This is a research study designed to look at the biological effects of two drugs on leukemia cells. In this study, we are comparing the effects of drugs called corticosteroids when used alone or with another drug called rapamycin. Rapamycin is a drug that prevents the body's immune system from working normally. It has been used for many years after kidney transplants to prevent rejection of the organ. Recent work suggests that rapamycin may also help treat leukemia and other cancers.

• Participants will be randomized into two groups; one group will receive corticosteroid alone, and the other group will receive rapamycin and corticosteroid.
• The length of treatment will be 5 days, during which time we will collect blood samples to measure the biologic effects of these drugs. Because these drugs will be given for a short period of time only, this study is not designed to treat or cure the participants leukemia. After the 5-day period, participants may resume other cancer-directed therapies.

Inclusion Criteria:

• Documented acute lymphoblastic leukemia (L1 or L2 subtypes)
• First or subsequent relapse
• 365 days of age or older
• Greater than 7 days from any chemotherapy or immunotherapy, with the exception of intrathecal chemotherapy
• Absolute peripheral leukemia blast count of 1000 cells/ul or greater
• Patient (or parent/guardian if patient is less than 18 years of age) must sign informed consent

Exclusion Criteria:

• Burkitts leukemia (acute lymphoblastic leukemia L3 subtype)
• Uncontrolled active infection
• Pregnancy or mothers who are nursing
• Patient currently taking rapamycin
• Patients with significant liver dysfunction as outlined in protocol
• Severe concurrent disease, which in the judgment of the investigator, would make the patient inappropriate for entry into the study
• Active psychiatric disease, substance abuse, or mental illness that would interfere with cooperation with the requirements of the trial