A Cre-driven allele-conditioning line to interrogate CD4+ conventional T cells

CD4+ T cells share common developmental pathways with CD8+ T cells, and upon maturation, CD4+ T conventional T (Tconv) cells lack phenotypic markers that distinguish these cells from FoxP3+ T regulatory cells. We developed a tamoxifen-inducible ThPOKCreERT2.hCD2 line with Frt sites inserted on either side of the CreERT2-hCD2 cassette, and a Foxp3Ametrine-FlpO strain, expressing Ametrine and FlpO in Foxp3+ cells. Breeding these mice resulted in a CD4conviCreERT2-hCD2 line that allows for the specific manipulation of a gene in CD4+ Tconv cells. As FlpO removes the CreERT2-hCD2 cassette, CD4+ Treg cells are spared from Cre activity, which we refer to as allele conditioning. Comparison with an E8IiCreERT2.GFP mouse that enables inducible targeting of CD8+ T cells, and deletion of two inhibitory receptors, PD-1 and LAG-3, in a melanoma model, support the fidelity of these lines. These engineered mouse strains present a resource for the temporal manipulation of genes in CD4+ T cells and CD4+ Tconv cells.