A Pilot Study of Fludarabine Plus Cyclophosphamide in Refractory Severe Aplastic Anemia

Severe aplastic anemia (SAA) is a life-threatening bone marrow failure disorder
characterized by pancytopenia and a hypocellular bone marrow. Allogeneic hematopoietic stem
cell transplantation (HSCT) offers the opportunity for cure in 70 percent of patients, but
most patients are not suitable candidates for this treatment modality due to advanced age,
comorbidities or lack of a histocompatible donor. For these patients, comparable long-term
survival is attainable with immunosuppressive treatment (IST) with anti-thymocyte globulin
(ATG) and cyclosporine (CsA). However, approximately 1/3 of patients do not show blood count
improvement after ATG/CsA and are considered to have refractory disease. Furthermore,
analysis of our own extensive clinical data suggests that poor blood count responses to a
single course of ATG (nonrobust responders), even when transfusion-independence is achieved,
predicts a markedly worse prognosis compared to those who achieve a robust hematologic
improvement (protocol 90-H-0146) .

In patients who are refractory to horse ATG (h-ATG) and do not have a histocompatible
sibling, alternative donor (AD) HSCT or a repeat course of IST are options. Registry data
suggests that outcome for AD HSCT in SAA is not as favorable compared to a matched sibling
HSCT with long-term survival at about 40-50 percent and a higher risk of graft-versus-host
disease. However, in recent smaller retrospective studies survival after AD HSCT in children
rivals that of a sibling transplant when an unrelated donor who matches in 10 human
leukocyte antigen (HLA) loci (matched unrelated donor) is available. With repeat IST,
response rates with rabbit anti-thymocyte has varied from 22 percent up to 77 percent. Our
experience in refractory SAA (protocol 03-H-0249) is that rabbit ATG + CsA and alemtuzumab
are equally efficacious as salvage therapies, with a response rate of about 30 percent for
each treatment. For the 20-30 percent of patients who remain refractory after 2 courses of
treatment, further courses of IST have been of limited value with responses observed only
occasionally. In addition, efforts to improve initial IST in treatment-na ve patients
(addition of mycophenolate mofetil and sirolimus) have not yielded promising regimens with
activity in SAA (protocols 00-H-0032, 03-H-0193, and 06-H-0034). Therefore, novel regimens
are needed to improve outcomes in SAA for those without a histocompatible sibling, which
encompass the majority of patients with this disease.

The current limitations of IST in SAA are: 1) the majority of the responses observed
following initial h-ATG/CsA are partial with only a few patients achieving normal blood
counts; 2) 1/3 of patients are refractory to initial h-ATG/CsA; 3) response rate in these
refractory patients who are retreated is only 30 percent; 4) hematologic relapses occur in
35 percent of responders following initial response to h-ATG/CsA; 5) among relapsed patients
chronic use of CsA is not infrequent which often leads to toxicities from the long term
exposure to this drug (especially in older patients); and 6) clonal evolution is still
observed in 10-15% of patients. Towards the goal of addressing these limitations we are
proposing a novel regimen of fludarabine (Flu) plus cyclophosphamide (Cy) in SAA patients
refractory to horse ATG/CsA. The Hematology Branch has considerable experience with Flu/Cy
as part of the condition regimen in allotransplantation protocols (protocols 99-H-0050,
97-H-0196, 99-H-0064, 99-H-0050, 97-H-0196, 02-H-0111, 01-H0162, 03-H-0192, 04-H-0112,
06-H-0248, 07-H-0136). In addition, this regimen has been incorporated into the NCI's
Surgery Branch preparative regimen for autologous HSCT prior to infusion of tumor
infiltrating lymphocytes. Flu/Cy is well tolerated and a potent immunosuppressive regimen
that is not myeloablative. Therefore, we propose to investigate Flu/Cy to address the
current limitations of IST in SAA.

The main objective of this study is to assess the safety and efficacy of Flu/Cy in
refractory SAA. The primary endpoint will be hematologic response, defined as no longer
meeting criteria for SAA, at 6 months. Secondary endpoints are relapse, robustness of
hematologic recovery at 6 months, response at 3 months and 12 months, survival, clonal
evolution to paroxysmal nocturnal hemoglobinuria (PNH), myelodysplasia and acute leukemia.
The primary endpoint will be changes absolute neutrophil count, platelet count, and
reticulocyte count at 6 months. Secondary endpoints will include time to relapse, changes in
cytogenetics, and time to death.

Eligibility:

- Individuals at least 2 years of age who have severe aplastic anemia that has not improved
after treatment with horse ATG or both horse and rabbit ATG.

Design:

- After initial screening, medical history, and blood tests, participants will be
admitted to the inpatient unit at the National Institutes of Health Clinical Center.

- Participants will receive 2 days of cyclophosphamide, followed by 5 days of
fludarabine.

- Participants will also receive antibiotics and other drugs to protect against
bacterial, fungal, and viral infections. Participants will take these drugs regularly
until their white blood cell counts improve.

- After discharge from the clinical center, participants will have follow-up evaluations
at 3 months, 6 months, and annually for 5 years. Evaluations will include blood samples
and periodic bone marrow biopsies.

-INCLUSION CRITERIA:

1. Severe aplastic anemia characterized by:

Bone marrow cellularity < 30 percent (excluding lymphocytes)

AND

At least two of the following:

- Absolute neutrophil count < 500/ microL

- Platelet count < 20,000/ microL

- Absolute reticulocyte count < 60,000/ microL

2. Failure to respond to an initial course of h-ATG/CsA at least 3 months post-treatment
or a suboptimal response to initial h-ATG/CsA defined by both platelet and
reticulocyte count < 50,000 /microL at 3 months post-treatment

OR

3. Refractory SAA unresponsive to both horse and rabbit ATG-based regimens

4. Age greater than or equal to 2 years old

5. Weight greater than or equal to 12 kg

EXCLUSION CRITERIA:

1. Diagnosis of Fanconi anemia

2. Cardiac ejection fraction < 30 percent (evaluated by ECHO)

3. Evidence of a clonal hematologic bone marrow disorder on cytogenetics. Patients with
the presence of trisomy 8, loss of Y or del(20q) will not be excluded in the absence
of dysplastic changes in the marrow. Patients with very severe neutropenia (ANC < 200
/microL) will not be excluded initially if cytogenetics are not available or pending.
If evidence of a clonal disorder is later identified, the patient will go off study)

4. Prior immunosuppressive therapy with high dose Cy

5. Infection not adequately controlled with appropriate therapy

6. Serologic evidence of HIV infection

7. Moribund status or concurrent hepatic, renal, cardiac, neurologic, pulmonary,
infectious, or metabolic disease of such severity that it would preclude the
patient's ability to tolerate protocol therapy, or that death within 30 days is
likely

8. Subjects with cancer who are on active chemotherapeutic treatment or who take drugs
with hematological effects

9. Current pregnancy or unwillingness to take oral contraceptives or refrain from
pregnancy if of childbearing potential

10. Not able to understand the investigational nature of the study or to give informed
consent