Antibody-mediated B-cell depletion before adoptive immunotherapy with T cells expressing CD20-specific chimeric T-cell receptors facilitates eradication of leukemia in immunocompetent mice

Optimization of anti-CD19 CAR T cell production for treatment of patients with chronic lymphocytic leukemia

T cells expressing anti-CD19 chimeric antigen receptors (CARs) have activity against chronic lymphocytic leukemia (CLL), but complete response rates range from 18% to 29%, so improvement is needed. Peripheral blood mononuclear cells (PBMCs) of CLL patients often contain high levels of CLL cells that can interfere with CAR T cell production, and T cells from CLL patients are prone to exhaustion and other functional defects. We previously developed an anti-CD19 CAR designated Hu19-CD828Z. Hu19-CD828Z has a binding domain derived from a fully human antibody and a CD28 costimulatory domain. We aimed to develop an optimized process for producing Hu19-CD828Z-expressing T cells (Hu19-CAR T) from PBMC of CLL patients. We determined that supplementing Hu19-CAR-T cultures with interleukin (IL)-7 + IL-15 had advantages over using IL-2, including greater accumulation of Hu19-CAR T cells during in vitro proliferation assays. We determined that positive selection with anti-CD4 and anti-CD8 magnetic beads was the optimal method of T cell purification because this method resulted in high T cell purity. We determined that anti-CD3/CD28 paramagnetic beads were the optimal T cell activation reagent. Finally, we developed a current good manufacturing practices-compliant clinical-scale protocol for producing Hu19-CAR T from PBMC of CLL patients. These Hu19-CAR T exhibited a full range of in vitro functions and eliminated leukemia from mice.

Effects of B Cell Depletion by CD19-Targeted Chimeric Antigen Receptor T Cells in a Murine Model of Systemic Sclerosis

OBJECTIVE

Our goal was to study the tolerance and efficacy of two B cell depletion strategies, including one with CD19-targeted chimeric antigen receptor (CAR) T cells, in a preclinical model mimicking the severe lung damages observed in systemic sclerosis.

METHODS

B cell depletion strategies were evaluated in the Fra-2 transgenic (Tg) mouse model. We considered a first group of 16 untreated mice, a second group of 15 mice receiving a single dose of anti-CD20 monoclonal antibody (mAb), and a third group of 8 mice receiving CD19-targeted CAR-T cells in combination with anti-CD20 monoclonal antibody. After six weeks of clinical evaluation, different validated markers of inflammation, lung fibrosis, and pulmonary vascular remodeling were assessed.

RESULTS

CD19-targeted CAR-T cells infusion in combination with anti-CD20 mAb resulted in a deeper B cell depletion than anti-CD20 mAb alone in the peripheral blood and lesional lungs of Fra-2 Tg mice. CAR-T cell infusion worsened the clinical score and increased mortality in Fra-2 Tg mice. In line with the above findings, CAR-T cell infusion significantly increased lung collagen content, the histological fibrosis score, and right ventricular systolic pressure. CAR-T cells accumulated in lesional lungs and promoted T activation and inflammatory cytokine production. Treatment with anti-CD20 mAb in monotherapy had no impact on lung inflammation-driven fibrosis and pulmonary hypertension.

CONCLUSION

B cell therapies failed to show efficacy in the Fra2 Tg mice. The exacerbated Fra-2 lung inflammatory burden stimulated accumulation and expansion of activated CD19-targeted CAR-T cells, secondarily inducing T cell activation and systemic inflammation, finally leading to disease worsening.

