Stem cell therapy uses your body’s own repair cells, or donor cells, to heal damaged tissue. The process involves harvesting cells that can develop into specialized tissue types, processing them, and delivering them to an injury or disease site. But the way these cells actually help is more nuanced than most people expect: rather than simply replacing damaged cells one-for-one, stem cells primarily work by releasing chemical signals that kick the body’s own healing processes into gear.
What Stem Cells Actually Do at the Injury Site
The original theory was straightforward: inject stem cells into damaged tissue, and they transform into the specific cells needed to rebuild it. Heart damage? The stem cells become heart muscle cells. Cartilage loss? They become cartilage. That idea turned out to be only partially correct.
Research in cardiovascular medicine found that the small number of stem cells that successfully attach to damaged tissue is far too low to directly generate enough new cells to explain the improvements doctors were seeing. Something else was happening. Current evidence points to a mechanism called paracrine signaling: the transplanted stem cells release biologically active proteins that act on the cells already living in the area. These proteins reduce inflammation, stimulate blood vessel growth, prevent cell death, and recruit the body’s own repair cells to the site.
This was confirmed when researchers took the liquid surrounding stem cells in a lab dish, filtered out the cells entirely, and applied just the liquid to damaged tissue. The results were nearly identical to transplanting the cells themselves. In other words, the stem cells act more like a command center issuing repair orders than like construction workers doing the building themselves. They can still differentiate into specialized cells in some cases, but the signaling role appears to drive most of the therapeutic benefit.
Types of Stem Cells Used in Treatment
Not all stem cells are interchangeable. The type used depends on the condition being treated.
- Hematopoietic stem cells (HSCs) are blood-forming cells found in bone marrow and circulating blood. They can develop into red blood cells, white blood cells, and platelets. For over 60 years, HSC transplants have been the primary curative therapy for blood cancers like leukemia, lymphoma, and genetic immune disorders. These are currently the only stem cell treatments routinely approved by the FDA.
- Mesenchymal stem cells (MSCs) can develop into bone, cartilage, fat, and connective tissue. They’re found in bone marrow, fat tissue, and umbilical cord tissue. MSCs are being investigated most actively for orthopedic injuries, autoimmune conditions, and tissue engineering because of their strong anti-inflammatory signaling and ability to differentiate into structural tissues.
- Induced pluripotent stem cells (iPSCs) are adult cells that have been genetically reprogrammed back to an embryonic-like state. They can theoretically become almost any cell type, which makes them powerful research tools. iPSCs have been used to generate blood-forming stem cells for regenerative medicine, though clinical applications remain limited.
The Treatment Process, Step by Step
The specifics vary depending on the type of stem cell therapy, but most treatments follow a similar arc: harvest, process, deliver.
Harvesting the Cells
When using your own cells (called autologous transplant), stem cells are typically collected from bone marrow, fat tissue, or blood. For blood-based collection, you receive daily injections of a medication that stimulates your body to produce more stem cells and pushes them from the bone marrow into the bloodstream, where they’re easier to collect. This mobilization phase takes about one to two weeks. A nurse will check your arm veins beforehand. If they’re too small or not healthy enough, a thin catheter is placed into a larger vein near the collarbone.
The actual collection works like a blood draw: blood is run through a machine that separates and captures the stem cells, then returns the remaining blood to your body. For bone marrow harvesting, a needle extracts marrow directly from the hip bone under anesthesia. Fat-derived stem cells are collected through a minor liposuction procedure, typically from the abdomen or thigh.
Processing and Delivery
Once collected, the cells are concentrated and sometimes cultured to increase their numbers. For orthopedic applications, the processed cells are injected directly into the affected joint, tendon, or disc. For blood cancers, cells are infused intravenously after chemotherapy has cleared the diseased bone marrow. In some cases, cells are stored frozen and transplanted at a later date.
Your Cells vs. Donor Cells
Using your own cells eliminates two major risks: your immune system rejecting the transplant, and graft-versus-host disease, a condition where immune cells from the transplant attack your healthy tissue. The downside is that your own cells may carry the disease being treated. In cancer patients, for example, cancer cells may not be fully removed from the collected stem cells before they’re returned, potentially causing recurrence months or years later. There’s also no “graft-versus-cancer” effect, where donor immune cells help hunt down remaining cancer cells.
Donor cells (allogeneic transplants) offer that cancer-fighting benefit but carry the risk of graft-versus-host disease, which can range from mild skin rashes to serious organ damage. Finding a well-matched donor, often a sibling or matched registry donor, reduces this risk significantly but doesn’t eliminate it.
Recovery Timeline and When Results Appear
For orthopedic stem cell injections, recovery follows a predictable pattern. The first one to two weeks involve an inflammatory response at the injection site, which is actually part of the healing process. Some patients feel relief within this window, but that’s unusually fast.
The core rebuilding phase runs from about week one through week twelve. Initial inflammation subsides, cellular activity accelerates, and you begin noticing gradual improvements in pain and function. Most patients need four to twelve weeks to experience tangible improvement. The most significant gains in stability, strength, and pain relief typically arrive between three and six months, as new tissue matures and strengthens. This is a slow process by design: the body is laying down and reinforcing new tissue, not just masking symptoms.
For blood stem cell transplants, the timeline is different. Engraftment, the point where transplanted cells start producing new blood cells, generally takes two to four weeks. Full immune recovery can take months to over a year.
What’s Actually FDA-Approved
This is where the gap between marketing and medicine is widest. According to the Harvard Stem Cell Institute, the only stem cell treatment routinely reviewed and approved by the FDA is hematopoietic stem cell transplantation for cancers and disorders affecting the blood and immune system. Everything else, including injections for knee arthritis, back pain, neuropathy, and neurological conditions, falls outside established FDA approval.
That doesn’t mean these treatments are all worthless. Many are being studied in clinical trials, and some patients report meaningful improvement. But the distinction matters because hundreds of clinics market unapproved stem cell procedures directly to consumers, sometimes for conditions where no credible evidence supports the treatment.
Costs for Common Procedures
Stem cell therapy is rarely covered by insurance outside of approved transplants for blood cancers. The average cost in the U.S. is roughly $10,000, though that number varies widely by condition. Knee injections typically run $5,000 to $10,000. Back pain and shoulder treatments range from $5,000 to $15,000. Vision loss treatments start around $20,000. Cord cell treatments for autism, offered primarily outside the U.S., generally cost $20,000 and up. Prices have been trending upward, with a growing share of procedures exceeding $20,000.
Risks of Unproven Treatments
The rise of “stem cell tourism,” where patients travel domestically or internationally for unregulated procedures, has created real dangers. Studies have documented patients suffering heart problems, neurological changes, accidental hepatitis infection, urinary incontinence, and in some cases, fatal organ failure from unlicensed transplants.
The less obvious risk is opportunity cost. Patients who pursue unproven stem cell therapies sometimes delay treatments with strong evidence behind them. By the time they return to conventional care, their disease may have advanced, narrowing their options and worsening their odds. If you’re considering stem cell therapy for a condition outside of blood cancers and immune disorders, look for treatments being studied in registered clinical trials, which you can search at clinicaltrials.gov, rather than those sold directly through private clinics with no published outcome data.