In the past 20 years, immunosuppressive theapy (IST) and hematopoietic stem cell transplantation (HSCT) have made great progress in the treatment of aplastic anemia (AR).
anemia (reblastosis) have made great progress, but there is still much room for improvement in clinical care. In terms of IST, the efficacy is 60C80%, but still about 30% of patients become refractory/relapsed. In this paper, we discuss the factors related to IST in order to optimize IST, improve the efficacy, and improve patient survival.
I. Differential diagnosis
The pathological mechanism of remittent disease is not yet fully understood. It can be simply explained that remittent disease is a hematopoietic failure caused by a decrease in hematopoietic stem cells (HSCs), but why and how are HSCs decreased? There is still a lot of uncertainty. The current consensus is that it is an autoimmune disease that results in remittance due to cytotoxic T cells attacking HSCs. The most direct and valid evidence is that about 2/3 of reoccurring disorders recover their own hematopoiesis with IST.
The Cammita criteria and Baciglupo criteria for superheavy reblasts, as well as the modified domestic diagnostic criteria, are morphologically based and determine the presence or absence, degree (mild/heavy/superheavy) and rate (acute/chronic) of hematopoietic failure. The recently proposed fulminant and intermediate reperfusion are still derived from this basis.IST is the restoration of hematopoiesis by killing/killing, suppressing T-cell function, and promoting residual hematopoiesis. The predictors of IST efficacy summarized in the literature are all related to immune function, residual hematopoietic function, and hematopoietic failure factors: high absolute lymphocyte values and small PNH clones suggest the presence of immune abnormalities; high absolute reticulocyte and neutrophil values suggest fair residual hematopoietic function and low risk of infection; young age and good hematopoietic reserve function; cyclosporine A , CsA) concentration is rapidly reached to be able to adequately suppress/modulate abnormal immunity; chromosomes often suggest a risk of clonal transformation and poor efficacy.
Thus, the poor IST effect may have a differential diagnostic error; although hematopoietic failure, it is not necessarily mediated by T-cell hyperfunction, and reperfusion occurs. Hematopoietic stem cell mass abnormalities, such as abnormal clones of hematopoietic stem cells [hypoproliferative myelodysplastic syndromes (Hypo-MDS), paroxysmal sleep hemoglobinuria], abnormalities of the DNA oxidative repair system (Fanconi anemia, especially in those with atypical symptoms), telomere/telomerase abnormalities ( congenital anomalies of keratinization, etc.), which are often difficult to distinguish from reoccurring disorders, do not work well against antithymocyte globulin (ATG), and are at risk of disease progression. In Germany, early detection of childhood reoccurrence secondary to MDS, acute myeloid leukemia (AML) after IST was high, and after switching to specialist centers for diagnosis and improving diagnostic accuracy, the rate has dropped from 23% in 1998 to 3% today! (Baumann J. Leuk Res, 2011,35:s1)
The US NIH systematic observation found telomere/telomerase abnormalities in some remissions and found that those with shortened telomere length were prone to relapse (hazard ratio = 6.25, P = 0.01), had a high rate of clonal evolution (hazard ratio = 3.45, P = 0.01) and a low survival rate (hazard ratio = 2.86, P = 0.005). So, should this group of patients be sorted out in a single column to facilitate further research and treatment (early HSCT)?
Immune-related hemocytopenia is a category of hematopoietic failure due to antihematopoietic autoantibodies, and such patients also have poor outcome with ATG. Autoantibodies have been successively reported to be found in ATG-refractory reperfusion, and remission has been achieved with rituximab.
II. Residual hematopoietic function and intensity of immunosuppression
IST does not introduce new hematopoietic stem cells, but restores the original hematopoietic system, which requires adequate residual hematopoietic function and timely blockade of abnormal immunity and regulation/repair of the immune system. Therefore, the interval between the onset of reoccurrence and IST has an impact on the efficacy of IST in those with prolonged disease, who may have few residual hematopoietic stem cells and an impaired hematopoietic microenvironment. The intensity of immunosuppression is necessary from a CsA perspective at adequate concentrations (trough concentrations of 150-250 ng/ul), but ATG clinical results suggest that intensive immunosuppression alone does not lead to better outcomes.
