Clinico-Immunobiologic Study By a Prospective Open-Label Clinical Trial of Deferasirox before & after Allogeneic HSCT in Adult Patients with AML - Preliminary Analysis Focusing on Outcomes with Immunocyte Subsets (I) -

Background: The ferritin contents in immature myeloid cells could be detected in both iron overload and in AML. Ferritin itself in leukemic cells could be regarded as an important marker for leukemic activity. Serialreports have shown that the serum ferritin level in patients with acute leukemia and myelodysplastic syndrome is a critical prognostic factor after hematopoietic stem cell transplantation (HSCT). However, the exact mechanism itself is not clear.

Methods: We evaluated the iron chelating efficacy and the immunomodulatory effect of deferasirox therapy as assessed by regular monitoring of serum ferritin levels and immunocyte subsets from the post-induction period to post-HSCT. In addition, we tried to reveal the effects of deferasirox on various clinical outcomes in patients with adult AML who were expected to receive allogeneic HSCT. A total of sixty-six consecutive adult patients with de novo AML who received allogeneic HSCT were prospectively enrolled during the period 2009 to 2011. Serum ferritin levels were monitored from initial diagnosis to the post-HSCT period from both the iron-chelated group (IC, n=28) and the non-treated group (NT, n=38) of patients. Among the patients of the IC group, the final 20 AML patients were followed and were collected peripheral blood samples until minimum 6 months post-HSCT. The overall median follow-up for total survivors (IC) was 58 months (range: 48~66). Deferasirox treatment was initiated at the outpatient clinic both after induction chemotherapy and post-HSCT 1 month. Various clinical outcomes in association with multiple parameters including serum ferritin levels and multiple immunocyte subsets of CD4, CD8, CD16, CD56, invariant NKT, Treg, central/effector memory T cells were simultaneously analyzed, mainly in the IC group of patients, with the usage of the multi-color flow cytometer at pre- and post-HSCT periods.

Results: The median duration of total (pre- + post-HSCT) medication in IC group of patients was 241 days (109-452). The median ferritin levels at diagnosis (IC, 651 ng/mL vs. NT, 667 ng/mL) and at peak levels (IC, 3,090 ng/mL vs. NT, 3,685 ng/mL) during chemotherapy did not differ significantly between groups. However, pre-HSCT levels were different between groups, as the median level of 1,555 ng/mL (335-3,800) (IC) vs. 964 ng/mL (229-7,360) (NT). The 5-year overall survival (OS) and event-free survival (EFS) rates of total AML patients were 63.6% and 60.6%, respectively. The Kaplan-Meier estimates of OS/EFS rates were all significantly different in pre-HSCT ferritin levels (P=0.0247, 0.0212) and duration of deferasirox treatment both pre- (P=0.028, 0.0166) and post-HSCT (P=0.0102, 0.0064). The levels of CD4⁺CD62L^-CD44⁺ (P=0.027) and CD8⁺CD62L^-CD44⁺ cells (P=0.006) post-induction chemotherapy were significantly associated with the duration of deferasirox treatment before HSCT. To note, the levels of CD4⁺ cells at 1 month post-HSCT deferasirox treatment (P=0.017), CD4⁺ effector memory T (T_EM)-cells pre-HSCT (P=0.029), and CD8⁺CD62L^-CD44⁺ cells post-HSCT 1 month (P=0.003) and 6 months (P=0.021) were closely related to the relapse of AML. Most of all, regulatory T (Treg) cells both pre-HSCT (P=0.002) and post-HSCT (P <0.001) periods after deferasirox therapy showed a very close correlation with various clinical outcomes, specifically with lower rates of relapse in patients with low levels of Treg after at least 120 days in total use of deferasirox before and after HSCT. Interestingly, patients who received deferasirox therapy for a sufficient duration showed consistently lower levels of Treg cells as well as higher levels of CD16⁺ NK cells along the timeline of chemotherapy and HSCT compared to those who did not. Furthermore, we found a marginal significance in the increased levels of CD4⁺CD161⁺ NKT cells at post-induction chemotherapy when patients received deferasirox before HSCT (P=0.056).

Conclusion: Our data suggest that despite small sample numbers, iron-chelation therapy for adult AML patients with hyperferritinemia pre- and post-HSCT is very closely related to the outcomes of allogeneic HSCT, and that it is especially associated with the modulation of immunobiologic properties during the period of immune reconstitution. Therefore, more cautious approaches to reduce iron overload by using iron chelating agents, such as deferasirox, may be warranted both before and after allogeneic HSCT.