In a study by Zhang et al, using CD19-specific CAR-T cells, it was shown that human orthogonal IL-2 (ortho-hIL-2) induced a 1000-fold increase in ortho-hIL-2Rβ+ CAR-T cell expansion in a dose-dependent manner in vivo, 2 weeks after adoptive transfer into immunodeficient mice bearing CD19+ Nalm6 leukemia xenografts. Here, CD19 is linked to leukemia.