Cellular Mechanisms Enabling Mitochondria Transfer and Transplantation.

Mitochondrial transfer and transplantation (mitoTT) has emerged as an experimental and potentially transformative therapeutic strategy, drawing attention for its ability to modulate cellular bioenergetics, stress responses, and tissue repair. Endogenous mitochondrial transfer can occur through tunneling nanotubes, extracellular vesicles, cell fusion, gap junction-associated communication, and phagocytosis-like internalization. These routes differ substantially in distance, directionality, cargo integrity, regulatory control, and physiological relevance. Preclinical studies indicate that exogenous mitochondria may transiently improve bioenergetic function, attenuate oxidative stress, and support recovery in models of cardiac, skeletal muscle, and nervous system injury, whereas clinical evidence remains limited and heterogeneous. Broad clinical implementation remains constrained by unresolved biological and translational barriers. These include inefficient or poorly controlled uptake of extracellular mitochondria, uncertain long-term persistence, incomplete functional integration, donor-recipient incompatibility, mitochondrial-nuclear mismatch, heteroplasmy-related risks, immunogenicity, and the lack of standardized potency and delivery assays. Here, we critically synthesize the cellular mechanisms enabling mitoTT, emphasizing the checkpoints that determine whether transferred mitochondria are integrated, remodeled, immunologically sensed, or eliminated. We further discuss cristae biology and the mitochondrial contact site and cristae organizing system, mitochondrial nucleoid maintenance, mitochondrial DNA replication, organelle contact sites, and emerging bioengineering strategies required to move mitoTT from experimental rescue toward reproducible therapeutic application.