Adoptive immunotherapy for acute leukemia:New insights in chimeric antigen receptors

Relapses remain a major concern in acute leukemia. It is well known that leukemia stem cells(LSCs) hide in hematopoietic niches and escape to the immune system surveillance through the outgrowth of poorly immunogenic tumor-cell variants and the suppression of the active immune response. Despitethe introduction of new reagents and new therapeutic approaches, no treatment strategies have been able to definitively eradicate LSCs. However, recent adoptive immunotherapy in cancer is expected to revolutionize our way to fight against this disease, by redirecting the immune system in order to eliminate relapse issues. Initially described at the onset of the 90's, chimeric antigen receptors(CARs) are recombinant receptors transferred in various T cell subsets, providing specific antigens binding in a non-major histocompatibility complex restricted manner, and effective on a large variety of human leukocyte antigen-divers cell populations. Once transferred, engineered T cells act like an expanding "living drug" specifically targeting the tumor-associated antigen, and ensure long-term antitumor memory. Over the last decades, substantial improvements have been made in CARs design. CAR T cells have finally reached the clinical practice and first clinical trials have shown promising results. In acute lymphoblastic leukemia, high rate of complete and prolonged clinical responses have been observed after anti-CD19 CAR T cell therapy, with specific but manageable adverse events. In this review, our goal was to describe CAR structures and functions, and to summarize recent data regarding pre-clinical studies and clinical trials in acute leukemia.

Chimeric Antigen Receptors and Regulatory T Cells:The Potential for HLA-Specific Immunosuppression in Transplantation

Chimeric antigen receptors(CARs)are a breakthrough in genetic engineering that have revolutio nized the field of adoptive cellular therapy(ACT).Cells expressing these receptors are rerouted to a predefined target by the inclusion of an antigen-specific binding region within the synthetic CAR construct.The advantage of cells with programmed specificity has been demonstrated clinically in the field of oncology,and it is clear that such cells have greater accuracy,potency,and reduced off-target therapeutic effects compared with their unmodified counterparts.In contrast to conventional T cells(Tconvs),regulatory T cells(Tregs)play a major role in suppressing immune activation and regulating the host immune response.CAR expression within Tregs has been proposed as a therapy for autoimmune and inflammatory diseases,graft-versus-host disease(GVHD),and organ transplant rejectio n.In the latter,they hold immense potential as mediators of immune tolerance for recipients of allotransplants.However,current research into CAR-Treg engineering is extremely limited,and there is uncertainty regarding optimal design for therapeutic use.This review examines the rationale behind the development of CAR-Tregs,their significance for human transplantation,potential designs,safety considerations,and comparisons of CAR-Tregs in transplantation models to date.

The human application of gene therapy to re-program T-cell specificity using chimeric antigen receptors

The adoptive transfer of T cells is a promising approach to treat cancers. Primary human T cells can be modified using viral and non-viral vectors to promote the specific targeting of cancer cells via the introduction of exogenous T-cell receptors(TCRs) or chimeric antigen receptors(CARs). This gene transfer displays the potential to increase the specificity and potency of the anticancer response while decreasing the systemic adverse effects that arise from conventional treatments that target both cancerous and healthy cells. This review highlights the generation of clinical-grade T cells expressing CARs for immunotherapy, the use of these cells to target B-cell malignancies and, particularly, the first clinical trials deploying the Sleeping Beauty gene transfer system, which engineers T cells to target CD19+ leukemia and non-Hodgkin's lymphoma.

