LFA-3/CD2 Pathway, Potential Target For Immunosuppressive Therapy In Aplastic Anemia: A Phase I/II Trial Of Alefacept In Patients With Relapsed/Refractory Aplastic Anemia

Aplastic Anemia (AA) is a rare bone marrow failure disorder characterized by pancytopenia, and an empty bone marrow. The disease can develop from unknown causes (idiopathic) or can be secondary to drugs, toxins, chemotherapy (acquired). Hematopoietic bone marrow transplant is a potential cure for idiopathic AA patients. Pharmacologic therapies remain the foremost therapy for patients who lack suitable donors or ineligible for bone marrow transplant. Antithymocyte globulin (ATG) is a first line treatment for these patients. However, relapsed and refractory cases of AA can occur even after ATG treatment. Patients with relapsed/ refractory AA may benefit from alternative immunosuppressive therapies. Alefacept is a novel immunosuppressive agent that targets the CD2-LFA3 pathway important in various T cell functions especially T cell activation. The occurrence of relapsed/ refractory cases of AA coupled with the side effect profile of ATG prompted us to test alefacept in refractory AA. This Phase I/II study was fully approved by the Institutional Review Board of the Cleveland Clinic and conducted in patients with relapsed/ refractory AA. This trial was registered under ClinicalTrial.Gov Identifier Number: NCT01267643. A total of four patients were successfully enrolled in this trial. All four patients had refractory AA. Antecedent treatment for three patients was immunosuppressive therapy: ATG in one case, cyclosporine in one, and both plus daclizumab in one case. All patients are female. Patient ages at the beginning of the study were 39, 57, 83, and 90 years. Three of the four patients were ECOG performance status 1 and one patient was ECOG 2. Three patients received dose level 1 (7.5 mg/ week) while one patient was treated at dose level 2 (10 mg/week). All patients received once weekly treatments for a total of 12 weeks. All 4 patients have been followed for 15, 13, 12, and 11 months, respectively. None of the patients had a PNH clone at presentation. Blood parameters at the beginning of the alefacept treatment indicated that two patients had three cytopenias (Hgb<10 g/dL, platelets<100 K/mL, ANC<1.5 K/mL) and two patients had two (platelets and ANC). Three of the four patients achieved a partial response. Side effects were very mild and included a grade 2 cough and grade 1 sore throat and nasal congestion in one patient and grade 1 muscle aches in a second. All side effects were transient and resolved after 2 weeks of treatment. No severe infections or grade 3 or 4 adverse events were reported. Complete blood cell count of two representative patients are shown below. Routine test values (absolute reticulocytes, ANC, Hgb, and platelets) are shown one per month for pre- and post-treatment while one per week during the treatment. We performed a flow cytometric measurement of intracellular cytokine profile before, during and after Alefacept treatment. Peripheral blood mononuclear cells were stimulated with PMA/ ionomycin for 6 hours in culture. We found a decrease in IFN-gamma, a cytokine implicated in AA pathogenesis post-treatment (Patient A: CD4 IFN-gamma 11.1 vs 1.7%,CD8 IFN-gamma 60.8% vs 16.9%; Patient B: CD4 IFN-gamma 32% vs 7% vs 5.7% ,CD8 IFN-gamma 76.7% vs 30.6% vs. 25.8%). Conversely we found an increase in IL-17, post-treatment (Patient A: CD4 IL-17 0.7 vs 56%,CD8 IL-17 61% vs 57.4%; Patient B: CD4 IL-17 1.6% vs 1.9% vs 29.4% ,CD8 IL-17 4.2% vs 6% vs. 31.9%) To date, three out of four patients who achieved a PR continue to be transfusion independent and none are on any other immunosuppressive therapies such as cyclosporine. All four patients remain progression-free and none have developed any PNH clone. On December, 2011 Astellas Pharma US announced that the company has voluntarily discontinued the promotion, manufacturing, distribution and sales of alefacept because of business needs but not related to safety issues. In conclusion, this pilot study even if conducted in a limited number of patients suggests targeting CD2-LFA-3 pathway using alefacept is a viable and safe option for treating patients with relapsed/ refractory AA.