Allogeneic stem cell transplantation in the treatment of acute myeloid leukemia: An overview of obstacles and opportunities

As an important treatment for acute myeloid leukemia, allogeneic hematopoietic stem cell transplantation(allo-HSCT) plays an important role in reducing relapse and improving long-term survival. With rapid advancements in basic research in molecular biology and immunology and with deepening understanding of the biological characteristics of hematopoietic stem cells, allo-HSCT has been widely applied in clinical practice. During allo-HSCT, preconditioning, the donor, and the source of stem cells can be tailored to the patient’s conditions, greatly broadening the indications for HSCT, with clear survival benefits. However, the risks associated with allo-HSCT remain high, i.e. hematopoietic reconstitution failure, delayed immune reconstitution, graft-versus-host disease, and posttransplant relapse, which are bottlenecks for further improvements in allo-HSCT efficacy and have become hot topics in the field of HSCT. Other bottlenecks recognized in the current treatment of individuals diagnosed with acute myeloid leukemia and subjected to allo-HSCT include the selection of the most appropriate conditioning regimen and post-transplantation management. In this paper, we reviewed the progress of relevant research regarding these aspects.

APPLICATION OF TWO-COLOR INTERPHASE FISH USING SEX PROBE IN ALLOGENEIC STEM CELL TRANSPLANTATION

Objective: To evaluate the significance of two-color interphase fluorescence in situ hybridization (FISH) using X and Y centromere probe in the engraftment estimation and minimal residual disease (MRD) monitoring after allogeneic stem cell transplantation (alloSCT). Methods: Samples from 12 cases patients in different periods after alloSCT were detected by interphase FISH. Results: All of the 12 patients were proved to obtain engraftment 22–35 days after alloSCT. While traditional karyotype showed as 100%XX or 100%XY invariably, FISH showed different percentages of donor original sex chromosome. Conclusion: Two-color interphase FISH is a more sensitive and simple test for engraftment evaluation and MRD monitoring post SCT, though, it can not entirely replace traditional karyotype analysis and gene detection by RT-PCR.

Allogeneic stem cell transplantation-A curative treatment for paroxysmal nocturnal hemoglobinuria with PIGT mutation:A case report

BACKGROUND Patients with paroxysmal nocturnal hemoglobinuria(PNH)have a clonal population of blood cells deficient in glycosylphosphatidylinositol-anchored(GPIanchored)proteins,most of the time resulting from a mutation in the X-linked gene PIGA.We report a patient with PNH resulting from a rare biallelic PIGT mutation on chromosome 20.CASE SUMMARY A 47-year-old man was referred to our hospital for febrile pancytopenia.The patient reported a history of recurrent urticaria and arthralgia and he presented during 3 mo recurrent acute dermo-hypodermitis and aseptic meningitidis.Based on clinical cases published with PIGT-PNH,with clinically typical PNH and autoinflammatory symptoms,we treated our patients with repeated infusions of eculizumab to decrease autoinflammatory symptoms and then we performed an allogeneic stem cell transplantation(allo-SCT)with a mismatched unrelated donor.Our patient experienced no acute Graft vs Host disease(GvHD)and a moderate chronic GvHD and is now considered cured at 24 mo after allo-SCT.CONCLUSION This case report suggests that allo-SCT should be considered to cure PIGT-PNH patients.

Breast and dorsal spine relapse of granulocytic sarcoma after allogeneic stem cell transplantation for acute myelomonocytic leukemia:A case report

BACKGROUND Granulocytic sarcoma(GS)is a rare malignant tumor,and relapse is even rarer in the breast and dorsal spine following allogeneic hematopoietic stem cell transplantation.Currently,a standard treatment regimen is not available.CASE SUMMARY A rare case of GS of the right breast and dorsal spine after complete remission of acute myelogenous leukemia is reported here.A 55-year-old female patient presented with a palpable,growing,painless lump as well as worsening dorsal compressive myelopathy.She had a history of acute myelomonocytic leukemia(AML M4)and achieved complete remission after chemotherapy following allogeneic hematopoietic stem cell transplantation.Imaging examinations showed the breast lump and C7-T1 epidural masses suspected of malignancy.Histologic results were compatible with GS in both the right breast and dorsal spine,which were considered extramedullary relapse of the AML treated 4 years earlier.CONCLUSION A rare case of GS relapse following allogeneic hematopoietic stem cell transplantation and guidelines for treatment are discussed.

