Itacitinib With High-dose Posttransplantation Cyclophosphamide in Older Patients

This research is being done to learn whether drug called itacitinib, which is a novel inflammation- and immune-lowering drug (immunosuppressant), can be given before and after non-myeloablative peripheral blood stem cell transplantation (PBSCT; also known as a 'mini' transplant) to help prevent certain complications such as cytokine release syndrome (CRS) for patients with blood cancers, using peripheral blood from a relative. The investigators will also examine if by using itacitinib the investigators can reduce the duration of MMF (other immune suppressive drug administration posttransplant).

Inclusion Criteria: * Presence of a suitable related, HLA-haploidentical (partially mismatched) stem cell donor. * Eligible diagnoses: 1. Acute leukemias in complete remission with minimal residual disease 2. Myelodysplastic syndrome (MDS) with at least one poor-risk feature 3. Chronic myelomonocytic leukemia with at least one poor-risk feature 4. T-cell PLL in PR or better prior to transplantation. 5. Tyrosine kinase-refractory CML in first chronic phase, TKI-intolerant CML in first chronic phase, or CML in second or subsequent chronic phase. 6. Philadelphia chromosome negative myeloproliferative disease (including myelofibrosis) 7. Multiple myeloma or plasma cell leukemia with a PR or better to the last treatment regimen * Age ≥ 60 years. * Adequate end-organ function as measured by: 1. Left ventricular ejection fraction ≥ 35% or shortening fraction \> 25% 2. Bilirubin ≤ 3.0 mg/dL (unless due to Gilbert's syndrome or hemolysis), and ALT and AST ≤ 5 x ULN 3. FEV1 and FVC ≥ 40% of predicted * ECOG performance status ≤ 2 or Karnofsky score ≥ 60 Exclusion Criteria: * No active extramedullary leukemia or known active CNS involvement by malignancy. * Any previous autologous HSCT must have occurred at least 3 months prior to start of conditioning. * No previous allogeneic HSCT. * Not pregnant or breast-feeding * No uncontrolled infection. * No known HIV infection. * No active replicating HBV or HCV infection detected by PCR that requires treatment or at risk for HBV reactivation (positive HBsAg)