CAR)-engineered T Cells Research Articles

Abstract 1514: A novel workflow to assess the T-cell and patient-derived organoid interaction

Abstract Immunotherapy is increasingly popular as a type of cancer treatment. These therapies include the use of Chimeric Antigen Receptor-engineered T-cells (CAR T-cells), tumor-infiltrating lymphocytes (TIL), and other genetically modified T-cells to specifically target the cancer cells. Although much success has been achieved with immunotherapy for treatment of blood cancers, its efficacy remains limited in solid tumors. One of the reasons for the low success rate is attributed to the solid tumor microenvironment (TME) where suppressive cytokines limit the tumor killing ability of T-cells. Thus, understanding the role the TME plays in T-cell responses is essential for the development of effective cancer therapies. The benefits of using 3-dimensional (3D) PDOs lie in the physical and chemical cues present within the TME that cannot be mimicked in traditional 2D monolayer cultures. Studies show that PDOs show similar responses to drugs as original tumors, suggesting the value of using PDOs to improve therapeutic outcomes. Thus, PDOs can provide more relevant physiological and pathological cancer models that recapitulate the basic features of primary tumors and is more suited for assessing the effectiveness of T-cell killing than 2D cell models. Despite the benefits associated with the use of PDOs, there are significant barriers to widespread adoption of PDOs in drug discovery. Organoid production is a costly and highly labor-intensive process. Moreover, organoid culture is a skilled manual process, and thus there can be significant variability between operators. To address the challenges associated with the use of PDOs in large scale applications, a semi-automated bioprocess has been developed for the large-scale expansion of assay ready organoids. Here, we developed a method to assess the effectiveness of T-cell invasion in solid tumors using patient derive organoids (PDOs). Using bioreactor expanded patient-derived colorectal cancer organoids (CRCs), activated PBMCs (human peripheral blood mononuclear cells) stained with CellTracker were added to CRCs (stained with MitoTracker) in a 96well microtiter plate and monitored on every 4 hours for 3 days using high content imager. To quantify T-cell invasion, we developed an image analysis method to measure the distance of each T-cell to the nearest organoid (interaction distance). We find that stimulated T-cell resulted in smaller interaction distance than non-stimulated T-cells. The results demonstrate the utility of the bioreactor-expanded organoids in large scale T-cell based screens. Citation Format: Zhisong Tong, Angeline Lim, Oksana Sirenko. A novel workflow to assess the T-cell and patient-derived organoid interaction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1514.

Antitumor effect of CAR-T cells targeting transmembrane tumor necrosis factor alpha combined with PD-1 mAb on breast cancers

BackgroundOur previous study showed that transmembrane tumor necrosis factor alpha (tmTNF-α) is overexpressed in primary breast cancers including triple-negative breast cancers (TNBCs). Chimeric antigen receptor engineered-T (CAR-T) cells have been...

Novel CD19 chimeric antigen receptor T cells manufactured next-day for acute lymphoblastic leukemia

Chimeric antigen receptor-engineered T (CAR-T) cells have shown promising efficacy in patients with relapsed/refractory B cell acute lymphoblastic leukemia (R/R B-ALL). However, challenges remain including long manufacturing processes that need to be overcome. We presented the CD19-targeting CAR-T cell product GC007F manufactured next-day (FasTCAR-T cells) and administered to patients with R/R B-ALL. A total of 21 patients over 14 years of age with CD19+ R/R B-ALL were screened, enrolled and infused with a single infusion of GC007F CAR-T at three different dose levels. The primary objective of the study was to assess safety, secondary objectives included pharmacokinetics of GC007F cells in patients with R/R B-ALL and preliminary efficacy. We were able to demonstrate in preclinical studies that GC007F cells exhibited better proliferation and tumor killing than conventional CAR-T (C-CAR-T) cells. In this investigator-initiated study all 18 efficacy-evaluable patients achieved a complete remission (CR) (18/18, 100.00%) by day 28, with 17 of the patients (94.4%) achieving CR with minimal residual disease (MRD) negative. Fifteen (83.3%) remained disease free at the 3-month assessment, 14 patients (77.8%) maintaining MRD negative at month 3. Among all 21 enrolled patients, the median peak of CAR-T cell was on day 10, with a median peak copy number of 104899.5/µg DNA and a median persistence period of 56 days (range: 7–327 days). The incidence of cytokine release syndrome (CRS) was 95.2% (n = 20), with severe CRS occurring in 52.4% (n = 11) of the patients. Six patients (28.6%) developed neurotoxicity of any grade. GC007F demonstrated superior expansion capacity and a less exhausted phenotype as compared to (C-CAR-T) cells. Moreover, this first-in-human clinical study showed that the novel, next-day manufacturing FasTCAR-T cells was feasible with a manageable toxicity profile in patients with R/R B-ALL.

