Research progress of ICOSL/ICOS pathway in maternal-fetal immune tolerance

Co-signaling molecules are molecules whose ligands on the surface of cells interact with receptors on the surface of T cells to convey stimulatory or inhibitory signals to regulate immune responses.Co-signaling molecules play an important role in tumor and autoimmune diseases.Lately,studies have shown that co-signaling molecules are also involved in the regulation of maternal-fetal immune tolerance,and abnormalities of co-signaling molecules may lead to the imbalance of maternal-fetal immune tolerance,resulting in recurrent abortion,eclampsia and other pregnancy complications.ICOSL/ICOS is a ligand and receptor of costimulatory signals,which regulates maternal and fetal immune tolerance by participating in T cell differentiation and Th1 and Th2 cytokine secretion.Therefore,this article reviews the structure of ICOSL/ICOS,the distribution of ICOSL/ICOS at the maternal-fetal interface and its immune regulation during pregnancy,in order to provide new ideas for the future study of immunotherapy of pregnancy complications caused by abnormal co-signaling molecules.

Role of maternal-fetal immune tolerance in the establishment and maintenance of pregnancy

Normal pregnancy is a contradictory and complicated physiological process.Although the fetus carries the human leukocyte antigen(HLA)inherited from the paternal line,it does not cause maternal immune rejection.As the only exception to immunological principles,maternal-fetal immune tolerance has been a reproductive immunology focus.In early pregnancy,fetal extravillous trophoblast cells(EVTs)invade decidual tissues and come into direct contact with maternal decidual immune cells(DICs)and decidual stromal cells(DSCs)to establish a sophisticated maternal-fetal crosstalk.This study reviews previous research results and focuses on the establishment and maintenance mechanism of maternal-fetal tolerance based on maternal-fetal crosstalk.Insights into maternal-fetal tolerance will not only improve understanding of normal pregnancy but will also contribute to novel therapeutic strategies for recurrent spontaneous abortion,pre-eclampsia,and premature birth.

Tumor-infiltrating T-Lymphocyte immunity-related immune tolerance and anti–programmed cell death protein 1/ligand of programmed cell death protein 1 therapy for advanced hepatocellular carcinoma

Systemic therapy has become the standard treatment for patients with advanced hepatocellular carcinoma(HCC)whose treatment options are limited.However,the long-term patient response to drugs and the survival outcomes remain a concern.With increasing exploration of the HCC microenvironment,particularly in terms of T lymphocyte immunity,a new era of immunomolecular targeted therapy,based on molecular signaling,has arrived for advanced HCC.In the study of immune tolerance of the intrinsic HCC microenvironment,we found that multiple immunosuppressive mechanisms and immune checkpoint inhibitors,such as anti–programmed cell death protein 1/ligand of programmed cell death protein 1 therapy,have improved clinical outcomes in some patients with advanced HCC.Furthermore,various combination therapies have been investigated,and HCC types have been categorized into different types based on anti–programmed cell death protein 1(PD-1)/ligand of programmed cell death protein 1(PD-L1)treatment.In this paper,we first discuss the tumor-infiltrating T lymphocyte immunity and immune tolerance of HCC.We then clarify the basic mechanism of anti–PD-1/PD-L1 therapy and discuss the types of HCC based on anti–PD-1/PD-L1 therapy.Thereafter,we explain the relevant studies and mechanisms of combination therapy of anti–PD-1/PD-L1 with antiangiogenesis drugs or multikinase kinase inhibitors,anti–T lymphocyte–related signaling pathways in HCC,and other anti-CD8+T cell immune checkpoints.In this way,this review offers a deeper understanding of anti–PD-1/PD-L1 immunotherapy for advanced HCC,in order to provide better individualized treatments for patients with advanced HCC.

