Predictors of recovery following allogeneic CD34+-selected cell infusion without conditioning to correct poor graft function

Model-Based Prediction of Clinically Relevant Thrombocytopenia after Allogeneic Hematopoietic Stem Cell Transplantation

Platelet reconstitution after allogeneic hematopoietic cell transplantation (allo-HCT) is heterogeneous and influenced by various patient- and transplantation-related factors, associated with poor prognoses for poor graft function (PGF) and isolated thrombocytopenia. Tailored interventions could improve the outcome of patients with PGF and post-HCT thrombocytopenia. To provide individual predictions of 180-day platelet counts from early phase data, we developed a model of long-term platelet reconstitution after allo-HCT. A large cohort (n = 1949) of adult patients undergoing their first allo-HCT was included. Real-world data from 1,048 retrospective patients were used for non-linear mixed-effects model development. Bayesian forecasting was used to predict platelet-time profiles for 518 retrospective and 383 prospective patients during internal and external model validation, respectively. Thrombocytopenia was defined as mean platelet count < 75 × 109/L, derived from the last 12 platelet measurements within the first 180 days post-HCT. Thrombocytopenia affected 37% of all patients and was associated with significantly reduced overall survival (P-value < 0.0001). On days +7, +14, +21, and +28, the developed model achieved areas under the receiver-operating characteristic of ≥ 0.68, ≥ 0.75, ≥ 0.78, and 0.81 for the prediction of post-HCT thrombocytopenia, respectively, with anti-thymocyte globulin, donor relation, and total protein measurements representing prognostic markers for post-HCT platelet kinetics. A publicly accessible web-based demonstrator of the model was established (https://hsct.precisiondosing.de). In summary, the developed model predicts individual platelet counts from day +28 post-HCT adequately, utilizing internal and external datasets. The web-based demonstrator provides a basis to implement model-based predictions in clinical practice and to confirm these findings in future clinical studies.

CD34-selected stem cell boost was an effective treatment for refractory poor hematopoietic reconstitution after haploidentical hematopoietic stem cell transplantation

BACKGROUND

Poor hematopoietic reconstitution (PHR), especially poor graft function (PGF) and prolonged isolated thrombocytopenia (PT), is a life-threatening complication after allo- hematopoietic stem cell transplantation (HSCT). Currently, almost no studies have analyzed CD34+-selected stem cells "boost" (SCB) after haplo-HSCT. Hence, in this study, we focused specifically on refractory PHR after haplo-HSCT.

OBJECTIVE

To retrospectively evaluate the safety and efficacy of donor- CD34+ SCB for the treatment of refractory PHR after haplo-HSCT.

STUDY DESIGN

Twenty-seven patients with refractory PHR who received a donor-CD34+ selected SCB at Peking University People's Hospital were retrospectively analyzed. The patients' hematopoietic response, incidence of graft-versus-host disease, and survival after CD34+ cell boost were evaluated.

RESULTS

Among the 27 patients with refractory PHR who received a CD34+ SCB, five patients (18.5%) were diagnosed with primary PGF, 17 patients (63%) were diagnosed with secondary PGF, and five patients (18.5%) were diagnosed with PT. The median time to PHR diagnosis was 63 days (range: 42-330 days), and the median time to the donor CD34+ boost was 456 days (range: 58-853 days). The median number of infused CD34+ cells was 2.589 × 106/kg (range: 0.738-16.8 × 106/kg). Among the 27 patients, 15 achieved hematologic response (55.56%). Among the responders, the median time of absolute neutrophil count (ANC) response was 15 days (range: 10-158 days), and the median time of erythroid reconstitution was 18 days (range: 7-158 days). The platelet reconstitution time was 22 days (range: 7-171 days). Patients with acute infection during CD34+ SCB were noted to have a worse hematologic response (1/15 vs. 5/12, P = 0.03). The mortality rate significantly differed between patients who achieved complete hematologic response and those who did not (100% vs. 33.3%, respectively; P < 00.001). Infections were the leading cause of death (n = 5/8, 62.5%).

