Efficacy of combination therapy with anti-thymocyte globulin and cyclosporine A as a first-line treatment in adult patients with aplastic anemia: a comparison of rabbit and horse formulations

The state of the art in the treatment of severe aplastic anemia: immunotherapy and hematopoietic cell transplantation in children and adults

Acquired aplastic anemia (AA) is an immune-mediated bone marrow (BM) failure where marrow disruption is driven by a cytotoxic T-cell-mediated autoimmune attack against hematopoietic stem cells. The key diagnostic challenge in children, but also in adults, is to exclude the possible underlying congenital condition and myelodysplasia. The choice of treatment options, either allogeneic hematopoietic cell transplantation (alloHCT) or immunosuppressive therapy (IST), depends on the patient's age, comorbidities, and access to a suitable donor and effective therapeutic agents. Since 2022, horse antithymocyte globulin (hATG) has been available again in Europe and is recommended for IST as a more effective option than rabbit ATG. Therefore, an update on immunosuppressive strategies is warranted. Despite an improved response to the new immunosuppression protocols with hATG and eltrombopag, some patients are not cured or remain at risk of aplasia relapse or clonal evolution and require postponed alloHCT. The transplantation field has evolved, becoming safer and more accessible. Upfront alloHCT from unrelated donors is becoming a tempting option. With the use of posttransplant cyclophosphamide, haploidentical HCT offers promising outcomes also in AA. In this paper, we present the state of the art in the management of severe AA for pediatric and adult patients based on the available guidelines and recently published studies.

Repeated immunosuppressive rabbit antithymocyte globulin therapy for adult patients with relapsed or refractory aplastic anemia

OBJECTIVES

Immunosuppressive therapy (IST) with antithymocyte globulin (ATG) and cyclosporin A is the standard treatment for aplastic anemia (AA). However, the efficacy of repeated IST with rabbit ATG (rATG) as salvage therapy remains unclear in patients with relapsed or refractory AA.

METHODS

We retrospectively evaluated the efficacy and safety of IST2 with rATG (IST2-rATG) in 19 consecutive patients with relapsed or refractory AA who received first-line IST with rATG in two centers between 2009 and 2020.

RESULTS

The overall 6-month response rate of the patients was 58%. The response rates were similar between patients with relapsed and refractory AA. The presence of glycophosphatidylinositol-deficient blood cells was associated with a better response to IST2-rATG. Despite retreatment with the same rATG, serum disease and severe allergic reactions were not observed.

CONCLUSION

IST2-rATG is effective and safe for the treatment of adult patients with relapsed and refractory AA after receiving first-line IST with rATG.

Antihuman T lymphocyte porcine immunoglobulin combined with cyclosporine as first-line immunosuppressive therapy for severe aplastic anemia in China: a large single-center, 10-year retrospective study

Background

Antihuman T lymphocyte porcine immunoglobulin (p-ATG) has been the most common ATG preparation in immunosuppressive therapy (IST) in Chinese patients with severe aplastic anemia (SAA) since 2009.

Objectives

This study aimed to evaluate the early hematologic response and long-term outcomes of a large cohort of patients with SAA who received p-ATG plus cyclosporine (CsA) as first-line therapy from 2010 to 2019.

Design

This is a single-center retrospective study of medical records.

Methods

We analyzed the data of 1023 consecutive patients with acquired aplastic anemia (AA) who underwent p-ATG combined with CsA as a first-line IST treatment from 2010 to 2019 at our department.

Results

The median age of the patients was 24 (4-75) years, and the median follow-up time was 57.2 months (3 days-137.5 months). There was an early mortality rate of 2.8% with a median death time of 0.9 months (3 days-2.9 months). The overall response rates were 40.6% and 56.1% at 3 and 6 months, respectively. The 5-year cumulative incidences of relapse and clonal evolution were 9.0% [95% confidence interval (CI) = 4.2-16.0%] and 4.5% (95% CI = 1.4-10.6%), respectively. The 5-year overall survival (OS) and event-free survival rates were 83.7% (95% CI = 81.1-86.0%) and 50.4% (95% CI = 47.1-53.5%), respectively.

Conclusion

p-ATG combined with CsA for the treatment of AA is effective and safe, and p-ATG can be used as an alternative ATG preparation for the standard IST regimen in areas in which h-ATG is not available.

