Clofarabine Bone Marrow Cytoreduction

For relapsed and refractory leukemia patients induction chemotherapy prior to initiating a conditioning regimen will decrease residual leukemia (as measured by bone marrow leukemia blast percentage) at the time of HCT. This should lead to reduced relapse while still maintaining low transplant related mortality.

Screening will be done prior to enrollment in the study. The following will be done as part of the screening process:

* Medical history review
* Physical exam
* Measurement of vital Signs
* Blood tests (approximately 6 teaspoons of blood) will be done to see if the liver and kidneys are healthy, HIV (the virus that causes AIDS) test for this study and pregnancy test.
* Urine test
* Bone marrow biopsy and aspirate

If the patient is ineligible or does not have a donor for Allogeneic Stem Cell transplantation, you will not be able to participate in this clinical trial.

After results of these tests are obtained, your doctor will decide whether you can participate in this study.

Study procedures:

The study drug will be given for 5 days.

Days 1 through 5:

The patient will receive dexamethasone 1.5 hours prior to the administration of Clofarabine as part of standard care for subjects receiving Clofarabine.

The patient will receive an intravenous (IV) injection (into the vein) of Clofarabine each day for 5 days. This injection is given in the hospital and will be given over approximately 60 minutes each day. The actual dose of Clofarabine is based on the weight and height of the subject.

The patient will have the following tests done to see the effects of the study drug:

Each day of Clofarabine administration, on day 12 and then each day until stem cell transplantation:

* Physical exam
* Vital signs
* Blood tests. About 3-4 teaspoons will be taken each time.

Day 12 after Clofarabine administration and then as outlined for stem cell transplantation:

• Bone marrow biopsy and aspirate.

After Clofarabine administration, there will be short resting period of 7-14 days. After the resting period, the patient will start receiving conditioning chemotherapy regimen (other standard of care drugs to better prepare your body for the stem cell transplant). This regimen will begin 15-21 days after they first received Clofarabine, and consists of additional treatment (chemotherapy and/or radiation). The type of treatment(s) the patient will receive for conditioning is dependent on the type of disease. In addition, this treatment will be decided by your doctor and is independent of this research. The duration of the conditioning period is variable and may take between 5-8 days. Stem cells are usually given one day after the completion of this regimen, which will be between 21 and 30 days after the patient has first received Clofarabine.

Follow-up Subjects who have a response and proceed with stem cell transplant will be followed weekly for the first three months and then every month for six months, then every two months for 12 months, then every three months for 18 months. The stem cell transplant will be done 21-30 days after first receiving Clofarabine. Subjects who do not go on to stem cell transplant will be followed for 3 months following administration of Clofarabine.

At these visits, the following will be done:

* A physical exam
* Medical history
* Blood tests (about 3 teaspoons blood will be taken) performed.

End of study

At this time, the following tests will be done:

* Physical exam
* Blood tests
* Bone marrow biopsy

Eligibility Criteria:
Inclusion Criteria:

* Capable of understanding the investigational nature, potential risks and benefits of the study, and able to provide valid informed consent.
* Adequate hepatobiliary function as indicated by the following laboratory values:

  * SGOT/SGPT \<=2.5 x upper limit of normal
  * Alkaline phosphatase \<=2.5 x upper limit of normal
  * Serum bilirubin \< 1.5 mg/dl
  * Adequate renal function as indicated by the following laboratory values:
  * Creatinine Clearance \>50 ml/min
* Age \>/=18 years
* Zebroid performance status \</= 2 (See Appendix A)
* Life expectancy is not severely limited by concomitant illness (i.e. \< 3months life expectancy from non-leukemic conditions).
* No evidence of chronic active hepatitis or cirrhosis.
* HIV-negative
* Male and female patients must use an effective contraceptive method during the study and for a minimum of 6 months after study treatment.
* Female patients of childbearing potential must have a negative serum pregnancy test within 2 weeks prior to enrollment.

Exclusion Criteria:

* Current concomitant chemotherapy, radiation therapy, or immunotherapy other than as specified in the protocol.
* Use of investigational agents within 30 days or any anticancer therapy within 2 weeks before study entry with the exception of hydroxyurea. The patient must have recovered from all acute non-hematologic toxicities from any previous .
* Have any other severe concurrent disease, or have a history of serious organ dysfunction or disease involving the heart, kidney, liver, or other organ system that may place the patient at undue risk to undergo treatment.
* Patients with a systemic fungal, bacterial, viral, or other infection not controlled (defined as exhibiting ongoing signs/symptoms related to the infection and without improvement, despite appropriate antibiotics or other treatment).
* Pregnant or lactating patients.
* Any significant concurrent disease, illness, or psychiatric disorder that would compromise patient safety or compliance, interfere with consent, study participation, follow up, or interpretation of study results.