*Purpose: STUDY PURPOSE: Acute rejection (AR) after Pancreas Transplant alone (PTA) continues to be a significant morbidity. We compared the outcomes of PTA recipients treated for rejection based on protocol and clinical biopsies.

*Methods: METHODS: Retrospective cohort study of PTA recipients at Mayo Clinic Rochester between 4/1/1998 and 8/31/2018 who experienced AR in first year post PTA. Outcomes of interest were mortality, composite end point of (HbA1c less than 6.5% no severe hypoglycemia [SH] and insulin independence), freedom from SH, diabetic ketoacidosis (DKA) and undetectable C-peptide. Protocol biopsies of pancreas allograft were done at 7 days, 1, 2, 4 mths and 1 yr, from 1998-2004 (period 1) and at 4 mths, 1 and 5 yrs from 2004 onward. AR was diagnosed and graded according to Banff classification.

*Results: RESULTS: We identified 112 PTA recipients of which nine had allograft thrombosis related primary non-function within 24 to 36 hours and were excluded from analysis. Baseline demographics for 103 subjects were age 42.7 ± 10 years, F/M 67/36, BMI 26 ± 4.9 (Kg/m²), HbA1c 9.1 ± 2.3 (%), c-peptide 0.09 ± 0.03 ng/ml and T1D duration 27 ± 11 yrs. Induction therapy included: Thymoglobulin (90.3%), OKT 3 (6.8%) or Zenapax (1.9%) and maintenance immunosuppression was Tacrolimus, Mycophenolate Mofetil and Prednisone (94.2%). Thirty seven patients experienced AR with 15 diagnosed on protocol biopsies (3 ± 2 mths) and 22 diagnosed clinically (4 ± 3mths). Four clinical biopsies and 14 protocol biopsies were indeterminate and 36 patients had normal protocol biopsies with biopsies not performed in 12. During period 1, 53 patients underwent PTA with 7 patients treated on the basis of protocol biopsy based rejection at 3 ± 4 mths (0.3-11 mths) and 8 patients treated for clinical AR at 3 ± 3 mths (0.4- 9mths), one patient had no biopsy or rejection, 18 were indeterminate biopsies and 19 had normal protocol biopsies. During period 2, 50 patients underwent PTA, 8 patients experienced treated protocol rejection at 3 ± 1 mths (2-5 mths) and 14 patients experienced treated clinical AR at 4 ± 4 mths (0.06-1yr) and 11 patients had no biopsy or rejection and 17 had normal protocol biopsies. We found no significant difference in incidence of clinical and protocol biopsy based AR in period 1 and period 2. Cohorts with treated clinical AR, treated protocol biopsy based AR and patients without AR showed no difference in mortality, composite end point, freedom from SH and DKA and undetectable C-peptide at 1 and 5 years. Similar outcomes were seen when AR and no AR cohorts were compared.

*Conclusions: CONCLUSIONS: We found no difference in incidence of clinical and protocol biopsy based AR with more frequent (4 in year 1) vs less frequent (2 in year) protocol biopsies after PTA for T1D. Five year comprehensive patient important outcomes were similar for cohorts with protocol biopsy and clinical biopsy and for cohorts with and without AR.

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