T cells expressing CD19-specific Engager Molecules for the Immunotherapy of CD19-positive Malignancies

Engineered T cells secreting anti-BCMA T cell engagers control multiple myeloma and promote immune memory in vivo

Multiple myeloma is the second most common hematological malignancy in adults and remains an incurable disease. B cell maturation antigen (BCMA)-directed immunotherapy, including T cells bearing chimeric antigen receptors (CARs) and systemically injected bispecific T cell engagers (TCEs), has shown remarkable clinical activity, and several products have received market approval. However, despite promising results, most patients eventually become refractory and relapse, highlighting the need for alternative strategies. Engineered T cells secreting TCE antibodies (STAb) represent a promising strategy that combines the advantages of adoptive cell therapies and bispecific antibodies. Here, we undertook a comprehensive preclinical study comparing the therapeutic potential of T cells either expressing second-generation anti-BCMA CARs (CAR-T) or secreting BCMAxCD3 TCEs (STAb-T) in a T cell-limiting experimental setting mimicking the conditions found in patients with relapsed/refractory multiple myeloma. STAb-T cells recruited T cell activity at extremely low effector-to-target ratios and were resistant to inhibition mediated by soluble BCMA released from the cell surface, resulting in enhanced cytotoxic responses and prevention of immune escape of multiple myeloma cells in vitro. These advantages led to robust expansion and persistence of STAb-T cells in vivo, generating long-lived memory BCMA-specific responses that could control multiple myeloma progression in xenograft models, outperforming traditional CAR-T cells. These promising preclinical results encourage clinical testing of the BCMA-STAb-T cell approach in relapsed/refractory multiple myeloma.

Challenges and solutions for therapeutic TCR-based agents

Recent development of methods to discover and engineer therapeutic T-cell receptors (TCRs) or antibody mimics of TCRs, and to understand their immunology and pharmacology, lag two decades behind therapeutic antibodies. Yet we have every expectation that TCR-based agents will be similarly important contributors to the treatment of a variety of medical conditions, especially cancers. TCR engineered cells, soluble TCRs and their derivatives, TCR-mimic antibodies, and TCR-based CAR T cells promise the possibility of highly specific drugs that can expand the scope of immunologic agents to recognize intracellular targets, including mutated proteins and undruggable transcription factors, not accessible by traditional antibodies. Hurdles exist regarding discovery, specificity, pharmacokinetics, and best modality of use that will need to be overcome before the full potential of TCR-based agents is achieved. HLA restriction may limit each agent to patient subpopulations and off-target reactivities remain important barriers to widespread development and use of these new agents. In this review we discuss the unique opportunities for these new classes of drugs, describe their unique antigenic targets, compare them to traditional antibody therapeutics and CAR T cells, and review the various obstacles that must be overcome before full application of these drugs can be realized.

Immunotherapeutic potential of blinatumomab-secreting γ9δ2 T Cells

Previous studies have explored the use of engineered blinatumomab-secreting autologous αβ T cells for CD19-targeted cancer therapy. To create a more flexible allogeneic delivery system, we utilized γ9δ2 T cells rather than αβ T cells in a similar application. First, we showed that γ9δ2 T cells could serve as effector cells for blinatumomab, and these effector memory cells could survive for at least 7 days after infusion. The genetically modified blinatumomab-secreting γ9δ2 T cells induced significant cytotoxicity in CD19⁺ tumor cell lines and primary cells from chronic lymphocytic leukemia patients. Of note, blinatumomab-secreting γ9δ2 T cells might also exhibit dual-targeting of CD19 and isopentenyl pyrophosphate, a universal tumor-associated antigen. Furthermore, blinatumomab-secreting γ9δ2 T cells killed CD19-transfected adherent cells, suggesting that the γ9δ2 T cells might be effective for treating solid tumors with appropriate cancer antigens. Together, these results demonstrate the promise of blinatumomab-secreting γ9δ2 T cells as a cancer therapy.

Development of a cGMP-compliant process to manufacture donor-derived, CD45RA-depleted memory CD19-CAR T cells

Autologous chimeric antigen receptor (CAR) T cells targeting the CD19 antigen have demonstrated a high complete response rate in relapsed/refractory B-cell malignancies. However, autologous CAR T cell therapy is not an option for all patients. Here we optimized conditions for clinical-grade manufacturing of allogeneic CD19-CAR T cells using CD45RA-depleted donor memory T cells (Tm) for a planned clinical trial. Tm were activated using the MACS GMP T Cell TransAct reagent and transduced in the presence of LentiBOOST with a clinical-grade lentiviral vector that encodes a 2nd generation CD19-CAR with a 41BB.zeta endodomain. Transduced T cells were transferred to a G-Rex cell culture device for expansion and harvested on day 7 or 8 for cryopreservation. The resulting CD19-CAR(Mem) T cells expanded on average 34.2-fold, and mean CAR expression was 45.5%. The majority of T cells were CD4+ and had a central memory or effector memory phenotype, and retained viral specificity. CD19-CAR(Mem) T cells recognized and killed CD19-positive target cells in vitro and had potent antitumor activity in an ALL xenograft model. Thus we have successfully developed a current good manufacturing practice-compliant process to manufacture donor-derived CD19-CAR(Mem) T cells. Our manufacturing process could be readily adapted for CAR(Mem) T cells targeting other antigens.

Efficient preclinical treatment of cortical T cell acute lymphoblastic leukemia with T lymphocytes secreting anti-CD1a T cell engagers

BACKGROUND

The dismal clinical outcome of relapsed/refractory (R/R) T cell acute lymphoblastic leukemia (T-ALL) highlights the need for innovative targeted therapies. Although chimeric antigen receptor (CAR)-engineered T cells have revolutionized the treatment of B cell malignancies, their clinical implementation in T-ALL is in its infancy. CD1a represents a safe target for cortical T-ALL (coT-ALL) patients, and fratricide-resistant CD1a-directed CAR T cells have been preclinically validated as an immunotherapeutic strategy for R/R coT-ALL. Nonetheless, T-ALL relapses are commonly very aggressive and hyperleukocytic, posing a challenge to recover sufficient non-leukemic effector T cells from leukapheresis in R/R T-ALL patients.

METHODS

We carried out a comprehensive study using robust in vitro and in vivo assays comparing the efficacy of engineered T cells either expressing a second-generation CD1a-CAR or secreting CD1a x CD3 T cell-engaging Antibodies (CD1a-STAb).

RESULTS

We show that CD1a-T cell engagers bind to cell surface expressed CD1a and CD3 and induce specific T cell activation. Recruitment of bystander T cells endows CD1a-STAbs with an enhanced in vitro cytotoxicity than CD1a-CAR T cells at lower effector:target ratios. CD1a-STAb T cells are as effective as CD1a-CAR T cells in cutting-edge in vivo T-ALL patient-derived xenograft models.

