*Purpose: Development of de novo donor specific antibodies (dnDSA) after kidney transplantation (KTx) has been associated with acute and chronic antibody-mediated rejection, transplant glomerulopathy and graft loss. While the optimal induction immunosuppressive therapy to prevent allograft rejection remains a topic of debate, only a scarce number of studies have investigated the difference in emergence of dnDSA following immunosuppression induction with alemtuzumab and thymoglobulin (ATG). We sought to compare the incidence of dnDSA between these two agents.

*Methods: We retrospectively analyzed 74 KTx recipients who were engrafted between 6/2017 and 7/2018 at our institution. Of these, 48 received ATG and 26 patients received alemtuzumab. Per protocol, patients underwent DSA screening at 1, 3, 6 and 12 months post-transplant. Mean fluorescence intensity (MFI) > 1000 was defined as positive. The evolution of preformed DSA, incidence of biopsy-proven acute rejection (BPAR) and survival at 1 year were also compared.

*Results: Patients were of comparable age, KDPI score and EPTS score in both groups. The population was largely of black race (ATG: 63% vs Alemtuzumab: 69%) with a median of 5 mismatched HLA antigens. There were statistically significantly more males and patients with cPRA >20% (58% vs 27%), and numerically more patients that were previously transplanted (15% vs 4%) or had a preformed DSA (23% vs 15%) in the ATG group. dnDSA are shown in Table 1. The incidence of dnDSA in the ATG group was 20.8% vs 11.5% in the alemtuzumab group (p=0.523). All four patients with preformed DSA in the alemtuzumab group cleared after KTx. Of the 11 with preformed DSA in the ATG group, two persisted with attenuated MFI following pre-transplant treatment with IVIG, one had increased MFI, and 8 disappeared post-transplant. There was one case of mixed BPAR in each group. There were two deaths in alemtuzumab group and one death in the ATG group, but no additional death-censored graft loss.

*Conclusions: Our study found higher occurrence of dnDSA in the ATG group, however this was not statistically significant. Since our sample size was small, and patients in the ATG group were of higher immunologic risk, larger, prospective randomized-control trials are needed.

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