Histone methyltransferase Nsd2 ensures maternal-fetal immune tolerance by promoting regulatory T-cell recruitment

Regulatory T cells(Tregs)are fundamentally important for maintaining systemic immune homeostasis and are also required for immune tolerance at the maternal-fetal interface during pregnancy.Recent studies have suggested that epigenetic regulation is critically involved in Treg development and function.However,the role of H3K36me has not yet been investigated.Here,we found that the H3K36me2 methyltransferase Nsd2 was highly expressed in Tregs.Although loss of Nsd2 did not impair systemic Treg development or function,the level of Tregs at the maternal-fetal interface was significantly decreased in pregnant Nsd2 conditional knockout mice.Consequently,maternal-fetal immune tolerance was disrupted in the absence of Nsd2 in Tregs,and the pregnant mice showed severe fetal loss.Mechanistically,Nsd2 was found to upregulate CXCR4 expression via H3K36me2 modification to promote Treg cell recruitment into the decidua and suppress the anti-fetal immune response.Overall,our data identified Nsd2 as a critical epigenetic regulator of Treg recruitment for maternal-fetal tolerance.

The Analogy between the Immune System and Human Life

The immune system operates as a complex organization with distinct roles and functions. Excitingly we recognized the similarities between the cellular dynamics of the immune system and our lives, activities, and behaviors. Observing the immune system can guide how to respond to various daily situations, including when to react, tolerate, or ignore. Recognizing this analogy between our lives and the immune system should motivate us to adopt a wisdom-based approach when investigating the mechanisms and future discoveries related to this system and to deepen our understanding of this complex system with newfound respect. In this context, the present review examines several integral biological processes of the immune system by drawing parallels between them and human life, activities, and behaviors to learn how we must behave based on the insights offered by this complex organization. The literature search was conducted in international databases such as PubMed/MEDLINE and Google Scholar search engine using English equivalent keywords from 1998 up to April 2023. The search strategy used the following subject heading terms: Immune system, analogy, human life, cellular dynamics, memory, tolerance, and ignorance. In conclusion, the immune system is a complex organization comprising various cells interacting within specific sites and networks, communicating, drawing experiences, and learning how to tolerate certain conditions that make it share certain similarities with human life.

Effect of Kupffer cells on immune tolerance in liver transplantation

Objective:To observe the effect of Kupfler cells on immune tolerance in liver transplantation. Methods:The rats were randomly divided into A,B and C groups.A group was sham operation group.The donor rats of group B had intraperitoneal injection of 1 nmol Kuppffer cells every other day for three days before liver transplantation.Rats of group C were injected with equal saline.The rat liver transplantation models were established by modified Kamada’s two-cuff technique.The rats were sacrificed after 24 hours.The concentrations of ALT and AST in serum were measured with the biochemical analyzer.The level of IL-2 and TNF- a in serum were measured by ELISA method.The apoptotic indexes were detected by immunohistochemical assay. Results:The concentration of ALT,AST,IL-1 and TNF- a in A,B and C groups were increased successively.The levels of group C were significantly higher than that of group B and A(P【0.05), and the levels of group B were significantly higher than that of group A(P【0.05).The apoptotic indexes of three groups were 3.40±0.37,14.70±2.54 and 26.33±3.65,respectively,with significant difference among three groups(P【0.05).Conclusions:Pretreatment with Kupfler cells can reduce liver injury and raise liver transplantation immune tolerance.

Role of T cell death in maintaining immune tolerance during persistent viral hepatitis

Virus-specific T cells play an important role in the resolution of hepatic infection. However, during chronic hepatitis infection these cells lack their effector functions and fail to control the virus. Hepatitis B virus and hepatitis C virus have developed several mechanisms to generate immune tolerance. One of these strategies is the depletion of virus-specific T cells by apoptosis. The immunotolerogenic liver has unique property to retain and activate na ve T cell to avoid the over reactivation of immune response against antigens which is exploited by hepatotropic viruses to persist. The deletion of the virus-specific T cells occurs by intrinsic (passive) apoptotic mechanism. The pro-apoptotic molecule Bcl-2 interacting mediator (Bim) has attracted increasing attention as a pivotal involvement in apoptosis, as a regulator of tissue homeostasis and an enhancer for the viral persistence. Here, we reviewed our current knowledge on the evidence showing critical role of Bim in viral-specific T cell death by apoptotic pathways and helps in the immune tolerance.