Chimeric antigen receptors:On the road to realising their full potential

Chimeric antigen receptors （CARs） are fusion molecules that may be genetically delivered ex-vivo to T-cells and other immune cell populations, thereby conferring specifcity for native target antigens found on the surface of tumour and other target cell types. Antigen recognition by CARs is neither restricted by nor dependent upon human leukocyte antigen antigen expression, favouring widespread use of this technology across transplantation barriers. Signalling is delivered by a designer endodomain that provides a tailored and target-dependent activation signal to polyclonal circulating T-cells. Recent clinical data emphasise the enormous promise of this emer-ging immunotherapeutic strategy for B-cell malignancy, notably acute lymphoblastic leukaemia. In that context, CARs are generally targeted against the ubiquitous B-cell antigen, CD19. However, CAR T-cell immunotherapy is limited by potential for severe ontarget toxicity, notably due to cytokine release syndrome. Furthermore, effcacy in the context of solid tumours remains unproven, owing in part to lack of availability of safe tumourspecific targets, inadequate CAR T-cell homing and hostility of the tumour microenvironment to immune effector deployment. Manufacture and commercial development encountered with more traditional drug products. Finally, there is increasing interest in the application of this technology to the treatment of non-malignant disease states, such as autoimmunity, chronic infection and in the suppression of allograft rejection. Here, we consider the background and direction of travel of this emerging and highly promising treatment for malignant and other disease types.

Influencing factors and solution strategies of chimeric antigen receptor T-cell therapy(CAR–T)cell immunotherapy

Chimeric antigen receptor T-cesll therapy(CAR–T)has achieved groundbreaking advancements in clinical application,ushering in a new era for innovative cancer treatment.However,the challenges associated with implementing this novel targeted cell therapy are increasingly significant.Particularly in the clinical management of solid tumors,obstacles such as the immunosuppressive effects of the tumor microenvironment,limited local tumor infiltration capability of CAR–T cells,heterogeneity of tumor targeting antigens,uncertainties surrounding CAR–T quality,control,and clinical adverse reactions have contributed to increased drug resistance and decreased compliance in tumor therapy.These factors have significantly impeded the widespread adoption and utilization of this therapeutic approach.In this paper,we comprehensively analyze recent preclinical and clinical reports on CAR–T therapy while summarizing crucial factors influencing its efficacy.Furthermore,we aim to identify existing solution strategies and explore their current research status.Through this review article,our objective is to broaden perspectives for further exploration into CAR–T therapy strategies and their clinical applications.

Advancement of chimeric antigen receptor-natural killer cells targeting hepatocellular carcinoma

With the advance of genome engineering technology,chimeric antigen receptors(CARs)-based immunotherapy has become an emerging therapeutic strategy for tumors.Although initially designed for T cells in tumor immunotherapy,CARs have been exploited to modify the function of natural killer(NK)cells against a variety of tumors,including hepatocellular carcinoma(HCC).CAR-NK cells have the potential to sufficiently kill tumor antigen-expressing HCC cells,independent of major histocompatibility complex matching or prior priming.In this review,we summarize the recent advances in genetic engineering of CAR-NK cells against HCC and discuss the current challenges and prospects of CAR-NK cells as a revolutionary cellular immunotherapy against HCC.

Chimeric antigen receptor-engineered T-cell therapy for liver cancer

Background: Chimeric antigen receptor-engineered T-cell(CAR-T) therapy is a newly developed immunotherapy used in the treatment of cancers. Because CAR-T therapy has shown great success in treating CD19-positive hematological malignancies, its application has been explored in the treatment of solid tumors, such as liver cancer. In this review, we discuss the immune characteristics of liver cancer, the obstacles encountered during the application of CAR-T therapy, and preclinical and clinical progress in the use of CAR-T therapy in patients with liver cancer.Data sources: The data on CAR-T therapy related to liver cancers were collected by searching Pub Med and the Web of Science databases prior to December 2017 with the keywords "chimeric antigen receptor","CAR-T", "liver cancer", "hepatocellular carcinoma", and "solid tumor". Additional articles were identified by manual search of references found in the primary articles. The data for clinical trials were collected by searching Clinical Trials.gov.Results: The liver has a tolerogenic nature in the intrahepatic milieu and its tumor microenvironment significantly affects tumor progression. The obstacles that reduce the efficacy of CAR-T therapy in solid tumors include a lack of specific tumor antigens, limited trafficking and penetration of CAR-T cells to tumor sites, and an immunosuppressive tumor microenvironment. To overcome these obstacles, several strategies have emerged. In addition, several strategies have been developed to manage the side effects of CAR-T, including enhancing the selectivity of CARs and controlling CAR-T activity. To date, no clinical trials of CAR-T therapy against HCC have been completed. However, preclinical studies in vitro and in vivo have shown potent antitumor efficacy. Glypican-3, mucin-1, epithelial cell adhesion molecule, carcinoembryonic antigen, and other targets are currently being studied.Conclusions: The application of CAR-T therapy for liver cancer is just beginning to be explored and more research is needed. However, we are optimistic that CAR-T therapy will offer a new approach for the treatment of liver cancers in the future.

