*Purpose: AMR in HTR portends poor clinical outcomes. Reported mortality range between 20-50%, with higher rates reported for late AMR occurring at least 1 year after HT. Optimal AMR treatment in HTR is unknown and impact of treatment on long-term outcomes remains limited. We examined the AMR treatment outcomes in HTR using our institution’s standardized treatment protocol after implementation in January 2016 (Figure 1).

*Methods: Adult HTR who received AMR treatment between January 2016 and November 2020 were retrospectively reviewed. Combined organ transplants were excluded. Patients were treated for AMR if they had positive DSAs and/or positive EMB. Outcomes included all-cause mortality, need for re-transplantation, freedom from inotropes, freedom from hospitalization, DSA trend, symptom improvement, and adverse effects (ADEs).

*Results: Forty HTR were included in the study. Majority of patients had a positive EMB (59%), were symptomatic (85%) and presented as late AMR occurring more than 1 year from HT (90%). Concurrent ACR ≥2R was observed in 5%. Anti-HLA DSAs were positive in 39, of which 41% had Class II DSAs and 56.4% had both Class I and II DSAs. C1q positive DSAs were present in 89.7% of patients. One patient had non-HLA DSAs. Nine patients (22.5%) required repeat AMR treatment for persistent symptoms, DSAs, and/or positive EMB. One patient required re-transplantation by 12-months posttreatment. Symptom improvement posttreatment occurred in 56.4%. However, 28.2% had no change or worsening DSAs, which was more common in those with Class II immunodominant DSAs. Mortality rate was 15% and 44.7% of patients were alive, free of hospitalization at 12-months posttreatment. Eight patients had early treatment discontinuation due to ADEs, of which most common was bone marrow suppression (Table 5).

*Conclusions: Despite most patients having late AMR, mortality rate in this cohort of HTR who received AMR treatment after implementation of a standardized protocol was 15%, which is lower than previously reported mortality rates. Further studies are warranted to evaluate optimal AMR treatment regimens and assess longer outcomes of AMR in HTR.

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