Efficacy and safety of equine anti-thymocyte immunoglobulin (eATG) in three Japanese patients with moderate to very severe aplastic anemia: a case series

Aplastic anemia results from lymphocyte-mediated destruction of hematopoietic stem cells. Immunosuppressive therapy with anti-thymocyte globulin (ATG) and cyclosporine is the standard front-line treatment for patients with severe aplastic anemia who are not suitable candidates for stem cell transplants. PF-06462700 is a potent equine ATG that targets T-lymphocytes and has been approved as a treatment for aplastic anemia outside of Japan for over 30 years. Due to the high medical need for PF-06462700, the Ministry of Health, Labor and Welfare requested its development for Japanese patients with aplastic anemia. In this case series, the efficacy and safety of PF-06462700, administered intravenously at 40 mg/kg/day for 4 days, were assessed over a 24-week period. This was as an open-label, single-arm, multicenter clinical study designed to enroll a minimum of three Japanese participants with aplastic anemia. Two participants met the primary outcome of hematologic response at week 12 and improvements in disease severity were observed. No deaths or serious adverse events were reported. The efficacy results from this case series suggest that administration of PF-06462700 is generally well-tolerated and produces a hematologic response in Japanese patients with aplastic anemia, which should be further evaluated in real-world studies.ClinicalTrials.gov identifier: NCT04350606.

A real-word experience of eltrombopag plus rabbit antithymocyte immunoglobulin-based IST in Chinese patients with severe aplastic anemia

Eltrombopag (EPAG), a thrombopoietin receptor agonist, was approved for the treatment of severe aplastic anemia (SAA) combined with immunosuppressive therapy (IST). However, the effects of real-life use of low doses of EPAG combined with rabbit antithymocyte globulin (ATG)-based IST in Asian patients with SAA are yet unknown. A total of 121 previously untreated Chinese patients with SAA were enrolled in a multicenter registry of the Chinese Eastern Collaboration Group of Anemia (2014-2020): 67 patients received IST alone and 54 patients received additional EPAG. Patients receiving IST plus EPAG had a higher overall response rate (ORR) at 1 month (P = 0.002), 3 months (P = 0.028), 6 months (P = 0.006), and 12 months (P = 0.031) compared to those receiving IST alone. EPAG was the favorable factor for response efficacy at 6 months. The complete response rate in the EPAG plus IST group was 17% at 3 months, 27% at 6 months, and 32% at 12 months, compared to 7% (P = 0.069), 14% (P = 0.11), and 33% (P = 0.92) for those treated with IST alone. The 2-year overall survival rate in EPAG plus IST and IST alone groups was 98% and 88%, respectively (P = 0.078). The rate of adverse events, including clonal evolution, infection, and transaminitis, was similar in the two cohorts. The addition of EPAG to IST was well-tolerated and associated with high rates of hematologic responses among the previously untreated Chinese patients with SAA.

First-line immunosuppressive therapy with rATG and CsA for severe aplastic anemia: 15 years' experience

Rabbit antithymocyte globulin (rATG) instead of horse ATG has been used for severe aplastic anemia (SAA) patients in China. This study aimed to investigate the hematologic responses and long-term overall survival (OS) outcomes in SAA patients who received rATG and cyclosporine as first-line immunosuppressive therapy. We analyzed data of 542 SAA patients treated with this therapy between 2005 and 2019. The median age was 20 (range, 2-80) years, and the median follow-up time was 45.5 (range, 0.1-191.4) months. The early mortality rate was 3.9%. The overall response rates (ORRs) were 40.2%, 56.1%, and 62.4% at 3, 6, and 12 months, respectively. The 6- and 12-month ORR of patients treated with 3 mg/kg/d of rATG in 2015-2019 seemed higher than that of patients treated with 3.5-3.75 mg/kg/day in 2005-2014 (60.2% vs. 54.9%, P = 0.30 and 69.9% vs. 60.1%, P = 0.049, respectively). The 10-year cumulative incidences of relapse and clonal evolution were 10.6 ± 2.9% and 7.5 ± 1.5%, respectively. The 10-year OS rate and event-free survival rate were 80.1 ± 2.1% and 75.6 ± 3.7%, respectively. Age, disease severity, treatment periods, and the interval from diagnosis to IST were independent predictors of OS. In conclusion, 3 mg/kg/day rATG is effective as first-line treatment for SAA.

