Fludarabine-based conditioning chemotherapy for allogeneic hematopoietic stem cell transplantation in acquired severe aplastic anemia

Cyclophosphamide and horse anti-thymocyte globulin versus fludarabine, reduced cyclophosphamide and rabbit anti-thymocyte globulin conditioning regimen for allogeneic hematopoietic stem cell transplantation from matched sibling donors in patients with acquired aplastic anemia

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative treatment for acquired aplastic anemia (acquired AA) in young patients. The objective of the study was to compare patient outcomes after Cyclophosphamide and horse antithymocyte globulin (Cy-hATG) versus Fludarabine-cyclophosphamide and rabbit ATG (Flu-Cy-rATG) as part of conditioning regimen in allo-HSCT for acquired AA.

RESEARCH DESIGN AND METHODS

Descriptive retrospective study conducted on patients with acquired AA who received allo-HSCT from HLA-matched sibling donors between January 2008 and August 2022 after conditioning regimen with Cy-hATG or Flu-Cy-rATG.

RESULTS

A total of 121 patients were enrolled. Cumulative incidence of graft failure was 11.2% in Cy-hATG and 5.3% Flu-Cy-rATG group. There were no significant differences between the two groups in terms of acute GVHD, chronic GVHD, and transplant related mortality. Flu-Cy-rATG group was associated with significantly higher CMV and EBV reactivation(s) compared to Cy-hATG group (p = 0.008 and 0.035, respectively). After a median follow-up of 58 months, estimated overall survival, event-free survival, and graft rejection-free survival were not statistically different between the two groups.

CONCLUSIONS

In high-risk population, Flu-Cy-rATG is associated with comparable outcomes to Cy-hATG in allo-HSCT from MSD. However, it seems to be associated with significant risk of viral infections.

Allogeneic hematopoietic stem cell transplantation in aplastic anemia: current indications and transplant strategies

Treatment options for newly diagnosed aplastic anemia (AA) patient includes upfront allogeneic hematopoietic stem cell transplant (HSCT) or immunosuppressive therapy (IST). With recent advances in supportive care, conditioning regimens and post-transplant immunosuppression the overall survival for HSCT approaches 70-90%. Transplant eligibility needs to be assessed considering age, comorbidities, donor availability and probability of response to immunosuppressive therapy (IST). Upfront HSCT should be offered to children and young adults with matched related donor (MRD). Upfront HSCT may also be offered to children and young adults with rapidly available matched unrelated donor (MUD) who require urgent HSCT. Bone marrow (BM) graft source and cyclosporine (CsA) plus methotrexate (MTX) as graft versus host disease (GVHD) prophylaxis are preferable when using anti-thymocyte globulin (ATG) based conditioning regimens. Alemtuzumab is an acceptable alternative to ATG and is used with CsA alone and with either BM or peripheral blood stem cells (PBSC). Cyclophosphamide (CY) plus ATG conditioning is preferable for patients receiving MRD transplant, while Fludarabine (Flu) based conditioning is reserved for older adults, those with risk factors of graft failure and those receiving MUD HSCT. For haploidentical transplant, use of low dose radiotherapy and post-transplant cyclophosphamide has resulted in a marked reduction in graft failure and GVHD.

Single-Agent Cyclosporine for Graft-versus-Host Disease Prophylaxis in Patients with Acquired Aplastic Anemia Receiving Fludarabine-Based Conditioning

Cyclosporine (CsA) combined with short-course methotrexate is considered standard-of-care graft-versus-host disease (GVHD) prophylaxis for patients with severe aplastic anemia (AA) who undergo transplantation using cyclophosphamide (Cy) plus anti-thymocyte globulin (ATG) conditioning. However, there is no consensus on optimal post-transplant GVHD prophylaxis for patients undergoing matched related donor (MRD) transplantation using fludarabine (Flu)-based conditioning. We conducted a single-center retrospective analysis of patients with acquired AA (n = 106) undergoing MRD transplantation from July 2007 through January 2019. All patients received Flu-Cy-ATG conditioning and single-agent CsA as GVHD prophylaxis. Median age of the study cohort was 20 years (range, 3 to 52) and male to female ratio was 3.8:1. Median time from diagnosis to transplant was 11.5 months (range, 2.8 to 62). Graft source was bone marrow harvest in 71 (68%), combined bone marrow and peripheral blood stem cells in 34 (31%), and peripheral blood alone in 1 (1%) patient. Cumulative incidence of neutrophil engraftment at day 28 was 93.4% (95% confidence interval [CI], 87.3% to 97.1%) while that of platelet engraftment at day 100 was 90.5% (95% CI, 84% to 96%). Cumulative incidence of primary graft failure at day 28 was 6.6% (95% CI, 4% to 8%) while secondary graft failure occurred at a median of 190 days (range, 90 to 415) at a cumulative incidence of 3.7% (95% CI, 2% to 5%). Cumulative incidence of grade II to IV acute GVHD at day 100 was 3.8% (95% CI, 1.4% to 9.9%), while a 1-year probability of chronic GVHD was calculated as 7.5% (95% CI, 2.6% to 15%). Median follow-up post-transplant was 61 months (range, 6 to 144). Overall survival was 84.9%, disease-free survival was 80.2%, and GVHD-free relapse-free survival was 76.3%. This study indicates that single-agent cyclosporine is a feasible option for GVHD prophylaxis in MRD hematopoietic stem cell transplantation using Flu-Cy-ATG conditioning and is associated with very low rates of acute and chronic GVHD.

