A 36-year-old male with history of acute icteric hepatitis 6 months ago presents with fever and gingival bleeding for 15 days. Examination shows severe anemic appearance, liver palpable 2 cm below costal margin, spleen just palpable below costal margin. Laboratory tests: RBC 1.8×10¹²/L, Hb 55 g/L, WBC 2.5×10⁹/L, PLT 32×10⁹/L, reticulocytes 0.2%. The most likely diagnosis is: