Evaluating the Safety of G-CSF Mobilization in Individuals With Beta Thalassemia Major

Overview

Beta thalassemia major is a serious genetic disease of the blood. Treatments are limited, and although a bone marrow transplant from a compatible donor can be curative, only a limited percentage of individuals with this disease have a matched donor available. A long-term goal of study researchers is to develop a gene transfer process as a method of curing beta thalassemia major. Gene transfer involves obtaining blood stem cells from an individual, adding a normal globin gene to the stem cells, and putting the cells back into the individual. Before gene transfer methods can be attempted in individuals with beta thalassemia major, a safe method of obtaining blood stem cells needs to be developed. The purpose of this study is to investigate the safety and feasibility of collecting peripheral blood stem cells (PBSC) from individuals with beta thalassemia major. Research participants will be given G-CSF (filgrastim) for several days to increase the number of stem cells in the blood, a process called "mobilization." After mobilization, participants will undergo a procedure called apheresis to remove the white blood cells. Researchers in the laboratory will purify the stem cells from the mixture and test methods of putting a normal globin gene into the stem cells. Half of the participants will receive hydroxyurea (HU) prior to G-CSF mobilization. HU is used in splenectomized patients to attempt to reduce the risk of clotting during mobilization. In non-splenectomized patients, HU is given in an attempt to decrease the size of the spleen.

Primary Objective: To determine the safety of PBSC mobilization with G-CSF, with or without HU pretreatment in adults with beta thalassemia major. Secondary Objective: To determine the number of CD34+ stem/progenitor cells that are mobilized under these conditions, as well as the ability of these cells to be transduced with a recombinant lentivirus vector for beta-globin and engraft immunodeficient mice. Study Design: The ability of G-CSF to safely and effectively mobilize PBSC in adults with beta thalassemia major will be assessed in 12 splenectomized and 12 non-splenectomized patients. Of the 12 splenectomized patients, 6 will be treated with HU and G-CSF, and 6 will be treated only with G-CSF. Likewise, of the 12 non-splenectomized patients, 6 will be treated with HU and G-CSF, and 6 will be treated only with G-CSF. G-CSF mobilized participants will undergo leukapheresis on 2 consecutive days, with a target yield of 2 million CD34+ cells per kg of body weight. Safety will be assessed by monitoring for study-related toxicity. Efficacy will be assessed by measuring the total number of CD34+ cells, the ability of these cells to be transduced with a recombinant lentivirus vector for beta-globin, and the ability of these cells to engraft immunodeficient mice. Population: Adults with beta thalassemia major. Sample size: A total of 24 subjects will be enrolled: 12 splenectomized participants and 12 non-splenectomized participants. End Points: This is a pilot study and no specific hypotheses are being tested. However, the study will allow for qualitative comparisons if outcomes between the various arms are markedly different. For example, the study will provide qualitative data on the safety and feasibility of utilizing HU and G-CSF to mobilize stem cells in individuals with beta thalassemia major. The study will be completed upon full enrollment, or when stopping criteria are met within specific study arms.