and chronic GVHD, CMV reactivation, survival, and immune reconstitution (examined by TREC content at various time points after transplant).

Patient and Transplant characteristics: Twenty-seven patients underwent a matched (n=24) or 1-antigen mismatched (n=3) related (n=13) or unrelated (n=14) allogeneic stem cell transplantation for various hematologic malignancies. Median age was 41 years (19–59). Disease stage at transplant was early for 48%, intermediate for 11% and late for 41%. Three patients received bone marrow and 24 received PBSC grafts. Conditioning regimen consisted of TBI 10 Gy with partial lung shielding, Thiotepa 500 mg/m², and Alemtuzumab 20 mg IV on day -4 and day -1. GVHD prophylaxis was with cyclosporine (n=13) or tacrolimus (n=14) and full-dose MTX. High-dose viral prophylaxis with valacyclovir 2000 mg QID was given to all recipients from a CMV seropositive recipient/donor pair starting at patient #9, due to a high incidence of CMV reactivation amongst the first 8 patients. Three patients received DLI for disease relapse. Median follow-up for survivors is 13 months (6–26).

Results: Of eighteen evaluable patients (3 relapsed, 5 expired, 1 not done) at day 100, 15 had ≥ 95% donor chimerism, and 3 had 90–94% donor chimerism. The cumulative incidence of acute GVHD grade II-IV at day 100 was 4% (95% CI 1–16%), and the cumulative incidence of chronic GVHD at 1 year was 31% (12–52%). Cumulative incidence of non-relapse mortality at day 100 was 18% (7–35%), and at 1 year 31% (14–49%). Cumulative incidence of relapse at 1 year was 28%, resulting in a projected 1-year disease-free survival of 41% (22–60%), and overall survival of 54% (33–71%). Amongst the first eight patients, all (5/5) at-risk recipients developed CMV reactivation. After initiation of prophylaxis with high-dose valacyclovir, 4/11 at-risk recipients developed CMV reactivation. No patient died from CMV disease. TREC analysis in a limited number of patients showed rapid increase in TREC between day 0 and day 180, but no further increment between day 180 and day 365.

Conclusions: The use of low-dose alemtuzumab results in low incidences of acute and chronic GVHD. CMV reactivation is common, and can be partially prevented by use of high-dose valacyclovir. Immune reconstitution data on a small subset of patients show limited output of thymic emigrant T cells after 6 months.