CONCLUSIONS

Our data suggest that CD1a-STAb T cells could be an alternative to CD1a-CAR T cells in coT-ALL patients with aggressive and hyperleukocytic relapses with limited numbers of non-leukemic effector T cells.

Engineering naturally occurring CD7- T cells for the immunotherapy of hematological malignancies

Chimeric antigen receptor (CAR) T-cell therapy targeting T-cell acute lymphoblastic leukemia (T-ALL) faces limitations such as antigen selection and limited T-cell persistence. CD7 is an attractive antigen for targeting T-ALL, but overlapping expression on healthy T cells leads to fratricide of CD7-CAR T cells, requiring additional genetic modification. We took advantage of naturally occurring CD7- T cells to generate CD7-CAR (CD7-CARCD7-) T cells. CD7-CARCD7- T cells exhibited a predominantly CD4+ memory phenotype and had significant antitumor activity upon chronic antigen exposure in vitro and in xenograft mouse models. Based on these encouraging results, we next explored the utility of CD7- T cells for the immunotherapy of CD19+ hematological malignancies. Direct comparison of nonselected (bulk) CD19-CAR and CD19-CARCD7- T cells revealed that CD19-CARCD7- T cells had enhanced antitumor activity compared with their bulk counterparts in vitro and in vivo. Lastly, to gain insight into the behavior of CD19-CAR T cells with low levels of CD7 gene expression (CD7lo) in humans, we mined single-cell gene and T-cell receptor (TCR) expression data sets from our institutional CD19-CAR T-cell clinical study. CD19-CARCD7lo T cells were present in the initial CD19-CAR T-cell product and could be detected postinfusion. Intriguingly, the only functional CD4+ CD19-CAR T-cell cluster observed postinfusion exhibited CD7lo expression. Additionally, samples from patients responsive to therapy had a higher proportion of CD7lo T cells than nonresponders (NCT03573700). Thus, CARCD7- T cells have favorable biological characteristics and may present a promising T-cell subset for adoptive cell therapy of T-ALL and other hematological malignancies.

Transgenic Expression of IL15 Retains CD123-Redirected T Cells in a Less Differentiated State Resulting in Improved Anti-AML Activity in Autologous AML PDX Models

Immunotherapy with T-cells expressing bispecific T-cell engagers (ENG T-cells) is a promising approach to improve the outcomes for patients with recurrent/refractory acute myeloid leukemia (AML). However, similar to T-cells expressing chimeric antigen receptors (CARs), their antitumor activity is limited in the setting of chronic antigen stimulation. We therefore set out to explore whether transgenic expression of IL15 improves the effector function of ENG T-cells targeting CD123-positive AML. T-cells expressing CD123-specific ENG (CD123-ENG) ± IL15 were generated by retroviral transduction from peripheral blood T cells from healthy donors or patients with AML. In this study, we characterized in detail the phenotype and effector functions of ENG T-cell populations in vitro and in vivo. IL15-expressing CD123-ENG (CD123-ENG.IL15) T-cells retained their antigen-specificity and effector function in the setting of chronic antigen exposure for more 30 days of coculture with AML blasts in contrast to CD123-ENG T-cells, whose effector function rapidly eroded. Furthermore, CD123-ENG.IL15 T-cells remained in a less differentiated state as judged by a high frequency of naïve/memory stem T-cell-like cells (CD45RA+CCR7+/CD45RO−CD62L+ cells) without evidence of T-cell exhaustion. Single cell cytokine profiling using IsoPlexis revealed enhanced T-cell polyfunctionality of CD123-ENG.IL15 T-cells as judged by effector cytokine production, including, granzyme B, IFN-γ, MIP-1α, perforin, TNF-α, and TNF-β. In vivo, CD123-ENG.IL15 T-cells exhibited superior antigen-specific anti-AML activity and T-cell persistence in both peripheral blood and tissues (BM, spleens, and livers), resulting in a significant survival advantage in one AML xenograft model and two autologous AML PDX models. In conclusion, we demonstrate here that the expansion, persistence, and anti-AML activity of CD123-ENG T-cells can be significantly improved by transgenic expression of IL15, which promotes a naïve/TSCM-like phenotype. However, we also highlight that targeting a single tumor antigen (CD123) can lead to immune escape, reinforcing the need to develop approaches to target multiple antigens. Likewise, our study demonstrates that it is feasible to evaluate autologous T cells in AML PDX models, which will be critical for future preclinical evaluations of next generation AML-redirected T-cell therapies.

Overcoming CAR-Mediated CD19 Downmodulation and Leukemia Relapse with T Lymphocytes Secreting Anti-CD19 T-cell Engagers

Chimeric antigen receptor (CAR)-modified T cells have revolutionized the treatment of CD19-positive hematologic malignancies. Although anti-CD19 CAR-engineered autologous T cells can induce remission in patients with B-cell acute lymphoblastic leukemia, a large subset relapse, most of them with CD19-positive disease. Therefore, new therapeutic strategies are clearly needed. Here, we report a comprehensive study comparing engineered T cells either expressing a second-generation anti-CD19 CAR (CAR-T19) or secreting a CD19/CD3-targeting bispecific T-cell engager antibody (STAb-T19). We found that STAb-T19 cells are more effective than CAR-T19 cells at inducing cytotoxicity, avoiding leukemia escape in vitro, and preventing relapse in vivo. We observed that leukemia escape in vitro is associated with rapid and drastic CAR-induced internalization of CD19 that is coupled with lysosome-mediated degradation, leading to the emergence of transiently CD19-negative leukemic cells that evade the immune response of engineered CAR-T19 cells. In contrast, engineered STAb-T19 cells induce the formation of canonical immunologic synapses and prevent the CD19 downmodulation observed in anti-CD19 CAR-mediated interactions. Although both strategies show similar efficacy in short-term mouse models, there is a significant difference in a long-term patient-derived xenograft mouse model, where STAb-T19 cells efficiently eradicated leukemia cells, but leukemia relapsed after CAR-T19 therapy. Our findings suggest that the absence of CD19 downmodulation in the STAb-T19 strategy, coupled with the continued antibody secretion, allows an efficient recruitment of the endogenous T-cell pool, resulting in fast and effective elimination of cancer cells that may prevent CD19-positive relapses frequently associated with CAR-T19 therapies.

