The adaptive immune response to cardiac injury-the true roadblock to effective regenerative therapies?

Abstract

The regenerative capacity of adult human tissues and organs is limited, but recent developments have seen the advent of promising new technologies for regenerative therapy. The human heart is of particular interest for regenerative medicine, as cardiac tissue damage is repaired by the formation of rigid scar tissue, which causes inevitable structural changes and progressive functional decline leading to heart failure. Cardiac regenerative medicine aims to prevent scar formation or replace existing scars to halt or reverse adverse remodeling and therapeutic approaches include the use of biomaterials, gene therapies, delivery of growth factors, and (stem) cell therapies. Regenerative therapies, however, face significant obstacles in a hostile microenvironment. While the early immune response to a myocardial infarct is essential to ensure tissue integrity and to avoid fatal cardiac rupture, excessive activation of endogenous repair mechanisms may lead to ongoing inflammation, fibrosis, and sustained autoimmune-mediated tissue damage. Anti-cardiac autoreactivity of the adaptive immune system has been suggested to be involved in structural remodeling, functional decline, and the development of heart failure. It is, therefore, crucial to first understand the endogenous response to cardiac tissue damage and how to restore immune tolerance to cardiac tissue, before additional regenerative therapies can achieve their full potential.

Fig. 1

The role of the innate and adaptive immune system post MI. A MI causes severe tissue damage and the release of DAMPs and cardiac self-antigens such as myosin and troponin. Immediately after injury, DAMPs lead to an acute inflammatory response, characterized by the influx of a vast number of innate immune cells, which initiate and orchestrate wound repair. Negative feedback mechanisms activated immediately and the declining availability of DAMPs eventually resolves early inflammation. However, in parallel, the release of massive amounts of self-antigens in an inflammatory environment breaks tolerance mechanisms and induces long-lived antigen-specific adaptive immune cells, which cause ongoing autoimmune tissue damage and continuous supply of self-antigen. IS; immune system

Fig. 2

Regenerative therapies are hampered by direct and indirect immunological mechanisms. Immunological rejection and a hostile inflammatory environment may prevent stem cell engraftment or change their beneficial properties. At the same time, anti-cardiac autoreactivity causes further and additional tissue damage. Immunomodulatory therapies may prevent anti-cardiac autoimmunity as well as immunological rejection and excessive inflammation