Chimeric TIM-4 receptor-modified T cells targeting phosphatidylserine mediates both cytotoxic anti-tumor responses and phagocytic uptake of tumor-associated antigen for T cell cross-presentation

To leverage complementary mechanisms for cancer cell removal, we developed a novel cell engineering and therapeutic strategy co-opting phagocytic clearance and antigen presentation activity into T cells. We engineered a chimeric engulfment receptor (CER)-1236, which combines the extracellular domain of TIM-4, a phagocytic receptor recognizing the "eat me" signal phosphatidylserine, with intracellular signaling domains (TLR2/TIR, CD28, and CD3ζ) to enhance both TIM-4-mediated phagocytosis and T cell cytotoxic function. CER-1236 T cells demonstrate target-dependent phagocytic function and induce transcriptional signatures of key regulators responsible for phagocytic recognition and uptake, along with cytotoxic mediators. Pre-clinical models of mantle cell lymphoma (MCL) and EGFR mutation-positive non-small cell lung cancer (NSCLC) demonstrate collaborative innate-adaptive anti-tumor immune responses both in vitro and in vivo. Treatment with BTK (MCL) and EGFR (NSCLC) inhibitors increased target ligand, conditionally driving CER-1236 function to augment anti-tumor responses. We also show that activated CER-1236 T cells exhibit superior cross-presentation ability compared with conventional T cells, triggering E7-specific TCR T responses in an HLA class I- and TLR-2-dependent manner, thereby overcoming the limited antigen presentation capacity of conventional T cells. Therefore, CER-1236 T cells have the potential to achieve tumor control by eliciting both direct cytotoxic effects and indirect-mediated cross-priming.

Cellular kinetics: A clinical and computational review of CAR-T cell pharmacology

To the extent that pharmacokinetics influence the effectiveness of nonliving therapeutics, so too do cellular kinetics influence the efficacy of Chimeric Antigen Receptor (CAR) -T cell therapy. Like conventional therapeutics, CAR-T cell therapies undergo a distribution phase upon administration. Unlike other therapeutics, however, this distribution phase is followed by subsequent phases of expansion, contraction, and persistence. The magnitude and duration of these phases unequivocally influence clinical outcomes. Furthermore, the "pharmacodynamics" of CAR-T cells is truly dynamic, as cells can rapidly become exhausted and lose their therapeutic efficacy. Mathematical models are among the translational tools commonly applied to assess, characterize, and predict the complex cellular kinetics and dynamics of CAR-T cells. Here, we provide a focused review of the cellular kinetics of CAR-T cells, the mechanisms underpinning their complexity, and the mathematical modeling approaches used to interrogate them.

A giant step forward: chimeric antigen receptor T-cell therapy for lymphoma

The combination of the immunotherapy (i.e., the use of monoclonal antibodies) and the conventional chemotherapy increases the long-term survival of patients with lymphoma. However, for patients with relapsed or treatment-resistant lymphoma, a novel treatment approach is urgently needed. Chimeric antigen receptor T (CAR-T) cells were introduced as a treatment for these patients. Based on recent clinical data, approximately 50% of patients with relapsed or refractory B-cell lymphoma achieved complete remission after receiving the CD19 CAR-T cell therapy. Moreover, clinical data revealed that some patients remained in remission for more than two years after the CAR-T cell therapy. Other than the CD19-targeted CAR-T, the novel target antigens, such as CD20, CD22, CD30, and CD37, which were greatly expressed on lymphoma cells, were studied under preclinical and clinical evaluations for use in the treatment of lymphoma. Nonetheless, the CAR-T therapy was usually associated with potentially lethal adverse effects, such as the cytokine release syndrome and the neurotoxicity. Therefore, optimizing the structure of CAR, creating new drugs, and combining CAR-T cell therapy with stem cell transplantation are potential solutions to increase the effectiveness of treatment and reduce the toxicity in patients with lymphoma after the CAR-T cell therapy.

Single-cell imaging of CAR T cell activity in vivo reveals extensive functional and anatomical heterogeneity

Cazaux et al. use intravital imaging to dissect anti-CD19 CAR T cell activity. This study uncovers both anatomical and functional diversity in the outcome of anti-CD19 CAR T cell interactions with tumor cells impacting engraftment, killing dynamics, and tumor immunoediting.