Eltrombopag in Combination with Rabbit Anti-thymocyte Globulin/Cyclosporine A in Immunosuppressive Therapy-naïve Patients with Aplastic Anemia in Japan

Objective In Japan, immunosuppressive therapy (IST) with anti-thymocyte globulin (ATG), and cyclosporine A (CsA) is the standard of care in patients with aplastic anemia (AA) who are not indicated for stem-cell transplantation, although some patients may experience relapse. This study assessed the efficacy and safety of eltrombopag in combination with rabbit-ATG/CsA in IST-naïve patients with non-severe or severe AA in Japan. Methods In this non-randomized, open-label, single-arm, phase II study, rabbit-ATG/CsA and eltrombopag were initiated on Days 1 and 15 (±3 days), respectively, and continued for ≥26 weeks; rabbit-ATG was given for 5 days (Days 1 to 5). The primary endpoint was the overall response rate (ORR) at Week 26. Patients Patients with AA who were IST-naïve and ≤70 years old or between 71 and 75 years old based on the recommendation of the investigator were enrolled in Japan. Results Of the 11 enrolled patients, 10 started treatment with eltrombopag. The ORRs at Weeks 26 and 52 were 70.0% and 60.0%, respectively. The ORR at Week 26 was 100% (all 3 patients) in patients with non-severe AA and 57.1% (4/7) in patients with severe AA. Among transfusion-dependent patients, 66.7% (4/6) and 62.5% (5/8) became red blood cell- and platelet-transfusion independent, respectively. The most common adverse events were nausea and headache. No deaths or hematologic malignancies were reported. A cytogenetic abnormality was reported in one patient. Conclusion This study confirmed the clinical benefit of eltrombopag plus rabbit-ATG/CsA in IST-naïve patients with non-severe or severe AA in Japan.

Acquired severe aplastic anaemia: how medical therapy evolved in the 20th and 21st centuries

The progress in aplastic anaemia (AA) management is one of success. Once an obscure entity resulting in death in most affected can now be successfully treated with either haematopoietic stem cell transplantation (HSCT) or immunosuppressive therapy (IST). The mechanisms that underly the diminution of haematopoietic stem cells (HSCs) are now better elucidated, and include genetics and immunological alterations. Advances in supportive care with better antimicrobials, safer blood products and iron chelation have greatly impacted AA outcomes. Working somewhat 'mysteriously', anti-thymocyte globulin (ATG) forms the base for both HSCT and IST protocols. Efforts to augment immunosuppression potency have not, unfortunately, led to better outcomes. Stimulating HSCs, an often-sought approach, has not been effective historically. The thrombopoietin receptor agonists (Tpo-RA) have been effective in stimulating early HSCs in AA despite the high endogenous Tpo levels. Dosing, timing and best combinations with Tpo-RAs are being defined to improve HSCs expansion in AA with minimal added toxicity. The more comprehensive access and advances in HSCT and IST protocols are likely to benefit AA patients worldwide. The focus of this review will be on the medical treatment advances in AA.

Efficacy of Rabbit Antithymocyte Globulin as a First-line Therapy in Children With Aplastic Anemia

BACKGROUND

The efficacy, safety, and outcome of rabbit antihuman thymocyte globulin (rATG) as initial therapy for children aplastic anemia (AA) were evaluated.

PATIENTS AND METHODS

Sixty-one children with AA were retrospectively analyzed, including 43 patients with severe AA and 18 patients with transfusion-dependent nonsevere AA. All patients received rATG in combination with cyclosporine A between September 2005 and January 2015.

RESULTS

The overall response rates were 55.7%, 68.9%, and 68.9% at 6, 12, and 18 months, respectively. Surprisingly, the overall complete response rate kept increasing from 9.8% at 12 months to 39.3% at 18 months, indicating a delayed response for rATG. Overall survival at 5 and 10 years was 72.1% and 67.2%, respectively. The overall survival of patients who responded between 3 and 12 months was significantly higher than that of nonresponders (71.4% vs. 47.4%).Antithymocyte globulin-related adverse reactions were significantly higher in severe AA (83.7%) than in nonsevere AA (55.6%) and these reactions were controllable and not life threatening with comprehensive measures.

