Incidence of mTORi Associated BOOP in Cardiac Transplant Recipients - A Single Center Perspective

Purpose The incidence of mammalian target of rapamycin inhibitor (mTORi) associated bronchiolitis obliterans organizing pneumonia (BOOP) varies in the literature. We have previously reported a 24% incidence of BOOP in patients transitioned to sirolimus. This high rate was believed to be related to the full withdrawal of calcineurin inhibitor (CI) therapy. The aim of this study is to compare those results to our current practice of maintaining a low-dose CI with mTORi-based regimens Methods This was a single-center retrospective review of adult heart transplant recipients initiated on an mTORi at least six months post-transplant. The primary outcome of the study was incidence of BOOP. Secondary outcomes included timing of mTORi conversion post-transplant and associated tacrolimus concentrations. Results During the study period, none of the 61 included heart transplant patients developed BOOP. Late mTORi transition (>1 year post transplant) was more common (72%) than early conversion (6 months - 1 year post transplant; 28%), and sirolimus was more commonly utilized than everolimus (90% vs 10%). Following our centers mTORi conversion policy, all patients were maintained on low-dose tacrolimus at initiation, with 84% of patients continuing concomitant tacrolimus at one year. Of these patients, 46% had an FK goal < 4 mcg/mL and 38% had an FK goal 4-8 mcg/mL. Conclusion No patients at our center experienced mTORi related BOOP while maintaining a low dose CI. The results of this study suggest calcineurin inhibitors have a protective effect from BOOP, even at low concentrations. The incidence of mammalian target of rapamycin inhibitor (mTORi) associated bronchiolitis obliterans organizing pneumonia (BOOP) varies in the literature. We have previously reported a 24% incidence of BOOP in patients transitioned to sirolimus. This high rate was believed to be related to the full withdrawal of calcineurin inhibitor (CI) therapy. The aim of this study is to compare those results to our current practice of maintaining a low-dose CI with mTORi-based regimens This was a single-center retrospective review of adult heart transplant recipients initiated on an mTORi at least six months post-transplant. The primary outcome of the study was incidence of BOOP. Secondary outcomes included timing of mTORi conversion post-transplant and associated tacrolimus concentrations. During the study period, none of the 61 included heart transplant patients developed BOOP. Late mTORi transition (>1 year post transplant) was more common (72%) than early conversion (6 months - 1 year post transplant; 28%), and sirolimus was more commonly utilized than everolimus (90% vs 10%). Following our centers mTORi conversion policy, all patients were maintained on low-dose tacrolimus at initiation, with 84% of patients continuing concomitant tacrolimus at one year. Of these patients, 46% had an FK goal < 4 mcg/mL and 38% had an FK goal 4-8 mcg/mL. No patients at our center experienced mTORi related BOOP while maintaining a low dose CI. The results of this study suggest calcineurin inhibitors have a protective effect from BOOP, even at low concentrations.