Human T-cell alloreactivity plays an important role in many disease processes, including the rejection of solid organ grafts and graft-versus-host disease (GVHD) following allogeneic stem cell transplantation. To develop a better understanding of the T cells involved in alloreactivity in humans, we developed a cytokine flow cytometry (CFC) assay that enabled us to characterize the phenotypic and functional characteristic of T cells responding to allogeneic stimuli. Using this approach, we determined that most T-cell alloreactivity resided within the CD4( ) T-cell subset, as assessed by activation marker expression and the production of effector cytokines (eg, tumor necrosis factor alpha [TNF]alpha) implicated in human GVHD. Following prolonged stimulation in vitro using either allogeneic stimulator cells or viral antigens, we found that coexpression of activation markers within the CD4( ) T-cell subset occurred exclusively within a subpopulation of T cells that significantly increased their surface expression of CD4. We then developed a simple sorting strategy that exploited these phenotypic characteristics to specifically deplete alloreactive T cells while retaining broad specificity for other stimuli, including viral antigens and third-party alloantigens. This approach also was applied to specifically enrich or deplete human virus-specific T cells.

The cancer "Stem cell" theory comes from studies with blood cancers such as leukemiaterm, which are known to grow out of a subset of corrupted hematopoetic stem cells. In some studies, antibodies to the CD44 marker have been able to attach to these cells and block them from attaching to the bone marrow in a new mouse. Here Stanford and Michigan researchers seperated cancer cells from a solid tumor according to the CD44 marker using a technique known as Fluorescense Activated Cell Sorting in which a Flow Cytometerterm physically separates the cells.

Researchers have found a marker on head and neck tumor cells that indicates which cells are capable of fueling the cancer's growth. The finding is the first evidence of cancer stem cells in head and neck tumors.