CONCLUSIONS

This retrospective study shows an encouraging response and survival results in children with AA treated with rATG. Prolonged assessments were needed to evaluate the delayed responses to rATG. rATG could be used as an alternative in the first-line treatment of childhood AA.

Treatment of Severe Aplastic Anemia with Porcine Anti-Human Lymphocyte Globulin

Aplastic anemia (AA) is a bone marrow failure syndrome characterized by pancytopenia. Decreased numbers of hematopoietic stem cells and impaired bone marrow microenvironment caused by abnormal immune function describe the major pathogenesis of AA. Hematopoietic stem cell transplantation and immunesuppressive therapy are the first-line treatments for AA. Porcine anti-lymphocyte globulin (p-ALG) is a new product developed in China. Several studies have shown that p-ALG exhibited good therapeutic effects in AA.

Cord blood infusion-accelerated hematopoietic recovery after combined immunosuppressive therapy with fludarabine and rabbit ATG in severe aplastic anemia

Immunosuppressive therapy (IST) with anti-thymocyte globulin (ATG) and cyclosporine A (CsA) is currently the standard treatment for patients with severe aplastic anemia (SAA) who have no suitable donor or are ineligible for allogeneic stem cell transplantation. However, the delayed hematopoietic recovery, which accounts for most early deaths, remains a key problem. Thus, we designed an IST protocol with fludarabine, rabbit ATG, and CsA followed by unrelated cord blood (UCB) infusion to study whether hematopoiesis could be accelerated. Nineteen patients were enrolled in this study. The median neutrophil recovery time was 22 days and the treatment-related mortality within 3 months was 5.3%. The median platelet recovery time was 180 days. Six patients had transient or sustained UCB engraftment and the median platelet recovery time of these patients was significantly shorter than those who had no UCB engraftment (46 days vs 206 days, p = 0.006). The cumulative incidence of response rate at 12 months was up to 88.7% with CR rate of 72.2%. The overall survival at 2 years and 5 years was 94.7% and 78.9%, respectively. These results suggest that UCB infusion may play an important role in accelerating hematopoietic recovery in this protocol.

Sustained clonal hematopoiesis by HLA-lacking hematopoietic stem cells without driver mutations in aplastic anemia

Clonal hematopoiesis by hematopoietic stem progenitor cells (HSPCs) that lack an HLA class I allele (HLA^- HSPCs) is common in patients with acquired aplastic anemia (AA); however, it remains unknown whether the cytotoxic T lymphocyte (CTL) attack that allows for survival of HLA^- HSPCs is directed at nonmutated HSPCs or HSPCs with somatic mutations or how escaped HLA^- HSPC clones support sustained hematopoiesis. We investigated the presence of somatic mutations in HLA^- granulocytes obtained from 15 AA patients in long-term remission (median, 13 years; range, 2-30 years). Targeted sequencing of HLA^- granulocytes revealed somatic mutations (DNMT3A, n = 2; TET2, ZRSR2, and CBL, n = 1) in 3 elderly patients between 79 and 92 years of age, but not in 12 other patients aged 27 to 74 years (median, 51.5 years). The chronological and clonogenic analyses of the 3 cases revealed that ZRSR2 mutation in 1 case, which occurred in an HLA^- HSPC with a DNMT3A mutation, was the only mutation associated with expansion of the HSPC clone. Whole-exome sequencing of the sorted HLA^- granulocytes confirmed the absence of any driver mutations in 5 patients who had a particularly large loss of heterozygosity in chromosome 6p (6pLOH) clone size. Flow-fluorescence in situ hybridization analyses of sorted HLA⁺ and HLA^- granulocytes showed no telomere attrition in HLA^- granulocytes. The findings suggest that HLA^- HSPC clones that escape CTL attack are essentially free from somatic mutations related to myeloid malignancies and are able to support long-term clonal hematopoiesis without developing driver mutations in AA patients unless HLA loss occurs in HSPCs with somatic mutations.

