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PDL1: Restoring the Peace
With great power comes great responsibility.
In superhero lore, special powers don’t separate the saviors from the evil villains they fight; instead, what matters is how the person behind the mask uses those powers. Immune cells are the superheroes of the body—they fight off infection and patrol the body for cancer. However, sometimes, even protective cells “go bad,” causing autoimmunity or graft-versus-host disease after transplant. Amarnath et al. now show that an inhibitory protein called programmed death ligand 1 (PDL1) can regulate renegade immune cells by converting immune response–promoting T helper type 1 (TH1) cells to regulatory T (Treg) cells—agents that selectively suppress activation of the immune system.
TH1 cells secrete proinflammatory cytokines and are critical for the immune response to infection and cancer cells. In contrast to other subsets of TH cells, researchers believed TH1 cells to be relatively stable. However, PDL1 caused human TH1 cells to convert to Treg cells both in vitro and in vivo. These TH1-derived Treg cells inhibited graft-versus-host disease in mice after transplant. Moreover, inhibiting Treg differentiation by blocking the PDL1 receptor PD1 or pharmacologically inhibiting SHP1 and SHP2, which are signaling molecules that act downstream of PD1 activation, restored graft-versus-host disease in mice. These data provide the basis for future therapies: Because PDL1 is highly expressed on many cancers, inhibiting this pathway may restore T cell–mediated cancer surveillance; alternately, accentuating signaling through this pathway may prevent autoimmunity or graft-versus-host disease. With this knowledge, scientists and doctors may be able to ensure that T cells are the superheroes they are meant to be.
Footnotes
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↵† These authors contributed equally to this work.
- Copyright © 2011, American Association for the Advancement of Science
