PD-1 (Programmed death-1) is mainly expressed on the surface of T cells and primary B cells. The two PD-1 ligands, PD-L1 and PD-L2, are widely expressed on antigen-presenting cells (APCs). PD-1 interacts with its ligands and plays an important role in the negative regulation of the immune response. PD-L1 protein expression is detected in many human tumor tissues. PD-L1 expression in tumor cells could be induced by the microenvironment of tumor cells. PD-L1 expression is favorable for tumorigenesis and growth, for induction of anti-tumor T Cell Apoptosis, and for escaping responses by the immune system. Inhibition of PD-1 binding to its ligand can result in tumor cells that are exposed to the killing version of the immune system, and thus is a target for cancer treatments.
CTLA4 (Cytotoxic T-lymphocyte-associated protein 4), also known as CD152, competitively binds to B7-1 (CD80) and B7-2 (CD86) on Antigen-Presenting Cells (APCs) to block the T cell activating signal by B7 and CD28 (on T cells) interaction. The inhibition of CTLA4 by its inhibitory antibodies enhances T cell activity. The CTLA4 antibody is the first FDA-approved antibody to treat advanced melanoma.
Gene targeting strategy for B-hPD-1/hCTLA4 mice. The exon 2 of mouse Pd-1 gene that encodes the extracellular domain was replaced by human PD-1 exon 2 in B-hPD-1/hCTLA4 mice. The exon 2 of mouse Ctla4 gene that encodes the extracellular domain was replaced by human CTLA4 exon 2 in B-hPD-1/hCTLA4 mice.
Protein Expression Analysis
Strain specific PD-1 and CTLA4 expression analysis in homozygous B-hPD-1/hCTLA4 mice by flow cytometry. Splenocytes were collected from WT and homozygous B-hPD-1/hCTLA4 (H/H) mice stimulated with anti-CD3ε in vivo, and analyzed by flow cytometry with species-specific anti-PD-1 and anti-CTLA4 antibody. Mouse PD-1 and CTLA4 were detectable in WT mice. Human PD-1 and CTLA4 were exclusively detectable in homozygous B-hPD-1/hCTLA4 but not WT mice.
Combination therapy of anti-human PD-1 antibody and anti-human CTLA4 antibody
Antitumor activity of anti-human PD-1 antibody combined with anti-human CTLA4 antibody in B-hPD-1/hCTLA4 mice. (A) Anti-human PD-1 antibody combined with anti-human CTLA4 antibody inhibited MC38 tumor growth in B-hPD-1/hCTLA4 mice. Murine colon cancer MC38 cells were subcutaneously implanted into homozygous B-hPD-1/hCTLA4 mice (female, 6-7 week-old, n=5). Mice were grouped when tumor volume reached approximately 100 mm3, at which time they were treated with pembrolizumab and ipilimumab with doses and schedules indicated in panel (B) Body weight changes during treatment. As shown in panel A, combination of pembrolizumab and ipilimumab shows more inhibitory effects than individual groups, demonstrating that the B-hPD-1/hCTLA4 mice provide a powerful preclinical model for in vivo evaluating combination therapy efficacy of hPD-1 antibodies and hCTLA4 antibodies. Values are expressed as mean ± SEM.
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