What is stem cell therapy? An overview

Stem cell therapy is a branch of regenerative medicine that uses stem cells or stem cell-derived products to help repair, replace or restore damaged cells and tissues. Stem cells are valued because they can self-renew and, depending on the cell type, differentiate into specialized cells. In clinical and research settings, stem cell-based approaches may use a patient’s own cells (autologous) or donor-derived cells (allogeneic), depending on the disease area, manufacturing strategy and treatment goal.

Stem cell therapy harnesses the unique characteristics of stem cells and their derivatives for healing. Stem cells can renew and differentiate into various cell types, which are being studied for their ability to rebuild or replace damaged cells and tissues. Autologous stem cell therapy uses stem cells harvested from the patient's own body. The cells are banked, manipulated and then reinfused during treatment.

Allogeneic stem cell therapy follows a similar process but differs in that the cell source is an unrelated donor. Stem cells being considered for therapeutic application are often classified by their differentiation potential or source, which is vital for understanding their capacity. Two major categories of stem cells are listed below with further descriptions.

Pluripotent stem cells (PSCs) have traditionally originated from early embryos and can differentiate into various cell types found in tissues and organs. They include human embryonic stem cells (hESCs) from blastocysts and induced pluripotent stem cells (iPSCs) created by reprogramming mature somatic cells.

Adult stem cells are resident progenitor cells found in organs and tissues or circulating in the blood. These cells can participate in repair processes to replace lost cells due to aging, injury or disease. Hematopoietic (HSCs) and mesenchymal stem cells (MSCs) are two examples of adult stem cells. HSCs are traditionally isolated from bone marrow aspirate. MSCs can also be isolated from bone marrow, umbilical cord blood, adipose tissue, peripheral blood and other tissues.

What types of stem cell therapies are being explored?

The following are some examples of stem cell-based therapies that are being clinically tested:

• Hematopoietic stem cells (HSCs) are used in medical procedures to replace or repair dysfunctional blood and immune system cells. This procedure has several benefits and may be used to treat both malignant and non-malignant conditions. In addition, it can generate functional immune and blood cells. HSCs can pose risks and complications, such as graft-versus-host disease (GVHD).
• Mesenchymal stem cells (MSCs) have gained prominence in regenerative medicine due to their multi-lineage potential. MSCs are touted for suppressing immune responses and promoting the generation of regulatory T cells, making MSCs valuable candidates for clinical trials and potential treatments for inflammatory and degenerative diseases.
• Stem cell-based tissue engineering constructs are designed to replace or enhance tissues to replicate developmental processes or tissue repair mechanisms. Stem cells are appealing because of their capacity for self-renewal, their potential for differentiation and their secretion of trophic factors that promote tissue regeneration.

What are the benefits and risks of stem cell therapy?

Stem cell therapy has become an established treatment option, continually monitored and studied by physicians and clinicians to identify its benefits and risks. Stem cells have shown curative potential as observed with HSCs and they can also provide tempered immune responses through paracrine signaling or direct modulation by MSCs.

Stem cell-based tissue-engineered grafts can replace damaged tissue and provide structural support, thereby improving overall function. These collective impacts of stem cell therapy profoundly affect the patient's quality of life.

Stem cell-based therapy carries numerous potential risks that need to be carefully studied and addressed. One of the most significant concerns is the ability of transplanted stem cells to survive, engraft, proliferate and regenerate tissue.

Additionally, the genetic and epigenetic changes that stem cells may undergo during in vitro manipulation can significantly impact their viability and clinical benefits after transplantation. Therefore, it is crucial to thoroughly evaluate and manage these risks to ensure the safety and efficacy of stem cell-based therapies.

Immune rejection poses another significant risk. This could necessitate immunosuppressive therapy, which brings risks of infections and adverse reactions. Additionally, the potential for transplanted stem cells to become oncogenic due to their replicative capacity raises safety concerns.

This may result from undifferentiated pluripotent cells in the administered dose. Therefore, researchers and clinicians are tasked with characterizing the identity of the cells before infusion or transplantation to ensure a homogenous population of the specific stem cells desired. This characterization step helps reduce the risk of tissue incompatibility, especially when considering a stem cell-based graft containing multiple cell types.