The US NIH randomly controlled equine ATG vs. rabbit ATG and found a 6-month efficacy of 68% in the equine ATG group vs. 37% in rabbit ATG (P < 0.001), with 3-year probable survival rates of 96%, 66% (P < 0.04), and 94% vs. 70% (P < 0.008) for those not including transplantation, respectively. Early (within 6 months) mortality was also higher in the rabbit ATG group than in the horse ATG group (9 vs 2). This result was validated by the European Bone Marrow Transplantation Task Force (EBMT) Working Group on Severe Recanalization, where 1/3 of cases were compared in pairs, with 2-year survival rates of 86% in the horse ATG group versus 68% in the rabbit ATG group (P < 0.009); graft-free survival (indicating that IST worked without transplantation) was also better in the horse ATG group at 76% than in the rabbit ATG group at 52% (P < 0.002). Fatal infections occurred in 1/3 of patients in the rabbit ATG group, also higher than in the horse ATG group.
What accounts for such a disparity? Both ATGs had similar roles in clearing CD8+ cytotoxic T cells, but the rabbit ATG had a stronger role in killing CD4+ T cells. In contrast, regulatory T cells are CD4+ cells and there is an interaction between hematopoietic stem cells and CD4T cells. The rabbit ATG is deeply immunosuppressed and has a high incidence of infection. The use of rabbit ATG as salvage therapy after failure of horse ATG was also based on the greater intensity of immunosuppression of the former, with an efficacy of 30C77%.
Therefore, in retrospect, we were correct in designing CsA for use 4 weeks after ATG for sequential intensive immunosuppressive therapy in China.
Studies showing comparable efficacy between equine and rabbit ATG have also been reported, with Cleveland, USA, showing no difference in 1-year efficacy (58% vs 50%) and survival (64% vs 65%) between the two groups; Spanish data showed a survival rate of about 70% for both possible treatment groups, with an efficacy rate of 58.5% vs 57.8%. Asian populations have a higher incidence of reoccurrence than Western populations, and the Korean results also showed 1-year efficiency (45.7% vs. 49.1%) and 5-year survival (83.5% vs. 82.7%) for both. Is the high infection rate of EBMT due to the high dosage of rabbit ATG (3.75 mg/kg/d,5 days)? We are currently conducting a randomized controlled trial with Japan and Korea on two doses of rabbit ATG, 2.5 mg and 3.75 mg, in the hope of answering this question.
So, while insufficient immunosuppression is certainly ineffective, augmentation may not be effective, especially with massive reduction of CD4+ regulatory T cells and induction of severe infections. The rest of the hope of enhancing immunosuppression, combined with a third immunosuppressant on the basis of ATG+ CsA, such as mycophenolate, sirolimus also did not achieve improved efficacy. alentuzumab also has stronger immunosuppressive effect than horse ATG, and the effect is not good for patients with primary remittent disease.
At present, there is no horse ATG in China, but there is domestic pig ATG. Pigs and horses belong to the same large animal, and their genetic background is similar, different from that of rabbits. What are the results of this drug compared with rabbit ATG? It is worth exploring.
III. CsA maintenance therapy and tacrolimus replacement therapy
There is a consensus on the long-term maintenance of oral CsA with slow dose reduction, on the grounds that it takes time to acquire and re-establish immunomodulation and immune homeostasis. although ATG clears a large number of cytotoxic T cells, subsequent continuous treatment is still necessary, and the clinical evidence shows that ATG+CsA is more effective than ATG alone.
So, how long does CsA last? How to reduce the dose?
According to the experience of hematopoietic stem cell transplantation, it usually takes 12 months for the immune function to be reconstituted, and reblindness is a hyperimmune disease. After ATG clears T cells, CsA continues immunosuppression/regulation to reach immune homeostasis, which should be no less than such a time.
Experience with pediatric remittent disease has shown that the relapse rate is only 7.6% with a slow reduction of CsA (0.3C0.7 mg/kg/month) and 60% with a rapid reduction (> 0.8 mg/ kg/month) (p<0.001). Therefore, to maintain stable efficacy, CsA is recommended to be tapered slowly, 5-10% per month after 12 months of ATG + CsA adequate dose (trough concentration 150-250ng/ul). The NIH compared CsA fast taper and gradual taper, with a relapse rate of 32% in those who discontinued after 6 months, compared to a 25% taper every 3 months after 6 months, and a 29% relapse rate in the completed taper group after 18 months, with no significant difference seen. However, in practice, the relapse rate was high in either group, and such a dose reduction method is not acceptable.
