Gene targeting strategy for B-hICOS/hICOSL mice. The exons 1-5 of mouse Icos gene that encode the full-length protein were replaced by human ICOS exons 1-5 in B-hICOS/hICOSL mice. The exons 3-5 of mouse IcosL gene that encode the extracellular domain were replaced by human ICOSLG exons 3-5 in B-hICOS/hICOSL mice.

Strain specific ICOS expression analysis in homozygous B-hICOS/hICOSL miceby flow cytometry. Splenocytes were collected from wild type (WT) mice (+/+) and homozygous B-hICOS/hICOSL mice (H/H; H/H) stimulated with anti-CD3ε in vivo and analyzed by flow cytometry with vopratelimab analog (in house), STIM-003 analog (in house) and GSK-3359609 analog (in house). ICOS was detectable in WT mice (+/+) and homozygous B-hICOS/hICOSL mice (H/H; H/H) due to the cross-reactivity of antibodies. Human ICOS was exclusively detectable in homozygous B-hICOS/hICOSL mice (H/H; H/H) but not in WT mice (+/+).

Strain specific ICOSL expression analysis in homozygous B-hICOS/hICOSL mice by flow cytometry. Splenocytes were collected from wild type (WT) mice (+/+) and homozygous B-hICOS/hICOSL mice (H/H; H/H) , and analyzed by flow cytometry with anti-human ICOSL antibody prezalumab analog (in house), antibody A and antibody B provided by the client. Human ICOSL was exclusively detectable in homozygous B-hICOS/hICOSL mice (H/H; H/H)  but not in WT mice (+/+).