CONCLUSION

CD34+-selected SCB is a potentially effective treatment for refractory PHR after haploidentical HSCT.

When and how to transplant in myelofibrosis - recent trends

Allogeneic hematopoietic stem cell transplantation (AHSCT) is currently the only treatment modality that is capable of curing myelofibrosis (MF). Although outcomes of AHSCT have improved vastly in recent years owing to advancements in HLA typing, conditioning regimens, and supportive care, it remains a procedure with a considerable risk in MF patients due to conditioning regimen related toxicity, higher rates of graft failure, infections, and graft versus host disease (GVHD). Recent progress in the treatment and prevention of GVHD with post-transplant cyclophosphamide has also rendered transplantation from alternative donors feasible and safer, thus improving access to patients without HLA-identical donors. Accordingly, all patients with intermediate or high-risk MF today should be referred for potential transplant evaluation to consider the pros and cons of an early versus a delayed transplant strategy. Individual risk assessment in MF is best facilitated by contemporary prognostic models that incorporate both clinical and genetic risk factors. The current review highlights new information regarding risk stratification in MF, anchored by practical algorithms that facilitate patient selection for specific treatment actions, including AHSCT.

Active infection at the time of CD34+ selected stem cell boost is associated with treatment failure and poor overall survival

ABSTRACT

The use of CD34+ selected stem cell boost (SCB) after allogeneic hematopoietic cell transplant (allo-HCT) has been increasing. Predictors of treatment failure after SCB, both in the context of poor graft function (PGF) or other settings, are not well characterized. We report among the largest single-center retrospective experiences of the use of SCB and evaluate potential predictors of response and outcomes. A total of 58 patients who underwent HCT between 2015 and 2022 and who received SCB, were identified. The indication for SCB was predominantly PGF, defined as the presence of ≥2 cytopenias for at least 2 consecutive weeks beyond day +14 after allo-HCT in the presence of ≤30% bone marrow cellularity and ≥90% donor myeloid chimerism in the absence of morphologic disease. The median dose of infused CD34+ selected SCB products was 3.88 × 106 CD34+ cells per kg (range, 0.99 × 106 to 9.92 × 106). The median 2-year overall survival and nonrelapse mortality after SCB was 47% and 38%, respectively. The cumulative incidences of 6-month grade 3 to 4 acute and 2-year moderate-severe chronic graft-versus-host disease after SCB were 3.4% and 12%, respectively. Overall response (complete response + partial response) was attained in 36 of 58 patients (62%) and in 69% of patients with PGF. On multivariable analysis, an active infection at the time of SCB was the greatest predictor of poor response and survival (P = .013) after SCB. SCB can restore hematopoiesis in the majority of patients, particularly for those with PGF and in whom there is no active infection at the time of infusion.

[Selected donor CD34(+) cell boosts for salvage treatment of poor graft function following allogeneic hematopoietic stem cell transplantation in primary myelofibrosis: 3 cases report]

A retrospective analysis was conducted on three patients with primary myelofibrosis who underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT) at Shanghai Zhaxin Traditional Chinese and Western Medicine Hospital from 2020 to 2023. They subsequently developed poor graft function. The patients received selected donor CD34(+) cell boosts as salvage therapy. There were two male patients and one female patient, with a median age of 68 (39-69) years. The median time from allo-HSCT to the selected donor CD34(+) cell boost was 83 (56-154) days. The median infusion of selected donor CD34(+) cells was 7.67 (7.61-9.06) ×10(6)/kg, with a CD34(+) cell purity of 97.76% (96.50%-97.91%) and a recovery rate of 70% (42%-75%) . Hematological recovery was achieved in two cases. No acute GVHD was observed in any of the three patients. One case of moderate oral chronic GVHD was noted. Selected donor CD34(+) cell boosts for the treatment of poor graft function after allo-HSCT in primary myelofibrosis was effective and no severe acute or chronic GVHD was observed.

