Transfer of total lymph node (LN) lymphocytes to severe combined immunodeficient (SCID) mice leads to the long term establishment of mucosal T cells within the epithelium and lamina propria of the intestine. Analysis of engrafted intraepithelial lymphocytes (IEL) showed that they acquired a surface phenotype (CD69+, αE+, CD62L-) which was typical of IEL, but distinct from the donor LN lymphocytes. In addition, the functional profile of engrafted IEL in vitro mimicked that of normal IEL in that the engrafted T cells exhibited strong cytolytic activity in redirected lysis assays, but poor proliferative responses to mitogenic stimuli. The donor LN population, on the other hand, proliferated well to mitogenic stimuli and had no de novo cytolytic activity. When SCID mice were transplanted with either sorted CD4+ or CD8+ LN T cells, IEL isolated from both subsets of mice were again cytolytic. This activity was specific to IEL, as cells isolated from the adjacent lamina propria or the spleen were not cytolytic. As a significant proportion of CD4+ T cells acquire expression of CD8α homodimer (CD8αα) once resident within the epithelium,(approaching 50%), experiments are currently underway to determine if cytolytic activity resides within the CD4 single positive subset or the CD4,CD8αα double positive subset or both. Our results demonstrate that LN T cells can migrate to the intestine and become functionally specialized within that milieu. This suggests that the intestinal epithelial microenvironment induces specific phenotypic changes and thereby broadens the functional specificity of post thymic T cells. Funded by the Robert Wood Johnson Foundation and the American Digestive Health Foundation (VC), Crohn's and Colitis Foundation of America (BCS) and NIH-DK46763 (MK).