Comparison between Anti-Thymocyte Globulin and Alemtuzumab and the Possible Impact of KIR-Ligand Mismatch in Melphalan/Fludarabine Dose-Reduced Conditioning Followed by HLA-Matched and Mismatched Unrelated Stem Cell Transplantation in Patients with Multiple Myeloma.

We compared anti-thymocyte globulin (ATG-Fresenius median dose 60 mg/kg: n= 48) with alemtuzumab (Campath-1H 100mg: n=25) in 73 patients with multiple myeloma, who underwent dose-reduced conditioning with melphalan and fludarabine, followed by allogeneic stem cell transplantation from matched (n=63) or mismatched (n=10) unrelated donors. Patients of the ATG group had higher age (median 50 vs 47 years, p=0.05), more prior high-dose chemotherapies (p<0.001), while in the Campath group more bone marrow as stem cell source was used (p<0.001). No primary graft failure occurred in both groups. Patients receiving alemtuzumab had a significant faster engraftment of leukocyte (p=0.03) and of platelets (p=0.02) and a lower incidence of acute GvHD grade II-IV (24 vs 47%, p=0.05). However, after treatment with donor lymphocyte infusion due to persistent disease or mixed hematopoietic chimerism the difference of acute GvHD grade II-IV between alemtuzumab and ATG treated patients did not reach statistical significance (32 vs 47%, p=0.2). No difference in incidence of chronic GvHD was observed (25 vs 33%, p=0.6) More CMV seropositive patients in the alemtuzumab group experienced CMV reactivation (100% vs 47%, p=0.001). The cumulative incidence of treatment related mortality at 2 years for ATG and Campath was 29.3% (CI=17–50%) vs 28.5% (CI=15–54%), p=0.7. No significant difference could be observed in the estimated 2 years OS and PFS between ATG and Campath: 53% (CI:38–75) vs 45% (CI:28–73) and 29% (CI:16–54) and 36% (CI: 20–62), respectively. For PFS, in a multivariate analysis relapse to prior high-dose chemotherapy was the strongest negative factor: HR 2.9, p= 0.001. Including only those patients who did not experienced any relapse at time of allogeneic stem cell transplantation the Campath-group had a 2.5 fold higher risk of progression in comparison to the ATG group, but without reaching statistical significance (HR: 2.5, p=0.15). Ten out of 73 patients had KIR-ligand mismatch in GvH direction. While in patients without KIR-ligand mismatch the cumulative incidence of relapse at two years was 50%, none of the KIR-ligand mismatched patients relapsed so far (p=0.02). The immunosuppressive effect from Campath is stronger than ATG resulting in less acute GvHD, but requires more DLI procedures to control diseases and resulted in a trend to a lower PFS in chemosensitive patients. This preliminary data further implicated a major role of KIR-ligand mismatch transplantation in multiple myeloma