CD8⁺CLTA-4^–/–T-cell–mediated autoimmunity required CD4⁺CLTA- 4^–/–T cells. (A) Lack of CD4⁺ T cells in pmel-1 Rag-1^–/– CTLA-4^–/– mice. Flow cytometry for CD4 and CD8 expression on splenocytes from pmel-1 Rag-1^–/– CTLA-4^–/– mice. Results are shown after lymphocyte gating. (B) Absence of coat depigmentation in pmel-1 Rag^–/– CTLA-4^–/– mice. Pmel-1 Rag^–/– CTLA-4^–/– (left) and pmel-1 CTLA-4^–/– (right) littermates are depicted at 10 weeks of age. Autoimmune vitiligo is present over more than 75% of the body surface of pmel-1 CTLA-4^–/– mice. (C) Pmel-1 Rag^–/– CTLA-4^–/– CD8⁺ T cells exhibit a naive phenotype. Flow cytometry for CD44 expression on CD8⁺ splenocytes from pmel-1 CTLA-4^–/– and pmel-1 Rag^–/– CTLA-4^–/– mice. Results are shown after gating for CD8.