1372O CLDN 18.2-targeted CAR-T cell therapy in patients with cancers of the digestive system

Efficacy of chimeric antigen receptor-engineered T (CAR-T) cell therapy against solid tumors is still limited. CLDN18.2 is a promising target highly expressed in various cancer types of the digestive system. CT041, an anti-CLDN18.2 CAR-T cell therapy, showed promising anti-tumor activities in preclinical studies and an investigator-initiated study (CT041-CG4003 NCT03159819). This newly initiated phase I study was conducted to assess the safety and efficacy of CT041 produced with a modified manufacturing process. Patients with CLDN18.2+ cancers of digestive system received CT041 at doses of 2.5×108, 3.75×108 or 5×108 CAR-T cells after preconditioning chemotherapy. The objective was to assess the safety, efficacy and cytokinetic profile of CT041. As of April 8, 2021, a total of 37 patients with cancer of digestive system, including 28 with gastric cancer (GC), 5 with pancreatic ductal adenocarcinoma (PDAC) and 4 with other cancer types, received CT041 infusion and completed at least 12 weeks of follow-up after the first infusion for the last subject. Cell doses of 2.5×108, 3.75×108 and 5×108 were administrated in 28, 6 and 3 patients, respectively. With a median follow-up of 7.6 months (95%CI 5.6, 8.6), all patients experienced ≥G3 hematologic toxicity while no DLT was observed. Immune effector cell-associated neurotoxicity syndrome, treatment-related death and ≥G3 cytokine release syndrome was not observed. The overall ORR for all patients and patients with GC were 48.6% (95%CI, 31.9%, 65.6%) and 57.1% (95%CI, 37.2, 75.5) respectively. At the dose level of 2.5×108, 18 patients with GC who have failed at least 2 prior lines of therapy including 44% (8/18) exposure to anti-PD-(L)1 antibody, the overall ORR, median PFS and OS was 61.1% (11/18), 5.4 months (95%CI, 2.6, NE) and 9.5 months (95%CI, 5.2, NE) respectively. CT041 showed acceptable safety profile and promising anti-tumor activities in patients with refractory CLDN18.2+ cancers of digestive system. In patients with GC who have failed at least 2 prior lines of therapy, CT041 displayed a significantly improved efficacy compared to historical data.

An overview of CAR T-cell clinical trial activity to 2021.

SummaryImmunotherapy of cancer using chimeric antigen receptor-engineered T-cells has transformed the management of selected haematological malignancies, triggering intense clinical trial activity in this arena. This article summarises trial activity that has been published to date across the spectrum of haematological and solid tumour types.

CAR-NK cells: A promising cellular immunotherapy for cancer.

Natural Killer (NK) cells and CD8+ cytotoxic T cells are two types of immune cells that can kill target cells through similar cytotoxic mechanisms. With the remarkable success of chimeric antigen receptor (CAR)-engineered T (CAR-T) cells for treating haematological malignancies, there is a rapid growing interest in developing CAR-engineered NK (CAR-NK) cells for cancer therapy. Compared to CAR-T cells, CAR-NK cells could offer some significant advantages, including: (1) better safety, such as a lack or minimal cytokine release syndrome and neurotoxicity in autologous setting and graft-versus-host disease in allogenic setting, (2) multiple mechanisms for activating cytotoxic activity, and (3) high feasibility for ‘off-the-shelf’ manufacturing. CAR-NK cells could be engineered to target diverse antigens, enhance proliferation and persistence in vivo, increase infiltration into solid tumours, overcome resistant tumour microenvironment, and ultimately achieve an effective anti-tumour response. In this review, we focus on recent progress in genetic engineering and clinical application of CAR-NK cells, and discuss current challenges and future promise of CAR-NK cells as a novel cellular immunotherapy in cancer.