Incidence of ocular manifestations in patients with graft versus host disease after allogeneic stem cell transplant in Riyadh, Saudi Arabia

AIM: To evaluate the incidence and severity of ocular graft versus host disease(o GVHD) in patients who underwent allogeneic stem cell transplant(SCT) in King Abdul-Aziz Medical City, Saudi Arabia.METHODS: This is a retrospective cohort study conducted in King Abdul Aziz Medical City on patients who underwent allogeneic hematopoietic cell transplant(allo-HCT) from 2010 to 2017. The ocular examination findings including visual acuity, meibomian gland dysfunction, corneal and conjunctival staining with severity, corneal scarring, tear film meniscus and breakup time, anterior and posterior segment examination findings, intraocular pressure, treatment given, punctual plugs used or not, and follow up response were collected.RESULTS: The five years cumulative incidence of o GVHD among post-transplant patients was 56.98%(95%CI 38.6%-71.7%). The potential risk factors assessed for developing ocular manifestation were age, gender, donor’s age, donor gender mismatch CD3 and CD34 infusion, while none of the correlates were identified as statistically significant risk factors of developing ocular manifestation. However, the incidence was statistically significantly different betweenpatients diagnosed with acute myelocytic leukemia and acute lymphocytic leukemia(P=0.038). The mean latent period to develop ocular symptoms was 20.5 mo. All patients had variable degree of dry eyes. None of the patients developed any posterior segment complication.CONCLUSION: The incidence of o GVHD is low in King Abdul-Aziz Medical City. This can be attributed to the preconditioning and immunosuppressive regime.

Comparable anti-CMV responses of transplant donor and third-party CMV-specific T cells for treatment of CMV infection after allogeneic stem cell transplantation

Adoptive transfer of cytomegalovirus(CMV)-specific cytotoxic T lymphocytes(CMV-CTLs)from original transplant donors or third-party donors was effective for the treatment of CMV infection after allogenic stem cell transplantation(allo-SCT),but the antiviral activity of CMV-CTL types has not been compared.To determine whether third-party CMV-CTLs provide comparable long-term antiviral efficacy to transplant donor CMV-CTLs,we first compared the antiviral abilities of transplant donors and third-party CMV-CTLs for treatment of CMV infection in two mouse models,compared the in vivo recovery of CMV-specific immunity,and analyzed the underlying mechanisms driving sustained antiviral immunity.The results showed that both donor and third-party CMV-CTLs effectively combated systemic CMV infection by reducing CMV pathology and tumor burden 28 days postinfusion.The in vivo recovery of CMV-specific immunity after CMV-CTL infusion was comparable in both groups.A detailed analysis of the source of recovered CMV-CTLs showed the proliferation and expansion of graft-derived endogenous CMV-CTLs in both groups.Our clinical study,which enrolled 31 patients who received third-party CMV-CTLs and 62 matched pairs of individuals who received transplant donor CMV-CTLs for refractory CMV infection,further showed that adoptive therapy with donor or third-party CMV-CTLs had comparable clinical responses without significant therapy-related toxicity.We observed strong expansion of CD8+tetramer+T cells and proliferation of recipient endogenous CMV-CTLs after CMV-CTL infusion,which were associated with a reduced or cleared viral load.Our data confirmed that adoptive therapy with third-party or transplant donor CMV-CTLs triggered comparable antiviral responses to CMV infection that might be mediated by restoration of endogenous CMV-specific immunity.

Ocular manifestations and quality of life in patients after hematopoietic stem cell transplantation

AIM:To explore the relationship between ocular and systemic conditions and the impact of ocular complications on the quality of life(QOL)in patients after allogeneic hematopoietic stem cell transplantation(ALLO-HSCT).METHODS:Forty-four patients with severe hematopoietic disease were enrolled after ALLO-HSCT at our center from July 2018 to October 2020.They completed two questionnaires:the Ocular Surface Disease Index(OSDI)and the quality-of-life scale for Chinese patients with visual impairment(SQOL-DV1).Ocular conditions and systemic conditions were also assessed.RESULTS:Eye damage was correlated with total bilirubin(P=0.005),and gamma-glutamyl transferase(GGT)(P=0.021).There was no significant correlation between the overall QOL score and OSDI(P=0.8226)or SQOLDV1(P=0.9526)scores.The OSDI and the overall QOL score were not correlated with ocular conditions,including best-corrected visual acuity(BCVA),intraocular pressure,Schirmer tear test II,sodium fluorescein staining,tear film breakup time,and tear meniscus height.SQOLDV1 was correlated with BCVA(P=0.0007),sodium fluorescein staining(P=0.007),and tear film breakup time(P=0.0146).CONCLUSION:In some patients,early ocular symptoms are not evident after ALLO-HSCT,while ocular surface complications can be observed after a comprehensive ophthalmological examination.Especially for those with elevated total bilirubin or GGT,regular ophthalmic follow-up visits are essential to diagnose and treat ocular graft versus host disease(o GVHD),especially for patients with elevated total bilirubin or GGT.