CAR T cells represent a potentially curative strategy for B cell malignancies. However, the outcome and dynamics of CAR T cell interactions in distinct anatomical sites are poorly understood. Using intravital imaging, we tracked interactions established by anti-CD19 CAR T cells in B cell lymphoma–bearing mice. Circulating targets trapped CAR T cells in the lungs, reducing their access to lymphoid organs. In the bone marrow, tumor apoptosis was largely due to CAR T cells that engaged, killed, and detached from their targets within 25 min. Notably, not all CAR T cell contacts elicited calcium signaling or killing while interacting with tumors, uncovering extensive functional heterogeneity. Mathematical modeling revealed that direct killing was sufficient for tumor regression. Finally, antigen-loss variants emerged in the bone marrow, but not in lymph nodes, where CAR T cell cytotoxic activity was reduced. Our results identify a previously unappreciated level of diversity in the outcomes of CAR T cell interactions in vivo, with important clinical implications.

Comparative analysis and optimization of protocols for producing recombinant lentivirus carrying the anti-Her2 chimeric antigen receptor gene

BACKGROUND

The production of anti-Her2 chimeric antigen receptor (CAR) T cells needs to be optimized to make it a reliable therapy.

METHODS

Three types of lentiviral vectors expressing anti-Her2 CAR together with packaging plasmids were co-transfected into 293 T-17 cells. The vector with the best packaging efficiency was selected, and the packaging cell culture system and packaging plasmid system were optimized. Centrifugation speed was optimized for the concentration of lentivirus stock. The various purification methods used included membrane filtration, centrifugation with a sucrose cushion and the novelly-designed instantaneous high-speed centrifugation. The recombinant lentiviruses were transduced into human peripheral T cells with an optimized multiplicity of infection (MOI). CAR expression levels by three vectors and the efficacy of CAR-T cells were compared.

RESULTS

When co-transfected, packaging cells in suspension were better than the commonly used adherent culture condition, with the packaging system psPAX2/pMD2.G being better than pCMV-dR8.91/pVSV-G. The optimal centrifugation speed for concentration was 20 000 g, rather than the generally used ultra-speed. Importantly, adding instantaneous centrifugation for purification significantly increased human peripheral T cell viability (from 13.25% to 62.80%), which is a technical breakthrough for CAR-T cell preparation. The best MOI value for transducing human peripheral T cells was 40. pLVX-EF1a-CAR-IRES-ZsGreen1 expressed the highest level of CAR in human peripheral T cells and the cytotoxicity of CAR-T cells reached 63.56%.

CONCLUSIONS

We optimized the preparation of recombinant lentivirus that can express third-generation anti-Her2 CAR in T cells, which should lay the foundation for improving the efficacy of CAR-T cells with respect to killing target cells.

Differences in Expansion Potential of Naive Chimeric Antigen Receptor T Cells from Healthy Donors and Untreated Chronic Lymphocytic Leukemia Patients

Introduction

Therapy with chimeric antigen receptor T (CART) cells for hematological malignancies has shown promising results. Effectiveness of CART cells may depend on the ratio of naive (T_N) vs. effector (T_E) T cells, T_N cells being responsible for an enduring antitumor activity through maturation. Therefore, we investigated factors influencing the T_N/T_E ratio of CART cells.

Materials and methods

CART cells were generated upon transduction of peripheral blood mononuclear cells with a CD19.CAR-CD28-CD137zeta third generation retroviral vector under two different stimulating culture conditions: anti-CD3/anti-CD28 antibodies adding either interleukin (IL)-7/IL-15 or IL-2. CART cells were maintained in culture for 20 days. We evaluated 24 healthy donors (HDs) and 11 patients with chronic lymphocytic leukemia (CLL) for the composition of cell subsets and produced CART cells. Phenotype and functionality were tested using flow cytometry and chromium release assays.

Results

IL-7/IL-15 preferentially induced differentiation into T_N, stem cell memory (T_SCM: naive CD27+ CD95+), CD4+ and CXCR3+ CART cells, while IL-2 increased effector memory (T_EM), CD56+ and CD4+ T regulatory (T_Reg) CART cells. The net amplification of different CART subpopulations derived from HDs and untreated CLL patients was compared. Particularly the expansion of CD4+ CART_N cells differed significantly between the two groups. For HDs, this subtype expanded >60-fold, whereas CD4+ CART_N cells of untreated CLL patients expanded less than 10-fold. Expression of exhaustion marker programmed cell death 1 on CART_N cells on day 10 of culture was significantly higher in patient samples compared to HD samples. As the percentage of malignant B cells was expectedly higher within patient samples, an excessive amount of B cells during culture could account for the reduced expansion potential of CART_N cells in untreated CLL patients. Final T_N/T_E ratio stayed <0.3 despite stimulation condition for patients, whereas this ratio was >2 in samples from HDs stimulated with IL-7/IL-15, thus demonstrating efficient CART_N expansion.

