Immune Effector Cell-Associated HLH-like Syndrome: A Review of the Literature of an Increasingly Recognized Entity

SIMPLE SUMMARY: Chimeric antigen receptor (CAR)-T cells are a novel type of therapy that is becoming more prominent in the treatment of many hematological malignancies. They are associated with serious side effects including hemophagocytic lymphohistiocytosis (HLH), which can be fatal. Diagnosis of HLH can be challenging due to the lack of a uniform diagnostic criteria and the overlap with other frequent toxicities of CAR-T cells. Available treatments have been previously used for HLH but may not be as effective in this setting. The purpose of this literature review was to examine the evolution of the diagnostic criteria and treatment recommendations for HLH specifically in the setting of CAR-T cell therapy in order to facilitate prompt diagnosis and the implementation of suitable treatment to improve patient outcomes. ABSTRACT: Since CAR-T cell therapy was initially approved in 2017, its use has become more prevalent and so have its side effects. CAR-T-related HLH, also named immune effector cell-associated HLH-like syndrome (IEC-HS), is a rare but fatal toxicity if not recognized promptly. We conducted a review of the literature in order to understand the prevalence of IEC-HS as well as clarify the evolution of the diagnostic criteria and treatment recommendations. IEC-HS occurrence varies between CAR-T cell products and the type of malignancy treated. Diagnosis can be challenging as there are no standardized diagnostic criteria, and its clinical features can overlap with cytokine release syndrome and active hematological disease. Suggested treatment strategies have been extrapolated from prior experience in HLH and include anakinra, corticosteroids and ruxolitinib. IEC-HS is a potentially fatal toxicity associated with CAR-T cell therapy. Early recognition with reliable diagnostic criteria and prompt implementation of treatment specific to IEC-HS is imperative for improving patient outcomes.