T cells expressing a LMP1-specific chimeric antigen receptor mediate antitumor effects against LMP1-positive nasopharyngeal carcinoma cells in vitro and in vivo

T cells modified with chimeric antigen receptor are an attractive strategy to treat Epstein-Barr virus（EBV） associated malignancies.The EBV latent membrane protein 1（LMP1） is a 66-KD integral membrane protein encoded by EBV that consists of transmembrane-spanning loops.Previously,we have identified a functional signal chain variable fragment（scFv） that specifically recognizes LMP1 through phage library screening.Here,we constructed a LMP1 specific chimeric antigen receptor containing anti-LMP1 scFv,the CD28 signalling domain,and the CD3ζchain（HELA/CAR）.We tested its functional ability to target LMP1 positive nasopharyngeal carcinoma cells.HELA/CAR cells were efficiently generated using lentivirus vector encoding the LMP1-specific chimeric antigen receptor to infect activated human CD3＋ T cells.The HELA/CAR T cells displayed LMP1 specific cytolytic action and produced IFN-γ and IL-2 in response to nasopharyngeal carcinoma cells overexpressing LMP1.To demonstrate in vivo anti-tumor activity,we tested the HELA/CAR T cells in a xenograft model using an LMP1 overexpressing tumor.Intratumoral injection of anti-LMP1 HELA/CAR-T cells significantly reduced tumor growth in vivo.These results show that targeting LMP1 using HELA/CAR cells could represent an alternative therapeutic approach for patients with EBV-positive cancers.

Focused evaluation of the roles of macrophages in chimeric antigen receptor (CAR) T cell therapy associated cytokine release syndrome

Cytokine release syndrome(CRS)is a major obstacle to the widespread clinical application of chimeric antigen receptor(CAR)T cell therapies.CRS can also be induced by infections(such as SARS-CoV-2),drugs(such as therapeutic antibodies),and some autoimmune diseases.Myeloid-derived macrophages play key roles in the pathogenesis of CRS,and participate in the production and release of the core CRS cytokines,including interleukin(IL)-1,IL-6,and interferon-γ.In this review,we summarize the roles of macrophages in CRS and discuss new developments in macrophage activation and the related mechanisms of cytokine regulation in CRS.

c-Met-targeted chimeric antigen receptor T cells inhibit hepatocellular carcinoma cells in vitro and in vivo