Early termination of immune tolerance state of hepatitis B virus infection explains liver damage

AIM: To assess an early termination of immune toler-ance state of chronic hepatitis B virus infection in Ban-gladesh and its clinical significance. METHODS: From a series of 167 treatment-naive chronic hepatitis B patients aged between 12 to 20 years(mean ± SD; 17.5 ± 2.8 years), percutaneous liver biopsies of 89 patients who were all hepatitis B e antigen negative at presentation were done. Of them, 81 were included in the study. They had persistently normal or raised serum alanine aminotransferase(ALT) values. A precore mutation(PCM) study was accom-plished in 8 patients who were randomly selected. RESULTS: Forty-four(53.7%) patients had significant necroinflammation(HAI-NI > 7), while significant fi-brosis(HAI-F ≥ 3) was seen in 15(18.5%) patients. Serum ALT(cut off 42 U/L) was raised in 29(35.8%) patients, while low HBV DNA load(< 105 copies/mL)was observed in 57(70.4%) patients. PCM was nega-tive in all 8 patients. CONCLUSION: This study indicates that the current concept of age-related immune tolerance state of HBV infection deserves further analyses in different popula-tion groups.

Ragweed pollen induces allergic conjunctivitis immune tolerance in mice via regulation of the NF-κB signal pathway

AIM:To investigate the feasibility and mechanism of immune tolerance in allergic conjunctivitis.METHODS:The allergic conjunctivitis immune tolerance mice model was established by ragweed pollen(RW)and the related cytokines were detected.The mice were divided into 9 groups and the maslinic acid(MA)or PBS were given for different group after modeling.The expression levels of chemokine ligand 5(CCL5)and P-65 in the conjunctival tissue were analyzed by immunohistochemistry,quantitative reverse transcription polymerase chain reaction(q RT-PCR)and Western blot.The percentage of interleukin-17(IL-17)and CD4+CD25+in the splenocyte supernatant was analyzed by flow cytometry.Fur thermore,the serum and splenocyte supernatant concentration of total-IgE,interleukin-10(IL-10),and IL-17 was analyzed by enzyme linked immune response(ELISA).RESULTS:After the model was established,symptoms of conjunctivitis were alleviated,the level of P-65,CCL5,IL-17,and total-IgE was raised,while the expression of IL-10,CD4+CD25+was decreased.This result fully demonstrated that a typical IL-17/regulatory-T-cells(Treg cells)imbalance and NF-κB activation.When the NF-κB signal pathway was suppressed,it showed that there was a further relief of conjunctivitis in mice.At the same time,the expression of total-IgE,IL-17,and CCL5 was decreased and the expression of anti-inflammatory factor(IL-10,CD4+CD25+)was increased.CONCLUSION:In the state of immune tolerance,symptoms of conjunctivitis in mice are alleviated,the Th-17 cells of allergic conjunctivitis mice are inhibited,and Treg cells activity is enhanced.

Diverse Roles of Immune Cells in Transplant Rejection and Immune Tolerance

Organ transplant rejection(OTR)is a complex immune reaction involving multiple cells,and it determines graft survival and patient prognosis.At present,most transplant recipients are administered a combination of immunosuppressive and biological agents to protect them from OTR.However,immunosuppressive agents negatively impact the immune system of the patients,causing them to suffer from serious complications,such as chronic infection and malignant tumors.Therefore,a thorough understanding of the mechanisms involved in immune tolerance and immune rejection with regard to organ transplant(OT)is essential for developing better treatment options and improving patient outcomes.This article reviews the role of immune cells in OTR and organ transplant tolerance(OTT),including the novel cell therapies that are currently under clinical trials for transplant recipients.

