Improving Immunosuppressive Treatment for Patients With Severe Aplastic Anemia

Severe aplastic anemia (SAA) is a life-threatening bone marrow failure disorder characterized
by pancytopenia and a hypocellular bone marrow. Allogeneic bone marrow transplantation and
immunosuppressive treatment with anti-thymocyte globulin (ATG) and cyclosporine (CsA) have
dramatically changed the natural course of this illness, with 5 year survival of 75% in
patients undergoing either treatment. Since most patients are not suitable candidates for
hematopoietic stem cell transplantation (HSCT) due to advanced age or lack of a
histocompatible sibling, efforts at NHLBI have focused on improving immunosuppression
treatment in order to improve response rates, survival, and to decrease relapse.

In our experience of 122 patients treated at NHLBI with the combination of ATG and
cyclosporine, one quarter to one third did not respond; about 50% of responders relapsed; and
5 year survival was correlated with the robustness in blood cell count improvement at 3
months (reticulocyte or platelet count greater than or equal to 50,000 /uL). Why some
patients do not respond initially while others relapse is unclear. Autoreactive T cells may
be resistant to the effect of ATG/CsA (nonresponders), while in others residual autoreactive
T cells expand post-treatment leading to hematopoietic stem cell destruction and recurrent
pancytopenia (relapse). Therefore, novel immunosuppressive regimens to increase response
rates and hematologic recovery at 3 months and to decrease relapse rates are needed. An
ongoing NHLBI trial, which is close to completing accrual, has added mycophenolate mofetil
(MMF) for a total of 18 months to standard ATG + CsA in an attempt to reduce the relapse rate
after cyclosporine is discontinued. Preliminary results have been disappointing, with no
marked reduction in relapse among patients who received MMF.

Sirolimus (rapamycin, Rapamune , RAPA) is a novel immunosuppressive agent, which acts
synergistically with cyclosporine by blocking T cell activation through CsA-resistant
pathways. The potentiation of the combination of CsA-RAPA has been established in vitro and
in the clinical setting, mainly in islet cell and solid organ transplantation. The
significant increase in response rate seen with the addition of CsA to ATG indicated that an
inhibitory effect on T lymphocytes is important in blocking autoreactive T cells in aplastic
anemia. The combination of CsA-RAPA may further block activated autoreactive T cells and
therefore lead to improved response rates (and survival) and decreased relapse rates.

This prospective randomized phase II study will investigate two different immunosuppressive
regimens in patients with severe aplastic anemia who have not received prior
immunosuppressive therapy. One arm will receive ATG + CsA in addition to sirolimus for 6
months, and the second arm will receive standard ATG + CsA for 6 months followed by a slow
taper of CsA with a 25% dose reduction every 3 months for the subsequent 18 months. This
trial will determine the effectiveness of sirolimus in patients with aplastic anemia as well
as the role of a cyclosporine taper in preventing relapses. Primary endpoint will be no
longer meeting criteria for severe aplastic anemia while secondary endpoints are relapse,
robustness of hematologic recovery at 3 months, survival, clonal evolution to PNH,
myelodysplasia and acute leukemia.

10/11/2005. The Sirolimus (Rapamune) arm of the trial was stopped for lack of efficacy. The
study will continue as a single arm study to establish if slow taper of CsA prevents relapse
rates after initial standard treatment with ATG followed by CsA for six months.

3/2/2006. The protocol was closed to new accrual.

- INCLUSION CRITERIA:

Severe aplastic anemia confirmed at NIH by:

1. . Bone marrow cellularity less than 30% (excluding lymphocytes)

2. . At least two of the following: Absolute neutrophil count less than 500/ uL; Platelet
count less than 20,000/ uL; Absolute reticulocyte count less than 60,000/ uL

Age greater than or equal to 2 years old

Weight greater than 12 kg

EXCLUSION CRITERIA:

Serum creatinine greater than 2.5 mg/dL

Underlying carcinoma (except local cervical, basal cell, squamous cell)

Prior immunosuppressive therapy with ATG, ALG, or high dose cyclophospamide.

Current pregnancy or lactation or unwillingness to take oral contraceptives or use an
effective method of birth control.

Diagnosis of Fanconi anemia or other congenital bone marrow failure syndromes

Evidence of a clonal disorder on cytogenetics. Patients with super severe neutropenia (ANC
less than 200/uL) will not be excluded if results of cytogenetics are not available or
pending.

Underlying immunodeficiency state including seropositivity for HIV

Inability to understand the investigational nature of the study or give informed consent

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 7-10 days is likely.