Prospects and Potential for Chimerism Analysis after Allogeneic Hematopoietic Stem Cell Transplantation

Chimerism analysis after allogeneic hematopoietic stem cell transplantation serves to confirm engraftment, indicate relapse of hematologic malignancy, and attribute graft failure to either immune rejection or poor graft function. Short tandem repeat PCR (STR-PCR) is the prevailing method, followed by quantitative real-time PCR (qPCR), with detection limits of 1-5% and 0.1%, respectively. Chimerism assays using digital PCR or next-generation sequencing, both of which are more sensitive than STR-PCR, are increasingly used. Stable mixed chimerism is usually not associated with poor outcomes in non-malignant diseases, but recipient chimerism may foretell relapse of hematologic malignancies, so higher detection sensitivity may be beneficial in such cases. Thus, the need for and the type of intervention, e.g., immunosuppression regimen, donor lymphocyte infusion, and/or salvage second transplantation, should be guided by donor chimerism in the context of the feature and/or residual malignant cells of the disease to be treated.

Definitions, incidence and outcome of poor graft function after hematopoietic cell transplantation: A systematic review and meta-analysis

Poor graft function (PGF) after allogeneic hematopoietic stem cell transplantation (HCT) is a serious complication with high morbidity and mortality. The reported incidence of PGF, its risk factors and outcome vary substantially between studies. This variability may be explained by heterogeneity in patient cohorts and HCT strategies, differences in the underlying causes of cytopenia, as well as by differences in PGF definition. In this systematic review and meta-analysis, we provide an overview of the various PGF definitions used and determined the impact of this variability on the reported incidence and outcome. We searched MEDLINE, EMBASE and Web of Science up to July 2022, for any study on PGF in HCT recipients. We performed random-effect meta-analyses for incidence and outcome and subgroup analyses based on different PGF criteria. Among 69 included studies (14.265 HCT recipients), we found 63 different PGF definitions, using various combinations of 11 common criteria. The median incidence of PGF was 7% (IQR: 5-11%, 22 cohorts). The pooled survival of PGF patients was 53% (95% CI: 45-61%, 23 cohorts). The most commonly reported risk factors associated with PGF were history of cytomegalovirus infection and prior graft-versus-host disease. Incidence was lower in studies with strict cytopenic cutoffs, while survival was lower for primary compared to secondary PGF. This work indicates that a standardized, quantitative definition of PGF is needed to facilitate clinical guideline development and to advance scientific progress.

CD34 Stem Cell Boost in Pediatric Allogeneic Stem Cell Transplant Recipients: A Case Series and Review of Literature

Patients with poor graft function (PGF) or declining donor chimerism (DC) post allogeneic hematopoietic cell transplantation (HCT) may benefit from a CD34-selected stem cell boost (SCB). We retrospectively studied outcomes of fourteen pediatric patients (PGF: 12 and declining DC: 2), with a median age of 12.8 (range 0.08-20.6) years at HCT, who received a SCB. Primary and secondary endpoints included resolution of PGF or improvement in DC (≥ 15% increase), overall survival (OS) and transplant-related mortality (TRM), respectively. The median CD34 dose infused was 7.47 × 10⁶/kg (range 3.51 × 10⁶-3.39 × 10⁷/kg). Among patients with PGF who survived ≥ 3 months post-SCB (n = 8), we observed a non-significant decrease in the cumulative median number of red cell transfusions, platelet transfusions, and GCSF but not intravenous immunoglobulin doses in the 3 months before and after SCB. Overall response rate (ORR) was 50%, with 29% complete and 21% partial responses. ORR was better in recipients who received lymphodepletion (LD) pre-SCB versus none (75% versus 40%; p = 0.56). The incidence of acute and chronic graft-versus-host-disease was 7% and 14%, respectively. The 1-year OS was 50% (95% CI 23-72%) and TRM was 29% (95% CI 8-58%). SCB was effective in half of our cohort with possible benefit of LD pre-SCB.