Synapse topology and downmodulation events determine the functional outcome of anti-CD19 T cell-redirecting strategies

Cancer immunotherapy strategies based on the endogenous secretion of T cell-redirecting bispecific antibodies by engineered T lymphocytes (STAb-T) are emerging as alternative or complementary approaches to those based on chimeric antigen receptors (CAR-T). The antitumor efficacy of bispecific anti-CD19 × anti-CD3 (CD19×CD3) T cell engager (BiTE)-secreting STAb-T cells has been demonstrated in several mouse models of B-cell acute leukemia. Here, we have investigated the spatial topology and downstream signaling of the artificial immunological synapses (IS) that are formed by CAR-T or STAb-T cells. Upon interaction with CD19-positive target cells, STAb-T cells form IS with structure and signal transduction, which more closely resemble those of physiological cognate IS, compared to IS formed by CAR-T cells expressing a second-generation CAR bearing the same CD19-single-chain variable fragment. Importantly, while CD3 is maintained at detectable levels on the surface of STAb-T cells, indicating sustained activation mediated by the secreted BiTE, the anti-CD19 CAR was rapidly downmodulated, which correlated with a more transient downstream signaling. Furthermore, CAR-T cells, but not STAb-T cells, provoke an acute loss of CD19 in target cells. Such differences might represent advantages of the STAb-T strategy over the CAR-T approach and should be carefully considered in order to develop more effective and safer treatments for hematological malignancies.

Antitumor activity of T cells secreting αCD133-αCD3 bispecific T-cell engager against cholangiocarcinoma

Cholangiocarcinoma (CCA) is a lethal cancer of bile duct epithelial cells with a high mortality rate and limited therapeutic options. An effective treatment is, therefore, urgently needed to improve treatment outcomes for these patients. To develop a new therapeutic option, we engineered T cells secreting αCD133-αCD3 bispecific T-cell engager and evaluated their antitumor effects against CD133-expressing CCA cells. The cDNA encoding αCD133-αCD3 bispecific T-cell engager (αCD133-αCD3-ENG) was cloned into pCDH lentiviral construct and its expression was tested in Lenti-X 293T cells. T cells from healthy donors were then transduced with engineered lentiviruses to create T cells secreting αCD133-αCD3 engager to evaluate their antitumor activities. The average transduction efficiency into T cells was approximately 60.03±21.65%. In the co-culture system containing T cells secreting αCD133-αCD3 engager (as effector cells) and mWasabi-luciferase-expressing CCA cells (KKU-100 and KKU-213A; as target cells), the effector T cells exhibited significantly higher cytolytic activities against the target CCA cells (49.0±9.76% and 64.10±13.18%, respectively) than those observed against the untransduced T cells (10.97±10.65%; p = 0.0103 and 9.80±11.05%; p = 0.0054) at an effector-to-target ratio of 5:1. In addition, the secreted αCD133-αCD3 engager significantly redirected both transduced T cells and bystander T cells to kill the target CCA cells (up to 73.20±1.68%; p<0.05). Moreover, the transduced and bystander T cells could kill the target CCA spheroids at a rate approximately 5-fold higher than that of the no treatment control condition (p = 0.0011). Our findings demonstrate proof-of-principle that T cells secreting αCD133-αCD3 engager can be an alternative approach to treating CD133-positive CCA, and they pave the way for future in vivo study and clinical trials.

Deleting DNMT3A in CAR T cells prevents exhaustion and enhances antitumor activity

Chimeric antigen receptor (CAR) T cell therapy is revolutionizing cancer immunotherapy for patients with B cell malignancies and is now being developed for solid tumors and chronic viral infections. Although clinical trials have demonstrated the curative potential of CAR T cell therapy, a substantial and well-established limitation is the heightened contraction and transient persistence of CAR T cells during prolonged antigen exposure. The underlying mechanism(s) for this dysfunctional state, often termed CAR T cell exhaustion, remains poorly defined. Here, we report that exhaustion of human CAR T cells occurs through an epigenetic repression of the T cell’s multipotent developmental potential. Deletion of the de novo DNA methyltransferase 3 alpha (DNMT3A) in T cells expressing first- or second-generation CARs universally preserved the cells’ ability to proliferate and mount an antitumor response during prolonged tumor exposure. The increased functionality of the exhaustion-resistant DNMT3A knockout CAR T cells was coupled to an up-regulation of interleukin-10, and genome-wide DNA methylation profiling defined an atlas of genes targeted for epigenetic silencing. This atlas provides a molecular definition of CAR T cell exhaustion, which includes many transcriptional regulators that limit the “stemness” of immune cells, including CD28, CCR7, TCF7, and LEF1. Last, we demonstrate that this epigenetically regulated multipotency program is firmly coupled to the clinical outcome of prior CAR T cell therapies. These data document the critical role epigenetic mechanisms play in limiting the fate potential of human T cells and provide a road map for leveraging this information for improving CAR T cell efficacy.

Engineered mRNA and the Rise of Next-Generation Antibodies

Monoclonal antibodies are widely used as therapeutic agents in medicine. However, clinical-grade proteins require sophisticated technologies and are extremely expensive to produce, resulting in long lead times and high costs. The use of gene transfer methods for in vivo secretion of therapeutic antibodies could circumvent problems related to large-scale production and purification and offer additional benefits by achieving sustained concentrations of therapeutic antibodies, which is particularly relevant to short-lived antibody fragments and next-generation, Fc-free, multispecific antibodies. In recent years, the use of engineered mRNA-based gene delivery has significantly increased in different therapeutic areas because of the advantages it possesses over traditional gene delivery platforms. The application of synthetic mRNA will allow for the avoidance of manufacturing problems associated with recombinant proteins and could be instrumental in consolidating regulatory approvals for next-generation therapeutic antibodies.

Potent ex vivo armed T cells using recombinant bispecific antibodies for adoptive immunotherapy with reduced cytokine release

BACKGROUND

T cell-based immunotherapies using chimeric antigen receptors (CAR) or bispecific antibodies (BsAb) have produced impressive responses in hematological malignancies. However, major hurdles remained, including cytokine release syndrome, neurotoxicity, on-target off-tumor effects, reliance on autologous T cells, and failure in most solid tumors. BsAb armed T cells offer a safe alternative.

METHODS

We generated ex vivo armed T cells (EATs) using IgG-[L]-scFv-platformed BsAb, where the anti-CD3 (huOKT3) scFv was attached to the light chain of a tumor-binding IgG. BsAb density on EAT, in vitro cytotoxicity, cytokine release, in vivo trafficking into tumors, and their antitumor activities were evaluated in multiple cancer cell lines and patient-derived xenograft mouse models. The efficacy of EATs after cryopreservation was studied, and gamma delta (γδ) T cells were investigated as unrelated alternative effector T cells.

RESULTS

The antitumor potency of BsAb armed T cells was substantially improved using the IgG-[L]-scFv BsAb platform. When compared with separate BsAb and T cell injection, EATs released less TNF-α, and infiltrated tumors faster, while achieving robust antitumor responses. The in vivo potency of EAT therapy depended on BsAb dose for arming, EAT cell number per injection, total number of EAT doses, and treatment schedule intensity. The antitumor efficacy of EATs was preserved following cryopreservation, and EATs using γδ T cells were safe and as effective as αβ T cell-EATs.