c-Met is a hepatocyte growth factor receptor overexpressed in many tumors such as hepatocellular carcinoma(HCC).Therefore,c-Met may serve as a promising target for HCC immunotherapy.Modifying T cells to express c-Met-specific chimeric antigen receptor(CAR)is an attractive strategy in treating c-Met-positive HCC.This study aimed to systematically evaluate the inhibitory effects of 2^(nd)-and 3^(rd)-generation c-Met CAR-T cells on hepatocellular carcinoma(HCC)cells.Here,2^(nd)-and 3^(rd)-generation c-Met CARs containing an anti-c-Met singlechain variable fragment(scFv)as well as the CD28 signaling domain and CD3ζ(c-Met-28-3ζ),the CD137 signaling domain and CD3ζ(c-Met-137-3ζ),or the CD28 and CD137 signaling domains and CD3ζ(c-Met-28-137-3ζ)were constructed,and their abilities to target c-Met-positive HCC cells were evaluated in vitro and in vivo.All c-Met CARs were stably expressed on T cell membrane,and c-Met CAR-T cells aggregated around c-Met-positive HCC cells and specifically killed them in vitro.c-Met-28-137-3ζCAR-T cells secreted more interferon-gamma(IFN-γ)and interleukin 2(IL-2)than c-Met-28-3ζCAR-T cells and c-Met-137-3ζCAR-T cells.Compared with c-Met low-expressed cells,c-Met CAR-T cells secreted more cytokines when co-cultured with c-Met high-expressed cells.Moreover,c-Met-28-137-3ζCAR-T cells eradicated HCC more effectively in xenograft tumor models compared with the control groups.This study suggests that 3^(rd)-generation c-Met CAR-T cells are more effective in inhibiting c-Met-positive HCC cells than 2^(nd)-generation c-Met CAR-T cells,thereby providing a promising therapeutic intervention for c-Met-positive HCC.

Chimeric antigen receptor-immune cells against solid tumors:Structures,mechanisms,recent advances,and future developments

The advent of chimeric antigen receptor(CAR)-T cell immunotherapies has led to breakthroughs in the treatment of hematological malignancies.However,their success in treating solid tumors has been limited.CAR-natural killer(NK)cells have several advantages over CAR-T cells because NK cells can be made from pre-existing cell lines or allogeneic NK cells with a mismatched major histocompatibility complex(MHC),which means they are more likely to become an"off-the-shelf"product.Moreover,they can kill cancer cells via CAR-dependent/independent pathways and have limited toxicity.Macrophages are the most malleable immune cells in the body.These cells can efficiently infiltrate into tumors and are present in large numbers in tumor microenvironments(TMEs).Importantly,CAR-macrophages(CAR-Ms)have recently yielded exciting preclinical results in several solid tumors.Nevertheless,CAR-T,CAR-NK,and CAR-M all have their own advantages and limitations.In this review,we systematically discuss the current status,progress,and the major hurdles of CAR-T cells,CAR-NK cells,and CAR-M as they relate to five aspects:CAR structure,therapeutic mechanisms,the latest research progress,current challenges and solutions,and comparison according to the existing research in order to provide a reasonable option for treating solid tumors in the future.

Roles of antigen receptors and CA215 in the innate immunity of cancer cells

Antigen receptors, including immunoglobulins and T-cell receptors, are known to be widely expressed by cancer cells through unconfirmed mechanisms and for unknown purposes. Recently, a monoclonal antibody, designated as RP215, was generated against the ovarian cancer cell line, OC-3-VGH, and was shown to react with CA215, which consisted mainly of these cancer cell-expressed antigen receptors. Experimental evidence has clearly indicated that cancerous immunoglobulins play significant roles in the growth and proliferation of cancer cells in vitro and in vivo. RP215 and anti-antigen receptor antibodies were equally effective in inducing apoptosis and complement-dependent cytotoxicity reactions to cultured cancer cells. Through gene regulation studies, both RP215 and antibodies against antigen-receptors were shown to affect more than a dozen of genes involved in cell proliferation (such as NFκB-1, IgG, P21, cyclin D1, ribosomal P1, and c-fos). Furthermore, selected toll-like receptor genes (TLR- 2, -3, -4, and -9) were also found to be highly regulated by both RP215 and anti-antigen receptor antibodies. For example, RP215 and anti-antigen receptor antibodies were found to both up-regulate TLR-2 and/or TLR-3 and down- regulate TLR-4 and TLR-9 intwo types of cancer cells. Based on these studies, it is reasonable to postulate that cancerous immunoglobulins play important roles in the modulation of the innate immune system to allow the growth and survival of cancer cells within the human body. Consequently, RP215 inits humanized forms may be utilized to target cancer cells for potential therapeutic purposes.

