Can ruxolitinib stop a deadly transplant complication in kids?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Documented informed consent of the participant and/or legally authorized representative * Assent, when appropriate, will be obtained per institutional guidelines * Agreement to allow the use of archival tissue from diagnostic tumor biopsies * If unavailable, exceptions may be granted with study primary investigator (PI) approval * Age: 2-22 * Weight ≥25kg * Eastern Cooperative Oncology Group (ECOG) ≤ 2 * Performance status: Karnofsky ≥ 60% for patients ≥ 16 years old OR Lansky status ≥ 60% for patients \< 16 years old * Candidate for allogeneic bone marrow transplant with and available matched related donor (MRD) or an 8/8 matched unrelated donor (MUD) who is willing to donate bone marrow (BM) or mobilized peripheral blood stem cells * Note: Donor selection process will be in accordance with City of Hope (COH)-standard operating procedures (SOPs) (B.001.09 Allogeneic Cellular Therapy Product Donor Evaluation, Selection \& Consent), which follows Food and Drug Administration (FDA) guidelines for donation of hematopoietic stem/progenitor cells (HPCs) obtained from peripheral blood or bone marrow * Diagnosis of acute leukemia (acute myeloid leukemia \[AML\] or acute lymphoblastic leukemia \[ALL\]) in complete remission, or myelodysplastic syndrome (MDS) * Fully recovered from the acute toxic effects (except alopecia) to ≤ grade 1 from prior anti-cancer therapy * Women of childbearing potential (WOCBP): negative urine or serum pregnancy test. If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required (to be performed within 30 days prior to day 1 of protocol therapy) * Agreement by females and males of childbearing potential to use an effective method of birth control or abstain from heterosexual activity for the course of the study through at least 6 months after the last dose of protocol therapy * Childbearing potential defined as not being surgically sterilized (men and women) or have not been free from menses for \> 1 year (women only) Exclusion Criteria: * Autologous stem cell transplant within 1 year prior to day 1 of protocol therapy * Prior allogeneic transplantation * Chemotherapy, radiation therapy, biological therapy, immunotherapy within 14 days prior to day 1 of protocol therapy * Note: Conditioning regimen within 21 days prior to day 1 of protocol therapy is not considered as an exclusion criterion. * Note: Patients on maintenance chemotherapy with agents listed are not excluded * Herbal medications * History of allergic reactions attributed to compounds of similar chemical or biologic composition to study agent * History of active tuberculosis * Patients with history of thrombosis including but not limited to myocardial infarction (MI)/stroke and pulmonary embolism (PE)/deep vein thrombosis (DVT) within 6 months of enrollment * Active diarrhea due to inflammatory bowel disease or malabsorption syndrome * Clinically significant uncontrolled illness * Active, uncontrolled systemic infection (viral, bacterial, or fungal) requiring antibiotics * Known history of immunodeficiency virus (HIV) or hepatitis B or hepatitis C infection * Other active malignancy * Females only: Pregnant or breastfeeding * Any other condition that would, in the investigator's judgment, contraindicate the patient's participation in the clinical study due to safety concerns with clinical study procedures * Prospective participants who, in the opinion of the investigator, may not be able to comply with all study procedures (including compliance issues related to feasibility/logistics)