Comparing Cyclophosphamide and Abatacept With Standard of Care Treatment Following Stem Cell Transplantation

The experimental GVHD prophylaxis arm consists of cyclophosphamide and abatacept. Cyclophosphamide induces apoptosis of activated T cells and abatacept (CTLA4Ig) blocks activation of T cells by inhibiting the co-stimulatory signal.

Compared to the standard-of-care control arm, the experimental arm is much more convenient and expected to be associated with fewer toxicities.

In addition there is a great theoretical potential for immunological synergy between cyclophosphamide and abatacept for inducing post-transplant immunologic tolerance that clinically might translate into less GVHD without increase in relapse Patients will be randomized 1:1 to the experimental vs the standard of care arm. Randomization will be done prior to the use of any conditional therapy.

The two arms will be stratified by disease (acute leukemia vs others) and donor type (MRD vs MUD/MUD vs Haplo) in an effort to keep them balanced.

The conditioning regimen for both arms will be mainly Busulfan/Fludarabine (A Total Body Irradiation based conditioning regimen will be allowed for diseases such as ALL)

The GVHD prophylaxis regimen on the experimental arm will consist of high dose Cyclophosphamide on Days +3 and +4 followed by abatacept for 6 months.

The GVHD prophylaxis regimen on the standard of care arm will consist of methotrexate on Days +1,+3, +6 and +11 and tacrolimus for patients with a 10/10 matched related or unrelated donor and of high dose cyclophosphamide on Days +3 and +4 followed by tacrolimus and mycophenolate for patients with a haploidentical donor.

Inclusion criteria

• High risk hematologic malignancy justifying the need for an allogeneic hematopoetic stem cell transplantation: AML, ALL, CML in accelerated or blast phase, MDS/MPN, NHL, Hodgkin lymphoma, and multiple myeloma
• Creatinine clearance > 40
• Adequate hepatic function
• Normal cardiac function (EF > 50%)

Exclusion criteria

• Patients with hematologic malignancies for which transplant is not the only curative option, such as AML with good or intermediate cytogenetics or molecular markers in CR1 or CML in chronic phase
• Inability to identify an 10/10 HLA-Matched Donor (related or unrelated) or a haploidentical donor
• Active malignant disease relapse
• Active, uncontrolled infection, uncontrolled cardiac angina, symptomatic congestive heart failure
• Life expectancy <3 months
• Pregnancy or lactation
• Patients may not be receiving any other investigational agents in the last 28 days
• Patients with chronic myeloid leukemia in first chronic phase