Chidamide and sintilimab combination in diffuse large B-cell lymphoma progressing after chimeric antigen receptor T therapy

BACKGROUND Diffuse large B-cell lymphoma(DLBCL)is curable with first-line chemoimmunotherapy but patients with relapsed/refractory(R/R)DLBCL still face a poor prognosis.For patients with R/R DLBCL,the complete response rate to traditional next-line therapy is only 7%and the median overall survival is 6.3 mo.Recently,CD19-targeting chimeric antigen receptor T cells(CAR-T)have shown promise in clinical trials.However,approximately 50%of patients treated with CAR-T cells ultimately progress and few salvage therapies are effective.CASE SUMMARY Here,we report on 7 patients with R/R DLBCL whose disease progressed after CAR-T infusion.They received a PD-1 inhibitor(sintilimab)and a histone deacetylase inhibitor(chidamide).Five of the 7 patients tolerated the treatment without any serious adverse events.Two patients discontinued the treatment due to lung infection and rash.At the 20-mo follow-up,the median overall survival of these 7 patients was 6 mo.Of note,there were 2 complete response rates(CRs)and 2 partial response rates(PRs)during this novel therapy,with an overall response rate(ORR)of 57.1%,and one patient had a durable CR that lasted at least 20 mo.CONCLUSION In conclusion,chidamide combined with sintilimab may be a choice for DLBCL patients progressing after CD19-targeting CAR-T therapy.

Refractory lymphoma treated with chimeric antigen receptor T cells combined with programmed cell death-1 inhibitor:A case report

BACKGROUND Diffuse large B-cell lymphoma(DLBCL)is a common aggressive non-Hodgkin's lymphoma(NHL),accounting for 30%-40%of adult NHL.Primary testicular(PT)lymphoma is an uncommon extranodal disease representing approximately 1%-2%of lymphoma.Approximately 30%–40%of patients are refractory to frontline therapy or relapse after complete remission.Refractory DLBCL responds poorly to other lines of chemotherapy,and experiences short-term survival.CASE SUMMARY We present a 41-year-old male patient who was diagnosed with PT-DLBCL.Further disease progression was observed after multiline chemotherapy.Chimeric antigen receptor T cells(CAR-T)therapy salvaged the patient.Unfortunately,a new mass was observed in the right adrenal area after six months.The patient was administered programmed cell death protein-1(PD-1)inhibitor therapy and maintained progression-free survival at more than 17 mo of follow-up.CONCLUSION Our findings support the potential benefit of CAR-T combined with PD-1 inhibitor therapies in this type of relapsed and refractory PT-DLBCL.

Programmed cell death protein-1 inhibitor combined with chimeric antigen receptor T cells in the treatment of relapsed refractory non- Hodgkin lymphoma: A case report

BACKGROUND Chimeric antigen receptor T cell(CART)therapy has benefited many refractory lymphoma patients,but some patients experience poor effects.Previous studies have shown that programmed cell death protein-1(PD-1)inhibitors can improve and prolong the therapeutic effect of CAR-T cell treatment.CASE SUMMARY A 61-year-old male presented with 15-d history of diarrhea and lower-limb edema.A large mass was detected in the pelvis,and pathology indicated non-Hodgkin diffuse large B-cell lymphoma.After three cycles of the R-CHOP chemotherapeutic regimen,the patient showed three subcutaneous nodules under the left armpit and both sides of the cervical spine.Pathological examination of the nodules indicated DLBCL again.The patient was diagnosed with relapsed and refractory diffuse large B-cell lymphoma.We recommended CAR-T cell treatment.Before treatment,the patient’s T cell function and expression of immune detection points were tested.Expression of PD-1 was obviously increased(52.7%)on cluster of differentiation(CD)3+T cells.The PD-1 inhibitor(3 mg/kg)was infused prior to lymphodepleting chemotherapy with fludarabine and cyclophosphamide.CAR-CD19 T cells of 3×10^(6)/kg and CAR-CD22 T cells 1×10^(6)/kg were infused,respectively.The therapeutic effect was significant,and the deoxyribonucleic acid copy numbers of CAR-CD19 T cells and CAR-CD22 T cells were stable.Presently,the patient has been disease-free for more than 12 mo.CONCLUSION This case suggests that the combination of PD-1 inhibitors and CAR-T cellsimproved therapeutic efficacy in B-cell lymphoma.

