Loss of T cell precursors after spaceflight and exposure to vector-averaged gravity

Using fetal thymus organ culture (FTOC), we examined the effects of spaceflight and vector-averaged gravity on T cell development. Under both conditions, the development of T cells was significantly attenuated. Exposure to spaceflight for 16 days resulted in a loss of precursors for CD4(+), CD8(+), and CD4(+) CD8(+) T cells in a rat/mouse xenogeneic co-culture. A significant decrease in the same precursor cells, as well as a decrease in CD4(-)CD8(-) T cell precursors, was also observed in a murine C57BL/6 FTOC after rotation in a clinostat to produce a vector-averaged microgravity-like environment. The block in T cell development appeared to occur between the pre-T cell and CD4(+)CD8(+) T cell stage. These data indicate that gravity plays a decisive role in the development of T cells.