CONCLUSIONS

EATs exerted potent antitumor activities against a broad spectrum of human cancer targets with remarkable safety. The antitumor potency of EATs depended on BsAb dose, cell number and total dose, and schedule. EATs were equally effective after cryopreservation, and the feasibility of third-party γδ-EATs offered an alternative for autologous T cell sources.

CD19 Chimeric Antigen Receptor-Exosome Targets CD19 Positive B-lineage Acute Lymphocytic Leukemia and Induces Cytotoxicity

CAR-T cell therapy is not without some clinical adverse effects, namely cytokine storms, due to a massive release of cytokines when CAR-T cells multiply in the body. Our goal was to develop exosomes expressing CD19 CAR to treat CD19-positive B-cell malignancies, instead of using whole CD19 CAR-T cells, thereby reducing the clinical risk of uncontrolled cytokine storms. Exosomes are extracellular nanovesicles (30-150 nm), composed of lipids, proteins, and nucleic acids, that carry the fingerprint of their parent cells. Exosomes are a preferred delivery system in nano-immunotherapy. Here, HEK293T parent cells were transduced with CD19 CAR plasmids and cellular CD19 CAR expression was confirmed. Exosomes (Exo-CD19 CAR) were isolated from the conditioned medium of non-transduced (WT) and CD19 CAR plasmid transduced HEK293T cells. Consequently, CD19 B-lineage leukemia cell lines were co-cultured with Exo-CD19 CAR and cell death was measured. Our data show that Exo-CD19 CAR treatment induced cytotoxicity and elevated pro-apoptotic genes in CD19-positive leukemia B-cells without inducing cell death in CD19-negative cells. Overall, the novel CD19 CAR exosomes target the CD19 surface antigens of leukemic B-cells and can induce contact-dependent cytotoxicity.

MyD88/CD40 signaling retains CAR T cells in a less differentiated state

Chimeric antigen receptor (CAR) T cell therapy for solid tumors has shown limited efficacy in early-phase clinical studies. The majority of CARs encode CD28 and/or 41BB costimulatory endodomains, and we explored whether MyD88 and CD40 (MC) costimulatory endodomains in CARs could improve their antitumor activity. We generated CD28-, 41BB-, and MC-CAR T cells and demonstrated that MC-CAR T cells have greater proliferative capacity and antitumor activity in repeat stimulation assays and in tumor models in vivo. Transcriptomic analysis revealed that MC-CAR T cells expressed higher levels of MYB and FOXM1, key cell cycle regulators, and were activated at baseline. After stimulation, MC-CAR T cells remained in a less differentiated state than CD28- and 41BB-CAR T cells as judged by low levels of transcription factor TBET and B lymphocyte induced maturation protein 1 expression and lower cytolytic activity in comparison with CD28- and 41BB-CAR T cells. Thus, including MyD88 and CD40 signaling domains in CARs may improve current CAR T cell therapy approaches for solid tumors.

Human macrophages engineered to secrete a bispecific T cell engager support antigen-dependent T cell responses to glioblastoma

BACKGROUND

Targeted and effective treatment options are needed for solid tumors, including glioblastoma (GBM), where survival rates with standard treatments are typically less than 2 years from diagnosis. Solid tumors pose many barriers to immunotherapies, including therapy half-life and persistence, tumor penetrance, and targeting. Therapeutics delivered systemically may not traffic to the tumor site. If cellular therapies or drugs are able to access the tumor site, or can be delivered directly within the tumor, treatments may not persist for the duration necessary to reduce or eliminate tumor burden. An approach that allows durable and titratable local therapeutic protein delivery could improve antitumor efficacy while minimizing toxicities or unwanted on-target, off-tissue effects.

METHODS

In this study, human monocyte-derived macrophages were genetically engineered to secrete a bispecific T cell engager (BiTE) specific to the mutated epidermal growth factor variant III (EGFRvIII) expressed by some GBM tumors. We investigated the ability of lentivirally modified macrophages to secrete a functional BiTE that can bind target tumor antigen and activate T cells. Secreted BiTE protein was assayed in a range of T cell functional assays in vitro and in subcutaneous and intracranial GBM xenograft models. Finally, we tested genetically engineered macrophages (GEMs) secreting BiTE and the proinflammatory cytokine interleukin (IL)-12 to amplify T cell responses in vitro and in vivo.

RESULTS

Transduced human macrophages secreted a lentivirally encoded functional EGFRvIII-targeted BiTE protein capable of inducing T cell activation, proliferation, degranulation, and killing of antigen-specific tumor cells. Furthermore, BiTE secreting macrophages reduced early tumor burden in both subcutaneous and intracranial mouse models of GBM, a response which was enhanced using macrophages that were dual transduced to secrete both the BiTE protein and single chain IL-12, preventing tumor growth in an aggressive GBM model.

CONCLUSIONS

The ability of macrophages to infiltrate and persist in solid tumor tissue could overcome many of the obstacles associated with systemic delivery of immunotherapies. We have found that human GEMs can locally and constitutively express one or more therapeutic proteins, which may help recruit T cells and transform the immunosuppressive tumor microenvironment to better support antitumor immunity.

Engineering Immune Cells for in vivo Secretion of Tumor-Specific T Cell-Redirecting Bispecific Antibodies

Immunotherapeutic approaches based on the redirection of T cell activity toward tumor cells are actively being investigated. The impressive clinical success of the continuously intravenously infused T cell-redirecting bispecific antibody (T-bsAb) blinatumomab (anti-CD19 x anti-CD3), and of engineered T cells expressing anti-CD19 chimeric antigen receptors (CAR-T cells) in hematological malignancies, has led to renewed interest in a novel cancer immunotherapy strategy that combines features of antibody- and cell-based therapies. This emerging approach is based on the endogenous secretion of T-bsAbs by engineered T cells (STAb-T cells). Adoptive transfer of genetically modified STAb-T cells has demonstrated potent anti-tumor activity in both solid tumor and hematologic preclinical xenograft models. We review here the potential benefits of the STAb-T strategy over similar approaches currently being used in clinic, and we discuss the potential combination of this promising strategy with the well-established CAR-T cell approach.