Cytokine release syndrome complicated with rhabdomyolysis after chimeric antigen receptor T-cell therapy:A case report

BACKGROUND Chimeric antigen receptor T-Cell(CAR-T)therapy is an effective new treatment for hematologic malignancies.Cytokine release syndrome(CRS)and neurologic toxicity are main toxicities.CRS-induced rhabdomyolysis(RM)followed by CART therapy treatment has not been previously reported.CASE SUMMARY We report a case of a 22-year-old woman with relapsed acute lymphoblastic leukemia obtained sequential cluster of differentiation(CD)19 and CD22 CAR-T infusion.This patient experienced grade 3 CRS with RM,mild hypotension requiring intravenous fluids,and mild hypoxia and was managed effectively with the IL-6 receptor antagonist tocilizumab.This patient had no signs of immune effector cell-associated neurologic syndrome.Restaging scans 30 d postCAR-T therapy demonstrated a complete remission,and the symptoms of muscle weakness improved through rehabilitation.CONCLUSION Myalgia is an easily overlooked symptom of severe CRS after CAR-T therapy.It is necessary to monitor myoglobin levels when a patient presents with symptoms of myalgia or acute renal insufficiency.

Genetic engineering of T cells with chimeric antigen receptors for hematological malignancy immunotherapy

The host immune system plays an instrumental role in the surveillance and elimination of tumors by recognizing and destroying cancer cells. In recent decades, studies have mainly focused on adoptive immunotherapy using engineered T cells for the treatment of malignant diseases. Through gene engraftment of the patient's own T cells with chimeric antigen receptor(CAR),they can recognize tumor specific antigens effectively and eradicate selectively targeted cells in an MHC-independent fashion.To date, CAR-T cell therapy has shown great clinical utility in patients with B-cell leukemias. Owing to different CAR designs and tumor complex microenvironments, genetically redirected T cells may generate diverse biological properties and thereby impact their long-term clinical performance and outcome. Meanwhile some unexpected toxicities that result from CAR-T cell application have been examined and limited the curative effects. Diverse important parameters are closely related with adoptively transferred cell behaviors, including CAR-T cells homing, CAR constitutive signaling, T cell differentiation and exhaustion. Thus, understanding CARs molecular design to improve infused cell efficacy and safety is crucial to clinicians and patients who are considering this novel cancer therapeutics. In this review, the developments in CAR-T cell therapy and the limitations and perspectives in optimizing this technology towards clinical application are discussed.

Relevant nursing measures for the adverse reactions associated with chimeric antigen receptor T cells(CAR-T) immunotherapy: a systematic review of case reports

Objective: Cytokine release syndrome (CRS) and tumor lysis syndrome (TLS) that occur after chimeric antigen receptor T (CAR-T) cells are reinfused, which severely affect the survival and prognosis of patients. Although several articles have reported on the care of CAR-T cell immunotherapy, the quality of the study and the effectiveness of holistic nursing interventions have not been systematically reviewed. The purpose of this study was to systematically evaluate the existing holistic nursing interventions of CAR-T cell immunotherapy. Methods: A literature search for keywords was performed in PubMed, EMBASE, the Cochrane Library, CNKI, CBM, and Wanfang Data from its inception until January 2018. Studies were deemed eligible if they comprised patients with tumor receiving CAR-T cell immunotherapy, described the holistic nursing process, and were published in Chinese and English. Results: A total of 6 articles on holistic nursing interventions of CAR-T cell immunotherapy are reported, and the nursing methods and results of each article are analyzed. The quality of the studies included was medium. All nursing measures were considered effective. Conclusions: Holistic nursing programs reduce the incidence of CRS and TLS and improve the quality of life of cancer patients.