Conclusion

Untreated CLL patients might constitute a challenge for long-lasting CART effects in vivo since only a low number of T_N among the CART product could be generated. Depletion of malignant B cells before starting CART production might be considered to increase the T_N/T_E ratio within the CART product.

Preclinical Optimization of a CD20-specific Chimeric Antigen Receptor Vector and Culture Conditions

Chimeric antigen receptor (CAR)-based adoptive T-cell therapy is a highly promising treatment for lymphoid malignancies, and CD20 is an ideal target antigen. We previously developed a lentiviral construct encoding a third generation CD20-targeted CAR but identified several features that required additional optimization before clinical translation. We describe here several improvements, including replacement of the immunogenic murine antigen-binding moiety with a fully human domain, streamlining the transgene insert to enhance lentiviral titers, modifications to the extracellular IgG spacer that abrogate nonspecific activation resulting from binding to Fc receptors, and evaluation of CD28, 4-1BB, or CD28 and 4-1BB costimulatory domains. We also found that restimulation of CAR T cells with an irradiated CD20 cell line boosted cell growth, increased the fraction of CAR-expressing cells, and preserved in vivo function despite leading to a reduced capacity for cytokine secretion in vitro. We also found that cryopreservation of CAR T cells did not affect immunophenotype or in vivo antitumor activity compared with fresh cells. These optimization steps resulted in significant improvement in antitumor activity in mouse models, resulting in eradication of established systemic lymphoma tumors in 75% of mice with a single infusion of CAR T cells, and prolonged in vivo persistence of modified cells. These results provide the basis for clinical testing of a lentiviral construct encoding a fully human CD20-targeted CAR with CD28 and 4-1BB costimulatory domains and truncated CD19 (tCD19) transduction marker.

Antigen-specific impairment of adoptive T-cell therapy against cancer: players, mechanisms, solutions and a hypothesis

Adoptive cell therapy (ACT) destroys tumors with infused cytotoxic T lymphocytes (CTLs). Although successful in some settings, ACT is compromised due to impaired survival or functional inactivation of the CTL. To better understand the mechanisms involved, we have exploited a mouse model of leukemia expressing ovalbumin as a tumor neoantigen to address these questions: (i) Is CTL impairment during ACT antigen specific? (ii) If yes, which are the antigen-presenting cells responsible? (iii) Can this information assist the development of complementary therapies to improve ACT? Our results indicate that the target (tumor) cells, not cross-presenting cells, are the main culprits of antigen-specific CTL inactivation. We find that the affinity/avidity of the CTL-tumor cell interaction has little influence on ACT outcomes, while tumor density is a major determinant. Reduction of tumor burden with mild non-lymphoablative and non-inflammatory chemotherapy can dramatically improve the efficacy of ACT and may minimize side-effects. We propose a general mechanism for the inactivation of anti-self CTL in the same tissues where the activity of anti-foreign CTL is preserved, based on the density of target cells. This mechanism, which we tentatively call stunning, may have evolved to protect infected sites from self-destruction and is exploited by tumors to inactivate CTL.

Chimeric-Antigen-Receptor (CAR) T Cells and the Factors Influencing their Therapeutic Efficacy

Immunotherapeutic treatments for malignant cancers have revolutionized the medical and scientific fields. Lymphocytes engineered to display chimeric antigen receptor (CAR) molecules contribute to the exciting advancements that have stemmed from a greater understanding of cell structure and function, biological interactions, and the unique tumor microenvironment. CAR T cells circumvent the unique immune evasion capability of tumors by acting in a major histocompatibility complex (MHC) independent manner. Various factors contribute to the efficacy of CAR therapy, including CAR structure, gene transfer strategies, in vitro culture system, target selection, and preconditioning regimens. While recent clinical trials have shown promising success, cytotoxicity and other various challenges need to be addressed before CAR therapy can reach its full clinical potency. This review will discuss factors associated with CAR therapeutic success and the difficulties that continue to be a focus of research around the world.