Innovative strategies to advance CAR T cell therapy for solid tumors

Current cancer treatment strategies have been advanced by chimeric antigen receptor (CAR) cell therapy, a rapidly emerging cellular immunotherapy. The numerous revolutionary achievements of CAR T cells against hematological malignancies initiated an upsurge in research on translating this therapy into a treatment for solid tumors. Unfortunately, no equivalent success has yet been achieved in treating solid tumors. The main challenges posed by solid tumors have gradually been recognized and include a lack of unique antigen targets, antigen heterogeneity, limited infiltration into the tumor, and an immunosuppressive tumor microenvironment. Surmounting the limitations of solid tumors remains critical in popularizing CAR T cell applications. Various approaches to augmenting the efficiency of CAR T cells through directly optimizing CAR constructs or through innovative combination strategies such as vaccines, biomaterials, and oncolytic virus have arisen. In addition to describing the main obstacles that restrict the promotion of CAR T cells, this paper focuses on reviewing new ongoing strategies to circumvent these limitations.

The Advent of CAR T-Cell Therapy for Lymphoproliferative Neoplasms: Integrating Research Into Clinical Practice

Research on CAR T cells has achieved enormous progress in recent years. After the impressive results obtained in relapsed and refractory B-cell acute lymphoblastic leukemia and aggressive B-cell lymphomas, two constructs, tisagenlecleucel and axicabtagene ciloleucel, were approved by FDA. The role of CAR T cells in the treatment of B-cell disorders, however, is rapidly evolving. Ongoing clinical trials aim at comparing CAR T cells with standard treatment options and at evaluating their efficacy earlier in the disease course. The use of CAR T cells is still limited by the risk of relevant toxicities, most commonly cytokine release syndrome and neurotoxicity, whose management has nonetheless significantly improved. Some patients do not respond or relapse after treatment, either because of poor CAR T-cell expansion, lack of anti-tumor effects or after the loss of the target antigen on tumor cells. Investigators are trying to overcome these hurdles in many ways: by testing constructs which target different and/or multiple antigens or by improving CAR T-cell structure with additional functions and synergistic molecules. Alternative cell sources including allogeneic products (off-the-shelf CAR T cells), NK cells, and T cells obtained from induced pluripotent stem cells are also considered. Several trials are exploring the curative potential of CAR T cells in other malignancies, and recent data on multiple myeloma and chronic lymphocytic leukemia are encouraging. Given the likely expansion of CAR T-cell indications and their wider availability over time, more and more highly specialized clinical centers, with dedicated clinical units, will be required. Overall, the costs of these cell therapies will also play a role in the sustainability of many health care systems. This review will focus on the major clinical trials of CAR T cells in B-cell malignancies, including those leading to the first FDA approvals, and on the new settings in which these constructs are being tested. Besides, the most promising approaches to improve CAR T-cell efficacy and early data on alternative cell sources will be reviewed. Finally, we will discuss the challenges and the opportunities that are emerging with the advent of CAR T cells into clinical routine.

Challenges and strategies for next-generation bispecific antibody-based antitumor therapeutics

Bispecific antibodies (bsAbs) refer to a large family of molecules that recognize two different epitopes or antigens. Although a series of challenges, especially immunogenicity and chain mispairing issues, once hindered the development of bsAbs, they have been gradually overcome with the help of rapidly developing technologies in the past 5 decades. In the meantime, an increasing number of bsAb platforms have been designed to satisfy different clinical demands. Currently, numerous preclinical and clinical trials are underway, portraying a promising future for bsAb-based cancer treatment. Nevertheless, bsAb drugs still face enormous challenges in their application as cancer therapeutics, including tumor heterogeneity and mutational burden, intractable tumor microenvironment (TME), insufficient costimulatory signals to activate T cells, the necessity for continuous injection, fatal systemic side effects, and off-target toxicities to adjacent normal cells. Therefore, we provide several strategies as solutions to these issues, which comprise generating multispecific bsAbs, discovering neoantigens, combining bsAbs with other anticancer therapies, exploiting natural killer (NK)-cell-based bsAbs and producing bsAbs in situ. In this review, we mainly discuss previous and current challenges in bsAb development and underscore corresponding strategies, with a brief introduction of several typical bsAb formats.

The Emerging Landscape of Immune Cell Therapies

Cell therapies present an entirely new paradigm in drug development. Within this class, immune cell therapies are among the most advanced, having already demonstrated definitive evidence of clinical benefits in cancer and infectious disease. Numerous features distinguish these "living therapies" from traditional medicines, including their ability to expand and contract in proportion to need and to mediate therapeutic benefits for months or years following a single application. Continued advances in fundamental immunology, genetic engineering, gene editing, and synthetic biology exponentially expand opportunities to enhance the sophistication of immune cell therapies, increasing potency and safety and broadening their potential for treatment of disease. This perspective will summarize the current status of immune cell therapies for cancer, infectious disease, and autoimmunity, and discuss advances in cellular engineering to overcome barriers to progress.

Oncolytic Adenovirus Armed with BiTE, Cytokine, and Checkpoint Inhibitor Enables CAR T Cells to Control the Growth of Heterogeneous Tumors

No single cancer immunotherapy will likely defeat all evasion mechanisms of solid tumors, including plasticity of tumor antigen expression and active immune suppression by the tumor environment. In this study, we increase the breadth, potency, and duration of anti-tumor activity of chimeric antigen receptor (CAR) T cells using an oncolytic virus (OV) that produces cytokine, checkpoint blockade, and a bispecific tumor-targeted T cell engager (BiTE) molecule. First, we constructed a BiTE molecule specific for CD44 variant 6 (CD44v6), since CD44v6 is widely expressed on tumor but not normal tissue, and a CD44v6 antibody has been safely administered to cancer patients. We then incorporated this BiTE sequence into an oncolytic-helper binary adenovirus (CAdDuo) encoding an immunostimulatory cytokine (interleukin [IL]-12) and an immune checkpoint blocker (PD-L1Ab) to form CAdTrio. CD44v6 BiTE from CAdTrio enabled HER2-specific CAR T cells to kill multiple CD44v6⁺ cancer cell lines and to produce more rapid and sustained disease control of orthotopic HER2⁺ and HER2^-/- CD44v6⁺ tumors than any component alone. Thus, the combination of CAdTrio with HER2.CAR T cells ensures dual targeting of two tumor antigens by engagement of distinct classes of receptor (CAR and native T cell receptor [TCR]), and significantly improves tumor control and survival.

Cytotoxic CD8+ Lymphocytes in the Tumor Microenvironment

In the tumor microenvironment, CD8⁺ T cells play a major role in tumor immunity. CD8⁺ T cells differentiate to cytotoxic T cells, traffic into the tumor microenvironment, and exhibit cytotoxicity against tumor cells. These processes have both positive and negative effects. Enhancements in the cytotoxic activity of tumor antigen-specific cytotoxic T cells in the tumor microenvironment are crucial for the development of cancer immunotherapy. To achieve this, several immunotherapies, including cancer vaccines, T cells engineered to express chimeric antigen receptors (CAR T cells), and bispecific T-cell engagers (BiTEs), have been developed. In contrast to cancer vaccines, CAR T cells, and BiTEs, immune checkpoint inhibitors enhance the activity of cytotoxic T cells by inhibiting the negative regulators of T cells.The total number, type, and activity of tumor antigen-specific cytotoxic T cells in the tumor microenvironment need to be clarified, particularly for the development of companion diagnostics to identify patients for whom these therapies are effective. Therefore, technologies including TCR repertoire, single-cell, and T-cell cytotoxicity analyses using BiTEs have been developed.Based on these and future innovations, the generation of effective cancer immunotherapies is anticipated.