Use of CART cells to selectively target autoantigen-specific T cells for the treatment of autoimmune diabetes

Abstract Previous clinical trials using biologics-based broad-spectrum T cell- and B cell-depleting molecules for the treatment of autoimmune diabetes have shown promising, yet mixed, results. Their varied extent of success may be due to their non-specific action and failure to permanently and completely remove the pathogenic subpopulations. As CD8+ T cells, the most dominant cell type in human insulitis, are thought to be the primary mediator of β-cells damage, we thus designed a strategy by adapting chimeric antigen receptor engineered T (CART) technology to directly target these pathogenic T cells. The newly generated CAR construct maintains original transmembrane and intracellular components, while the extracellular scFv antigen-binding domain was replaced with HLA-A2/β2-microglobulin (B2M) complex that is linked with either diabetes-associated immunodominant peptide zinc transporter 8(ZnT8)186–194 or negative control peptide HIV Gag77–85. We have shown that HLA-A2/B2M complexes were correctly folded and presenting right peptide epitopes on CART cells. The CAR signaling was also sustained, as the expression levels of CD25 and CD69 were significantly elevated only on CAR-transduced Jurkat cells presenting ZnT8186–194 peptide co-cultured with a T-cell line that expresses TCRs recognizing the same peptide. To determine the killing ability of CART cells, we further engineered primary human T cells to express our CAR construct and demonstrated that CART cells can selectively deplete human antigen-specific CD8+ T cells in vitro. Therefore, our results have provided proof-of-principle for the development of a novel immunotherapy for disease treatment.

The NOTCH-FOXM1 Axis Plays a Key Role in Mitochondrial Biogenesis in the Induction of Human Stem Cell Memory-like CAR-T Cells.

Recent studies have shown that stem cell memory T (TSCM) cell-like properties are important for successful adoptive immunotherapy by the chimeric antigen receptor-engineered-T (CAR-T) cells. We previously reported that both human and murine-activated T cells are converted into stem cell memory-like T (iTSCM) cells by coculture with stromal OP9 cells expressing the NOTCH ligand. However, the mechanism of NOTCH-mediated iTSCM reprogramming remains to be elucidated. Here, we report that the NOTCH/OP9 system efficiently converted conventional human CAR-T cells into TSCM-like CAR-T, "CAR-iTSCM" cells, and that mitochondrial metabolic reprogramming played a key role in this conversion. NOTCH signaling promoted mitochondrial biogenesis and fatty acid synthesis during iTSCM formation, which are essential for the properties of iTSCM cells. Forkhead box M1 (FOXM1) was identified as a downstream target of NOTCH, which was responsible for these metabolic changes and the subsequent iTSCM differentiation. Like NOTCH-induced CAR-iTSCM cells, FOXM1-induced CAR-iTSCM cells possessed superior antitumor potential compared with conventional CAR-T cells. We propose that NOTCH- or FOXM1-driven CAR-iTSCM formation is an effective strategy for improving cancer immunotherapy. SIGNIFICANCE: Manipulation of signaling and metabolic pathways important for directing production of stem cell memory-like T cells may enable development of improved CAR-T cells.

Cellular Immunotherapy for Refractory Diffuse Large B Cell Lymphoma in the Chimeric Antigen Receptor-Engineered T Cell Era: Still a Role for Allogeneic Transplantation?

Chimeric antigen receptor-engineered T (CART) cells are a promising new treatment option for patients with multiply relapsed and refractory (R/R) diffuse large B cell lymphoma (DLBCL). Because of the favorable outcome data reported for CART cells, uncertainty is emerging if there is still a role for allogeneic hematopoietic cell transplantation (allo-HCT) in the treatment of R/R DLBCL. This article provides an overview of available evidence and theoretical considerations to put these 2 types of cellular immunotherapy (CI) into perspective. Altogether, current data suggest that CART cells are preferred now over transplantation as first-choice CI in many clinical situations. However, the majority of patients will fail CART therapy, resulting in an unmet medical need where allo-HCT could be beneficial. In contrast, employing allo-HCT instead of CART cells as first CI should be presently restricted to situations where CART cell therapy is deemed not feasible or useful, such as patients with refractory cytopenia or incipient myelodysplastic syndrome. However, allo-HCT remains a standard treatment option as first CI for patients with chemosensitive R/R DLBCL when CARTs are not available or transplantation is preferred by the patient. Continuous collection and analysis of CI outcome data by professional registries appear to be of key importance for developing rational strategies of CI allocation and sequencing.

