During a stem cell transplant, healthy stem cells replace damaged stem cells after high-dose chemotherapy. Stem cells are cells in the bone marrow that have the ability to make blood cells. Before a stem cell transplant, patients receive treatment to control the cancer. Then, healthy stem cells are collected from the patient or from a donor. The patient then receives high-dose chemotherapy to empty their bone marrow. The healthy cells are put in the patient’s body to “fill in” the empty bone marrow and start producing healthy blood cells again. 

In CAR T-cell therapy, T-cells are removed from the patient’s body. T cells are a type of immune blood cell. They have the ability to find specific proteins on the cell surface (targets) and kill the cells that have those specific proteins. After T cells are collected from a patient’s blood, they are modified in a lab to target proteins on the surface of lymphoma cells. Once the cells have been made and are ready, patients receive a few days of chemotherapy to make room for the modified T cells. This is called lymphodepleting chemotherapy. Unlike a stem cell transplant (described above), the purpose of this treatment is not only to empty a patient’s bone marrow. Patients are given the modified T cells via an intravenous (IV) infusion. The modified T cells are able to find and kill the lymphoma cells.

An important difference between stem cell transplantation and CAR T-cell therapy is that CAR-T is given when a patient has cancer you can see on scans such as a CT scan or a PET/CT scan. Stem cell transplantation is usually only done when patients have completed treatment and you and your doctor can no longer see the cancer on repeat scans, or are in remission.