Comparison of Conventional Cyclophosphamide versus Fludarabine-Based Conditioning in High-Risk Aplastic Anemia Patients Undergoing Matched-Related Donor Transplantation

Allogeneic stem cell transplant for high-risk aplastic anemia (AA) yields inferior results using conventional cyclophosphamide (CY)-based conditioning. The use of fludarabine (Flu)-based regimens has resulted in improved outcomes in high-risk patients. Limited data are available comparing these two conditioning regimens in such patients. We retrospectively analyzed 192 high-risk patients undergoing matched-related donor transplantation from July 2001 to December 2018. The median age was 19.5 (2–52) years. Patients were divided into 2 groups, Cy²⁰⁰ anti-thymocyte globulin (ATG)²⁰ (Gp1 n = 79) or Flu^120–150 Cy^120–160 ATG²⁰ (Gp2 n = 113). The risk of graft failure was significantly higher in Gp1, and the majority occurred in patients with >2 risk factors (p = 0.02). The incidence of grade II-IV acute graft versus host disease (GVHD) and chronic GVHD was not significantly different between the two groups. The overall survival (OS) of the study cohort was 81.3 %, disease-free survival (DFS) 76.6 % and GVHD-free relapse-free survival (GRFS) was 64.1%. DFS and GRFS were significantly higher in Gp2 as compared to Gp1: DFS 84.1% versus 68.4 % (p = 0.02), GRFS 77.9% versus 54.4% (p = 0.01), respectively. We conclude that Flu-based conditioning is associated with superior OS, DFS and GRFS as compared to the conventional Cy-based regimen in high-risk AA.

G-CSF-primed haplo-identical HSCT with intensive immunosuppressive and myelosuppressive treatments does not increase the risk of pre-engraftment bloodstream infection: a multicenter case-control study

A multicenter retrospective study in 131 patients (44 females/87 males) with hematological disorders who underwent G-CSF-primed/haplo-identical (Haplo-ID) (n = 76) or HLA-identical (HLA-ID) HSCT (n = 55) from February 2013 to February 2016 was conducted to compare the incidence and risk factors for pre-engraftment bloodstream infection (PE-BSI). In the Haplo-ID group, 71/76 patients with high-risk (n = 28) or relapsed/refractory hematological malignancies (n = 43) received FA5-BUCY conditioning (NCT02328950). All received trimethoprim-sulfamethoxazole (TMP-SMX) prophylaxis. Blood cultures and catheter tip cultures were obtained to confirm the BSI. PE-BSI was detected in 24/131 HSCT patients (18/76 in Haplo-ID and 6/55 in HLA-ID) after 28 febrile neutropenic episodes. Among 28 isolates for the 24 patients, 21 (75%) were G^neg bacteria, 6 (21.4%) G^pos and 1 (3.6%) fungi. Bacteria sources were central venous line infection (7/29.2%), gastroenteritis (6/25%), lower respiratory tract infection (LRTI; 5/20.8%), perianal skin infection (4/16.7%), and unknown (2/8.3%). The duration of neutropenia (P = 0.046) and previous G^neg bacteremia (P = 0.037) were important risk factors by univariate analysis, while the type of HSCT was not. A trend of TMP-SMX-resistant BSI in both groups may be due to routine antibacterial prophylaxis strategies. Our data show that G-CSF-primed Haplo-ID HSCT did not increase the risk of PE-BSI, even with intensive immunosuppressive treatments.