IMMUNE TOLERANCE INDUCED BY GAMMA-RAY IRRADIATION

Objective: To detect the existence of immune tolerance induced by gamma-ray irradiation. Methods: Peritoneal cells were harvested from mice subjected to 5 Gy 60Co gamma-ray total body irradiation at 3d, 7d, 15d and 30d, then their counts, morphological changes and IL-12 gene expression were investigated. Results: After irradiation, the peritoneal cells were sharply reduced, the cell morphology shifted from round-like to polymorphic and fusiform with some processes, expression of IL-12 p35 was seriously suppressed, while that of IL-12 p40 greatly enhanced. Conclusion: Our data highly suggest that the gamma-ray irradiation could potentially induce dendritic cell (DC) commitment and immune tolerance.

Research Progress of the Maternal-Fetal Interface Immune Microenvironment Regulated by Traditional Chinese Medicine in the Treatment of Recurrent Spontaneous Abortion

This article is a summary of the research progress of the maternal-fetal interface immune microenvironment regulated by traditional Chinese medicine in the treatment of recurrent spontaneous abortion.The imbalance of the immune microenvironment at the maternal-fetal interface is closely related to the occurrence of recurrent spontaneous abortion.Traditional Chinese medicine can maintain the homeostasis of the immune microenvironment at the maternal-fetal interface by regulating the function of immune cells and the expression of related cytokines.

Induction of Oral Tolerance in Neonatal Mice by Transfer of Food Allergens as IgA-Immune Complexes in Breast Milk

Various opinions have been presented on the merits and demerits that breastfeeding gives for the allergic onset of the babies. In this report, we focused on whether food proteins eaten by mother mice and secreted into breast milk as IgA-immune complexes contribute to the allergy prevention through oral tolerance in infants who ingest the milk. BALB/c mice were divided into two groups;E-group fed only egg white proteins and M-group fed only cow’s milk proteins as a dietary protein source. After immunizing M-group infants fed their own mother’s milk with ovalbumin/alum, diarrhea associated with experimental Th2 intestinal inflammation was induced by oral administration of ovalbumin. The diarrhea was dramatically suppressed in E-group infants. Concomitantly, low level of serum anti-ovalbumin- and ovomucoid-IgG1 and IgE, suppression of IL-4 synthesis by spleen cells, and low incidence of anaphylactic death after intravenous injection of ovalbumin were observed preferentially in E-infants. Immune complexes of respective dietary proteins and IgA were found in the breast milk obtained from each group of mother. Oral administration of pseudo immune complex chemically synthesized with ovalbumin and monoclonal mouse IgA in advance effectively suppressed anti-ovalbumin-IgG1 synthesis in adult mice after immunization with ovalbumin. The tolerance induced by the pseudo immune complex of ovalbumin diminished spontaneously while mice did not take egg white proteins. Thus, immune tolerance and then prevention of allergic disorder against dietary proteins were acquired via breastfeeding by mothers feeding the relevant proteins, probably through the immune complexes of dietary proteins and sIgAs secreted into breast milk.

Induction of immune tolerance with heart-thymus composite allotransplantation in rats

Objective To study on the role of thymus transplantation for heart allograft in rats. Methods Vascularized heart-thymus combined transplantation was performed with microsurgical technique. Graft survival, histopathology, level of IL-2, IL-4 and its mRNA expression in serum and cardiac grafts were investigated. Results Heart-thymus combined transplantation achieved effect in the prolongation of cardiac graft survival with short-term administration of cyclosporine. Conclusions Vascularized thymus transplantation induced immune tolerance in thymectomized rats.