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.

Donor CD19 CAR T cells exert potent graft-versus-lymphoma activity with diminished graft-versus-host activity

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative therapy for hematological malignancies. However, graft-versus-host disease (GVHD) and relapse after allo-HSCT remain major impediments to the success of allo-HSCT. Chimeric antigen receptors (CARs) direct tumor cell recognition of adoptively transferred T cells. CD19 is an attractive CAR target, which is expressed in most B cell malignancies, as well as in healthy B cells. Clinical trials using autologous CD19-targeted T cells have shown remarkable promise in various B cell malignancies. However, the use of allogeneic CAR T cells poses a concern in that it may increase risk of the occurrence of GVHD, although this has not been reported in selected patients infused with donor-derived CD19 CAR T cells after allo-HSCT. To understand the mechanism whereby allogeneic CD19 CAR T cells may mediate anti-lymphoma activity without causing a significant increase in the incidence of GVHD, we studied donor-derived CD19 CAR T cells in allo-HSCT and lymphoma models in mice. We demonstrate that alloreactive T cells expressing CD28-costimulated CD19 CARs experience enhanced stimulation, resulting in the progressive loss of both their effector function and proliferative potential, clonal deletion, and significantly decreased occurrence of GVHD. Concurrently, the other CAR T cells that were present in bulk donor T cell populations retained their anti-lymphoma activity in accordance with the requirement that both the T cell receptor (TCR) and CAR be engaged to accelerate T cell exhaustion. In contrast, first-generation and 4-1BB-costimulated CAR T cells increased the occurrence of GVHD. These findings could explain the reduced risk of GVHD occurring with cumulative TCR and CAR signaling.

Antibody targeting facilitates effective intratumoral siRNA nanoparticle delivery to HER2-overexpressing cancer cells

The therapeutic potential of RNA interference (RNAi) has been limited by inefficient delivery of short interfering RNA (siRNA). Tumor-specific recognition can be effectively achieved by antibodies directed against highly expressed cancer cell surface receptors. We investigated the utility of linking an internalizing streptavidin-conjugated HER2 antibody to an endosome-disruptive biotinylated polymeric nanocarrier to improve the functional cytoplasmic delivery of siRNA in breast and ovarian cancer cells in vitro and in an intraperitoneal ovarian cancer xenograft model in vivo, yielding an 80% reduction of target mRNA and protein levels with sustained repression for at least 96 hours. RNAi-mediated site specific cleavage of target mRNA was demonstrated using the 5′ RLM-RACE (RNA ligase mediated-rapid amplification of cDNA ends) assay. Mice bearing intraperitoneal human ovarian tumor xenografts demonstrated increased tumor accumulation of Cy5.5 fluorescently labeled siRNA and 70% target gene suppression after treatment with HER2 antibody-directed siRNA nanocarriers. Detection of the expected mRNA cleavage product by 5′ RLM-RACE assay confirmed that suppression occurs via the expected RNAi pathway. Delivery of siRNA via antibody-directed endosomolytic nanoparticles may be a promising strategy for cancer therapy.

The Tumor Microenvironment Regulates CD19 and CD20 Immunotherapy for Lymphoma

B cells have diverse functions during immune responses, including antibody production, antigen presentation, and cytokine secretion. Multiple lymphomas and leukemias derive from malignant B cells, so therapies that deplete B cells are clinically important, particularly antibodies targeting the B cell-specific surface molecules CD19 and CD20. Macrophages are the principal mediators of CD19 and CD20 monoclonal antibody-dependent B-cell and lymphoma depletion in mice through Fcγ receptor-dependent phagocytosis. Thereby, the extent of CD19 or CD20 antibody-induced B cell and tumor depletion in vivo is influenced by molecular changes within tumors and genetic variations between individuals. In addition to Fcγ receptor polymorphisms, lymphoma- and regulatory B cell-derived cytokine production and macrophage localization and function within tumor microenvironments influence tumor clearance. Given the dynamic interactions of these factors, the identification of effector cell and tumor microenvironment genetic alterations will identify molecular targets that enhance immunotherapies for the treatment of human diseases.

