Immune Response Checkpoint Inhibitors: New Risks of a New Class of Antitumor Agents

Abstract

The introduction into clinical practice of immune checkpoint inhibitors that block cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein-1 (PD-1), and programmed cell death ligand-1 (PD-L1), has improved the prognosis of patients with malignant neoplasms of diff erent localisation. The antitumour eff ect of immune checkpoint inhibitors is based on blocking CTLA-4 and PD-1/PD-L1 signaling pathways and enhancing lymphocyte antitumour activity. However, inhibition of immune checkpoints may lead to dysregulation of immune responses and appearance of a new type of adverse reactions resulting from changes in the activity of immunocompetent cells. The aim of the study was to analyse adverse reactions associated with the use of immune checkpoint inhibitors. It was demonstrated that the structure of immune-mediated adverse reactions varied depending on the class of immune checkpoint inhibitors. The incidence of immune-mediated adverse reactions was higher with CTLA-4 inhibitors as compared with PD-1/PD-L1 inhibitors, and increased signifi cantly in the case of combination therapy. The treatment with CTLA-4 inhibitors most often resulted in skin reactions (rash, itching), gastrointestinal tract reactions (diarrhea, colitis), and endocrine gland problems (hypophysitis). The treatment with PD-1 inhibitors most often led to respiratory disorders (pneumonitis), and in some cases to gastrointestinal disorders (diarrhea, colitis), skin reactions (rash, itching), and endocrine gland problems (hypothyroidism), but they were less common. The treatment with PD-L1 inhibitors was associated with the development of pneumonitis. The development of immune-mediated adverse reactions may require discontinuation of treatment and administration of immunosuppressants, therefore early diagnosis and timely treatment of complications are important prerequisites for successful antitumour therapy. Further study of the mechanisms of immune-mediated adverse reaction development will optimise antitumour therapy with immune checkpoint inhibitors.