Treatments of disease relapse after allogeneic stem cell transplantation focusing on donor lymphocyte infusion

Hematopoietic stem cell transplantation （SCT） is a potentially curative treatment for patients with hematologic malignancies, such as acute myeloid leukemia （AML） and myelodysplastic syndromes （MDS）. There has been tremendous progress in the past several decades in allogeneic SCT with better outcomes through improvements in supportive care, expansion of stem cell donor options （HLA-matched unrelated donors （MUD）, haploidentical related donors, and cord blood units （CBUs） etc.）, and introduction of better tolerated reduced intensity conditioning （RIC） regimens.

Decitabine for Relapsed Acute Lymphoblastic Leukemia after Allogeneic Hematopoietic Stem Cell Transplantation

Relapse after allogeneic hematopoietic stem cell transplantation（allo-HSCT） remains a main question on treatment failure. Current strategies for management that usually include salvage chemotherapy, donor lymphocytic infusion and second transplantation. Our study assessed the efficacy of decitabine（DAC） for treating patients with acute lymphoblastic leukemia（ALL） who relapsed after allogeneic hematopoietic stem cell transplantation（allo-HSCT）. We retrospectively analyzed the outcomes of 12 patients with relapsed ALL after allo-HSCT who received DAC therapy. Nine patients received DAC combined with chemotherapy and donor stem cell infusion, and 3 patients received single-agent DAC. Ten of the 12 patients achieved complete remission（CR）, 1 achieved a partial remission（PR）, and 1 had no response（NR） after treatment at the latest follow-up（LFU）, the median survival was 11.2 months（range, 3.8–34, 7 months）. The 1-and 2-year overall survival（OS） rates were 50%（6/12） and 25%（3/12）, respectively. Five patients were still alive; 4 had maintained CR and 1 was alive with disease. Patients with Philadelphia chromosome-positive ALL had higher survival rate than patients with Philadelphia chromosome-negative ALL（57.1% vs. 20%）. No aggravated flares of graft-versus-host disease（GVHD） were observed during DAC treatment. Therefore, DAC may be a promising therapeutic agent for ALL recurrence after allo-HSCT.

Gut microbiome in allogeneic hematopoietic stem cell transplantation and specific changes associated with acute graft vs host disease

Allogeneic hematopoietic stem cell transplantation(aHSCT)is a standard validated therapy for patients suffering from malignant and nonmalignant hematological diseases.However,aHSCT procedures are limited by potentially life-threatening complications,and one of the most serious complications is acute graft-versus-host disease(GVHD).During the last decades,DNA sequencing technologies were used to investigate relationship between composition or function of the gut microbiome and disease states.Even if it remains unclear whether these microbiome alterations are causative or secondary to the presence of the disease,they may be useful for diagnosis,prevention and therapy in aHSCT recipients.Here,we summarized the most recent findings of the association between human gut microbiome changes and acute GVHD in patients receiving aHSCT.

Allogeneic Peripheral Blood Hematopoietic Stem Cell Transplantation for Patients with Hematologic Malignancies

To investigate the therapeutic effects and associated complications of allogeneic peripheral blood stem cell transplantation （allo-PBSCT）, 40 patients with various malignant hematopoietic diseases received allo-PBSCT. The preparative regimens were based on BUCY2 or modified BUCY2, The acute graft-versus host disease （aGVHD） was prevented by cyclosporin A and shortterm MTX regimen in all patients. Two patients from donors with one fully mismatched HLA on DRB1 locus and 4 from unrelated donor also administered Zenapox （CD25 MAb） at dosage of 1 rag/ kg every day on the day before transplantation and day 4 after transplantation. These 6 patients were also treated with mycophenolate mofetil （MMF）. Transfusion of the donor cells： The median of the transfused nucleated cells was 5.38×10^8/kg and that of the CD34^＋ cells was 7.8×10^6/kg respectively. All the patients gained hematopoietic reconstruction except one who died of infection before engraftment. Seven patients got Ⅱ°-Ⅳ° aGVHD and the incidence was 17.5 %. Fourteen patients got cGVHD and the incidence was 53.8 % in the patients who survived over 6 months. Twenty-eight patients had fever or other characteristics of infection. The median follow-up time was 13.8 months. The incidence of transplantation related mortality （TRM） was 17.5 %and 2 patients relapsed （5.0 %）. It was concluded that allo-PBSCT can reconstruct hematopoiesis quickly and is a favorable therapeutic method for leukemia.