Genetically Modified T-Cell Therapy for Osteosarcoma: Into the Roaring 2020s

T-cell immunotherapy may offer an approach to improve outcomes for patients with osteosarcoma who fail current therapies. In addition, it has the potential to reduce treatment-related complications for all patients. Generating tumor-specific T cells with conventional antigen-presenting cells ex vivo is time-consuming and often results in T-cell products with a low frequency of tumor-specific T cells. Furthermore, the generated T cells remain sensitive to the immunosuppressive tumor microenvironment. Genetic modification of T cells is one strategy to overcome these limitations. For example, T cells can be genetically modified to render them antigen specific, resistant to inhibitory factors, or increase their ability to home to tumor sites. Most genetic modification strategies have only been evaluated in preclinical models; however, early clinical phase trials are in progress. In this chapter, we will review the current status of gene-modified T-cell therapy with special focus on osteosarcoma, highlighting potential antigenic targets, preclinical and clinical studies, and strategies to improve current T-cell therapy approaches.

[PD-1 expression, mRNA level and cytotoxicity changes in CD19CAR-T cells]

目的

探讨CD19 CAR-T细胞培养过程中其PD-1蛋白、mRNA水平及细胞杀伤活性变化。

方法

收集6例外周血PD-1高表达恶性淋巴瘤患者、6例健康志愿者的外周血T细胞，作为CAR-T培养的T细胞来源。流式细胞术检测PD-1蛋白表达、PCR法检测PD-1 mRNA水平，CCK-8法检测细胞增殖，LDH法检测细胞杀伤活性。

结果

①PD-1高表达患者T细胞来源CD19 CAR-T细胞，与志愿者T细胞来源者相比，转染率无差异（P>0.05）；②PD-1高表达T细胞来源CAR-T细胞与PD-1抑制剂联合与否，以及健康志愿者CAR-T之间，细胞增殖差异无统计学意义（P>0.05）；③PD-1高表达T细胞与CAR-T细胞对淋巴瘤细胞株杀伤活性，低于二者联合PD-1抑制剂及志愿者CAR-T细胞（P<0.001），而PD-1高表达T细胞来源CAR-T细胞联合PD-1抑制剂与健康志愿者CAR-T细胞间差异无统计学意义（P>0.05）；④各组细胞培养过程中PD-1表达均下降，差异无统计学意义（P>0.05），但各组细胞培养过程中，PD-1 mRNA的变化差异无统计学意义（P>0.05）；⑤PD-1高表达T细胞来源CAR-T收获后，与PD-1抑制剂共培养与否，其PD-1表达差异无统计学意义（P>0.05），但CAR-T与淋巴瘤细胞株接触后，其PD-1表达随培养时间延长而增高，加入PD-1抑制剂可拮抗该作用；各组间PD-1 mRNA的变化差异无统计学意义（P>0.05）。

结论

PD-1高表达T细胞来源CAR-T细胞与肿瘤细胞接触后，其PD-1表达随培养时间延长而增高；而包括PD-1抑制剂在内，不能改变其PD-1 mRNA的表达。

Current Perspectives in Cancer Immunotherapy

Different immunotherapeutic approaches have proved to be of significant clinical value to many patients with different types of advanced cancer. However, we need more precise immunotherapies and predictive biomarkers to increase the successful response rates. The advent of next generation sequencing technologies and their applications in immuno-oncology has helped us tremendously towards this aim. We are now moving towards the realization of personalized medicine, thus, significantly increasing our expectations for a more successful management of the disease. Here, we discuss the current immunotherapeutic approaches against cancer, including immune checkpoint blockade with an emphasis on anti-PD-L1 and anti-CTLA-4 monoclonal antibodies. We also analyze a growing list of other co-inhibitory and co-stimulatory markers and emphasize the mechanism of action of the principal pathway for each of these, as well as on drugs that either have been FDA-approved or are under clinical investigation. We further discuss recent advances in other immunotherapies, including cytokine therapy, adoptive cell transfer therapy and therapeutic vaccines. We finally discuss the modulation of gut microbiota composition and response to immunotherapy, as well as how tumor-intrinsic factors and immunological processes influence the mutational and epigenetic landscape of progressing tumors and response to immunotherapy but also how immunotherapeutic intervention influences the landscape of cancer neoepitopes and tumor immunoediting.

T-cell Activity against AML Improved by Dual-Targeted T Cells Stimulated through T-cell and IL7 Receptors

The development of engineered T cells to treat acute myeloid leukemia (AML) is challenging due to difficulty in target selection and the need for robust T-cell expansion and persistence. We designed a T cell stimulated to kill AML cells based on recognition of the AML-associated surface marker CLEC12A, via secretion of a CLEC12AxCD3 bispecific "engager" molecule (CLEC12A-ENG). CLEC12A-ENG T cells are specifically activated by CLEC12A, are not toxic to hematopoietic progenitor cells, and exhibit antigen-dependent AML killing. Next, we coupled stimulation of T-cell survival to triggering of a chimeric IL7 receptor with an ectodomain that binds a second AML-associated surface antigen, CD123. The resulting T cells, identified as CLEC12A-ENG.CD123IL7Rα T cells, demonstrate improved activation upon dual target recognition, kill AML, and exhibit antitumor activity in xenograft models. Enhanced T-cell activation conferred by CD123.IL7Rα was dependent both on recognition of the CD123 target and on IL7Rα-mediated downstream signaling. Expression of a chimeric IL7R targeted to a second tumor-associated antigen (TAA) should improve T-cell activity not only against hematologic malignancies, but perhaps against all cancers.

Current and future role of bispecific T-cell engagers in pediatric acute lymphoblastic leukemia

INTRODUCTION

The clinical application of immunotherapy has resulted into a significant improvement in the outcome of children with relapsed/refractory B-cell precursor acute lymphoblastic leukemia (r/r BCP-ALL). In this setting, the use of bispecific T-cell-engager antibodies (BiTEs), such as blinatumomab, which harness the cytotoxic activity of T cells against CD19-positive lymphoblasts, has emerged as a most promising and impactful strategy. Areas covered: This review discusses the main structural and functional features of BiTEs, as well as the current status of their clinical application in childhood ALL. Moreover, future prospects to increase the efficacy of BiTEs are addressed. Expert commentary: The promising results obtained in patients with advanced BCP-ALL pave the way for further improvement in the context of less resistant/advanced disease. Future research is rapidly progressing on several aspects, including the use of blinatumomab in first-line protocols, identification of factors predicting response, use of combinatorial approaches and bioengineering of new molecules with dual specificity or increased potency, stability and half-life. The results of these studies, expected to be available in the next future, will provide further advancement in the development of effective, impactful, targeted immunotherapy for treatment of childhood BCP-ALL, with the concrete potential to revolutionize the clinical practice.

