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Autologous stem cell transplantation is a treatment option that is usually reserved for elderly patients who cannot tolerate a standard allogeneic transplant or patients for whom a suitable HLA-matched donor cannot be found. In an autologous transplant, stem cells are obtained from the marrow or peripheral blood of the patient before chemotherapy is initiated and the stem cells are then treated with special chemicals in a technique called "purging" that destroys the leukemic cells but does not harm the small proportion of residual normal stem cells in the marrow or blood sample. The purged stem cell sample is then frozen and stored for later use. The stem cells are returned back into the patient's body by intravenous infusion after high-dose chemotherapy has been completed.

Although autologous stem cell transplantation is associated with a lower treatment-related mortality as compared to allogeneic stem cell transplantation, it is not considered as a curative treatment for CLL. Approximately 20% of patients with CLL who undergo autologous stem cell transplantation develop another type of cancer that includes:

• Myelodysplastic syndromes (MDS)
• Non-Hodgkin's lymphoma
• Lung cancer
• Skin cancer
• Breast cancer
• Colorectal cancer

Graft-Versus-Host-Disease

This is perhaps the most serious potential complication that may develop in patients receiving an allogeneic stem cell transplant. As mentioned previously, in an allogeneic transplant, the source of the stem cells used for transplantation is another individual who serves as the donor. Graft-versus-host disease (GVHD) occurs when the donor's transplanted cells (the graft) begins to attack the recipient's (the host's) own tissues and organs. It should be noted that GVHD can occur with an allogeneic transplant even in cases where the donor and recipient's HLA markers are a "perfect match". This is because currently the degree of compatibility (match) between the donor and recipient is determined on the basis of evaluating similarities of tissue types for six major HLA markers. However, there are other antigens present on the donor's transplanted cells which may differ slightly from those of the recipient's own cells that can lead to the development of GVHD.

Graft-versus-host disease can develop within the first 3 months following allogeneic stem cell transplantation (acute GVHD) or it may develop after 3 months (chronic GVHD). Symptoms of acute GVHD include:

• An itchy, red rash on the hands and feet
• Nausea, diarrhea, and severe stomach cramps
• Jaundice (due to liver damage)

The chronic form of GVHD can be very severe and disabling and, in some cases, may even be fatal. Patients who develop GVHD are treated with various combinations of immunosuppressive drugs such as cyclosporine, methotrexate, and corticosteroids.

In addition to GVHD, other potential complications of stem cell transplantation include recurrent infections, interstitial pneumonitis, graft failure or rejection, veno-occlusive disease (complete blockage of the central veins of the liver leading to liver damage), and recurrence of the cancer following transplantation.