Quorum regulation via nested antagonistic feedback circuits mediated by the receptors CD28 and CTLA-4 confers robustness to T cell population dynamics Por Zenke, S, Palm, MM, Braun, J, Gavrilov, A, Meiser, P, Böttcher, JP, Beyersdorf, N, Ehl, S, Gerard, A, Lämmermann, T, Schumacher, TN, Beltman, JB, Rohr, JC