Bispecific light T-cell engagers for gene-based immunotherapy of epidermal growth factor receptor (EGFR)-positive malignancies

The recruitment of T-cells by bispecific antibodies secreted from adoptively transferred, gene-modified autologous cells has shown satisfactory results in preclinical cancer models. Even so, the approach's translation into the clinic will require incremental improvements to its efficacy and reduction of its toxicity. Here, we characterized a tandem T-cell recruiting bispecific antibody intended to benefit gene-based immunotherapy approaches, which we call the light T-cell engager (LiTE), consisting of an EGFR-specific single-domain VHH antibody fused to a CD3-specific scFv. We generated two LiTEs with the anti-EGFR VHH and the anti-CD3 scFv arranged in both possible orders. Both constructs were well expressed in mammalian cells as highly homogenous monomers in solution with molecular weights of 43 and 41 kDa, respectively. In situ secreted LiTEs bound the cognate antigens of both parental antibodies and triggered the specific cytolysis of EGFR-expressing cancer cells without inducing T-cell activation and cytotoxicity spontaneously or against EGFR-negative cells. Light T-cell engagers are, therefore, suitable for future applications in gene-based immunotherapy approaches.

Bispecific antibodies in haematological malignancies

Bispecific antibodies (bsAbs) combine the binding sites of two monoclonal antibodies in one molecule. The close proximity of a tumor specific antigen and an effector cell antigen results in a targeted activation of effector cells. The mechanism is similar to the chimeric antigen receptor (CAR) T-cells, recently approved in two haematologic cancers. CAR T-cells and bsAb represent the most powerful tools for major-histocompatibility complex (MHC) independent T-cell immune response against cancer. In contrast to CAR T-cells, bsAbs are "off the shelf" drugs. As a drawback, the efficacy is dependent on a prolonged application. More than 40 years of intensive research generate a plethora of bispecific constructs with a remarkable difference in manufacturability, stability, half-life time and receptor affinity. Blinatumomab was the first approved bsAb in relapsed and refractory acute lymphoblastic leukemia. By the mature experience of blinatumomab in more than 10 clinical trials over more than one decade, we learned some lessons on how to use this new principle. The efficacy is higher in patients with less tumor burden, suggesting the use as consolidation more than for initial debulking. Main resistance mechanisms are extramedullary relapses and the expression of the inhibitory PD-L1 molecule, suggesting the value of combination with checkpoint inhibitors. CD19 loss is infrequent after blinatumomab, preserving the option for alternative CD19-direct treatments. New bsAbs in lymphoma, myeloma and acute myeloid leukemia enter phase-I trials, together with many new constructs in solid cancer.

Redirecting T cells to hematological malignancies with bispecific antibodies

There is a need to improve outcomes for patients with recurrent and/or refractory hematological malignancies. Immunotherapy holds the promise to meet this need, because it does not rely on the cytotoxic mechanism of conventional therapies. Among different forms of immunotherapy, redirecting T cells to hematological malignancies with bispecific antibodies (BsAbs) is an attractive strategy. BsAbs are an "off-the-shelf" product that is easily scalable in contrast to adoptive T-cell therapies. Among these, the bispecific T-cell engager blinatumomab has emerged as the most successful BsAb to date. It consists of 2 single-chain variable fragments specific for CD19 present on B-cell malignancies and CD3 expressed on almost all T cells. Blinatumomab has shown potent antitumor activity as a single agent, particularly for acute lymphoblastic leukemia, resulting in its US Food and Drug Administration approval. However, although successful in inducing remissions, these are normally short-lived, with median response durations of <1 year. Nevertheless, the success of blinatumomab has reinvigorated the BsAb field, which is bustling with preclinical and clinical studies for not only B-cell-derived lymphoblastic leukemia and lymphoma but also acute myeloid leukemia and multiple myeloma. Here, we will review the successes and challenges of T-cell-targeted BsAbs for the immunotherapy of hematological malignancies with special focus on conducted clinical studies and strategies to improve their efficacy.

CD28 and 41BB Costimulation Enhances the Effector Function of CD19-Specific Engager T Cells

T cells expressing CD19-specific chimeric antigen receptors (CARs) with endodomains that encode a signaling domain derived from CD3ζ and CD28 or 41BB have potent antitumor activity in early-phase clinical studies for B-cell malignancies. Besides CD19-specific CARs, other approaches are actively being pursued to redirect T cells to CD19, including recombinant bispecific T-cell engager (BiTE) proteins or T cells genetically modified to express BiTEs [engager (ENG) T cells]. As BiTEs provide no costimulation, we investigated here if provision of costimulation through CD28 and 41BB enhances the effector function of CD19-ENG T cells. CD19-ENG T cells expressing CD80 and 41BBL on their cell surface (CD19-ENG.41BBL/CD80 T cells) were generated by retroviral transduction. CD19-ENG.41BBL/CD80 T cells retained their antigen specificity and had superior effector function compared with both unmodified T cells and CD19-ENG T cells expressing either CD80, 41BBL, or no costimulatory molecule, as judged by cytokine (IFNγ and IL2) production, T-cell proliferation, and their ability to sequentially kill target cells. In vivo, CD19-ENG.41BBL/CD80 T cells had superior antileukemia activity in the BV173 xenograft model, resulting in a survival advantage in comparison to CD19-ENG T cells. Thus, provision of costimulation is critical for the effector function of ENG T cells. Cancer Immunol Res; 5(10); 860-70. ©2017 AACR.

Immune modulation by a cellular network of mesenchymal stem cells and breast cancer cell subsets: Implication for cancer therapy

The immune modulatory properties of mesenchymal stem cells (MSCs) are mostly controlled by the particular microenvironment. Cancer stem cells (CSCs), which can initiate a clinical tumor, have been the subject of intense research. This review article discusses investigative studies of the roles of MSCs on cancer biology including on CSCs, and the potential as drug delivery to tumors. An understanding of how MSCs behave in the tumor microenvironment to facilitate the survival of tumor cells would be crucial to identify drug targets. More importantly, since CSCs survive for decades in dormancy for later resurgence, studies are presented to show how MSCs could be involved in maintaining dormancy. Although the mechanism by which CSCs survive is complex, this article focus on the cellular involvement of MSCs with regard to immune responses. We discuss the immunomodulatory mechanisms of MSC-CSC interaction in the context of therapeutic outcomes in oncology. We also discuss immunotherapy as a potential to circumventing this immune modulation.

