If Plan A Does Not Work - The CD47 Ectodomain as a Target for Immune Tolerance

Sep 23, 2026

Uploaded by hdkawk

Cell surface immune checkpoint receptors are targets for therapeutic strategies designed to enhance immune-mediated cancer cell killing. Checkpoint ectodomains (ECDs) interact with natural ligands, which reduce baseline restraints on immune cells; blocking these interactions is expected to improve killing and survival. Evidence supporting this logic is strong for PD-L1, but not for the broadly expressed CD47 ECD. Clinical data for CD47 ECD-binding approaches show limited antitumor signals, prompting analysis of why “Plan A” underperforms and discussion of “Plan B” options to modulate tolerance in autoimmune disease.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages21

Reading Time53 min

AccessFree to download

Introduction

What Is CD47?

Review If Plan A Does Not Work: The CD47 Ectodomain as a Target for Immune Tolerance Enrique Montero 1,3, * and Jeffrey S. Isenberg 2,3, * Academic Editor: Qiwei Wang Received: 11 December 2025 Revised: 26 December 2025 Accepted: 29 December 2025 Published: 31 December 2025 Copyright: © 2025 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license. 1 Department of Diabetes Immunology, 1500 Duarte Road, Duarte, CA 91010, USA 2 Department of Diabetes Complications & Metabolism, 1500 Duarte Road, Duarte, CA 91010, USA 3 Arthur Riggs Diabetes & Metabolism Research Institute, Beckman Research Institute, City of Hope National Medical Center, Duarte, CA 91010, USA * [Correspondence: jcasimiro@coh.org](Correspondence: jcasimiro@coh.org) (E.M.); [jisenberg@coh.org](jisenberg@coh.org) (J.S.I.) Abstract Cell surface immune checkpoint receptors are objects for therapeutic intervention to stimulate immune cell attack of cancers. Interference between the checking ectodomain (ECD) and the natural ligand lowers constitutive restraints exerted on immune cells. This approach assumes that immune cells can do more, that a checkpoint blocker will make immune cells more effective at killing cancer cells, and that checkpoint molecules might have limited physiological roles. These assumptions may be warranted, as in the case of checkpoint-blockers towards the programmed death-ligand 1 (PD-L1) ECD, where clinical outcomes are consistently good. However, this does not appear to be the case for the universally expressed CD47 ECD. Much effort has been directed at engineering molecules that bind to the CD47 ECD to increase T cell and macrophage killing of cancers. But a wealth of clinical data do not indicate strong signals, improved killing, or meaningful survival advantages. This suggests that the CD47 ECD is a subpar target for cancer therapy. Consideration of reasons accounting for the modest benefits realized by molecules that bind to the CD47 ECD in cancer, also known as Plan A, is provided. This is followed by thoughts on what might be done, known as plan B, to identify advantages within the CD47 ECD for modulating tolerance in autoimmune diseases. Keywords: CD47; TSP1; HLA-I; checkpoint; ectodomain; binding affinity; cancer; autoimmunity 1. Introduction Removing and disrupting the sense-of-self that standard surface antigens provide isone of the basic objectives of checkpoint therapies [1] . Checkpoint-directed molecules go after intrinsic immune inhibitory pathways that restrain T [2], NK [3,4], and dendritic [5] cells. This is especially true for CD47 . Acting through SIRPα, the checkpoint action is embodied in macrophages as a ‘don’t-eat-me’ brake on phagocytosis [6] . The checkpoint paradigm found its best realization in the case of the PD-1/PD-L1, since the signal is narrow in its address, residing mostly within the cancer microenvironment [7] . For other checking pathways,‘bleeding’ of the immune signal beyond the cancer is a significant issue [8,9] and a source of off-target complications [10] . The lack of local tumor effect and the tendency to generalize, besides accounting for the modest effects of some checkpoint blockers [11,12], imply that such genes are less critical for cancers to retain their self-status. The ability to leverage such pathways for cancer killing may be overly optimistic [13–15] . Data indicate that checkpoint molecules perform beyond suppressing immune cells. For instance, T-cell immunoglobulin domain and mucin domain containing molecule-3 (TIM-3) drives angiogenesis [16], lymphocyte activation gene 3 (LAG-3) is involved in lipid raft formation [17], T-cell immunoglobulin and ITIM domain (TIGIT) is adhesive [18], and PD-L1 participates in glycolysis [19] . Basic studies of these and other checkpoint genes have revealed insights into their roles in allo-an

FAQs

What is the main therapeutic rationale behind targeting immune checkpoint ectodomains?

The rationale is that disrupting the ectodomain (ECD) interaction with its natural ligand lowers baseline restraints on immune cells, allowing checkpoint blockers to improve immune cell attack and killing.

Why is the Plan A strategy less convincing for the CD47 ECD than for PD-L1?

While PD-L1 ECD-targeting shows consistently good clinical outcomes, CD47 ECD-binding efforts have not demonstrated strong signals such as improved killing or meaningful survival advantages.

What does CD47 do at the cellular level according to the article?

CD47 decorates cells and participates in maintaining cell balance through roles tied to its interactions and expression characteristics, including its involvement in organizing cell homeostasis.

Sep 23, 2026

Uploaded by hdkawk