Humans who have inherited the class I major histocompatibility allele HLA-A29 have a markedly increased relative risk of developing the eye disease termed birdshot chorioretinopathy. This disease affecting adults is characterized by symmetrically scattered, small, cream-colored spots in the fundus associated with retinal vasculopathy and inflammatory signs causing damage to the ocular structures, leading regularly to visual loss. To investigate the role of HLA-A29 in this disease, we introduced the HLA-A29 gene into mice. Aging HLA-A29 transgenic mice spontaneously developed retinopathy, showing a striking resemblance to the HLA-A29-associated chorioretinopathy. These results strongly suggest that HLA-A29 is involved in the pathogenesis of this disease. Elucidation of the role of HLA-A29 should be assisted by this transgenic model.

In the thymus, T cell development proceeds by successive steps of differentiation, expansion, and selection. Control of thymocyte proliferation is critical to insure the full function of the immune system and to prevent T cells from transformation. Deletion of the cell cycle inhibitor p16INK4a is frequently observed in human T cell neoplasias and, in mice, gene targeted inactivation of the Ink4a locus enhances thymocyte expansion and predisposes mutant animal to tumorigenesis. Here, we investigate the mechanism by which p16Ink4a controls thymocyte development by analyzing transgenic mice expressing the human p16INK4a into the T cell lineage. We show that forced expression of p16INK4a in thymocytes blocked T cell differentiation at the early CD4−CD8−CD3−CD25+ stage without significantly affecting the development of γδ T cells. Pre-TCR function was mimicked by the induction of CD3 signaling in thymocytes of recombinase activating gene (RAG)-2-deficient mice (RAG-2−/−). Upon anti-CD3ε treatment in vivo, p16INK4a-expressing RAG-2−/− thymocytes were not rescued from apoptosis, nor could they differentiate. Our data demonstrate that expression of p16INK4a prevents the pre-TCR-mediated expansion and/or survival of differentiating thymocytes.