Azacitidine maintenance therapy for blastic plasmacytoid dendritic cell neoplasm allograft: A case report

BACKGROUND Blastic plasmacytoid dendritic cell neoplasm(BPDCN)is a rare,highly invasive malignant neoplasm.There is no universally accepted standard of care because of its rarity and the dearth of prospective research.It is still challenging for some patients to achieve persistent clinical remission or cure,despite the success of allogeneic hematopoietic stem cell transplantation(allo-HSCT),indicating that there is still a significant recurrence rate.We report a case of prevention of BPDCN allograft recurrence by azacitidine maintenance therapy and review the relevant literature.CASE SUMMARY We report a 41-year-old man with BPDCN who was admitted to hospital due to skin sclerosis for>5 mo’duration.BPDCN was diagnosed by combined clinical assessment and laboratory examinations.Following diagnosis,the patients underwent induction consolidation chemotherapy to achieve the first complete remission,followed by bridging allo-HSCT.Post-transplantation,azacitidine(75 mg/m2 for 7 d)was administered as maintenance therapy,with repeat administration every 4–6 wk and appropriate extension of the chemotherapy cycle.After 10 cycles,the patient has been disease free for 26 mo after transplantation.Regular assessments of bone marrow morphology,minimal residual disease,full donor chimerism,Epstein–Barr virus,and cytomegalovirus all yielded normal results with no abnormalities detected.CONCLUSION Azacitidine may be a safe and effective maintenance treatment for BPDCN following transplantation because there were no overt adverse events during the course of treatment.

Advantageous tactics with certain probiotics for the treatment of graft-versus-host-disease after hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation(HSCT)becomes a standard form of cellular therapy for patients with malignant diseases.HSCT is the first-choice of immunotherapy,although HSCT can be associated with many complications such as graft-versus-host disease(GVHD)which is a major cause of morbidity and mortality after allogeneic HSCT.It has been shown that certain gut microbiota could exert protective and/or regenerative immunomodulatory effects by the production of short-chain fatty acids(SCFAs)such as butyrate in the experimental models of GVHD after allogeneic HSCT.Loss of gut commensal bacteria which can produce SCFAs may worsen dysbiosis,increasing the risk of GVHD.Expression of G-protein coupled receptors such as GPR41 seems to be upre-gulated in the presence of commensal bacteria,which might be associated with the biology of regulatory T cells(Tregs).Treg cells are a suppressive subset of CD4 positive T lymphocytes implicated in the prevention of GVHD after allogeneic HSCT.Here,we discuss the current findings of the relationship between the modification of gut microbiota and the GVHD-related immunity,which suggested that tactics with certain probiotics for the beneficial symbiosis in gut-immune axis might lead to the elevation of safety in the allogeneic HSCT.

Profiles of interferon-gamma and interleukin-2 in patients after allogeneic hematopoietic stem cell transplantation

