Characterization of the TRP-1 CD4⁺ model. (A) Characteristic cappuccino phenotype of white-based brown mutation (B^w) after 8 rounds of backcrossing onto a C57BL/6 background using “speed congenics.” The coat color appearance derives from a defect in exon 1 of tyrosinase-related protein-1 (tyrp1) gene. The MHC class II–restricted TCR used to create the TRP-1–specific transgenic mouse was isolated from B^w mice after multiple rounds of vaccination. (B) RAG1^−/−B^w TRP-1 Tg⁺ animals are marginally protected against the B16 challenge. C57BL/6, RAG1^−/−, RAG1^−/−B^w, and their RAG1^−/−B^wTRP-1 TCR transgenic littermates were injected subcutaneously with 0.5 × 10⁶ B16 melanoma cells. Results for tumor area are the mean of measurements from at least 5 mice per group (± SEM). Data shown are representative of 2 independent experiments. (C) Adoptive transfer of 0.25 × 10⁶ naive purified TRP-1 CD4⁺ T cells into a tyrp1^+/+ (wt, black) RAG1^−/− mouse results in a rapid development of massive vitiligo. (D) H&E staining of ocular tissue from the mice that received adoptive transfer of naive TRP-1 cells revealed diffuse damage with edema, retinal folding, disruption of pigmented epithelium, and inflammatory infiltrate in the choroid. (E) An H&E stain of a normal eye at a similar magnification from an untreated RAG1^−/− mouse is shown as a control.