The study's primary objective is to determine the maximum tolerated dose (MTD) and dose-limiting toxicity (DLT) of Panobinostat when administered within 150 days after hematopoietic stem cell transplantation (HSCT) and given in conjunction with standard immunosuppressive therapy after HSCT for patients with high-risk Myelodysplastic Syndrome (MDS) or Acute Myeloid Leukemia (AML).