CRLF2 and Splenomegaly: A subset of recipient mice transplanted with Eμ-Crlf2 FLCs expressing Jak2 mutants (Jak2R683G and Jak2P933R) succumbed to disease with outgrowth of GFP+ populations in the spleen and bone marrow and elevated peripheral white blood cell (WBC) counts and/or splenomegaly (Supplemental Fig. S2C–G).