Immunosuppressive therapy with rabbit antithymocyte globulin therapy for acquired aplastic anemia: a multi-institutional retrospective study in Japanese adult patients

We retrospectively analyzed efficacy and safety of therapy with rabbit antithymocyte globulin (rATG) in combination with cyclosporine A (CsA) in 30 Japanese adult patients with acquired aplastic anemia (AA) in the Kyoto Clinical Hematology Study Group. The median observation period was 31 months and the median age of the patients was 54 years. The objective response rates (ORRs) to rATG plus CsA increased over time until 18 months after the start of treatment; the rate of achievement of better than partial response at 18 months was 66.7%. The 2-year overall survival (OS) rate was 79% in all patients. In eight patients aged ≥ 75 years old, the ORR was 62.5% and the 2-year OS rate of 50% was not significantly inferior to that in patients aged ≤ 74 years old. The overall mortality rate was 16.7% in our cohort, while the mortality rate in patients aged ≥ 75 years old was 37.5%, which was higher than that in patients aged ≤ 74 years old (9.1%), although the difference was not statistically significant. Collectively, rATG combined with CsA is an effective and feasible treatment for AA, while patients should be appropriately selected.

Rabbit antithymocyte globulin dose does not affect response or survival as first-line therapy for acquired aplastic anemia: a multicenter retrospective study

In a prospective randomized study, treatment for aplastic anemia (AA) with rabbit antithymocyte globulin (r-ATG) and cyclosporine showed inferior hematological response and survival in comparison to horse antithymocyte globulin (h-ATG) and cyclosporine. However, h-ATG was discontinued in most Asian, South American, and European countries, where r-ATG became the only ATG formulation available. We retrospectively evaluated consecutive patients with acquired AA who received either rabbit (n = 170) or horse (n = 85) ATG and cyclosporine for first-line treatment from 1992 to 2014 in seven referral centers in Brazil and Argentina. Overall response at 3 months was 17% (95%CI, 11-23%) for r-ATG and 44% (95%CI, 33-55%) for h-ATG (p < 0.001). At 6 months, it was 31% (95%CI, 34-39%) for r-ATG and 59% (95%CI, 48-69%) for h-ATG (p < 0.001). Overall survival at 5 years was 57% (95%CI, 47-65%) for r-ATG and 80% (95%CI, 69-87%) for h-ATG (log-rank = 0.001). Relapse was significantly higher in patients receiving h-ATG (28%; 95%CI, 17-43%) as compared to r-ATG (9.4%; 95%CI, 4-21%; log-rank, p = 0.01). The type of ATG was the only factor associated with both response and survival. The r-ATG dose varied from 1 to 5 mg/kg/day, but it did not correlate with outcomes. In summary, this is the largest multicenter study comparing the two ATG formulations in AA. Our results indicate that the dose of r-ATG does not influence hematologic response or survival in first-line therapy for acquired AA. Considering the toxicity and costs of r-ATG, our findings challenge its aggregate benefit to cyclosporine therapy and further strengthen that h-ATG should remain standard therapy in AA.

First line treatment of aplastic anemia with thymoglobuline in Europe and Asia: Outcome of 955 patients treated 2001-2012

The aim of this study was to assess the outcome of patients with aplastic anemia (AA), receiving rabbit anti‐thymocyte globulin (Thymoglobulin, SANOFI) and cyclosporin, as first line treatment. Eligible were 955 patients with AA, treated first line with Thymoglobulin, between 2001 and 2008 (n = 492), or between 2009 and 2012 (n = 463). The median age of the patients was 21 years (range 1‐84). Mortality within 90 days was 5.7% and 2.4%, respectively in the two time periods (P = .007).The actuarial 10‐year survival for the entire population was 70%; transplant free survival was 64%. Predictors of survival in multivariate analysis, were severity of the disease, patients age and the interval between diagnosis and treatment. Survival was 87% vs 61% for responders at 6 months versus nonresponders (P < .0001). The 10‐year survival of nonresponders at 6 months, undergoing a subsequent transplant (n = 110), was 64%, vs 60% for patient not transplantated (n = 266) (P = .1). The cumulative incidence of response was 37%, 52%, 65% respectively, at 90, 180, and 365 days. In multivariate analysis, negative predictors of response at 6 months, were older age, longer interval diagnosis treatment, and greater severity of the disease. In conclusion, early mortality is low after first line treatment of AA with Thymoglobulin, and has been further reduced after year 2008. Patients age, together with interval diagnosis—treament and severity of the disease, remain strong predictors of response and survival.