Idelalisib Post Allogeneic Hematopoietic Stem Cell Transplant (HSCT) in B Cell Derived Malignancies

INCLUSION CRITERIA 1. \>18 years of age 2. Has undergone allo HSCT to treat a B-cell derived hematologic malignancy: accepted alloHSCT regimens include: myeloablative or reduced intensity conditioning from any donor (matched, partially mismatched or cord) and any source (peripheral blood, bone marrow, or cord). 3. T bili ≤ 1.5 mg/dL except for patients with Gilbert's syndrome or hemolysis 4. AST, ALT and alk phos all \< 2.5X ULN 5. Karnofsky performance score ≥ 40 6. ECOG ≤3 7. For women of childbearing potential, a negative serum or urine pregnancy test with sensitivity less than 50 mIU/m within 72 hours before the start of study medication. 8. Use of two forms of contraception with less than a 5% failure rate or abstinence by all transplanted patients for a minimum of 1 month after the last dose of Idelalisib. For the first 60 days post-transplant, transplant recipients should be encouraged to use non-hormonal contraceptives due to the potential adverse effect of hormones on bone marrow engraftment. 9. Ability to receive oral medication. 10. Ability to understand and provide informed consent. EXCLUSION CRITERIA 1. ECOG \>3 (Karnofsky \<40%) 2. ALT, AST \>2.5 ULN or total bilirubin \>1.5 ULN (not attributable to Gilbert's) 3. Women who are pregnant or breastfeeding. 4. Exclude if patient has cirrhosis or is currently being actively treated for hepatitis C. 5. History of positive HIV-1 or HIV-2 serologies or nucleic acid test. 6. Active hepatitis B infection as documented by positive Hepatitis B PCR assay 7. Use of investigational drug, other than the study medications specified by the protocol, within 30 days of transplantation. 8. Receipt of a live vaccine within 30 days of receipt of study therapy. 9. ≥ Grade II aGVHD 10. The presence of any medical condition that the Investigator deems incompatible with participation in the trial 11. Subjects who are required to use a medication classified as a strong CYP3A inducer of inhibitor.