Fludarabine-based reduced intensity regimen for matched related donor hematopoietic stem cell transplantation in acquired severe aplastic anemia

Different conditioning regimens have been evaluated in matched-related donor allogeneic hematopoietic stem cell transplantation (allo-HSCT) for acquired severe aplastic anemia (SAA) with varying results. In this manuscript, we report our experience with fludarabine (120mg/m²), very low dose cyclophosphamide (1200mg/m²) and antithymocyte globulin (7.5mg/kg). Low dose total body irradiation (2Gy) was added to the conditioning regimen for patients older than 15 years. Nineteen patients (median age 23years) underwent transplant between 2008 and 2015. The majority (89%) were younger than 40 years. Stem cell source was BM (n=11) or PBSC (n=8). GvHD prophylaxis consisted of cyclosporine and either a short course of methotrexate (n=9) or mycophenolate mofetil (n=10). Eighteen (94.7%) patients achieved sustained engraftment. The median times to neutrophil and platelet engraftments were 19 (range: 14-34) and 17.1 (range: 12-25) days, respectively. The day-30 cumulative incidence of neutrophil and platelet engraftment was 89.4% and 94.7%, respectively. No secondary graft rejection was observed. The 1-year cumulative incidence of aGvHD (grade II-IV) and cGvHD was 11.7% and 0%, respectively. The 2-year GvHD-free survival rate was 78.6% (95% CI: 52.5-91.4%). Fludarabine-based reduced intensity regimen for MRD allo-HSCT in SAA compares favorably to other available regimens. This regimen deserves further investigations with larger cohort of patients.

Improved outcome of haploidentical transplantation in severe aplastic anemia using reduced-intensity fludarabine-based conditioning

Significant improvements in hematopoietic stem cell transplantation (HSCT) with haploidentical family donors (HFD) have confirmed its therapeutic role in severe aplastic anemia (SAA) and led to the evolution of treatment algorithms. However, the optimal conditioning regimen for HFD-HSCT remains undefined, especially the dosage of cyclophosphamide (Cy). A total of 77 patients with SAA from two research centers, who received HFD-HSCT with reduced-intensity fludarabine + cyclophosphamide + thymoglobulin ± busulfan conditioning regimen plus third-party cells infusion were included in this study, of which 67 pairs had 4-5 loci mismatched. We were particularly interested in whether the dosage of Cy significantly impacted graft failure (GF) and overall survival (OS). All patients showed sustained hematopoietic engraftment without any increase in severe aGVHD and transplantation-related mortality (TRM). The incidences of grade II-IV aGVHD, grade III-IV aGVHD and extensive cGVHD were 18%, 10% and 7%, respectively. The probabilities of 1-year and 5-year OS were 93.1% and 87.9%, respectively. Furthermore, patient age <15 years, MNC cells >8×10⁸/kg and donor age <45 years were associated with better survival (P=0.043, P=0.023, and P=0.037, respectively) and engraftment (P=0.019, P=0.008, and P=0.001, respectively). Our findings indicated that SAA patients lack MSD benefited the most if HFD-HSCT was performed with reduced-intensity fludarabine-based conditioning regimen. Improved outcomes with HFD-HSCT may lead to a salvaged therapy and an expanded direct role for SAA in the future.

Population pharmacokinetics of fludarabine in patients with aplastic anemia and Fanconi anemia undergoing allogeneic hematopoietic stem cell transplantation

Although hematopoietic stem cell transplantation (HSCT) with a conditioning regimen consisting of fludarabine (F-araA) and cyclophosphamide (Cy) is associated with improved outcome in young patients with aplastic anemia (AA) and Fanconi anemia (FA), several factors limit the success of the procedure. We evaluated the population pharmacokinetics (POPPK) of F-araA and its influence on HSCT outcome in patients (n=53) with AA and FA undergoing HSCT. Patients carrying a 5′-UTR polymorphism in NT5E gene (rs2295890 G>C) exhibited significantly lower plasma F-araA clearance compared to those with wild-type genotype (7.12 vs 5.03 L/h/m² (29%) P<0.05). F-araA clearance was significantly higher in patients with AA compared to FA (2.46 ×, P<1e−6). Of all the outcome parameters evaluated (engraftment, rejection/graft failure, GvHD, TRM, OS), high F-araA AUC (>29.4 μm*h) was the only significant factor associated with the development of aGvHD by both univariate and multivariate analysis (P=0.02). The influence of plasma F-araA levels need to be evaluated in a larger cohort of patients to propose the need for therapeutic drug monitoring.