Chimeric Antigen Receptor-Engineered T-Cells - A New Way and Era for Lymphoma Treatment.

Patients with refractory or relapsed diffuse large B-cell lymphoma have a poor prognosis with the current standard of care. Chimeric Antigen Receptor T-cells (CAR T-cells) are functionally reprogrammed lymphocytes, which are able to recognize and kill tumor cells. The aim of this study is to make progress in this area. A mini-review was achieved using the articles published in Web of Science and PubMed in the last year and the new patents were made in this field. The responses to CAR T-cell products axicabtagene ciloleucel and tisagenlecleucel are promising; the objective response rate can reach up to 83%, and the complete response rate ranges between 40 and 58%. About half of the patients may have serious side effects, such as cytokine release syndrome and neurotoxicity. Current and future developments include the improvement of CAR T-cell expansion and polyfunctionality, the combined use of CAR T-cells with a fusion protein between interferon and an anti-CD20 monoclonal antibody, with checkpoint inhibitors or small molecule sensitizers that have apoptotic-regulatory effects. Furthermore, the use of IL-12-expressing CAR T-cells, an improved technology for the production of CAR T-cells based on targeted nucleases, the widespread use of allogeneic CAR T-cells or universal CAR T-cells obtained from genetically engineered healthy donor T-cells are future developments actively considered. CAR T-cell therapy significantly improved the outcome of patients with relapsed or refractory diffuse large B-cell lymphoma. The advances in CAR T-cells production technology will improve the results and enable the expansion of this new immunotherapy.

EGFR-specific CAR-T cells trigger cell lysis in EGFR-positive TNBC.

Triple-negative breast cancer (TNBC) is an aggressive cancer subtype for which effective therapies are lacking. Epidermal growth factor receptor (EGFR) is overexpressed in various types of TNBC cells, and several EGFR-specific immunotherapies have been used to treat cancer patients. Chimeric antigen receptor engineered T (CAR-T) cells have also been used as cancer therapies. In this study, we generated two types of EGFR-specific CAR-modified T cells using lentiviral vectors with DNA sequences encoding the scFv regions of two anti-EGFR antibodies. The cytotoxic and antitumor effects of these CAR-modified T cells were examined in cytokine release and cytotoxicity assays in vitro and in tumor growth assays in TNBC cell line- and patient-derived xenograft mouse models. Both types of EGFR-specific CAR-T cells were activated by high-EGFR-expressing TNBC cells and specifically triggered TNBC cell lysis in vitro. Additionally, the CAR-T cells inhibited growth of cell-line- and patient-derived xenograft TNBC tumors in mice. These results suggest that EGFR-specific CAR-T cells might be a promising therapeutic strategy in patients with high-EGFR-expressing TNBC.

Efficacy and Safety of CAR-T Therapy with Safety Switch Targeting Bcma for Patients with Relapsed/Refractory Multiple Myeloma in a Phase 1 Clinical Study