Sinomenine promotes differentiation of induced pluripotent stem cells into immature dendritic cells with high induction of immune tolerance

BACKGROUND Immature dendritic cells(imDCs)play an important role in the induction of donor-specific transplant immunotolerance.However,these cells have limitations,such as rapid maturation and a short lifespan in vivo.In previous studies,induced pluripotent stem cells(iPSCs)differentiated into imDCs,and sinomenine(SN)was used to inhibit the maturation of imDCs.AIM To study the capacity of SN to maintain iPSC-derived imDCs(SN-iPSCs-imDCs)in an immature state and the mechanism by which SN-iPSCs-imDCs induce immunotolerance.METHODS In this study,mouse iPSCs were induced to differentiate into imDCs in culture medium without or with SN(iPSCs-imDCs and SN-iPSCs-imDCs).The imDCrelated surface markers,endocytotic capacity of fluorescein isothiocyanate Dextran and apoptosis were analyzed by flow cytometry.The effects of iPSCs-imDCs and SNiPSCs-imDCs on T-cell stimulatory function,and regulatory T(Treg)cell proliferative function in vitro were analyzed by mixed lymphocyte reaction.Cytokine expression was detected by ELISA.The apoptosis-related proteins of iPSCs-DCs and SN-iPSCs-DCs were analyzed by western blotting.The induced immunotolerance of SN-iPSCs-DCs was evaluated by treating recipient Balb/c skin graft mice.Statistical evaluation of graft survival was performed using Kaplan–Meier curves.RESULTS Both iPSCs-imDCs and SN-iPSCs-imDCs were successfully obtained,and their biological characteristics and ability to induce immunotolerance were compared.SN-iPSCs-imDCs exhibited higher CD11c levels and lower CD80 and CD86 levels compared with iPSCs-imDCs.Reduced major histocompatibility complex II expression,worse T-cell stimulatory function,higher Treg cell proliferative function and stronger endocytotic capacity were observed with SN-iPSCs-imDCs(P<0.05).The levels of interleukin(IL)-2,IL-12,interferon-γin SN-iPSCs-imDCs were lower than those in iPSCs-imDCs,whereas IL-10 and transforming growth factor-βlevels were higher(P<0.05).The apoptosis rate of these cells was significantly higher(P<0.05),and the expression levels of cleaved caspase3,Bax and cleaved poly(ADP-ribose)polymerase were higher after treatment with lipopolysaccharides,but Bcl-2 was reduced.In Balb/c mice recipients immunized with iPSCsimDCs or SN-iPSCs-imDCs 7 d before skin grafting,the SN-iPSCs-imDCs group showed lower ability to inhibit donor-specific CD4+T-cell proliferation(P<0.05)and a higher capacity to induce CD4+CD25+FoxP3+Treg cell proliferation in the spleen(P<0.05).The survival span of C57bl/6 skin grafts was significantly prolonged in immunized Balb/c recipients with a donor-specific pattern.CONCLUSION This study demonstrated that SN-iPSCs-imDCs have potential applications in vitro and in vivo for induction of immunotolerance following organ transplantation.

Facing challenges with hope:universal immune cells for hematologic malignancies

Many patients have achieved a favorable overall survival rate since allogenic hematopoietic stem cell transplantation(allo-HSCT)has been widely implemented to treat hematologic malignancies.However,graft-versus-host disease(GVHD)and complications of immunosuppressive drugs after allo-HSCT are the main causes of non-relapse mortality and a poor quality of life.In addition,GVHD and infusion-induced toxicity still occur with donor lymphocyte infusions(DLIs)and chimeric antigen receptor(CAR)T-cell therapy.Because of the special immune tolerance characteristics and anti-tumor ability of universal immune cells,universal immune cell therapy may strongly reduce GVHD,while simultaneously reducing tumor burden.Nevertheless,widespread application of universal immune cell therapy is mainly restricted by poor expansion and persistence efficacy.Many strategies have been applied to improve universal immune cell proliferation and persistence efficacy,including the use of universal cell lines,signaling regulation and CAR technology.In this review we have summarized current advances in universal immune cell therapy for hematologic malignancies with a discussion of future perspectives.

