• CD28 (Cluster of Differentiation 28) is one of the proteins expressed on T cells that provide co-stimulatory signals required for T cell activation and survival. T cell stimulation through CD28 in addition to the T-cell receptor (TCR) can provide a potent signal for the production of various interleukins (IL-6 in particular).
• CD28 is the receptor for CD80 (B7.1) and CD86 (B7.2) proteins. When activated by Toll-like receptor ligands, the CD80 expression is upregulated in antigen-presenting cells (APCs). The CD86 expression on antigen-presenting cells is constitutive (expression is independent of environmental factors).
• The exons 2-3 of mouse Cd28 gene that encode the extracellular domain were replaced by human CD28 exons 2-3 in B-hCD28 mice.
• Mouse CD28 was exclusively detectable in wild-type mice. Human CD28 was detectable in homozygous B-hCD28 mice(C).
• B-hCD28 mice can be used to study the in vivo efficacy and safety evaluation of CD28 antibody drugs.

Gene targeting strategy for B-hCD28 mice(C). The exons 2-3 of mouse Cd28 gene that encode the extracellular domain were replaced by human CD28 exons 2-3 in B-hCD28 mice(C).

Strain specific CD28 expression analysis in homozygous B-hCD28 mice(C) by flow cytometry. Splenocytes were collected from wild-type BALB/cCrSlcNifdc mice (+/+) and homozygous B-hCD28 mice(C) (H/H) stimulated with anti-CD3ε antibody (7.5ug/200uL, 24h, i.p.) in vivo, analyzed by flow cytometry with species-specific anti-CD28 antibody. Mouse CD28 was exclusively detectable in wild-type mice. Human CD28 was detectable in homozygous B-hCD28 mice(C).

Frequency of leukocyte subpopulations in spleen by flow cytometry. Splenocytes were isolated from wild-type BALB/cCrSlcNifdc mice (Female, n=3, 8-week-old) and homozygous B-hCD28 mice(C) (Female, n=3, 8-week-old). A. Flow cytometry analysis of the splenocytes was performed to assess the frequency of leukocyte subpopulations. B. Frequency of T cell subpopulations. Percentages of T cells, B cells, NK cells, dendritic cells, monocytes, macrophages, CD4+ T cells, CD8+ T cells and Tregs in B-hCD28 mice(C) were similar in wild-type BALB/cCrSlcNifdc mice.