Background: Encouraging results are seen from several early phase clinical trials on the cellular immunotherapy based on chimeric antigen receptor (CAR)-engineered T (CAR-T) targeting B cell maturation antigen (BCMA) for the treatment of relapsed/refractory (RR) multiple myeloma (MM). We developed an anti-BCMA CAR-T cell product manufactured via gamma-retrovirus-mediated transduction of activated T cells to express a second-generation CAR with the 4-1BB costimulatory domain along with a truncated epidermal growth factor receptor (tEGFR) as a safety switch. The preclinical study confirmed its high reactivity against MM cells. Methods: A phase 1 clinical trial (NCT03093168) has been launched to evaluate the safety and feasibility of this BCMA CAR-T cell product for treating RRMM. The enrolled RRMM patients had received at least 2 prior treatment regimens, including a proteasome inhibitor and an immunomodulatory agent, or are double-refractory, and have over 5% BCMA expression on plasma cells (Nine patient with extramedullary plasmacytoma does not express BCMA). Patients were subjected to a lymphodepleting regimen with Cy (300 mg/m2, d-5 to d-3) and Flu daily for 3 days (25 mg/m2, d-5 to d-3) prior to the CAR-T infusion (d0) at a dose of 9×106CAR+ cells/kg. The efficacy was assessed by the International Uniform Response Criteria for Multiple Myeloma, and the toxicity is graded by CTCAE 4.03. Results: As of March 1th, 2019, 46 patients had been infused with this intended dose of the autologous BCMA CAR-T cells, and 44 patients had reached at least 1 month of follow-up. As of this data cut-off, the overall response rate (ORR) for the 44 evaluable patients was 79.6%, including 2sCRs, 16CRs, 8VGPRs and 8PRs, and 16 patients reached MRD-negative response. The CAR-T cell expansion and persistence were consistently observed throughout these patients. The medianPFS is 15mon, and the median OS result has not been reached (49.16% progression-free survival, and 53.95% overall survival at 24 months). Among the 44 infused patients, 22.7% had grade 1-2 Cytokine release syndrome (CRS ) and 6.8% (3 patients) had grade 3 CRS. No grade 4 CRS reactions developed and all toxicities were fully reversible. Conclusions: Our result demonstrates the high potential of this single CAR-T infusion therapy for RRMM, including 2sCRs, 16CRs and ongoing clinical responses for more than 26 months, with manageable CRS to date. These initial data provide strong evidence to support the further development of this anti-myeloma cellular immunotherapy. Disclosures No relevant conflicts of interest to declare.

Super-resolution microscopy reveals ultra-low CD19 expression on myeloma cells that triggers elimination by CD19 CAR-T

Immunotherapy with chimeric antigen receptor-engineered T-cells (CAR-T) is under investigation in multiple myeloma. There are reports of myeloma remission after CD19 CAR-T therapy, although CD19 is hardly detectable on myeloma cells by flow cytometry (FC). We apply single molecule-sensitive direct stochastic optical reconstruction microscopy (dSTORM), and demonstrate CD19 expression on a fraction of myeloma cells (10.3–80%) in 10 out of 14 patients (density: 13–5,000 molecules per cell). In contrast, FC detects CD19 in only 2 of these 10 patients, on a smaller fraction of cells. Treatment with CD19 CAR-T in vitro results in elimination of CD19-positive myeloma cells, including those with <100 CD19 molecules per cell. Similar data are obtained by dSTORM analyses of CD20 expression on myeloma cells and CD20 CAR-T. These data establish a sensitivity threshold for CAR-T and illustrate how super-resolution microscopy can guide patient selection in immunotherapy to exploit ultra-low density antigens.

TREM1/Dap12-based CAR-T cells show potent antitumor activity.

Aim: Chimeric antigen receptor-engineered T (CAR-T) cells have gained huge success in treating hematological malignancies, yet the CD3ζ-based CAR-T therapies have not shown comparable clinical benefits in solid tumors. We designed an alternative chimeric immunoreceptor in which a single-chain variable fragment was fused to the transmembrane-cytoplasmic domains of triggering receptor expressed on myeloid (TREM1), which may show potent antitumor activity. Methods: To generate TREM1/DNAX activation protein of 12 kDa (Dap12)-based CAR-T cells, TREM1 along with DAP12 was transduced into T cells. Results: TREM1/Dap12-based CAR-T cells showed more lysis in vitro and a similar antitumor effect in mouse models compared with CD19BBζ CAR-T cells. Conclusion: In this study, we designed a TREM1/Dap12-based CAR, which was not reported previously and demonstrated that TREM1/Dap12-based CAR-T cells had potent antitumor activity in vitro and in vivo.

Induced CD20 Expression on B-Cell Malignant Cells Heightened the Cytotoxic Activity of Chimeric Antigen Receptor Engineered T Cells.

