Surviving rapamycin

T cell survival in the face of the immunosuppressive drug rapamycin depends on the expression of prosurvival proteins Pim-1 and Pim-2, according to a report by Fox et al. on page 259. Pim-1 and Pim-2 transmit signals that compensate for those that are wiped out by rapamycin; without the Pim proteins, rapamycin is deadly.

Rapamycin, a drug used to prevent rejection of transplants in humans, blocks the activation of a protein kinase called TOR (target of rapamycin), a component of a T cell signaling pathway that is important for cell survival and activation. Rapamycin works in transplant patients, but treatment of T cells with this drug in vitro or elimination of a signaling protein upstream of TOR in mice has little effect on T cell activation or survival....