What Is Stem Cell Therapy? A Patient Guide

Stem cell therapy is one of the most talked about topics in regenerative medicine, but it is also one of the most misunderstood.

Understanding the biology behind these cells makes it easier to understand where stem cell therapy fits into orthopedic and sports medicine care today.

Stem cell therapy is an area of medical research that has expanded substantially over the past decade. Researchers continue to study how different types of stem cells interact with the body’s immune system and healing processes, and new areas of investigation continue to emerge.

Below is an overview of the biology behind stem cells, how they work, and considerations for patients who want to understand this area of research.

What Are Stem Cells?

According to a 2025 review published in Signal Transduction and Targeted Therapy, stem cells are unique cells that have the ability to develop into other specialized cell types or help regulate how surrounding tissues function.¹

There are several different sources of stem cells, each with different biological properties. In medicine, sources for cells include bone marrow, adipose tissue (fat), birthing tissue including placenta and umbilical cord. Cells can be used in its native form or through culture expansion where they are grown in the laboratory.

When people discuss stem cell therapy, they are typically referring to mesenchymal stem cells, also called mesenchymal stromal cells or MSCs.^1,2

Mesenchymal Stem Cells (MSCs)

MSCs are found throughout the body, including in bone marrow and adipose (fat) tissue, and are also present in placental and umbilical cord tissue. Published research describes anti-inflammatory, immunomodulatory, and regenerative properties associated with these cells.¹

Researchers now describe MSCs as “medicinal signaling cells” rather than cells whose primary role is to replace damaged tissue.² MSCs are capable of differentiating into other tissue types, and some studies have documented new cartilage formation in study participants, most often fibrocartilage rather than the original hyaline cartilage.³ In most settings, much of their contribution comes from communicating with surrounding cells, which is described in the literature as supplementing the body’s response to injury.

Published research describes MSC activity in the following areas:

What the Research Describes About MSC Activity
Helping regulate inflammation
Influencing immune system activity
Recruiting the body’s own repair mechanisms
Supporting tissue healing through cell-to-cell communication
Recruiting signaling molecules that influence nearby cells

These biological effects are why MSCs remain an active focus of regenerative medicine research.^1,2

How Do Mesenchymal Stem Cells Work?

A common expectation of MSC therapy is that stem cells are injected into a damaged joint where they become new cartilage or transform into new tissue such as muscle, tendon, or ligaments. As science advances, therapies designed to do exactly that are an active goal of ongoing research.

Current scientific understanding suggests that much of the effect works differently. Researchers believe much of the therapeutic activity associated with MSCs occurs through paracrine signaling.²

Paracrine signaling is a way cells communicate with nearby cells. Rather than replacing damaged tissue directly, MSCs release biologically active molecules that send signals to surrounding tissues.

This communication occurs via naturally occurring proteins, growth factors, cytokines, and extracellular vesicles. Among these extracellular vesicles are exosomes, microscopic particles that carry proteins, RNA, and other signaling molecules between cells.

Because exosomes are one component of MSC signaling, they have become an active area of regenerative medicine research. Scientists continue to investigate how these signaling pathways contribute to tissue repair and immune regulation.⁴

Why Are Researchers Interested in MSC Therapy?

Scientists have studied mesenchymal stem cells since the 1960s, and research has accelerated over the past decade.¹ Laboratory studies and human clinical trials have evaluated their potential role, and their safety, across numerous medical specialties.

You can browse actively enrolling mesenchymal stem cell studies at ClinicalTrials.gov. 

Areas of investigation described in published literature include:

• Rheumatologic and autoimmune diseases
• Orthopedic and sports medicine injuries
• Inflammatory disorders
• Cardiovascular disease
• Neurologic disease
• Pulmonary disease
• Skin disease and cosmetics
• Gastric disease

What Does an Injection-Based Stem Cell Therapy Involve?

For orthopedic applications, stem cell therapy generally involves injecting a biologic product into a specific area using image guidance.

