Interference with the MHC class 2 pathway inhibits CTCL cell expression of a Treg phenotype. Coexpression of membrane CD3 and cytoplasmic CTLA-4 was measured in responding CTCL cells by flow cytometry. (A) CTCL cells cocultured overnight with nonloaded DCs. (B) CTCL cells stimulated with DCs that had been pulsed with CD3-treated apoptotic tumor cells and cultured in the presence of an isotype-matched control antibody (immunoglobulin G2a [IgG2a]). (C) An anti-DR antibody was added to cocultures of tumor-loaded DCs and responding CTCL cells. Coexpression of the clonotypic TCR was measured by monitoring the expression of membrane Vβ8 and cytoplasmic CTLA-4 in responding CTCL cells. (D) CTCL cells were incubated overnight with nonpulsed DCs. (E) CTCL cells were stimulated with DCs that had ingested apoptotic tumor cells. (F) CTCL cells were stimulated with tumor-loaded DCs in the presence of Brefeldin A.