B6-hCD28 Mouse

The CD28 gene encodes the CD28 protein, a crucial co-stimulatory receptor found primarily on T cells, with expression typically on over 80% of human CD4+ T cells and about 50% of CD8+ T cells. It is also expressed, though less understood, on bone marrow stromal cells, plasma cells, neutrophils, and eosinophils, and some B cells ^[1]. The encoded protein is a disulfide-linked homodimer belonging to the immunoglobulin superfamily, serving as a receptor for CD80 (B7-1) and CD86 (B7-2) found on antigen-presenting cells (APCs) ^[2]. Its primary function is to provide essential "second signals" for optimal T cell activation, proliferation, survival, and differentiation (including cytokine production like IL-2, IL-4, IL-10, and T-helper type-2 development), complementing the T-cell receptor (TCR) signal. Without CD28 engagement, TCR stimulation often leads to T cell anergy (unresponsiveness) ^[3]. The gene's expression can be modulated, with some antigen-experienced T cells losing CD28 expression, particularly with age or during chronic infections, leading to a "senescent" or "exhausted" phenotype. Dysregulation of CD28 signaling is implicated in various associated diseases, including autoimmune disorders such as rheumatoid arthritis, Sjogren's syndrome, and systemic sclerosis, as well as in transplant rejection, certain cancers (e.g., T-cell lymphomas, acute myeloid leukemia, breast cancer), and chronic infections like HIV, where its downregulation by viral proteins can impair T cell function ^[4].

The B6-hCD28 mouse is a humanized model, constructed by replacing the mouse Cd28 endogenous extracellular domain (aa.20~150) with the human CD28 extracellular domain (aa.19~152). The murine signal peptide (aa.1~19) and aa.151~218 are preserved. B6-hCD28 mice can be used for research into the pathogenesis of autoimmune disorders such as rheumatoid arthritis, Sjogren's syndrome, and systemic sclerosis, as well as in transplant rejection, certain cancers (e.g., T-cell lymphomas, acute myeloid leukemia, breast cancer), and chronic infections like HIV. They are also useful for the screening, development, and safety evaluation of CD28-targeted drugs.