Hematological and Extra-Hematological Autoimmune Complications after Checkpoint Inhibitors

The TSP1-CD47-SIRPα interactome: an immune triangle for the checkpoint era

The use of treatments, such as programmed death protein 1 (PD1) or cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) antibodies, that loosen the natural checks upon immune cell activity to enhance cancer killing have shifted clinical practice and outcomes for the better. Accordingly, the number of antibodies and engineered proteins that interact with the ligand-receptor components of immune checkpoints continue to increase along with their use. It is tempting to view these molecular pathways simply from an immune inhibitory perspective. But this should be resisted. Checkpoint molecules can have other cardinal functions relevant to the development and use of blocking moieties. Cell receptor CD47 is an example of this. CD47 is found on the surface of all human cells. Within the checkpoint paradigm, non-immune cell CD47 signals through immune cell surface signal regulatory protein alpha (SIRPα) to limit the activity of the latter, the so-called trans signal. Even so, CD47 interacts with other cell surface and soluble molecules to regulate biogas and redox signaling, mitochondria and metabolism, self-renewal factors and multipotency, and blood flow. Further, the pedigree of checkpoint CD47 is more intricate than supposed. High-affinity interaction with soluble thrombospondin-1 (TSP1) and low-affinity interaction with same-cell SIRPα, the so-called cis signal, and non-SIRPα ectodomains on the cell membrane suggests that multiple immune checkpoints converge at and through CD47. Appreciation of this may provide latitude for pathway-specific targeting and intelligent therapeutic effect.

Check this out: treatment paradigms in immune-checkpoint inhibitor colitis

PURPOSE OF REVIEW

Immune checkpoint inhibitors (ICI) have become a pillar of cancer therapy for many people around the world. However, up to two-thirds of all patients undergoing ICI therapy will have immune-related adverse events (irAEs), including immune-checkpoint inhibitor colitis (ICIC). This review summarizes the most valuable and currently available information about the mechanism, diagnosis, and management of ICIC.

RECENT FINDINGS

Recent findings include several developments on the leading theories for the mechanisms of ICIC such as the role of the gut microbiome. New emerging therapy strategies include tocilizumab, ustekinumab, mycophenolate mofetil, and calcineurin inhibitors.

SUMMARY

The occurrence of irAEs remains a limiting factor for the use of immunotherapy in cancer treatment. Prompt diagnosis of ICIC with endoscopy and histologic confirmation can lead to early utilization of known effective treatments such as corticosteroids, infliximab, vedolizumab, and other emerging therapy strategies. We summarize the key points of this review article in our abstract video, Supplemental Digital Content 1, http://links.lww.com/COG/A44.