Abstract
A new paradigm of cell therapy-based approaches as a solution to several diseases caused by damage or loss of cells/tissues leading to organ failure heralded the birth of a new branch in medicine called regenerative medicine (RM), which was further fueled by in vitro cell expansion and tissue engineering (TE) technologies, including the ability to grow embryonic stem cells, induce pluripotent stem cells, and so on. RM addresses organ failure by repair, regeneration, or restoration, rejuvenation using cells, stem cells, or progenitor cells as tools having added cell-derived products also as a tool, and extracellular matrix component-based support, either direct or indirect (e.g., matrix induced autologous chondrocyte implantation) using scaffolds. Now, the main objective of RM is to solve the functional loss of cells that have evolved from cells as tools to cell-derived factors and scaffolds per se as tools. In this context, an important yet indispensable group of cells that constitute the major portion of the human body in terms of the number of cells having several essential roles to play, both directly and indirectly, starting from digestion and the immune system to the growing evidence of influencing neuronal function, aging, and carcinogenesis has been ignored. We would like to focus on these in this review as they should essentially be considered as a tool of RM, especially for neurological disorders for their vital role. What we are indicating is the second genome or the gut microbiome.