Stem cell-based therapies may require a substantial number of cells to achieve the desired outcomes. For autologous stem cell therapies, the patient’s condition and prior treatments, such as chemotherapy or radiation, can affect the number and quality of available stem cells. However, allogeneic stem cell therapies may be an option to overcome quantity and quality challenges associated with patient conditions or age.

What are the current limitations of stem cell therapy?

• Biological variability: Stem cell identity, potency and behavior can vary across donors, tissues and manufacturing runs, which can affect consistency
• Engraftment and durability: Even when cells survive administration, long-term persistence, functional integration and predictable clinical benefit are not guaranteed
• Safety concerns: Risks may include immune reactions, ectopic tissue formation, unwanted differentiation, tumorigenicity and complications linked to cell processing
• Manufacturing complexity: Expansion, characterization, storage, transport and quality control can be technically demanding and costly, especially for personalized cell products
• Regulatory and access barriers: Some stem cell applications remain investigational and reimbursement, infrastructure and equitable access continue to limit broad adoption

What ethical questions surround stem cell-based therapies?

The use of embryonic stem cells in scientific research remains a topic of intense debate due to the moral and ethical implications surrounding their acquisition. Obtaining these cells requires the destruction of human embryos, resulting in limitations on their usage and funding from government agencies around the world.

While some argue that the embryos used in research are obtained through legal means such as IVF clinics or cell banks, not all parties find this viewpoint satisfactory. Stem cell-based therapies have raised ethical concerns related to their safety, efficacy and accessibility. One of the primary ethical concerns is the potential for stem cell clinics to offer unproven and potentially harmful treatments to vulnerable patients, taking advantage of their desperation for a cure. The lack of regulation and oversight of these clinics has led to numerous cases of patient harm and even death.

Additionally, stem cell-based therapies can be costly, raising concerns about access and equity in healthcare. As a result, it is essential to ensure that stem cell-based therapies are thoroughly evaluated and regulated, with appropriate clinical trials and oversight to ensure their safety and efficacy. Furthermore, it is crucial to ensure that effective therapies are accessible to all who need them, regardless of their ability to pay, to promote equity in healthcare.

Where is stem cell therapy being used or studied today?

Combinatorial therapies pairing stem cells with other active pharmaceutical agents could enhance therapeutic potential and constitute a new research area. This approach has implications for personalized treatment.

Regenerative medicine remains a focus for many stem cell biologists and translational scientists. The field is optimistic about repairing damaged tissues and organs using engineered tissues derived from stem cells. This bioengineering approach aims to reduce deaths due to wait times or organ rejection by growing immunocompatible human organs in the lab.

A regenerative medicine approach is being applied to dentistry, with endodontists exploring dental pulp stem cells to heal and restore dental pulp tissue. Stem cell therapies have the potential to regenerate nerves and improve the quality of life for those with neurodegenerative diseases or spinal cord injuries. Stem cells can also be applicable for orthopedics, addressing bone defects, promoting nerve and tissue healing and aiding recovery in various conditions.

• Blood and immune disorders: Hematopoietic stem cell transplantation remains one of the most established uses of stem cells, particularly in selected blood cancers, immune disorders and inherited metabolic diseases
• Orthopedics and musculoskeletal repair: Stem cell-based approaches are being studied for cartilage, bone and soft tissue repair, although outcomes can vary by indication, cell source and delivery method
• Neurology: Researchers are evaluating stem cell strategies for spinal cord injury, Parkinson’s disease and other neurodegenerative conditions, with the goal of supporting repair, replacement or neuroprotection
• Cardiovascular disease: Investigational programs are exploring whether stem cell-derived products can improve cardiac repair after ischemic injury or support vascular regeneration
• Ophthalmology: Retinal and ocular applications are active areas of regenerative medicine research because localized delivery and defined cell targets may support more controlled therapeutic development
• Disease modeling and drug discovery: Beyond direct therapy, stem cells and iPSC-derived cell models are widely used to study disease biology, test drug responses and support precision medicine research