CD20 is an effective immunotherapy target for CD20+ B-cell malignant cells. Monoclonal antibody, especially rituximab, has been a conventional strategy in the treatment of B-cell malignancies such as non-Hodgkin's lymphoma. However, treatment with monoclonal antibodies has not been enough to overcome the refractory/relapse problems. Chimeric antigen receptor engineered T (CAR-T) cells have exhibited excellent therapeutic effect on lymphocytic leukemia in recent years. In this study, a CD20-specific CAR was constructed and the cytotoxic efficacy of CD20 CAR-T cells on B-cell malignant cells was evaluated by CD107a degranulation, pro-inflammation cytokine production, and true lytic ability in vitro and in vivo. It was found that CD20 CAR-T cells possessed stronger cytotoxic ability against CD20 highly expressed cells. Furthermore, when histone deacetylase inhibitor was used to enhance the expression of CD20 antigen on the surface of B-cell malignant cells via inducing acetylation of H3K9 on CD20 promoter site, it revealed that the cytotoxicity of CD20 CAR-T cells against histone deacetylase inhibitor-treated B-cell malignant cells was significantly enhanced.

Durable Remission Achieved from Bcma-Directed CAR-T Therapy Against Relapsed or Refractory Multiple Myeloma

Background: Promising results are seen from several early phase clinical trials on the cellular immunotherapy based on chimeric antigen receptor (CAR)-engineered T (CAR-T) targeting B cell maturation antigen (BCMA) for the treatment of relapsed/refractory (RR) multiple myeloma (MM). We developed an anti-BCMA CAR-T cell product manufactured via gamma-retrovirus-mediated transduction of activated T cells to express a second-generation CAR with the 4-1BB costimulatory domain along with a truncated epidermal growth factor receptor (tEGFR) as a safety switch. The preclinical study confirmed its high reactivity against MM cells.Methods: We initiated a phase 1 clinical trial (NCT03093168) to evaluate the safety and feasibility of this BCMA CAR-T autologous cellular therapy for treating RRMM. The enrolled RRMM patients either had received at least 3 prior treatment regimens, including a proteasome inhibitor and an immunomodulatory agent, or were double-refractory, and have over 5% BCMA expression on plasma cells (One patient with extramedullary plasmacytoma does not express BCMA). Patients were subjected to a lymphodepleting regimen with Cy (300 mg/m2, d-5 to d-3) and Flu daily for 3 days (25 mg/m2, d-5 to d-3) prior to the CAR-T infusion (d0) at a dose of 9´106 CAR+ cells/kg. The efficacy was assessed by the International Uniform Response Criteria for Multiple Myeloma, and the toxicity was graded by CTCAE 4.03.Results: As of July 6th, 2018, 17patients had been infused with this intended dose of the autologous BCMA CAR-T cells, and 14 patients had reached at least 1 month of follow-up. As of this data cut-off, the most common non-haematologicalgrade 3 adverse events were pneumonia, hypophosphatemiaand hypocalcemia(two[14%] of 14patients), and fever, cytokine release syndrome,and neurotoxicities (one[7%]of 14patients).All toxicities were fully reversible. The overall response rate (ORR) for the 14 evaluable patients was 79%, including 3 sCRs, 4 CRs and 2 MRD-negative responses (2 VGPR). The CAR-T cell expansion and persistence were consistently observed throughout these patients.The durable remission was observed for two early enrolled patients, with the ongoing objective response (1 sCR and 1 VGPR) lasting more than 15 months.Conclusions: Our result demonstrates the high potential of this single CAR-T infusion therapy for RRMM, including 3 sCRs and ongoing durable clinical responses, with only mild and manageable CRS to date. These initial data provide strong evidence to support the further development of this anti-myeloma cellular immunotherapy. DisclosuresLiu:HRAIN Biotechnology: Employment. Fang:HRAIN Biotechnology: Employment. He:HRAIN Biotechnology: Employment. Xie:HRAIN Biotechnology: Employment. Chen:HRAIN Biotechnology: Employment. Wei:HRAIN Biotechnology: Employment. Tao:HRAIN Biotechnology: Employment. Wang:Immune Design: Equity Ownership; HRAIN Biotechnology: Consultancy, Equity Ownership.