Graft failure in allogeneic hematopoietic stem cell recipients: diagnosis and treatment

Graft failure is a group of complications after allogeneic hematopoietic stem cell transplantation, which occurs according to different data up to 30%. The group of complications includes primary and secondary graft failure, primary, secondary and transient poor graft function and graft rejection. Diagnostic difficulties consist in the lack of unified diagnostic criteria accepted in the transplantation community and in the dual interpretation of these complications according to the foreign literature. The purpose of this literature review was to identify the most common criteria of different types of graft failure and determine the tactics of diagnosis and treatment. In this review we analyzed data from various literature sources, gave definitions of graft failure and poor graft function. We analyzed the literature data on the methods used to treat these conditions.

Durable Engraftment and Excellent Overall Survival After CD34-Selected Peripheral Blood Stem Cell Boost in Pediatric Patients With Poor Graft Function Following Allogeneic Stem Cell Transplantation

Poor graft function (PGF) is a life-threatening complication after allogeneic stem cell transplantation (alloSCT). Historically, outcomes of patients with PGF have been very poor, and there are no standardized approaches to treatment. Furthermore, few outcomes after CD34-selected stem cell boost (CD34+SCB) for PGF in pediatric alloSCT recipients have been reported. Here we report on a single center experience with CD34+SCB for PGF after alloSCT in patients treated on the Pediatric Transplant and Cellular Therapy Service at MSK Kids, Memorial Sloan Kettering Cancer Center. A retrospective analysis of patients transplanted for malignant and nonmalignant disorders who received a CD34+SCB between 2008 to 2020 for treatment of PGF defined as the need for granulocyte colony-stimulating factor (G-CSF) and/or packed red blood cell or platelet transfusion support with bone marrow donor chimerism ≥85%. Peripheral blood stem cells from the original donor were the source for CD34+SCB. Durable complete recovery (durable CR) was defined as recovery of peripheral blood counts without recurrent need for G-CSF or transfusion support. The main outcomes of interest were recovery of hematopoiesis and overall survival. Development of graft versus host disease (GVHD) was an additional outcome of interest. Fourteen patients with PGF received a boost. Six patients had no known infection, while 8 patients had PGF associated with an infection. The probability of CR at 60 days was 79% (95% confidence interval [CI], 57%-100%). The overall survival at both 2 and 5 years was 78% (95% CI, 56%-100%). One patient developed GVHD, which was fatal. No other CD34+SCB-related toxicities were observed. While including patients with PGF as recently defined by the American Society for Transplantation and Cellular Therapy, as well as PGF in patients with concomitant infections, we demonstrate that CD34+SCB is safe and can provide for durable trilineage hematopoietic recovery and long-term survival in pediatric patients after alloSCT.

Innovative strategies to improve hematopoietic stem cell transplant outcomes in myelofibrosis

Myelofibrosis (MF) is a clonal myeloproliferative neoplasm characterized by inflammation, marrow fibrosis, and an inherent risk of blastic transformation. Hematopoietic allogeneic stem cell transplant is the only potentially curative therapy for this disease, however, survival gains observed for other transplant indications over the past two decades have not been realized for MF. The role of transplantation may also evolve with the use of novel targeted agents. The chronic inflammatory state associated with MF necessitates pretransplantation assessment of end-organ function. Applying the transplant methodology employed for other myeloid disorders to patients with MF fails to acknowledge differences in the underlying disease pathophysiology. Limited understanding of the causes of poor transplant outcomes in this cohort has prevented refinement of transplant eligibility criteria in MF. There is increasing evidence of heterogeneity in molecular disease grade, beyond the clinical manifestations which have traditionally guided transplant timing. Exploring the physiological consequences of disease chronicity unique to MF, acknowledging the heterogeneity in disease grade, and using advanced prognostic models, molecular diagnostics and other organ function diagnostic tools, we present an innovative review of strategies with the potential to improve transplant outcomes in this disease. Larger, prospective studies which consider the impact of molecular-based disease grade are needed for MF transplantation.

