Hematopoietic stem cell transplantation (HSCT) is an intensive treatment option for certain individuals living with Multiple Sclerosis (MS). MS is an autoimmune disease where the immune system mistakenly attacks the protective myelin sheath surrounding nerve fibers in the brain and spinal cord, causing neurological symptoms. The goal of HSCT is to “reboot” the faulty immune system, aiming to halt inflammation and disease activity. This procedure is typically referred to as Autologous HSCT (AHSCT) because it uses the patient’s own stem cells, avoiding complications from donor cells.
The Immune System Reset
The central objective of HSCT is to eliminate the self-reactive immune cells responsible for attacking the central nervous system in MS. This autoimmune process is driven by specific populations of T and B cells that promote inflammation. HSCT works by first eradicating these harmful, mature immune cells using high-dose chemotherapy.
Hematopoietic stem cells are immature cells found primarily in the bone marrow that develop into all types of blood and immune cells. Before chemotherapy, these healthy stem cells are collected from the patient’s bloodstream and stored. After the existing immune system is destroyed, the stored stem cells are returned to the patient, migrating back to the bone marrow. The new immune cells that develop are “re-educated” by the thymus gland to tolerate the body’s own tissues, reducing the autoimmune attack. This establishes a new, less inflammatory immune state that suppresses disease activity long-term.
The Treatment Process
The HSCT procedure is a multi-phase process beginning with preparing the patient’s body to harvest the necessary cells. The first phase is Mobilization and Collection, where medications, including growth-stimulating factors, encourage stem cells to leave the bone marrow and enter the bloodstream. Once sufficient stem cells are circulating, apheresis is used to collect them from the blood. The collected cells are then frozen until they are needed for the transplant.
The next intense phase is Conditioning, which involves administering high-dose chemotherapy drugs. The goal of this chemotherapy is to eliminate the existing, faulty immune cells, suppressing the autoimmune response. This is a critical period because the patient’s immune system is severely compromised, making them vulnerable to infections. The specific chemotherapy regimen varies between treatment centers, affecting the intensity of immune suppression.
After conditioning, the patient moves into the Infusion phase, which is similar to a blood transfusion. The previously collected and frozen stem cells are thawed and returned to the patient intravenously. These reinfused cells travel through the bloodstream to the bone marrow in a process called homing.
The final phase is Engraftment and Recovery, where the transplanted stem cells settle in the bone marrow and begin to produce new, healthy blood and immune cells. This period typically takes several weeks, during which the patient is closely monitored in a protective environment. Full immune system reconstruction is a gradual process that continues for several months post-transplant.
Determining Eligibility and Measuring Success
HSCT is an intensive treatment and is not a first-line option for most people with MS. Eligibility is reserved for patients with highly active, inflammatory MS, often the relapsing-remitting form, who have not responded adequately to standard disease-modifying therapies (DMTs). Criteria include evidence of recent disease activity, such as frequent relapses or new lesions visible on MRI. Younger age (generally under 50) and a shorter duration of the disease often predict better outcomes. Patients must undergo comprehensive screening to ensure their heart, lung, and other organ functions can withstand the procedure.
The efficacy of HSCT is measured using clinical and radiological metrics. A primary indicator is achieving No Evidence of Disease Activity (NEDA), meaning the absence of relapses, no new or enlarging lesions on MRI, and no worsening of disability. Studies show that a significant percentage of patients with highly active relapsing MS achieve long-term remission, with relapse-free survival rates over 80% at five years. Improvement in disability, measured by the Expanded Disability Status Scale (EDSS), is a key metric rarely seen with other MS treatments.
Potential Risks and Long-Term Recovery
The significant risks of HSCT relate directly to the intensive chemotherapy used during the conditioning phase. This process temporarily wipes out the immune system, leading to severe immunosuppression where the risk of life-threatening infections is high. Patients are isolated during engraftment to minimize exposure to pathogens, and supportive care includes antibiotics and blood product transfusions.
Beyond immediate infection, chemotherapy can cause toxicity to organs, including the heart, liver, and kidneys. Long-term effects include an increased risk of secondary autoimmune disorders and a high likelihood of infertility. While the mortality rate associated with HSCT has decreased as protocols have improved, a small risk of treatment-related death remains. Patients require months of careful monitoring post-procedure; full return to normal activity is often delayed until the immune system has substantially recovered, typically three to six months after the transplant.