T Cell Depletion with Alemtuzumab Is Associated with a High Incidence of EBV Viraemia but Low Risk of PTLD Following Allogeneic Stem Cell Transplantation

Re-activation of latent EBV infection is a significant risk following T-cell depleted (TCD) allogeneic HSCT. The clinical course can range from asymptomatic viraemia to the development of post-transplantation lymphoproliferative disease (PTLD) and death. Since alemtuzumab depletes both T and B cells, it has been proposed that the risk of PTLD will be reduced compared to other TCD protocols. In an attempt to determine the risk of EBV viraemia or PTLD following allogeneic HSCT employing alemtuzumab-containing conditioning protocols, we reviewed outcomes in 91 consecutive adult patients treated at our institution. Of these, 84 patients had >6 months follow-up and are included in this analysis. Two strategies of TCD were employed in this cohort:

1. in vivo TCD with alemtuzumab (median dose 100mg) as part of a reduced intensity regimen (fludarabine based n=51); and

2. in vitro TCD of the PBSC graft with 20 mg alemtuzumab ‘in the bag’ following conventional myeloablative conditioning (n=33).

We have shown previously that alemtuzumab antibody levels persist for longer periods (up to 8 weeks ) following this in vivo depletion strategy compared to the in vitro approach [Morris et al. Blood 2003 102:404–6]. The median follow-up is 337 days and median age was 43 years (range 16–67 years). Diagnoses were AML/MDS (n=39), NHL (n=16), Hodgkins lymphoma (n=11), MPD (n=7), CLL (n=5) and other (n=6). 41/84 had HLA-identical sibling donors, 2 mismatched sibling donors, 21 matched unrelated donors and 20 mismatched unrelated donors. Monitoring for EBV load was performed by TaqMan whole blood real time PCR on a weekly basis for 100 days post transplantation and then as seen for follow-up. Positive results defined as >200 copies/ml of EBV DNA. All patients with high levels of EBV viraemia (EBV DNA level > 40,000 copies/ml) underwent CT imaging, bone marrow examination and lumbar puncture followed by withdrawal of immunosuppression and a single infusion of 375mg/m² Rituximab as per institution policy. Of 82 patients where serostatus was available, 92.7 % were anti-EBV IgG positive. The 12-month cumulative incidence (CI) of EBV reactivation was 34.5% (39.2% following in vivo TCD versus 27.3% following in vitro TCD, p=0.2). Median peak viral load was 1,922 copies/ml (range 205–6,210,000). The 12 month CI of high-level EBV viraemia (>40,000 copies/ml) was 11.9% (7.84% following in vivo TCD versus 18.2% following in vitro TCD, p=0.19). Patients re-activated EBV at a median of 86 days post transplant (range 21–380 days). The median duration of viraemia was 42 days (range 1–460 days). The 12-month CI of recurrent EBV re-activation (>1 episode) was 21.4% (15.5% following in vivo TCD versus 25.5% following in vitro TCD, p=0.4). Of 10 patients with high-level EBV viraemia, 1 patient had PTLD as confirmed by histology. 8 of 10 patients received a single dose of Rituximab and this was associated with a rapid decline in EBV DNA load to undetectable levels in all cases. No adverse events secondary to Rituximab were noted. The patient with PTLD was given a second dose of Rituximab and attained a CR that persists at 334 days post treatment. 12-month non-relapse mortality was 10% in patients who had EBV reactivation and 27.7% in patients without EBV reactivation (p=0.06). Baseline and post-transplantation characteristics of sex, age, diagnosis, in vivo vs. in vitro alemtuzumab, donor type, CMV viraemia and presence of past or active acute GVHD were not related to re-activation of EBV by uni- or multivariate analysis in this patient cohort. In summary, this report demonstrates that TCD using alemtuzumab-containing conditioning protocols is associated with a high frequency of EBV viraemia but low risk of PTLD or non-relapse death in a cohort of patients treated pre-emptively with Rituximab for high EBV DNA loads.