Recent Advancements in Poor Graft Function Following Hematopoietic Stem Cell Transplantation

Poor graft function (PGF) is a life-threatening complication that occurs after transplantation and has a poor prognosis. With the rapid development of haploidentical hematopoietic stem cell transplantation, the pathogenesis of PGF has become an important issue. Studies of the pathogenesis of PGF have resulted in some success in CD34⁺-selected stem cell boosting. Mesenchymal stem cells, N-acetyl-l-cysteine, and eltrombopag have also been investigated as therapeutic strategies for PGF. However, predicting and preventing PGF remains challenging. Here, we propose that the seed, soil, and insect theories of aplastic anemia also apply to PGF; CD34⁺ cells are compared to seeds; the bone marrow microenvironment to soil; and virus infection, iron overload, and donor-specific anti-human leukocyte antigen antibodies to insects. From this perspective, we summarize the available information on the common risk factors of PGF, focusing on its potential mechanism. In addition, the safety and efficacy of new strategies for treating PGF are discussed to provide a foundation for preventing and treating this complex clinical problem.

Improving allogeneic stem cell transplantation in myelofibrosis

In this review, we will outline dimensions in which outcome of patients with myelofibrosis undergoing curative treatment can be optimized: patient selection, transplant procedure, and posttransplant prevention or treatment of relapse. For patient selection, fortunately, as with several other hematologic malignancies, the management of patients with myelofibrosis has very much entered the molecular era, with the establishment of several driver and nondriver mutations, allowing more individualized selection for treatment. For the transplant procedure itself, different conditioning intensities do not seem to play a distinctive role with regards to outcome posttransplant but still need to be compared in the molecular era. While many patients nowadays may receive ruxolitinib before transplant, recent studies may facilitate fine-tuning and integration of ruxolitinib into the transplant algorithm. The role of novel inhibitors for the transplant setting remains unclear. For the posttransplant phase, evidence remains scarce, with experiences of donor-lymphocyte infusions for relapse management but more efforts are needed in understanding relapse and identifying and treating patients at high risk for relapse.

Clinical features, pathophysiology, and therapy of poor graft function post-allogeneic stem cell transplantation

Poor graft function (PGF), defined by the presence of multilineage cytopenias in the presence of 100% donor chimerism, is a serious complication of allogeneic stem cell transplant (alloSCT). Inducers or potentiators of alloimmunity such as cytomegalovirus reactivation and graft-versus-host disease are associated with the development of PGF, however, more clinical studies are required to establish further risk factors and describe outcomes of PGF. The pathophysiology of PGF can be conceptualized as dysfunction related to the number or productivity of the stem cell compartment, defects in bone marrow microenvironment components such as mesenchymal stromal cells and endothelial cells, or immunological suppression of post-alloSCT hematopoiesis. Treatment strategies focused on improving stem cell number and function and microenvironment support of hematopoiesis have been attempted with variable success. There has been limited use of immune manipulation as a therapeutic strategy, but emerging therapies hold promise. This review details the current understanding of the causes of PGF and methods of treatment to provide a framework for clinicians managing this complex problem.

CD26 expression on donor harvest as a risk predictive biomarker for developing graft-versus-host disease post-allogeneic hematopoietic stem cell transplantation: A ten-year follow-up study

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (ASCT) is the preferred treatment option for patients with several hematologic disorders and immunodeficiency syndromes. Graft-versus-host disease (GVHD) is an immune mediated post-transplant complication which has a major impact on long-term transplant outcomes.

OBJECTIVE

Current efforts are focused on identification of new markers that serve as potential predictors of GVHD and other post-transplant clinical outcomes.

