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.