The fact that CsA can be applied in pediatric patients in full doses and courses is related to the good organ function and good tolerance of the drug in patients of this age group. Common adverse effects of CsA include hypertension, gingival hyperplasia, intrahepatic biliary stasis, renal impairment and interstitial nephritis. Replacement of CsA with tacrolimus has been found to alleviate gingival hyperplasia in pediatric patients with severe reoccurrence and does not affect the efficacy. We replaced tacrolimus with CsA in patients with mild/medium reoccurrence, adverse reactions and refractory/relapsed patients, maintaining blood levels above 6 ng/ul. 22 cases with ineffective CsA were replaced with hematological improvement in 12 cases (54.54%), with a median onset of action of 8 weeks. The median time to recovery of renal function was 13 weeks, the median time to recovery of liver function was 6.5 weeks, and the median time to improvement of gingival hyperplasia was 6 weeks. 6 cases of CsA intolerance showed improvement in adverse reactions after switching, the median time to recovery of normal renal function was 10 weeks, and the median time to improvement of gingival hyperplasia was 6 weeks, but 1 case died after switching to FK506 and losing efficacy. In vitro studies on reperfusion T cells also confirmed that tacrolimus can effectively inhibit effector T cell function and promote the release of immunomodulatory factors.
In order to effectively prevent relapse in remittent disease, relying solely on empirical drug reduction and discontinuation is not reliable. The effect of chemotherapy/transplantation should be evaluated by similar means as micro-residual disease and quantitative genetic techniques in leukemia, and the reduction of immunosuppressive drugs should be determined by evaluating the hematopoietic function, immune index and organ function in reoccurrence, using objective indexes.
Hematopoietic growth factor
Infection is the first cause of death in IST with severe reoccurrence, and it occurs mostly in the first month of IST. However, it was subsequently questioned whether G-CSF increases the risk of clonal disease, especially MDS/AML.
One of the largest recent prospective randomized controlled trials showed that G-CSF did not increase the risk of clonal disease. the EBMT Reentry Working Group study showed that G-CSF, while not affecting survival, disease-free survival, mortality, incidence of clonal disease, or relapse rates, did increase neutrophil counts and reduce infections and hospitalization in the first 3 months of IST. And at 30 days of IST, G-CSF responders – absolute neutrophil values of 0.5 × 109/L suggest that patients are responding efficaciously to IST.
G-CSF and Epo have synergistic effects in improving transfusion dependence in the low-risk group of MDS, and the NIH recommends the combination of G-CSF and Epo in those with poor IST outcomes, and our expert consensus on reoccurrence also recommends the combination of G-CSF and Epo in patients with reoccurrence. Although IL-11 and thrombopoietin have a stimulating effect on platelet production, no clear improvement in platelet transfusion has been reported in reoccurrence.
Eltrombopag
is an orally administered non-peptide small molecule compound that is a thrombopoietin receptor (c-MPL) analogue that promotes megakaryocyte maturation and platelet release. MPL mutations in congenital megakaryocyte-deficient thrombocytopenia are often followed by trilineage reduction in hematopoietic failure, suggesting that the c-MPL signaling pathway system is involved in the survival and expansion of hematopoietic stem/progenitor cells. Twenty-five cases of refractory reperfusion were treated with Eltrombopag
A phase 2 clinical trial was conducted to evaluate the efficacy and adverse effects of the drug, and 11 cases were found at 12 weeks
(44.0%) had at least 1 lineage hematopoietic improvement and 9 (36.0%) no longer required platelet transfusion (median increase of 4.4×109/L); 6 (24.0%) had elevated hemoglobin (median 44g/L), including 3 off red blood cell transfusion; 9 (36.0%) had elevated neutrophil counts (median 1.35×109/L); the effective ones had a restored 3 lineage hematopoietic ratio in the bone marrow and did not see The hematopoietic ratio was restored and no increase in bone marrow fibrosis was seen. This result suggests whether IST in combination with eltrombopag should be used to improve the efficacy and long-term survival of reperfusion.