METHODS

This study includes donor harvests collected from twenty-three allogeneic donors during period 2008-2009 and respective transplant recipients followed for clinical outcomes till March 2019. Percent CD26+ and CD34+ cells in donor harvest were analyzed using flow cytometry. Percent expression and infused dose of CD26+ and CD34+ cells were evaluated for association with various clinical outcomes.

RESULTS

Total 23 healthy donors with median age of 28 years (13 males), and transplant recipients with median age of 24 years (17 males) formed the study cohort. The diagnosis included malignant (n= 13) and non-malignant (n= 10) hematological disorders. Median CD34brCD45lo HSC expression was 0.57% (IQR 0.24-1.03) while median CD26 expression was 19.64% (IQR 8.96-33.56) of all nucleated cells. CD26 expression was associated with donor age (P= 0.037). CD26 percent expression correlated with WBC engraftment (P= 0.015) and with acute GVHD (P= 0.023) whereas infused CD26 cell dose correlated with WBC engraftment (P= 0.004) and risk of CMV reactivation (P= 0.020). There was no statistically significant correlation of either CD26 expression or cell dose with chronic GVHD, EFS or OS.

CONCLUSIONS

Our findings suggest a role of CD26 expression on human donor harvest as a potential predictor of acute GVHD. This association warrants further exploration.

Outcomes with CD34-Selected Stem Cell Boost for Poor Graft Function after Allogeneic Hematopoietic Stem Cell Transplantation: A Systematic Review and Meta-Analysis

Poor graft function (PGF) is a life-threatening complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT) characterized by multilineage cytopenia in the absence of mixed donor chimerism (<95% donor), relapse, or severe graft-versus-host disease (GVHD). We present a systemic review and meta-analysis aimed at assessing the outcomes with CD34-selected stem cell boost (SCB) for PGF in adult allo-HSCT recipients. We screened a total of 1753 records identified from 4 databases (PubMed, Embase, Cochrane, and ClinicalTrials.gov) following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines, using the search terms "hematological malignancies," "hematopoietic stem cell transplantation," "CD34 antigen(s)," "graft failure," and "poor graft function," from the date of inception to January 2021. After excluding review, duplicate, and nonrelevant articles, we included 7 studies reporting outcomes following administration of CD34-selected SCB for PGF after allo-HSCT, including hematologic complete response (CR) and overall response rate (ORR), GVHD, and overall survival (OS). Quality evaluation was done using the National Institutes of Health quality assessment tool. Pooled analysis was done using the R 'meta' package, and proportions with 95% confidence intervals (CIs) were computed. The inter-study variance was calculated using the Der Simonian-Laird estimator. We identified 209 patients who received CD34-selected SCB for PGF after allo-HSCT. The median age was 49 years (range, 18 to 69 years), and 61% were men. Primary graft sources included peripheral blood stem cells (72%) and bone marrow (28%). Donor types were matched sibling (37%), matched unrelated (36%), mismatched unrelated (22%), and haploidentical donors (5%). The median time from allo-HSCT to SCB was 138 days (range, 113 to 450 days). The median SCB dose was 3.45 × 106 CD34 cells/kg (range, 3.1 to 4.9 × 106 cells/kg). CR and ORR were 72% (95% CI, 63% to 79%; I2 = 26%) and 80% (95% CI, 74% to 85%; I2 = 0%), respectively. After a median follow-up of 42 months (range, 30 to 77 months), the actuarial survival rate was 54% (95% CI, 47% to 61%; I2 = 0%). OS ranged from 80% at 1 year to 40% at 9 years. The incidences of acute and chronic GVHD after SCB were 17% (95% CI, 13% to 23%; I2 = 0%) and 18% (95% CI, 8% to 34%; I2 = 76%), respectively. Nonrelapse mortality was reported in 42 patients, with a pooled rate of 27% (95% CI, 17% to 40; I2 = 59%), and death due to relapse was reported in 25 patients, with a pooled rate of 17% (95% CI, 11% to 23%; I2 = 0%). Our data show that CD34-selected SCB improves outcomes after PGF post allo-HSCT with an acceptable toxicity profile. The literature lacks high-quality randomized evidence, and there remains an unmet need for prospective studies to address the optimal dosing and manipulation of SCB. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

