TEM CELLS ARE UNDIFFERENTIated cells that through replication have the capability of both self-renewal and differentiation into mature specialized cells. In broad terms, there are 2 types of stem cells, embryonic stem cells and adult stem cells. Human embryonic stem cells are isolated from a 50-to 150-cell, 4-to 5-dayold postfertilization blastocyst. Embryonic stem cells generate every specialized cell in the human body and, while capable of indefinite ex vivo proliferation, exist only transiently in vivo (during embryogenesis). Adult stem cells are located in tissues throughout the body and function as a reservoir to replace damaged or aging cells. Under physiologic conditions, adult stem cells are traditionally thought to be restricted in their differentiation to cell lineages of the organ system in which they are located. Embryonic stem cells have great promise and versatility but, compared with adult stem cells, are currently difficult to control due to their tendency to form tumors containing all types of tissue, ie, teratomas. Embryonic stem cell biology has been associated with ethical controversy, and feeder cellfree and xenogeneic-free culture methods approved by the US Food and Drug Administration are still being per-Author Affiliations are listed at the end of this article.
Patients undergoing autologous hematopoietic stem cell transplantation (auto-HSCT) for autoimmune disease may have an added propensity to develop a second autoimmune disorder, given the genetic predisposition to autoimmunity. Therefore, we undertook a retrospective analysis of all patients who have undergone auto-HSCT for an autoimmune disease in our institution to determine the occurrence of a second autoimmune disorder and possible risk factors. In all, 155 patients underwent auto-HSCT for various autoimmune diseases; of those patients, 6 manifested a distinct secondary autoimmune disease at a median of 8.5 months (range, 2-30 months) after auto-HSCT. There were 2 patients with systemic lupus erythematosus, conditioned with a regimen containing antithymocyte globulin (ATG), who developed factor VIII inhibitors with severe bleeding. There were 4 patients (2 with multiple sclerosis, one each with lupus and systemic sclerosis) who received an alemtuzumab-containing conditioning regimen who developed autoimmune cytopenias. Among the 155 patients, the frequency of secondary autoimmune complications was 16.0% with alemtuzumab (4/25), 1.9% for ATG (2/102), and 0% for conditioning regimens without lympho-depleting antibodies (0/28)-a difference that was found to be significantly higher with alemtuzumab exposure (P ؍ .011). In contrast, sex, type of ATG used, and CD34-selection of peripheral blood stem cells were not found to be significantly associated with development of a secondary autoimmune disorder. (Blood. 2007;109:2643-2648)
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