T Cell-Activating Mesenchymal Stem Cells as a Biotherapeutic for HCC

The outcome for advanced stage hepatocellular carcinoma (HCC) remains poor, highlighting the need for novel therapies. Genetically modified mesenchymal stem cells (MSCs) are actively being explored as cancer therapeutics due to their inherent ability to migrate to tumor sites. We reasoned that MSCs can be genetically modified to redirect T cells to Glypican-3 (GPC3)⁺ HCC, and genetically modified these with viral vectors encoding a GPC3/CD3 bispecific T cell engager (GPC3-ENG), a bispecifc T cell engager specific for an irrelevant antigen (EGFRvIII), and/or costimulatory molecules (CD80 and 41BBL). Coculture of GPC3⁺ cells, GPC3-ENG MSCs, and T cells resulted in T cell activation, as judged by interferon γ (IFNγ) production and killing of tumor cells by T cells. Modification of GPC3-ENG MSCs with CD80 and 41BBL was required for antigen-dependent interleukin-2 (IL-2) production by T cells and resulted in faster tumor cell killing by redirected T cells. In vivo, GPC3-ENG MSCs ± costimulatory molecules had antitumor activity in the HUH7 HCC xenograft model, resulting in a survival advantage. In conclusion, MSCs genetically modified to express GPC3-ENG ± costimulatory molecules redirect T cells to GPC3⁺ tumor cells and have potent antitumor activity. Thus, further preclinical exploration of our modified approach to GPC3-targeted immunotherapy for HCC is warranted.

In Vivo Murine-Matured Human CD3+ Cells as a Preclinical Model for T Cell-Based Immunotherapies

Adoptive cellular immunotherapy is a promising and powerful method for the treatment of a broad range of malignant and infectious diseases. Although the concept of cellular immunotherapy was originally proposed in the 1990s, it has not seen successful clinical application until recent years. Despite significant progress in creating engineered receptors against both malignant and viral epitopes, no efficient preclinical animal models exist for rapidly testing and directly comparing these engineered receptors. The use of matured human T cells in mice usually leads to graft-versus-host disease (GvHD), which severely limits the effectiveness of such studies. Alternatively, adult apheresis CD34⁺ cells engraft in neonatal non-obese diabetic (NOD)-severe combined immunodeficiency (SCID)-common γ chain^–/– (NSG) mice and lead to the development of CD3⁺ T cells in peripheral circulation. We demonstrate that these in vivo murine-matured autologous CD3⁺ T cells from humans (MATCH) can be collected from the mice, engineered with lentiviral vectors, reinfused into the mice, and detected in multiple lymphoid compartments at stable levels over 50 days after injection. Unlike autologous CD3⁺ cells collected from human donors, these MATCH mice did not exhibit GvHD after T cell administration. This novel mouse model offers the opportunity to screen different immunotherapy-based treatments in a preclinical setting.

Balanced secretion of anti-CEA × anti-CD3 diabody chains using the 2A self-cleaving peptide maximizes diabody assembly and tumor-specific cytotoxicity

Adoptive transfer of genetically engineered human cells secreting bispecific T-cell engagers has shown encouraging therapeutic effects in preclinical models of cancer. However, reducing the toxicity and improving the effectiveness of this emerging immunotherapeutic strategy will be critical to its successful application. We have demonstrated that for gene-based bispecific antibody strategies, two-chain diabodies have a better safety profile than single-chain tandem scFvs (single-chain variable fragments), because their reduced tendency to form aggregates reduces the risk of inducing antigen-independent T-cell activation. Here, we demonstrate that the incorporation of a 2A self-processing peptide derived from foot-and-mouth disease virus conveying co-translational cleavage into a two-chain anti-CD3 × anti-CEA diabody gene enables near-equimolar expression of diabody chains 1 and 2, and thus increases the final amount of assembled diabody. This was found to maximize diabody-mediated T-cell activation and cytotoxicity against carcinoembryonic antigen-positive tumor cells.

Treatment of Human B-Cell Lymphomas Using Minicircle DNA Vector Expressing Anti-CD3/CD20 in a Mouse Model

Bispecific antibodies (BsAbs), capable of directing T cells to kill specific cancer cells by transiently binding the two cell types, have emerged as one class of promising cancer immunotherapies. However, their wide clinical application might be hampered by two deficiencies: high cost and inconvenience in drug administration. This study presents concept-proving data that these problems could be bypassed by using an enhanced nonviral DNA vector minicircle (MC) to produce BsAb in vivo. It was found that the anti-CD3/CD20 produced from the minicircle (MC.CD20) could effectively mediate the T-cell killing of multiple CD20-positive human B-cell lymphoma cell lines in vitro. More importantly, it was demonstrated that delivery of 5 μg of MC.CD20 to mouse liver via hydrodynamic injection resulted in both the expression of a therapeutic level of anti-CD3/CD20 throughout the 32-day experiment and effective anticancer activity in a B-cell lymphoma xenograft mouse model. The data suggest that MC encoding the BsAbs may become an attractive cancer immunotherapy modality based on its excellent features of safety, efficacy, and convenience in both preparation and use, and its affordability once the delivery technology matures.

CD123-Engager T Cells as a Novel Immunotherapeutic for Acute Myeloid Leukemia

Immunotherapy with CD123-specific T-cell engager proteins or with T cells expressing CD123-specific chimeric antigen receptors is actively being pursued for acute myeloid leukemia. T cells secreting bispecific engager molecules (ENG-T cells) may present a promising alternative to these approaches. To evaluate therapeutic potential, we generated T cells to secrete CD123/CD3-bispecific engager molecules. CD123-ENG T cells recognized primary acute myeloid leukemia (AML) cells and cell lines in an antigen-dependent manner as judged by cytokine production and/or tumor killing, and redirected bystander T cells to AML cells. Infusion of CD123-ENG T cells resulted in regression of AML in xenograft models conferring a significant survival advantage of treated mice in comparison to mice that received control T cells. At high effector to target ratios, CD123-ENG T cells recognized normal hematopoietic stem and progenitor cells (HSPCs) with preferential recognition of HSPCs from cord blood compared to bone marrow. We therefore introduced the CD20 suicide gene that can be targeted in vivo with rituximab into CD123-ENG T cells. The expression of CD20 did not diminish the anti-AML activity of CD123-ENG T cells, but allowed for rituximab-mediated ENG-T cell elimination. Thus, ENG-T cells coexpressing CD20 suicide and CD123 engager molecules may present a promising immunotherapeutic approach for AML.