Allogeneic haematopoietic cell transplantation for myelofibrosis: proposed definitions and management strategies for graft failure, poor graft function and relapse: best practice recommendations of the EBMT Chronic Malignancies Working Party

Allogeneic haematopoietic cell transplantation (allo-HCT) remains the only curative approach in myelofibrosis (MF). Despite advances over recent decades, relapse and non-relapse mortality rates remain significant. Relapse rates vary between 15 and 25% across retrospective studies and management strategies vary widely, ranging from palliation to adoptive immunotherapy and, in some cases, a second allo-HCT. Moreover, in allo-HCT, there is a higher incidence of poor graft function and graft failure due to splenomegaly and a hostile "pro-inflammatory" marrow niche. The Practice Harmonisation and Guidelines subcommittee of the Chronic Malignancies Working Party (CMWP) of EBMT convened an international panel consisting of transplant haematologists, histopathologists and molecular biologists to propose practical, clinically relevant definitions of graft failure, poor graft function and relapse as well as management strategies following allo-HCT. A systematic approach to molecular monitoring, histopathological assessment and chimerism testing is proposed. These proposed recommendations aim to increase the accuracy and uniformity of reporting and to thereby facilitate the development of more consistent approaches to these challenging issues. In addition, we propose management strategies for these complications.

Impaired Hematopoiesis after Allogeneic Hematopoietic Stem Cell Transplantation: Its Pathogenesis and Potential Treatments

Impaired hematopoiesis is a serious complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Bone marrow aplasia and peripheral cytopenias arise from primary and secondary graft failure or primary and secondary poor graft function. Chimerism analysis is useful to discriminate these conditions. By determining the pathogenesis of impaired hematopoiesis, a timely and appropriate treatment can be performed. Hematopoietic system principally consists of hematopoietic stem cells and bone marrow microenvironment termed niches. Abnormality in hematopoietic stem and progenitor cells and/or abnormality in the relevant niches give rise to hematological diseases. Allo-HSCT is intended to cure each hematological disease, replacing abnormal hematopoietic stem cells and bone marrow niches with hematopoietic stem cells and bone marrow niches derived from normal donors. Therefore, treatment for graft failure and poor graft function after allo-HSCT is required to proceed based on determining the pathogenesis of impaired hematopoiesis. Recent progress in this area suggests promising treatment manipulations for graft failure and poor graft function.

Advances in the understanding of poor graft function following allogeneic hematopoietic stem-cell transplantation

Poor graft function (PGF) following allogeneic hematopoietic stem-cell transplantation (allo-HSCT) is a life-threatening complication and is characterized by bilineage or trilineage blood cell deficiency and hypoplastic marrow with full chimerism. With the rapid development of allo-HSCT, especially haploidentical-HSCT, PGF has become a growing concern. The most common risk factors illustrated by recent studies include low dose of infused CD34+ cells, donor-specific antibody, cytomegalovirus infection, graft versus host disease (GVHD), iron overload and splenomegaly, among others. Because of the poor prognosis of PGF, it is crucial to uncover the underlying mechanism, which remains elusive. Recent studies have suggested that the bone marrow microenvironment may play an important role in the pathogenesis of PGF. Deficiency and dysfunction of endothelial cells and mesenchymal stem cells, elevated reactive oxygen species (ROS) levels, and immune abnormalities are believed to contribute to PGF. In this review, we also discuss recent clinical trials that evaluate the safety and efficacy of new strategies in patients with PGF. CD34+-selected stem-cell boost (SCB) is effective with an acceptable incidence of GVHD, despite the need for a second donation. Alternative strategies including the applications of mesenchymal stem cells, N-acetyl-l-cysteine (NAC), and eltrombopag have shown favorable outcomes, but further large-scale studies are needed due to the small sample sizes of the recent clinical trials.