*Purpose: The optimal induction immunosuppressive therapy to prevent kidney transplant rejection remains controversial, specifically among high immunologic risk patients. Our aim was to compare the safety and efficacy of alemtuzumab versus thymoglobulin in high risk kidney transplant recipients.

*Methods: In this retrospective, single center study including 179 immunologically high risk renal transplant recipients. High-risk was defined based on Oregon Health & Science University protocol for induction therapy. A total of 179 consecutive kidney transplant recipients from 2006 through 2016 were identified. Of these, 95 (53%) patients received alemtuzumab [30 mg single dose] and 84 (47%) received thymoglobulin [total of 6 mg/kg]. Alemtuzumab was obtained from US Campath® Distribution Program at no cost, while cost of thymoglobulin is $20,000/treatment.

*Results: In this immunologic high risk population, a total of 52 patients (29%) experienced evidence of biopsy proven rejection, 25 recipients (26%) in the alemtuzumab treatment group and 27 (32%) in the thymoglobulin group (NS). There was a significant difference between the time to rejection among the two groups, with thymoglobulin rejecting earlier (p=0.015). When divided up into the three time periods of possible rejection (<6 months, 6-12 months, and >12 months), the rates of rejection were statistically significant (p<0.05); with thymoglobulin rejecting earlier. Despite the thymoglobulin group having significantly more patients with donor specific antibodies (DSA) compared to alemtuzumab (42% vs 14%; p-value: <0.00003), when subgroup analysis was performed, there was no difference in time to rejection amongst those with and without DSA in the present study. Of those with DSA, 8 (61%) and 17 (48%) rejected in the alemtuzumab and thymoglobulin group respectfully (p-value NS). Similar rejection rates were observed among those without DSA in the alemtuzumab and thymoglobulin group (20.7% vs 20.4%).

*Conclusions: Higher rates of rejection were noted in thymoglobulin treated patients compared to alemtuzumab. Alemtuzumab is comparable to that of thymoglobulin in all the aspects evaluated in the study. However due to the small number of patients with DSA in each group we cannot exclude a possible difference that may exist. Use of alemtuzumab in all patients would have resulted in a cost savings of $2,000,000. Given the current significant cost savings with alemtuzumab, further study is warranted in immunologically high risk patients with DSA.

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