# Case Report: Successful treatment of steroid-refractory severe immunotherapy-induced pneumonitis with equine antithymocyte globulin

## TL;DR

A patient with severe immunotherapy-induced lung inflammation was successfully treated with equine antithymocyte globulin after other treatments failed.

## Contribution

This is the first reported case of successful treatment of steroid-refractory immunotherapy-induced pneumonitis using equine antithymocyte globulin.

## Key findings

- Equine antithymocyte globulin (eATG) led to clinical and radiological improvement in a patient with severe steroid-refractory pneumonitis.
- Monitoring CD2+/CD3+ T lymphocyte counts during eATG treatment may help manage refractory immunotherapy-induced pneumonitis.
- The patient remained stable for 12 months after treatment with no recurrence of lung issues or melanoma.

## Abstract

Immune checkpoint inhibitors (ICI) have revolutionized melanoma treatment but are associated with autoimmune toxicities. Immunotherapy-induced pneumonitis (IIP) is a potentially fatal immune-related adverse event. Current management of IIP involves corticosteroids, mycophenolate mofetil (MMF), intravenous immunoglobulin, or infliximab for severe cases. Limited data exist for corticosteroid-refractory pneumonitis. This case report is the first to describe successful treatment of refractory grade 4 IIP with equine antithymocyte globulin (eATG) after failure of corticosteroids and MMF. A 50-year-old woman with recurrent unresectable melanoma in the right ankle developed grade 4 IIP after receiving two cycles of ipilimumab and nivolumab. Despite intravenous high-dose corticosteroid and MMF, her clinical condition continued to rapidly deteriorate. eATG was administered due to its rapid onset of T lymphocyte depletion and its use in immunotherapy-induced myocarditis. An 8-day course was delivered with dose adjustment to achieve therapeutic CD2+/CD3+ lymphocyte depletion. Clinical and radiological improvement was demonstrated, with successful weaning of oxygen and corticosteroids. At 12 months, the patient remained well from a respiratory standpoint, with no recurrence of melanoma. This case highlights the potential for eATG, with therapeutic CD2+/CD3+ T lymphocyte count monitoring, to address an unmet therapeutic need in patients with refractory ICI-induced IIP.