JAK2 and myeloproliferative disorder: JAK2 inhibitor persistence in MPN was originally described by Koppikar et al. [41] who demonstrated that MPN model cells could be made to grow in high concentrations of ruxolitinib (and other type 1 JAK2 kinase inhibitors) and that this drug resistant state was reversible—cells cultured after removing the drug regain their sensitivity to JAK2 inhibitors.