V. Other immunosuppressive agents
Daclizumab is a humanized IL-2 receptor monoclonal antibody, and clinical trials in non-severe remitting disease have shown
Alentuzumab is a CD52 monoclonal antibody that has been shown to be effective at 3 months in 19/45 cases (42%) and to have responded at 6 months in 2 other cases.
is a CD52 monoclonal antibody that was closed early in a randomized controlled trial with only 19% efficacy in primary heavy remissions. However, the drug was 37% effective in refractory remitting disease, comparable to 33% in the rabbit ATG group, with a slightly higher 3-year survival rate of 83% vs 60%, but not statistically different. Given the good efficacy of alentuzumab in autoimmune hemocytopenia, and whether many of these “refractory remissions” reported by the NIH are post-ATG screening for IRP mediated by anti-myelopoietic autoantibodies, alentuzumab has been shown to be effective in refractory cases. Therefore, alentuzumab is more effective in such refractory patients? Also, alentuzumab is more immunosuppressive than equine ATG. Is it possible that, as with rabbit ATG, immunosuppression does not need to be strong for primary remissions, while stronger immunosuppression is required for refractory remissions after equine ATG screening?
The Johns Hopkins Hospital used cyclophosphamide 50 mg/kg/day intravenously for 5 days to achieve a 10-year overall survival rate of 88%, a response rate of 71%, and an event-free survival rate of 58% in patients with primary SAA, and a 10-year overall survival rate of 62%, a response rate of 48%, and an event-free survival rate of 27% in patients with refractory SAA. However, the NIH failed to replicate the results and was forced to discontinue it due to severe myelosuppression, high mortality, long hospital stays, and high transfusion volumes.
Recently, the NIH has tried again to reduce the dose of cyclophosphamide, using a medium-dose cyclophosphamide combined with CsA regimen (cyclophosphamide 30 mg/kg/d x 4d, total 120 mg),
CsA at a low dose, 100-200 mg/L, was studied again to evaluate the safety and efficacy of cyclophosphamide. The study population was first-episode heavy remission, and the clinical blood evaluation endpoint was 6-month efficiency (i.e., blood picture recovery above heavy remission criteria at 6 months of treatment), with the hope of achieving a remission rate of 30% or more. In view of a serious infection with cyclophosphamide in the previous NIH, prophylactic voriconazole, ciprofloxacin, and cotrimoxazole were administered.
A total of 22 patients with severe remissions were enrolled from October 2010 to April 2012. The toxicity of cyclophosphamide, while expected by the investigators, was still unexpected in its intensity – regardless of the pre-treatment neutrophil values, it commonly reached 0 after treatment. 5 patients had to be infused with granulocytes because the infection was uncontrollable. There have been 5 deaths in the trial group to date, all due to infection. Ten patients had ANC >500/ul before treatment, but five of them were still in severe granulocyte deficiency 6 months after treatment and were in urgent need of salvage therapy. one case developed pulmonary trichomoniasis and required frequent granulocyte infusions.
A total of 4 cases were in complete remission and 5 cases were in partial remission, with an efficiency rate of 9/22 (40.9%). During the relatively short follow-up, four cases developed cytogenetic abnormalities: one monosomy 7, one 20q-, one 15 trisomy, and one 17q-.
The authors conclude that although cyclophosphamide (120 mg/kg) + CsA was effective in some heavy remissions, severe toxic reactions occurred even with strong prophylaxis and supportive therapy. This regimen resulted in prolonged hospitalization and frequent bacterial and fungal infections. Hematologic relapse and clonal transformation were also higher than expected. Given the high toxicity of cyclophosphamide and the fact that it did not reduce relapse rates or clonal transformation to the benefit of patients, the NIH Data and Safety Monitoring Committee terminated this clinical trial.
Cyclophosphamide is not currently recommended for the treatment of reoccurrence in Europe.
VI. Outlook
Although there is a convergence of opinion that remittent disease is a hematopoietic failure due to T-cell hyperfunction, in practice, some other factors of hematopoietic failure have not yet been fully distinguished from the remittent disease group and need to be taken into account and treated differently. In addition to the conventional focus on MDS, PNH, myelofibrosis, MPL, TERC and TERT gene mutations, Faconi anemia (especially in atypical cases), congenital dyskeratosis, and large granular lymphocytic leukemia should be placed in the differential diagnostic tests for reblastosis. This will lead to better results in the study of the pathomechanism of remitting disease and IST.
Is the group and timing of IST treatment, especially ATG+ CsA intensive immunosuppression, forward to medium-sized remitting disease? How is the treatment of fulminant remitting disease selected? How are these two subgroups defined and new questions such as the combination of IST with novel hematopoietic stimulants need to be further explored.