Increase in survival in Jak2V617F C57Bl/6 compared with Jak2V617F Balb/c mice. (A) Kaplan-Meier survival plot showing death of all Jak2V617F-expressing Balb/c mice between 50 and 95 days marked by the red line (n = 22), of 3 C57Bl/6 mice between 65 and 75 days marked by the blue line (3 of 18), and normal life expectancy for Jak2wt Balb/c and C57Bl/6 mice marked by the green line (n = 10 for each group). (B) Southern blot analysis demonstrating oligoclonal retroviral integration in spleen cells of 5 Jak2V617F mice after transplantation, which was polyclonal in Jak2wt mice and absent in the spleen of an untransduced wild-type animal. (C) Inverse correlation between high endogenous HCTs of 0.65 to 0.75 and low serum EPO levels of 10 pg/mL in 4 Balb/c mice and 1 C57Bl/6 mouse expressing Jak2V617F and normal serum EPO levels of 150 and 250 pg/mL in 1 Balb/c mouse and 1 C57Bl/6 mouse expressing Jak2wt with normal HCTs and appropriately high serum EPO levels in 5-fluorouracil–treated anemic animals.