Rejection of Experimental Hodgkins Lymphoma by T-Cells Engineered with a CD19 Chimeric Antigen Receptor

T cells engineered to express chimeric antigen receptors (CARs) combining an external antibody binding domain with the CD3ζ T cell receptor (TCR) signaling domain for triggering cell activation are being used for immunotherapeutic targeting of tumor cells in a non-HLA restricted manner. In this study we transduced T cells with a CD19-CAR construct containing a truncated CD34 gene (tCD34) marker and used these to target the B cell antigen CD19 on the surface of a Hodgkin’s lymphoma (HL) cell line (L591) both in vitro and in vivo. Levels of tCD34 expression in transduced peripheral blood mononuclear cells (PBMCs) ranged from 6% - 20% and this was increased to 82% after selection for transduced tCD34+ cells. In vitro cytotoxicity testing on a CD19+ HL cell line (L591) showed specific cell lysis initiated by the CD19-CAR transduced PBMCs. Importantly, CD19-CAR T cells prevented the growth of L591 HL tumor cells when co-injected subcutaneously (sc) in 6/6 severe combined immunodeficient (SCID) mice. There was no evidence of anti-tumor activity when CD19-CAR T cells were infused intravenously (iv) at the same time as L591 HL tumor cells were injected sc. However, 3/6 SCID mice showed tumor rejection within 83 days after iv infusion of CD19-CAR T cells 3 - 9 days after establishment of L591 HL tumors, while all control animals succumbed to tumors within 60 days. Interestingly, immuno-histochemical analysis of L591 HL tumors demonstrated that CD19-CAR T cells were detected not earlier than 11 days after infusion within the tumor mass. These results suggest that CD19 is a potentially attractive target for the immunotherapy of HL.

Axonal growth inhibitors and their receptors in spinal cord injury:from biology to clinical translation

Axonal growth inhibitors are released during traumatic injuries to the adult mammalian central nervous system, including after spinal cord injury. These molecules accumulate at the injury site and form a highly inhibitory environment for axonal regeneration. Among these inhibitory molecules, myelinassociated inhibitors, including neurite outgrowth inhibitor A, oligodendrocyte myelin glycoprotein, myelin-associated glycoprotein, chondroitin sulfate proteoglycans and repulsive guidance molecule A are of particular importance. Due to their inhibitory nature, they represent exciting molecular targets to study axonal inhibition and regeneration after central injuries. These molecules are mainly produced by neurons, oligodendrocytes, and astrocytes within the scar and in its immediate vicinity. They exert their effects by binding to specific receptors, localized in the membranes of neurons. Receptors for these inhibitory cues include Nogo receptor 1, leucine-rich repeat, and Ig domain containing 1 and p75 neurotrophin receptor/tumor necrosis factor receptor superfamily member 19(that form a receptor complex that binds all myelin-associated inhibitors), and also paired immunoglobulin-like receptor B. Chondroitin sulfate proteoglycans and repulsive guidance molecule A bind to Nogo receptor 1, Nogo receptor 3, receptor protein tyrosine phosphatase σ and leucocyte common antigen related phosphatase, and neogenin, respectively. Once activated, these receptors initiate downstream signaling pathways, the most common amongst them being the Rho A/ROCK signaling pathway. These signaling cascades result in actin depolymerization, neurite outgrowth inhibition, and failure to regenerate after spinal cord injury. Currently, there are no approved pharmacological treatments to overcome spinal cord injuries other than physical rehabilitation and management of the array of symptoms brought on by spinal cord injuries. However, several novel therapies aiming to modulate these inhibitory proteins and/or their receptors are under investigation in ongoing clinical trials. Investigation has also been demonstrating that combinatorial therapies of growth inhibitors with other therapies, such as growth factors or stem-cell therapies, produce stronger results and their potential application in the clinics opens new venues in spinal cord injury treatment.