Reduced intensity conditioning, combined transplantation of haploidentical hematopoietic stem cells and mesenchymal stem cells in patients with severe aplastic anemia

We examined if transplantation of combined haploidentical hematopoietic stem cells (HSC) and mesenchymal stem cells (MSC) affected graft failure and graft-versus-host disease (GVHD) in patients with severe aplastic anemia (SAA). Patients with SAA-I (N = 17) received haploidentical HSCT plus MSC infusion. Stem cell grafts used a combination of granulocyte colony-stimulating factor (G-CSF)-primed bone marrow and G-CSF-mobilized peripheral blood stem cells of haploidentical donors and the culture-expanded third-party donor-derived umbilical cord MSCs (UC-MSCs), respectively. Reduced intensity conditioning consisted of fludarabine (30 mg/m²·d)+cyclosphamide (500 mg/m²·d)+anti-human thymocyte IgG. Transplant recipients also received cyclosporin A, mycophenolatemofetil, and CD25 monoclonal antibody. A total of 16 patients achieved hematopoietic reconstitution. The median mononuclear cell and CD34 count was 9.3×10⁸/kg and 4.5×10⁶/kg. Median time to ANC was >0.5×10⁹/L and PLT count >20×10⁹/L were 12 and 14 days, respectively. Grade III-IV acute GVHD was seen in 23.5% of the cases, while moderate and severe chronic GVHD were seen in 14.2% of the cases. The 3-month and 6-month survival rates for all patients were 88.2% and 76.5%, respectively; mean survival time was 56.5 months. Combined transplantation of haploidentical HSCs and MSCs on SAA without an HLA-identical sibling donor was safe, effectively reduced the incidence of severe GVHD, and improved patient survival.

A combination of fludarabine, half-dose cyclophosphamide, and anti-thymocyte globulin is an effective conditioning regimen before allogeneic stem cell transplantation for aplastic anemia

Conditioning regimens consisting of reduced-dose cyclophosphamide (CY) and fludarabine (FDR) have been investigated for use in allogeneic hematopoietic stem cell transplantation (allo-HSCT) in patients with aplastic anemia to reduce the toxicities associated with CY. However, the ideal dose of CY has not been identified. In addition, little information is available regarding donor cell chimerism after allo-HSCT with these regimens. Therefore, we retrospectively analyzed 13 patients who underwent allo-HSCT with half-dose CY (100 mg/kg in total), FDR, and anti-thymocyte globulin at total doses of 2.5-10 mg/kg at our center. All the patients except one, who died due to encephalopathy on day 20, achieved neutrophil engraftment a median of 18.5 days after HSCT with complete donor-type chimerism. Two patients who received a graft from an HLA-matched donor subsequently developed mixed chimerism (MC) associated with transfusion-dependent cytopenia. One became transfusion-independent after donor lymphocyte infusion, but continues to exhibit MC. The other regained complete donor-type chimerism after the cessation of cyclosporine, but remains transfusion-dependent. These findings suggest that a conditioning regimen with half-dose CY and FDR is effective for achieving neutrophil engraftment and complete donor-type chimerism. However, subsequent MC may be observed, especially after HLA-matched HSCT.

Management of adult patients older than 40 years refractory to at least one immunosuppressive course: HLA-identical sibling HSCT using fludarabine-based conditioning

Allogeneic hematopoietic SCT (HSCT) from an HLA-identical sibling donor is the recommended upfront therapeutic option for young patients with SAA. The outcome of allogeneic sibling HSCT has remarkably improved during the last decade as a function of improvement in transplantation supportive care. However, there is still much debate concerning the upper age limit for sibling HSCT in SAA, particularly in patients who are refractory to at least one immunosuppressive course. Recent studies suggest that fludarabine-based conditioning may improve HSCT outcome in older patients with SAA. This review discusses available data about the use of fludarabine-based conditioning in transplantation of older patients with SAA. More definitive conclusions are needed from larger studies before the wide adoption of fludarabine-based conditioning as an alternative to the standard CY and ATG-based conditioning.

Clinical management of aplastic anemia

Acquired aplastic anemia is a potentially fatal bone marrow failure disorder that is characterized by pancytopenia and a hypocellular bone marrow. Hematopoietic stem-cell transplantation or bone marrow transplantation (BMT) is the treatment of choice for young patients who have a matched sibling donor. Immunosuppression with either anti-thymocyte globulin and cyclosporine or high-dose cyclophosphamide is an effective therapy for patients who are not suitable BMT candidates owing to age or lack of a suitable donor. Results of BMT from unrelated and mismatched donors are improving, but presently this treatment option is best reserved for those patients who do not respond, relapse or develop secondary clonal disorders following immunosuppressive therapy. Efforts are currently underway to both improve immunosuppressive regimens and to expand the application of BMT.