Hepatitis B:Who should be treated?-managing patients with chronic hepatitis B during the immune-tolerant and immunoactive phases

New hepatitis B virus(HBV)infections are decreasing owing to improved antiviral therapy and increased HBV vaccination worldwide;however,the number of HBV infections remains a major cause of liver carcinogenesis.HBV triggers cytotoxic immunity to eliminate HBV-infected cells.Therefore,the HBV pathophysiology changes in persistently infected individuals depending on host immune responses and HBV DNA proliferation state.To prevent liver cirrhosis and carcinogenesis caused by HBV,it is important to treat HBV infection at an early stage.Active treatment is recommended for the immunoactive hepatitis B surface-antigen-positive and-negative phase,but not during the immune-inactive phase or immune-tolerant phase;instead,follow-up is recommended.However,these patients should be monitored through regular blood tests to accurately diagnose the immune-inactive or-tolerant phases.The treatment regimen should be determined based on the age,sex,family history of liver cancer,and liver fibrosis status of patients.Early treatment is often recommended due to various problems during the immune-tolerant phase.This review compares the four major international practice guidelines,including those from the Japanese Society of Hepatology,and discusses strategies for chronic hepatitis B treatment during the immune-tolerant,immune-inactive,and resolved phases.Finally,recommended hepatitis B antiviral therapy and follow-up protocols are discussed.

Immunological tolerance of human hepatocyte xenograft induced by adenovirus vector-mediated CTLA4Ig gene transfer

BACKGROUND:Systemic administration of CTLA4Ig has been applied in inducing immunological tolerance of hepatocyte implants,but has potential for systemic immune inhibition.This study was designed to induce hepatocyte immunological tolerance by locally expressing CTLA4Ig in an attempt to improve the effectiveness of cell transplantation.METHODS:A normal human liver cell line(L02) was transfected with adenovirus vector containing the CTLA4Ig gene(Ad-CTLA4Ig-EGFP) in vitro,and the expression of CTLA4Ig by transfected cells was assessed by fluorescent imaging and immunocytochemical staining.Transfected cells then were injected into the spleen of Sprague-Dawley rats,the survival of cells was determined by immunohistochemistry,and the immune status was examined through CD4 + and CD69 + T cellcounts and ELISA detection of IL-2 in peripheral blood.RESULTS:L02 cells expressed CTLA4Ig in the cytoplasm for >4 weeks.Surviving L02 cells were observed in the experimental group at 3 and 4 weeks post-transplantation,while none was detected in the control group.Furthermore,the percentages of CD4 + and CD4 + CD69 + T cells in the CTLA4-transfected group were 24.5% and 45.1%,markedly lower than those in the control group at 4 weeks post-transplantation(P<0.01).Furthermore,the IL-2 level was also lower in the CTLA4transfected group than in the control group.CONCLUSION:Adenovirus-mediated CTLA4Ig gene transfer into human hepatocytes has the potential to become an effective method of inducing immunological tolerance in hepatocyte transplantation.

