JAK1/2 Inhibitor Ruxolitinib for Relapsed/Refractory Immune Bone Marrow Failure

Background: Immune bone marrow failure is a condition that occurs when a person s immune system attacks the cells of the bone marrow. This can lead to diseases including different types of anemias and blood cancers. Some of these diseases can be deadly. Better treatments are needed. Objective: To test a drug (ruxolitinib) in people with different types of immune bone marrow failure. Eligibility: Adults aged 18 and older with an immune bone marrow failure. Design: Participants will be screened. They will have a physical exam. They will give samples of blood and saliva. They will have a bone marrow biopsy: A large needle will be inserted into a small cut to remove a sample of the soft tissue inside the bone. Some participants may have a skin biopsy: A small piece of skin will be removed. Some may have a computed tomography (CT) scan: They will lie on a table that slides into a donut-shaped machine that uses X-rays to make pictures of the inside of the body. Ruxolitinib is a tablet taken by mouth. Participants will take the drug twice a day for up to 6 months. Participants will have blood tests every week while they are taking the drug. These tests can be done by the participant s own physician and the results sent to the researchers. Participants will have clinic visits after taking the drug for 3 months and 6 months and then after 1, 2, and 3 years. The blood tests and bone marrow biopsy will be repeated. Participants who improve while taking the drugs may go on to an extension phase of the study.

* INCLUSION/EXCLUSION CRITERIA: Participants of both sexes will be considered for inclusion in this study. There will be no racial, ethnic, or sex discrimination. To be eligible to participate in the treatment portion of this study, an individual must meet all of the following inclusion criteria and none of the following exclusion criteria: INCLUSION CRITERIA: ALL COHORTS: * Ability of the participant or legally authorized representative (LAR) to understand and be willing to sign a written informed consent document * Age 18 or older * For females of childbearing potential, stated willingness to use an accepted method of contraception for the duration of the study. Accepted methods of contraception are: * Total abstinence * Use of an implanted or intrauterine hormonal device for at least 30 consecutive days before study drug administration * Use of oral, patch or injectable contraceptives or a vaginal hormonal device for at least 30 consecutive days before study drug infusion * Use of a non-hormonal intrauterine device for at least 30 consecutive days before study drug administration * Two barrier methods such as a diaphragm with spermicide or a condom with spermicide * For sexually active males with a female partner of childbearing potential, stated willingness to agree to use a condom with spermicide for the duration of the study. * Diagnosis of immune bone marrow failure (see specific cohort) COHORT 1: RELAPSED/REFRACTORY SAA: Meet all 3 criteria below: Severe aplastic anemia\*: -Bone marrow cellularity \