• Interleukin 12 (IL12) is a powerful cytokine encoded by two separate genes, IL12A (p35) and IL12B (p40), which exist in the form of an active heterodimer referred to as p70. The main producers of IL12 are dendritic cells and macrophages in response to antigenic stimulation. IL12 receptor (IL12R) is a complex consisting of interleukin 12 receptor beta 1 (IL12Rβ1) and interleukin 12 receptor beta 2 (IL12Rβ2) chains. IL12 is a major regulator of innate resistance and adaptive immunity, which can induce proliferation, activates cytotoxic lymphocytes and natural killer (NK) cells, increases interferon (IFN)-γ production, as well as favoring differentiation, augments the production of TH1-associated immunoglobulin. Because of its ability in pro-inflammatory and immunoregulatory, it can turn the tumor from “cold” to “hot”. IL12 is a promising anti-tumor drug. However, the administration of unmodified IL-12 may insufficiently accumulate in the tumor microenvironment specifically. In turn, it's hard to be effective and may cause severe immune-related adverse effects. So, modified IL12 or combined with other therapy agents may enhance its efficacy and overcome safety challenges.
• Protein expression analysis: Mouse PD-1 was only detectable in wild-type C57BL/6 mice. Human PD-1 was exclusively detectable in homozygous B-hPD-1 plus/hIL12RB1 /hIL12RB2 mice, but not in wild-type C57BL/6 mice.
• Functional analysis: Human IL12 induced the IFN-γ production in CD4+ T cells sorted from splenocytes of homozygous B-hPD-1 plus/hIL12RB1/hIL12RB2 mice.

Gene targeting strategy for B-hPD-1 plus/hIL12RB1/hIL12RB2 mice.

• The extracellular region sequences of mouse Il12rb1 were replaced by human IL12RB1 counterpart gene sequences in B-hPD-1 plus/hIL12RB1/hIL12RB2 mice.
• Chimeric CDS, composed of human IL12RB2 extracellular region plus mouse Il12rb2 transmembrane and cytoplasmic region, was inserted into the mouse Il12rb2 gene exon2 in B-hPD-1 plus/hIL12RB1/hIL12RB2 mice.
• Human PD-1 gene encoding the extracellular region and mouse Pd-1 gene encoding the transmembrane and cytoplasmic region were inserted after the initiation codon ATG of mouse Pd-1 gene in B-hPD-1 plus/hIL12RB1/hIL12RB2 mice.

Strain specific PD-1 expression analysis in wild-type C57BL/6 mice and homozygous humanized B-hPD-1 plus/hIL12RB1/hIL12RB2 mice by flow cytometry. Splenocytes were collected from wild-type C57BL/6 mice (+/+) and homozygous B-hPD-1 plus/hIL12RB1/hIL12RB2 mice (H/H) stimulated with anti-mouse CD3ε antibody (7.5 μg, i.p.) in vivo for 24 hrs. Protein expression was analyzed with anti-mouse PD-1 antibody (Biolegend, 109104) and anti-human PD-1 antibody (Biolegend, 329904) by flow cytometry. Mouse PD-1 was only detectable in wild-type C57BL/6 mice. Human PD-1 was exclusively detectable in homozygous B-hPD-1 plus/hIL12RB1/hIL12RB2 mice, but not in wild-type C57BL/6 mice.

IL12 induced the IFN-γ production in CD4+ T cells sorted from splenocytes. CD4+ T cells were sorted from the splenocytes in the wild-type C57BL/6 mice (+/+) and homozygous B-hPD-1 plus/hIL12RB1/hIL12RB2 mice (H/H), then the production of IFN-γ in supernatants were assessed after 48 h of incubation with rmIL-12 and rhIL-12 in combination with bead-associated CD3 and CD28 mAbs, under the condition in the panel. Mouse IFN-γ were both increased after responsiveness to rmIL-12 in wild-type C57BL/6 mice (+/+) and homozygous B-hPD-1 plus/hIL12RB1/hIL12RB2 mice (H/H). Mouse IFN-γ were increased after responsiveness to rhIL-12 in homozygous mice mice but not in wild-type mice.