Inclusion Criteria

- INCLUSION CRITERIA:

- Patients greater than or equal to 18 years old with pathologically confirmed
smoldering or chronic adult T- cell leukemia as defined by Shimoyama.

- Patients must have serum antibodies directed to HTLV-1.

- Patients must have measurable or evaluable disease. Patients with > 10% of the PBMCs
having the characteristic abnormal (i.e., CD3dim, CD4 plus CD25 plus expressing) FACS
profile for circulating ATL cells will be considered to have evaluable disease.

- Patients must have adequate physiologic parameters:

- Absolute granulocyte count greater than or equal to 1000 K/microL, platelet count
greater than or equal to 75,000 K/microL and hemoglobin greater than or equal to 10
g/dL.

- Bilirubin and creatinine less than or equal to 1.5 times institutional ULN.

- AST, ALT less than or equal to 3.0 times institutional ULN.

- Karnofsky Performance Score greater than or equal to 70% or ECOG less than or equal
1.

- Patients must be able to understand and sign Informed Consent Form.

EXCLUSION CRITERIA:

- Patients previously treated with a JAK inhibitor.

- Patients with symptomatic leukemic meningitis, bony or GI tract involvement, serum
calcium or LDH > 1.5 times the upper limit of normal will be excluded. However,
patients that have both ATL and another HTLV-1 associated disease such as tropical
spastic paraparesis (HAM/TSP) will be included.

- Patients who have received high doses of systemic corticosteroids for the treatment
of their ATL within 4 weeks prior to the start of therapy.

- Patients who have received any cytotoxic therapy, immunotherapy, antitumor vaccines
or monoclonal antibodies in the 4 weeks prior to the start of the study.

- Life expectancy of less than 3 months.

- Documented HIV, active bacterial infections, active or chronic hepatitis B, hepatitis
C or HTLV-II infection.

- A positive hepatitis B serology indicative of previous immunization (i.e., HBsAb
positive and HBc Ab negative), or a fully resolved acute hepatitis B infection is not
an exclusion criterion.

- A positive hepatitis C serology is an exclusion criterion.

- Pregnant and breast-feeding patients are not eligible for the study because the
effects of ruxolitinib on the developing fetus are unknown.

- Inability or refusal to practice effective contraception during therapy. Men and
women of childbearing potential must use an effective method of birth control or
abstinence during treatment and for 4 months after completion of the treatment.

- Patient has significant and/or uncontrolled cardiac, renal, hepatic or other systemic
disorders or significant psychological conditions at baseline visit that in the
investigator's judgment would jeopardize subject enrollment or compliance with the
study procedures.