Physicians may use:

• Ultrasound guidance
• Fluoroscopic (X-ray) guidance
• CT guidance

Image guidance helps ensure the injection is delivered to the intended anatomical target rather than relying on external landmarks alone. It also lets the physician place the needle without causing damage to surrounding structures, such as nerves, and to allow for further assessment while injecting into the injured area.

Some stem cell therapies are administered intravenously or through other delivery methods. The route of administration, whether injection, intravenous, or otherwise, varies by application.

Orthopedic Conditions Studied in the Research

The published literature on orthobiologic injections spans a range of orthopedic conditions. Patients frequently ask about the research behind biologic and stem cell injections for study populations that include:

• Osteoarthritis and chondromalacia of the knee, shoulder, and hip
• Meniscus injuries
• Rotator cuff injuries
• Labral tears
• Tendon injuries, including tendinitis, tendinosis, and partial tears
• Ligament and muscle injuries
• Other degenerative joint conditions

These remain active areas of clinical research, and findings vary by study population and therapy studied.

The published literature in these areas has grown substantially over the past decade, and research is ongoing. In December 2024, the first mesenchymal stem cell treatment received FDA approval, an early sign of broader recognition for this class of therapy.⁵

Questions to Ask Your Physician

Stem cell therapy is physician-directed, and a conversation with your doctor could be helpful to understand if it is right for you. A few questions can help you get the most out of that visit.

Before undergoing MSC therapy or other orthobiologic injections, consider asking:

• What does the current research show for my condition?
• What outcomes can I expect?
• Is image guidance used?
• How should I prepare for stem cell therapy?
• When can I return to normal activities?
• How will we evaluate my progress?
• What does follow-up care look like after stem cell therapy?

Your physician can explain how the therapy relates to your specific situation and what to expect from it.

What This Means for Patients Today

Stem cell therapy is an area of regenerative medicine grounded in decades of scientific research and continuing clinical investigation.

For orthopedic conditions, current cellular research suggests that MSCs primarily work by communicating with surrounding tissues, modulating inflammation, influencing immune activity, and supporting the body’s own repair processes through paracrine signaling, rather than simply replacing damaged cartilage or tendon.

Patients who understand both the underlying biology and the current evidence are better equipped to ask informed questions, evaluate recommendations, and make decisions that align with their goals.

Dr. Steve Yoon is a sports medicine and regenerative medicine physician in Los Angeles. He serves as Head Team Physician for the LA Clippers and Team Physician for the Los Angeles Angels, and has practiced in regenerative medicine for over 15 years. You can learn more about his practice here.

Frequently Asked Questions

What are mesenchymal stem cells?

Mesenchymal stem cells (MSCs), also called mesenchymal stromal cells, are cells found throughout the body that are described in the medical literature as helping regulate inflammation, influence immune responses, and support tissue repair. Rather than directly replacing damaged tissue, MSCs release signaling molecules, including exosomes and other bioactive factors, that communicate with surrounding cells through a process known as paracrine signaling.²

Are all stem cell therapies the same?

No. Stem cells can originate from different tissue sources. These include cells taken from bone marrow, fat tissue, donor-derived birth tissue such as umbilical cord or amniotic tissue. Clinical studies may use cells that differ in how they are sourced, processed, regulated, and dosed.

References

1. Han, X., et al. (2025). Mesenchymal stem cells in treating human diseases. Signal Transduction and Targeted Therapy.

2. Caplan AI. Mesenchymal Stem Cells: Time to Change the Name! Stem Cells Translational Medicine. 2017;6(6):1445-1451.

3. Armiento AR, Alini M, Stoddart MJ. Articular fibrocartilage: Why does hyaline cartilage fail to repair? Advanced Drug Delivery Reviews. 2019.

4. Kalluri, R., & LeBleu, V. S. (2020). The biology, function, and biomedical applications of exosomes. Science, 367(6478).

5. U.S. Food and Drug Administration. (2024, December 18). FDA approves first mesenchymal stromal cell therapy to treat steroid-refractory acute graft-versus-host disease. fda.gov