CD39 Expression identifies terminally exhausted CD8+ T cells by Gupta, P, Godec, J, Wolski, D, Adland, E, Yates, K, Pauken, K, Cosgrove, C, Ledderose, C, Junger, W, Robson, S, Wherry, E, Alter, G, Goulder, P, Klenerman, P, Sharpe, A, Lauer, G, Haining, W