*Purpose: Thrombotic microangiopathy (TMA) can happen after kidney transplant. It may occur de novo or as a recurrent disease. De novo is usually associated with immunosuppressive drugs such as calcineurin inhibitors (CNI) and sirolimus, or can be seen as part of endothelial damage that accompanies antibody-mediated rejection (AMR). Treatment for de novo TMA is limited to plasma exchange and change in immunosuppression and in extreme cases, addition of Eculizumab. Belatacept is a co-stimulation blocking agent and considered least nephrotoxic, and may provide an immunosuppression option in patients with post-transplant TMA.

*Methods: A retrospective review of prospectively collected data was conducted on kidney transplants from 2013 to 2019. 45 kidney transplant patients were switched from CNI to Belatacept due to concerns of TMA. Seventy percent of the patients had kidney biopsy proven changes of TMA. We report their outcomes post switch. Continuous variables are being reported as mean with SD. A paired t-test was used and P value of <0.05 was considered to be significant.

*Results: Majority of patients were Hispanic with age 54Y± 11.9, 55% were females. Post belatacept switch follow up on these patients was 37+/- 15 months. Significant improvement in pre and post switch serum creatinine (p=0.0001) and urine protein/creatinine (0.006) was observed. 14 patients had detectable donor specific antibodies (DSA) at the time of switch, out of these four patients were still positive at last follow up, whereas two new patients developed DSAs. Four (8%) patients developed acute cellular rejection, and one (2%) patient had AMR. One patient died due to infectious complications at 9 months post-transplant, and one patient lost her kidney allograft at 30 months post switch due to non-resolving AMR. Three year death censored graft survival in these patients is 97.7%.

*Conclusions: Belatacept appears to be a useful alternative immunosuppressive agent in kidney transplant patients with TMA without increasing the risk of rejection or infection. Switching maintenance immunosuppression to Belatacept will likely result in a significant improvement in renal outcome.

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