Gastric cancer liver metastasis will reduce the efficacy of immunotherapy

Immune checkpoint inhibitors augment the antitumor activity of T cells by inhibiting the negative regulatory pathway of T cells,leading to notable efficacy in patients with non-small cell lung cancer,melanoma,and other malignancies through immunotherapy utilization.However,secondary malignant liver tumors not only lower the liver's sensitivity to immunotherapy but also trigger systemic immune suppression,resulting in reduced overall effectiveness of immune therapy.Patients receiving immunotherapy for non-small cell lung cancer and melanoma experience reduced response rates,progression-free survival,and overall survival when secondary malignant tumors develop in the liver.Through Liu's retrospective analysis,valuable insights are provided for the future clinical management of these patients.Therefore,in patients with gastric cancer(GC),the occurrence of liver metastasis might be indicative of reduced efficacy of immuno-therapy.Overcoming liver immune tolerance mechanisms and their negative impacts allows for the potential benefits of immunotherapy in patients with GC and liver metastasis.INTRODUCTION Gastric cancer(GC)ranks among the prevalent malignancies affecting the digestive system globally.Based on the latest epidemiological data[1,2],it holds the fifth position for incidence and the fourth position for mortality among all malignant tumors.GC cases and fatalities in China make up roughly half of the worldwide figures.Earlier investigations[3]have demonstrated that the median overall survival(mOS)among advanced GC patients left untreated typically ranges from 3 to 4 months.Systemic chemotherapy recipients often experience a mOS of around one year,accompanied by a marked improvement in the quality of life among patients with advanced GC.The mainstay of treatment for advanced GC patients involves chemotherapeutic medications such as fluoropyrimidines,platinum compounds,and taxanes.However,their efficacy in tumor control is constrained by acquired resistance and primary resistance.The rise of personalized precision therapy has propelled immunotherapy into the spotlight as a crucial component of comprehensive treatment[4].By blocking the negative regulatory pathways of T cells,immune checkpoint inhibitors(ICIs)boost the anti-tumor effect of T cells.Immunotherapy has brought about significant therapeutic benefits for patients diagnosed with non-small cell lung cancer,melanoma,and related illnesses[5,6],instilling newfound hope in those with advanced GC[7].However,phase III clinical trial data[8-12]reveals that the incorporation of immunotherapy into chemotherapy regimens improves overall survival(OS)outcomes for patients with advanced GC.The liver's immune-exempt nature renders it less responsive to immunotherapy when secondary malignant tumors are present,fostering systemic immune suppression and yielding unfavorable outcomes in immune therapy[13-15].In retrospective research[16-20]pertaining to non-small cell lung cancer and melanoma,it has been observed that the presence of secondary liver malignancies may lower the response rate,progression-free survival(PFS),and OS rates in patients treated with immunotherapy,independent of factors such as tumor mutation burden and PD-L1 expression.Despite this,there is a paucity of studies examining whether the existence of secondary malignant liver tumors affects the effectiveness of immunotherapy in patients diagnosed with advanced HER-2 negative GC.

Low-dose immune tolerance induction for severe hemophilia A inhibitor patients:Immunosuppressants are generally not necessary for inhibitor-titer below 200 BU/mL

Importance:It remained unclear that the efficacy comparison between low-dose immune tolerance induction(LD-ITI)incorporating immunosuppressants(IS)when severe hemophilia A(SHA)patients had inhibitor-titer≥200 Bethesda Units(BU)/mL(LD-ITI-IS^(200) regimen)and LD-ITI combining with IS when SHA patients had inhibitor-titer≥40 BU/mL(LD-ITI-IS^(40) regimen).Objective:To compare the efficacy of the LD-ITI-IS^(200) regimen with that of the LD-ITI-IS^(40) regimen for SHA patients with high-titer inhibitors.Methods:A prospective cohort study on patients receiving LD-ITI-IS^(200) compared to those receiving LD-ITI-IS^(40) from January 2021 to December 2023.Both received LD-ITI[FVIII 50 IU/kg every other day].IS(rituximab+prednisone)was added when peak inhibitor tier≥200 BU/mL in the LD-ITI-IS^(200) regimen and≥40 BU/mL in the LD-ITI-IS^(40) regimen.Success is defined as a negative inhibitor plus FVIII recovery≥66%of the expected.Results:We enrolled 30 patients on LD-ITI-IS^(200) and 64 patients on LD-ITI-IS^(40),with similar baseline clinical characteristics.A lower IS-use rate was discovered in the LD-ITI-IS^(200) regimen compared to the LD-ITI-IS^(40) regimen(30.0%vs.62.5%).The two regimens(LD-ITI-IS^(200) vs.LD-ITI-IS^(40))had similar success rate(70.0%vs.79.7%),median time to success(9.4 vs.10.6 months),and annualized bleeding rate during ITI(3.7 vs.2.8).The cost to success was lower for LD-ITI-IS^(200) than for LD-ITI-IS^(40)(2107 vs.3256 US Dollar/kg).Among patients with peak inhibitor-titer 40-199 BU/mL,10 non-IS-using(on LD-ITI-IS^(200) regimen)and 28 IS-using(on LD-ITI-IS^(40) regimen)had similar success rates(70.0%vs.78.6%)and time to success(9.0 vs.8.8 months).Interpretation:In LD-ITI,IS are not necessary for inhibitor titer<200 BU/mL.