A 29-year-old male presents with dizziness and fatigue for 3 months, scattered petechiae, non-palpable spleen. Lab findings: Hb 80 g/L, WBC 3.5×10<sup>9</sup>/L (neutrophils 35%, lymphocytes 55%), platelets 50×10<sup>9</sup>/L. Acidified serum hemolysis test is negative, and megakaryocytes are absent on bone marrow smear. The most likely diagnosis is: