Engineering a healing immune response: Infections, surgeries, and trauma can all cause major tissue damage. Biomaterial scaffolds, which help to guide regenerating tissue, are an exciting emerging therapeutic strategy to promote tissue repair. Sadtler et al. tested how biomaterial scaffolds interact with the immune system in damaged tissue to promote repair (see the Perspective by Badylak). Scaffolds derived from cardiac muscle and bone extracellular matrix components trigger a tissue-reparative T cell immune response in mice with injured muscles. Science , this issue p. 366 ; see also p. 298

Senescent cells (SnCs) are associated with age-related pathologies. Osteoarthritis is a chronic disease characterized by pain, loss of cartilage, and joint inflammation, and its incidence increases with age. For years, the presence of SnCs in cartilage isolated from patients undergoing total knee artificial implants has been noted, but these cells' relevance to disease was unclear. In this Review, we summarize current knowledge of SnCs in the multiple tissues that constitute the articular joint. New evidence for the causative role of SnCs in the development of posttraumatic and age-related arthritis is reviewed along with the therapeutic benefit of SnC clearance. As part of their senescence-associated secretory phenotype, SnCs secrete cytokines that impact the immune system and its response to joint tissue trauma. We present concepts of the immune response to tissue trauma as well as the interactions with SnCs and the local tissue environment. Finally, we discuss therapeutic implications of targeting SnCs in treating osteoarthritis.