Reduced-Intensity Conditioning (RIC) with Busulfan, Fludarabine and Campath-1H Is Complicated by a High Rate of Graft Failure and Severe Viral Complications in Patients with CLL.

Recently we demonstrated that RIC with busulfan, fludarabine and ATG followed by allogeneic hematopoietic stem cell transplantation (HSCT) induced molecular remissions in patients (pts) with advanced CLL. However, this approach was hampered by severe GVHD. In an attempt to lower the rate of severe GVHD we replaced ATG by campath in a new study protocol.

Patients and Methods: 20 pts with a median age of 54 years (range, 43 to 64) and advanced CLL were included. A median of 3 prior chemotherapy regimens had been given before HSCT, including fludarabine-containing regimens in all but two pts with autoimmune hemolysis. High risk cytogenetic features (17p−, 11q−, +12) were present in 9 pts. After conditioning with busulfan (8 mg/kg), fludarabine (150 mg/m²) and campath (75 mg) on days −9 to −5 peripheral blood stem cells from matched related (n=4) or unrelated donors (n=16) were transplanted. GVHD prophylaxis consisted of CSA monotherapy. Campath levels were analysed in frozen serum samples by BioAnaLab, Oxford, UK.

Results: Two pts had no detectable campath level at the day of HSCT, while four pts had levels between 0.5 to 1.8 microgram/mL. Regeneration of neutrophils (>0.5/nl) and platelets (>20/nl) required a median of 17 (range, 14–25) and 10 (range, 0–27) days, respectively. Incomplete T-cell chimerism (<50%) was observed in 7 pts and subsequently 3 pts experienced secondary graft failure on days 134, 152 and 324. Six pts received donor lymphocyte infusions (DLI) for the conversion of incomplete T-cell chimerism (N=4) or progressive disease (N=2). Sponaneous acute GVHD II° to IV° occurred in 9/20 pts. After DLI four additional pts developed acute GVHD II° to IV°. Limited chronic GVHD occurred in 9 and extensive disease in 2 pts. In CMV seropositive pts the day 100 probability of CMV infection was 74% (95% CI, 44% to 100%). Severe encephalitis (HHV6, EBV and JC virus as suspected agents) was observed in 5 pts. Two pts recovered without sequelae, 2 pts are cognitively handicaped and one pt died. Hemorrhagic cystitis (CTC 2/3) occurred in 2 pts. After a median follow-up of 13 months (range, 6 – 26 months), 15 pts are alive. Four pts died from treatment related complications. Causes of death were pneumonia of unknown etiology (N=2), encephalitis (N=1) and GVHD grade IV (N=1). One pt died from severe acute GVHD subsequent to the treatment of relapse with DLI. One-year overall and progression-free survival was 75% (95% CI, 55% to 95%) and 50% (95% CI, 25% to 75%), respectively. The one-year probability of non-relapse mortality was 20% (95% CI, 2% to 38%). The number of binding sites for campath is highly variable in pts with progressive CLL resulting in interindividually highly variable pharmacokinetics.

Differences in the extent of in vivo T-cell depletion might therefore explain the individually varying T-cell engraftment pattern. In addition, the high incidence of severe viral infections reflects impaired immunoreconstitution. Including pts after DLI we observed a substantial rate of severe GVHD. Based on these data we decided to skip the strategy of in vivo T-cell depletion with campath in patients with CLL.