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(1) CTLA-4 is a negative regulator of T-cell activation. (2) Conventional T-cells are activated by engagement of MHC and B7. (3) Upon activation, T-cells express CTLA-4 on the cells surface and the union of CTLA-4 with B7 inhibits T-cell activation. (4) Antibody blockade of CTLA-4 produces the liberation of CD28 which could engage with B7 with the best activation of T-cells.
