*Purpose: Induction immunosuppression with alemtuzumab and rabbit anti-thymocyte globulin (r-ATG) reduces acute rejection following kidney transplantation. Efficacy is thought to be similar between the agents but less is known regarding differences in safety. Specifically, prolonged leukopenia may prompt dose reductions in maintenance medications, potentially increasing risk for infection and rejection. We sought to characterize the safety of alemtuzumab compared to r-ATG when used for induction therapy following kidney transplant.

*Methods: Kidney transplant patients 18 years of age or older that received alemtuzumab or r-ATG from January 1, 2009 through December 31, 2014 were retrospectively evaluated. Patients with a prior kidney transplant receiving a pre-emptive transplant or those that received desensitization with rituximab or intravenous immunoglobulin prior to transplant were excluded. The primary outcome was incidence of leukopenia within 12 months of transplant. Secondary outcomes included incidence of maintenance medication adjustments, infection and biopsy proven acute rejection (BPAR).

*Results: In total, 340 patients (218 receieved alemtuzumab, 122 received r-ATG) were analyzed. Incidence of leukopenia within 12 months of transplant was similar between groups (56.9% alemtuzumab vs 59.0% r-ATG, p=0.789). The incidence of mycophenolic acid derivative dose decreases within the first 3 months of transplant was higher in the alemtuzumab group (70.2% vs 56.6%, p=0.016). Anti-infective prophylaxis dose adjustments, were similar between groups. The incidence of infections requiring hospitalization within 1 year of transplant was also similar between groups (21.6% alemtuzumab vs 29.5% r-ATG, p=0.121). BPAR within 1 year of transplant was higher in the r-ATG group (5.0% vs 11.5%, p=0.047) but the overall rate at 3 years post-transplant was similar. Accounting for other known risk factors, r-ATG was found to be a significant predictor for BPAR at 1 year post-transplant along with cytomegalovirus infection within 1 year of transplant.

*Conclusions: We failed to demonstrate a significant difference in prolonged leukopenia rates between kidney transplant patients that received alemtuzumab versus r-ATG. With similar safety profiles, and potentially lower efficacy with r-ATG, alemtuzumab may be the preferred induction immunosuppressant following kidney transplantation; however, patients receiving thymoglobulin tend to be higher immunologic risk which may affect the rate of BPAR post-transplant. Patients in our study were not stratified according to immunologic risk.

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