In short
The homing effect describes stem cells migrating toward inflamed or injured tissue following chemical signals. In practice most intravenously delivered cells are initially trapped in the lungs, with only a small fraction reaching target tissue, so observed effects are usually attributed to secreted factors.
Delivery routes studied
Intravenous delivery is most common in research because it is straightforward. Others include direct intra-articular injection in joint disease, intra-arterial delivery to a target organ and local tissue injection. Each carries different risks and considerations.
Safety considerations
Reported risks include infusion reactions, thrombosis, infection from substandard preparation and immune reactions with donor cells. Administration should therefore occur in regulated medical facilities.