Inclusion Criteria:
Pre-Transplant Inclusion Criteria (Step 1)
* Male or female subject aged ≥ 18 years.
* Diagnosis of primary or secondary myelofibrosis.
* Eligible to undergo a myeloablative or reduced intensity conditioning regimen (MAC or RIC)
* Eligible to undergo a standard of care bone marrow biopsy with aspirate as part of his or her routine pre-transplant work-up.
* Peripheral blood stem cell (PBSC) graft
* 10/10 HLA matched related or matched unrelated donor
* ECOG performance status ≤ 2.
* For female subjects: Negative pregnancy test or evidence of post-menopausal status. The post-menopausal status will be defined as having been amenorrheic for 12 months without an alternative medical cause. The following age-specific requirements apply:
* Women \< 50 years of age:
* Amenorrheic for ≥ 12 months following cessation of exogenous hormonal treatments; and
* Luteinizing hormone and follicle-stimulating hormone levels in the post-menopausal range for the institution; or
* Underwent surgical sterilization (bilateral oophorectomy or hysterectomy).
* Women ≥ 50 years of age:
* Amenorrheic for 12 months or more following cessation of all exogenous hormonal treatments; or
* Had radiation-induced menopause with last menses \>1 year ago; or
* Had chemotherapy-induced menopause with last menses \>1 year ago; or
* Underwent surgical sterilization (bilateral oophorectomy, bilateral salpingectomy, or hysterectomy).
* Female subjects of childbearing potential and male subjects with a sexual partner of childbearing potential must agree to use a highly effective method of contraception as described in Section 5.4.1.
Treatment Inclusion Criteria (Step 2)
* Male or female subject aged ≥ 18 years.
* Diagnosis of primary or secondary myelofibrosis.
* Have undergone a myeloablative or reduced-intensity conditioning regimen (MAC or RIC) and be 50-80 days from Day 0 of transplant at initiation of study therapy.
* Peripheral blood stem cell (PBSC) graft
* 10/10 HLA matched related or matched unrelated donor
* ECOG Performance Status ≤ 2.
* Adequate organ function as defined as:
* Hepatic:
* Total Bilirubin ≤ 1.5x institutional upper limit of normal (ULN)
* AST(SGOT)/ALT(SGPT) ≤ 3 × institutional ULN
* Renal:
* Estimated creatinine clearance ≥ 30 mL/min by Cockcroft-Gault formula:
* TSH and T4 within normal limits or adequately controlled thyroid function.
* For female subjects: Negative pregnancy test or evidence of post-menopausal status. The post-menopausal status will be defined as having been amenorrheic for 12 months without an alternative medical cause. The following age-specific requirements apply:
* Women \< 50 years of age:
* Amenorrheic for ≥ 12 months following cessation of exogenous hormonal treatments; and
* Luteinizing hormone and follicle-stimulating hormone levels in the post-menopausal range for the institution; or
* Underwent surgical sterilization (bilateral oophorectomy or hysterectomy).
* Women ≥ 50 years of age:
* Amenorrheic for 12 months or more following cessation of all exogenous hormonal treatments; or
* Had radiation-induced menopause with last menses \>1 year ago; or
* Had chemotherapy-induced menopause with last menses \>1 year ago; or
* Underwent surgical sterilization (bilateral oophorectomy, bilateral salpingectomy, or hysterectomy).
* Female subjects of childbearing potential and male subjects with a sexual partner of childbearing potential must agree to use a highly effective method of contraception as described in Section 5.4.1.
* Male subjects must agree to use a condom during intercourse for the duration of study therapy as described in Section 5.4.1.
* Recovery to baseline or ≤ Grade 1 CTCAE v5.0 from toxicities related to any prior cancer therapy, unless considered clinically not significant by the treating investigator.
* Able to provide informed consent and willing to sign an approved consent form that conforms to federal and institutional guidelines.
Exclusion Criteria:
Exclusion Criteria (Step 2)
* Receiving other investigational agents concurrently
* Prior systemic anti-cancer therapy or any investigational therapy within five half-lives prior to starting study treatment.
* Prior radiotherapy within 6 weeks prior to the first dose of study treatment.
* Major surgery within 6 weeks prior to starting study drug or patients who have not fully recovered from major surgery.
* The diagnosis of another malignancy within ≤ 2 years before study enrollment, except for those considered to be adequately treated with no evidence of disease or symptoms and/or will not require therapy during the study duration (i.e., basal cell or squamous cell skin cancer, carcinoma in situ of the breast, bladder or of the cervix, or low-grade prostate cancer with Gleason Score ≤ 6).
* Current evidence of uncontrolled, significant intercurrent illness including, but not limited to, the following conditions:
* Graft-versus-host disease:
---Acute or chronic
* Cardiovascular disorders:
* Congestive heart failure New York Heart Association Class III or IV, unstable angina pectoris, serious cardiac arrhythmias.
* Stroke (including transient ischemic attack \[TIA\]), myocardial infarction (MI), or other ischemic events, or thromboembolic event (eg, deep venous thrombosis, pulmonary embolism) within 3 months before the first dose.
* QTc prolongation defined as a QTcF \> 500 ms.
* Known congenital long QT.
* Left ventricular ejection fraction \< 55%.
* Uncontrolled hypertension defined as ≥ 140/90 as assessed from the mean of three consecutive blood pressure measurements taken over 10 minutes.
* Any other condition that would, in the Investigator's judgment, contraindicate the subject's participation in the clinical study due to safety concerns or compliance with clinical study procedures (e.g., infection/inflammation, intestinal obstruction, unable to swallow medication, \[subjects may not receive the drug through a feeding tube\], social/ psychological issues, etc.)
* Active infection including HIV, tuberculosis (clinical evaluation that includes clinical history, physical examination, radiographic findings, and TB testing in line with local practice) or hepatitis C.
* Note: Subjects with a past or resolved HBV infection (defined as the presence of hepatitis B core antibody \[anti-HBc\] and absence of HBsAg) are eligible.
* Autoimmune hepatitis or decompensated hepatic disease
* Medical, psychiatric, cognitive, or other conditions that may compromise the subject's ability to understand the subject information, give informed consent, comply with the study protocol or complete the study.
* Known prior severe hypersensitivity to investigational product (IP) or any component in its formulations (NCI CTCAE v5.0 Grade ≥ 3).
* Subjects taking prohibited medications as described in Section 6.5.1. A washout period of prohibited medications for a period of at least five half-lives or as clinically indicated should occur before the start of treatment.
* History of neuropsychiatric disease, autoimmune disease, or pancreatitis.
* Presence of active interstitial lung disease or pneumonitis, bronchiolitis obliterans, pulmonary hypertension, ulcerative and hemorrhagic/ischemic colitis, and ophthalmologic disorders.