BACKGROUND Allogeneic hematopoietic stem cell transplantation(allo-HSCT)may be related to the occurrence of complications,including graft-versus-host disease(GvHD)and infections.The pathogenesis of acute GvHD is connected with T lymphocytes,which identify alloantigens on host's antigen-presenting cells,activate production of interferon-gamma(IFN-gamma)and interleukin-2(IL-2),and act on the immune effector cells and damage tissues and organs.AIM The aim of the study was to investigate and distinguish serum concentration profiles of IFN-gamma and IL-2 within a 30-d period after allo-HSCT.METHODS We enrolled 62 patients,i.e.,30(48%)male and 32(52%)female subjects[median age 49.5(19-68)years],after allo-HSCT from siblings(n=12)or unrelated donors(n=50)due to acute myeloid leukemia with myeloablative conditioning(n=26;42%)and with non-myeloablative conditioning(n=36;58%).All patients were given standard immunosuppressive therapy with cyclosporin-A and methotrexate and pre-transplant antithymocyte globulin in the unrelated setting.Blood samples were collected pre-transplant before and after(on day-1)the conditioning therapy and on days+2,+4,+6,+10,+20,and+30 after allo-HSCT.Serum levels of IL-2 and IFNgamma were determined using ELISA.RESULTS Patients were divided into four groups depending on the presence of acute GvHD and clinical manifestations of infection.Group I included patients with neither acute GvHD nor infections[n=15(24%)],group II consisted of patients with infections without acute GvHD[n=17(27%)],group III was comprised of patients with acute GvHD without infections[n=9(15%)],and group IV included patients with both acute GvHD and infections[n=21(34%)].IFN-gamma concentrations were higher in Group II than in other groups on days+20(P=0.014)and+30(P=0.008).Post-hoc tests showed lower concentrations of IFN-gamma on day+30 in groups I(P=0.039)and IV(P=0.017)compared to group II.The levels of IL-2 were mostly undetectable.CONCLUSION Serum levels of IFN-gamma following allo-HSCT progressively escalate.High serum levels of IFN-gamma are related to infectious complications rather than acute GvHD.Serum concentrations of IL-2 in most patients are undetectable.

Allogeneic hematopoietic stem cell transplantation in 24 patients with β-thalassemia major

Objective To investigate the effect of allgeneic hematopoietic stem cell transplantation ( allo - HSCT ) for β - thalassemia major. Methods Twenty - four β - thalassemia major patients with median age of 4 years ( range: 2 -15 years) ,18 boys and 6 girls,received al-

Treatment of syringomyelia using uncultured umbilical cord mesenchymal stem cells: A case report and review of literature

BACKGROUND Syringomyelia is a disease caused by the formation of a cavity inside the spinal cord and is accompanied by such symptoms as pain,paresthesia,and urination and defecation disorders,and in severe cases causes various paralyses.Currently,there are only surgical methods for the treatment of syringomyelia,but these methods carry the possibility of failure,recurrence,and side effects.CASE SUMMARY The patient was a 59-year-old woman who suffered from pain due to syringomyelia.For treatment,the patient received transplant of uncultured umbilical cord-derived mesenchymal stem cells.As intended,the patient's pain was relieved after treatment.Interestingly,an additional benefit was found in that the size of the cavity also decreased.After 2 years from the last treatment,the patient's cavity had almost completely disappeared and her syringomyelia was deemed cured.CONCLUSION Using uncultured umbilical cord-derived mesenchymal stem cells may be a new treatment alternative for syringomyelia.

Novel agents targeting leukemia cells and immune microenvironment for prevention and treatment of relapse of acute myeloid leukemia after allogeneic hematopoietic stem cell transplantation

Relapse remains the worst life-threatening complications after allogeneic hematopoietic stem cell transplantation(allo-HSCT)in patients with acute myeloid leukemia(AML),whose prognosis has been historically dismal.Given the rapid development of genomics and immunotherapies,the interference strategies for AML recurrence have been changing these years.More and more novel targeting agents that have received the U.S.Food and Drug Administration(FDA)approval for de novo AML treatment have been administrated in the salvage or maintenance therapy of post-HSCT relapse.Targeted strategies that regulate the immune microenvironment of and optimize the graft versus leukemia(GVL)effect of immune cells are gradually improved.Such agents not only have been proven to achieve clinical benefits from a single drug,but if combined with classic therapies,can significantly improve the poor prognosis of AML patients who relapse after allo-HSCT.This review will focus on currently available and promising upcoming agents and also discuss the challenges and limitations of targeted therapies in the allogeneic hematopoietic stem cell transplantation community.

Fludarabine and cytarabine combined chemotherapy followed by transfusion of donor blood stem cells for treating relapse of acute leukaemia after allogeneic haematopoietic stem cell transplantation

