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-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. PD-L1 (Programmed cell death ligand-1), also known as B7-H1 and CD274, is mainly expressed in antigen-presenting cells (APCs) and activated T cells, and is one of the two ligands of PD-1. The interaction between PD1 and PD-L1 plays an important role in the negative regulation of the immune response. PD-L1 is highly expressed in a variety of solid tumors. PD-1 and PD-L1 interactions can reduce T cell activation and promote tumor immune escape. The PD-1/PD-L1 signaling pathway can be blocked and antitumor immune response can be restored by using by anti-PD-1 or anti-PD-L1 antibodies to block the binding of PD1 to PD-L1. CD25 is a 55 kD glycoprotein, also known as the low affinity IL-2Rα, Ly-43, p55, or Tac. It is expressed on activated T and B cells, thymocyte subset, pre-B cells, and T regulatory cells. In association with CD122 (IL-2Rβ) and CD132(common γ chain), CD25 forms the high affinity signaling IL-2 receptor. Its afﬁnity for IL2 and cellular function are tightly regulated and vary in different cell types. The high frequency of CD25 on the surface of many different haematological tumour cells is now well established and, apart from its prognostic signiﬁcance, CD25 may be present on leukaemic stem cells and enable oncogenic signalling pathways in leukaemic cells. Additionally, high CD25 expression in activated circulating immune cells and Tregs is a factor that has already been exploited by IL2 immunotherapies for treatment of tumours and autoimmune disease. The relative clinical safety and efﬁcacy of administering anti-CD25 radioimmunoconjugates and immunotoxins in various haematological tumour indications has been established and clinical trials of a novel CD25-directed antibody drug conjugate are underway.
Gene targeting strategy for B-hPD-1/hPD-L1/hIL2RA 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/hPD-L1/hIL2RA mice. The exon 3 of mouse Pd-l1 gene that encodes the extracellular domain was replaced by human PD-L1 exon 3 in B-hPD-1/hPD-L1/hIL2RA mice. The exons 2-6 of mouse Il2ra gene that encode the extracellular domain were replaced by human IL2RA exons 2-6 in B-hPD-1/hPD-L1/hIL2RA mice.
Protein expression analysis in T cells
Strain specific PD-1, PDL1 and IL2RA expression analysis in homozygous B-hPD-1/hPD-L1/hIL2RA mice by flow cytometry. Splenocytes were collected from WT and homozygous B-hPD-1/hPD-L1/hIL2RA mice stimulated with anti-CD3ε in vivo, and analyzed by flow cytometry with species-specific PD-1, PD-L1 and IL2RA antibody. Mouse PD-1, PD-L1 and IL2RA were detectable in WT mice. Human PD-1, PD-L1 and IL2RA were exclusively detectable in homozygous B-hPD-1/hPD-L1/hIL2RA but not WT mice.
Protein expression analysis of IL2RA in Tregs
Strain specific IL2RA expression analysis in homozygous B-hPD-1/hPD-L1/hIL2RA mice by flow cytometry. Splenocytes were collected from WT and homozygous B-hPD-1/hPD-L1/hIL2RA mice stimulated with anti-CD3ε in vivo, and analyzed by flow cytometry with species-specific IL2RA antibody. Mouse IL2RA were detectable in WT mice. Human IL2RA were exclusively detectable in homozygous B-hPD-1/hPD-L1/hIL2RA but not WT mice.