Durable clinical responses observed from non-Hodgkin lymphoma patients treated with autologous CAR-T cells targeting CD19.

3045Background: Cellular immunotherapy based on chimeric antigen receptor (CAR)-engineered T (CAR-T) cells has shown to be one of the most promising immunotherapeutic strategies for cancer treatmen...

Progress in clinical studies of chimeric antigen receptor engineered T cells for treatment of childhood cancer

Nowadays, the 5-year survival rate of childhood cancer patients can be more than 80%, but some patients with relapse and refractory cancers have shown no good response to traditional strategies. Chimeric antigen receptor engineered T (CAR-T) cell therapy is promising for these patients. CAR-T cells recognize the tumor-associated antigens in a non-major histocompatibility complex-restricted manner, so their anti-tumor ability is enhanced. There are four generations of CAR-T cells now. The complete remission rate of pediatric patients with relapse and refractory acute lymphoblastic leukemia can be as high as 90% when treated with CD19-targeting CAR-T cells. Furthermore, CAR-T cell therapy can also be used to bridge to transplantation and donor CAR-T cell infusion can be a strategy to prevent relapse after hematopoietic stem cell transplantation. As to solid tumors, only patients with neuroblastoma present good response to the GD2-targeting CAR-T cell therapy. The toxic or side effects of CAR-T cell therapy include cytokine release syndrome, off-tumor effect, tumor lysis syndrome, and insertion mutation. Although the CD19-targeting CAR-T cell therapy for childhood cancer can result in a high remission rate, the relapse rate is high, including CD19+ and CD19- relapse. The mechanisms for relapse merit further investigatio.

Masked Chimeric Antigen Receptor for Tumor-Specific Activation

Adoptive cellular therapy based on chimeric antigen receptor (CAR)-engineered T (CAR-T) cells is a powerful form of cancer immunotherapy. CAR-T cells can be redirected to specifically recognize tumor-associated antigens (TAAs) and induce high levels of antitumor activity. However, they may also display "on-target off-tumor" toxicities, resulting from low-level expression of TAAs in healthy tissues. These adverse effects have raised considerable safety concerns and limited the clinical application of this otherwise promising therapeutic modality. To minimize such side effects, we have designed an epidermal growth factor receptor (EGFR)-specific masked CAR (mCAR), which consists of a masking peptide that blocks the antigen-binding site and a protease-sensitive linker. Proteases commonly active in the tumor microenvironment can cleave the linker and disengage the masking peptide, thereby enabling CAR-T cells to recognize target antigens only at the tumor site. Invitro mCAR showed dramatically reduced antigen binding and antigen-specific activation in the absence of proteases, but normal levels of binding and activity upon treatment with certain proteases. Masked CAR-T cells also showed antitumor efficacy invivo comparable to that of unmasked CAR. Our study demonstrates the feasibility of improving the safety profile of conventional CARs and may also inspire future design of CAR molecules targeting broadly expressed TAAs.

Engineering Hematopoietic Cells for Cancer Immunotherapy: Strategies to Address Safety and Toxicity Concerns.

Advances in cancer immunotherapies utilizing engineered hematopoietic cells have recently generated significant clinical successes. Of great promise are immunotherapies based on chimeric antigen receptor-engineered T (CAR-T) cells that are targeted toward malignant cells expressing defined tumor-associated antigens. CAR-T cells harness the effector function of the adaptive arm of the immune system and redirect it against cancer cells, overcoming the major challenges of immunotherapy, such as breaking tolerance to self-antigens and beating cancer immune system-evasion mechanisms. In early clinical trials, CAR-T cell-based therapies achieved complete and durable responses in a significant proportion of patients. Despite clinical successes and given the side effect profiles of immunotherapies based on engineered cells, potential concerns with the safety and toxicity of various therapeutic modalities remain. We discuss the concerns associated with the safety and stability of the gene delivery vehicles for cell engineering and with toxicities due to off-target and on-target, off-tumor effector functions of the engineered cells. We then overview the various strategies aimed at improving the safety of and resolving toxicities associated with cell-based immunotherapies. Integrating failsafe switches based on different suicide gene therapy systems into engineered cells engenders promising strategies toward ensuring the safety of cancer immunotherapies in the clinic.