Background Relapse remains an obstacle to successful allogeneic haematopoietic stem cell transplantation （allo-HSCT） for patients with acute leukaemia and no standard treatment is available. We assessed fludarabine and cytarabine with transfusion of donor haematopoietic stem cell in treating the relapse of acute leukaemia after allo-HSCT. Methods Seven patients, median age 34 years, with relapse of acute leukaemia after allo-HSCT received combination chemotherapy of fludarabine with cytarabine for 5 days. Five patients suffered from acute myeloid leukaemia （2 refractory） and 2 refractory acute lymphoblastic leukaemia. After the transplantation, the median relapse time was 110 days （range, 38-185 days）. Two days after chemotherapy, 5 patients received infusion of donor＇s peripheral blood stem cells, mobilized by granulocyte colony stimulating factor. No prophylactic agents of graft versus host diseases were administered, Results Six patients achieved haematopoietic reconstitution. DNA sequence analysis at day 30 after treatment identified all as full donor chimera type. The median observation time was 189 days. After the treatment, the median time for neutrophilic granulocyte value 〉0.5×10^9/L and for platelet value 〉20×10^9/L were 13 days （range, 10-18 days） and 15 days （range, 11-24 days）, respectively. Graft versus host disease occurred in 2 patients （acute） and 3 （chronic）. Five patients suffered from pulmonary fungal infection （2 died）, 3 haemorrhagic cystitis and 2 cytomegalovirus viraemia. The other patients died of leukaemia related deaths. Three patients with chronic graft versus host disease who had received donor peripheral blood stem cells reinfusion have survived for 375 days, 232 days and 195 days, respectively. Conclusions Fludarabine with cytarabine plus the donor haematopoietic stem cell should be considered as an effective therapeutic regimen for relapse of acute leukaemia after alIo-HSCT. The disease free state of patients may increase, though with high risk of secondary fungal infection.

Risk factors for bronchiolitis obliterans syndrome in allogeneic hematopoietic stem cell transplantation

Background The occurrence of bronchiolitis obliterans syndrome （BOS） after allogeneic hematopoietic stem cell transplantation （alIo-HSCT） is rare but severe. We examine the role of pre-HSCT chemotherapeutic exposure, pre-HSCT comorbidities, and transplant-related complications in the development of BOS after alIo-HSCT. Methods A nested case-control study was designed. Cases with BOS and controls matched for the year of alIo-HSCT and length of the follow-up were identified from a cohort of 1646 patients who underwent alIo-HSCT for treatment of hematologic malignancies between 2006 and 2011. Antithymocyte globulin was used in the partial matched related and unrelated matched donor HSCT, or patients with severe aplastic anemia. Results Thirty-six patients suffered from BOS; the mean age at the time of presentation was （32.7±2.4） years, and the mean time to presentation was （474±350） days post-HSCT. A pre-HSCT cyclophosphamide dose of 〉3.2 g/m2 （OR=8.74, P=0.025）, chronic graft-versus-host disease （moderate to severe） （OR=12.02, P=0.000）, and conditioning regimens without antithymocyte globulin （OR=2.79, P=0.031） were independently associated with BOS. Conclusions We found that higher pre-HSCT cyclophosphamide exposure, a conditioning regimen without antithymocyte globulin, and moderate to severe chronic graft-versus-host disease are significantly and independently associated with BOS. Based on these results, we can identify patients who are at a higher risk of developing BOS after alIo-HSCT, select a more appropriate therapeutic strategy, and improve the outcome of HSCT recipients.

Uncovering the multifaceted roles played by neutrophils in allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation(alloHSCT)is a life-saving procedure used for the treatment of selected hematological malignancies,inborn errors of metabolism,and bone marrow failures.The role of neutrophils in alloHSCT has been traditionally evaluated only in the context of their ability to act as a first line of defense against infection.However,recent evidence has highlighted neutrophils as key effectors of innate and adaptive immune responses through a wide array of newly discovered functions.Accordingly,neutrophils are emerging as highly versatile cells that are able to acquire different,often opposite,functional capacities depending on the microenvironment and their differentiation status.Herein,we review the current knowledge on the multiple functions that neutrophils exhibit through the different stages of alloHSCT,from the hematopoietic stem cell(HSC)mobilization in the donor to the immunological reconstitution that occurs in the recipient following HSC infusion.We also discuss the influence exerted on neutrophils by the immunosuppressive drugs delivered in the course of alloHSCT as part of graft-versushost disease(GVHD)prophylaxis.Finally,the potential involvement of neutrophils in alloHSCT-related complications,such as transplant-associated thrombotic microangiopathy(TA-TMA),acute and chronic GVHD,and cytomegalovirus(CMV)reactivation,is also discussed.Based on the data reviewed herein,the role played by neutrophils in alloHSCT is far greater than a simple antimicrobial role.However,much remains to be investigated in terms of the potential functions that neutrophils might exert during a highly complex procedure such as alloHSCT.