Lymphoma Immunotherapy: Current Status

The rationale to treat lymphomas with immunotherapy comes from long-standing evidence on their distinctive immune responsiveness. Indolent B-cell non-Hodgkin lymphomas, in particular, establish key interactions with the immune microenvironment to ensure prosurvival signals and prevent antitumor immune activation. However, reports of spontaneous regressions indicate that, under certain circumstances, patients develop therapeutic antitumor immunity. Several immunotherapeutic approaches have been thus developed to boost these effects in all patients. To date, targeting CD20 on malignant B cells with the antibody rituximab has been the most clinically effective strategy. However, relapse and resistance prevent to cure approximately half of B-NHL patients, underscoring the need of more effective therapies. The recognition of B-cell receptor variable regions as B-NHL unique antigens promoted the development of specific vaccines to immunize patients against their own tumor. Despite initial promising results, this strategy has not yet demonstrated a sufficient clinical benefit to reach the regulatory approval. Several novel agents are now available to stimulate immune effector functions or counteract immunosuppressive mechanisms, such as engineered antitumor T cells, co-stimulatory receptor agonist, and immune checkpoint-blocking antibodies. Thus, multiple elements can now be exploited in more effective combinations to break the barriers for the induction of anti-lymphoma immunity.

Using gene therapy to manipulate the immune system in the fight against B-cell leukemias

INTRODUCTION

Over 20 years ago, chimeric antigen receptors (CARs) were created to endow T cells with new antigen-specificity and create a therapy that could eradicate cancer and provide life-long protection against recurrence. Steady progress has led to significant improvements with CAR design and CAR T-cell production, allowing evaluation of CAR T cells in patients. The initial trials have targeted CD19, which is expressed on normal and malignant B cells.

AREAS COVERED

We review data from trials for patients with chronic lymphocytic leukemia (CLL) and B-cell acute lymphoblastic leukemia (B-ALL). In addition, we discuss the on-target toxicities, B-cell aplasia and cytokine release syndrome (CRS), which is uniquely associated with T-cell immunotherapies.

EXPERT OPINION

We compare the results when targeting the same antigen in CLL or B-ALL and speculate on reasons for outcome differences and future directions to enhance outcomes. Furthermore, the dramatic results targeting B-ALL require further analysis in Phase II trials, and we discuss important components of these future trials. We also suggest a management scheme for CRS. The next several years will be critical and may lead to the first clinical indication of a gene-engineered cell therapy for cancer.

Combining a CD20 chimeric antigen receptor and an inducible caspase 9 suicide switch to improve the efficacy and safety of T cell adoptive immunotherapy for lymphoma

Modification of T cells with chimeric antigen receptors (CAR) has emerged as a promising treatment modality for human malignancies. Integration of co-stimulatory domains into CARs can augment the activation and function of genetically targeted T cells against tumors. However, the potential for insertional mutagenesis and toxicities due to the infused cells have made development of safe methods for removing transferred cells an important consideration. We have genetically modified human T cells with a lentiviral vector to express a CD20-CAR containing both CD28 and CD137 co-stimulatory domains, a "suicide gene" relying on inducible activation of caspase 9 (iC9), and a truncated CD19 selectable marker. Rapid expansion (2000 fold) of the transduced T cells was achieved in 28 days after stimulation with artificial antigen presenting cells. Transduced T cells exhibited effective CD20-specific cytotoxic activity in vitro and in a mouse xenograft tumor model. Activation of the iC9 suicide switch resulted in efficient removal of transduced T cells both in vitro and in vivo. Our work demonstrates the feasibility and promise of this approach for treating CD20(+) malignancies in a safe and more efficient manner. A phase I clinical trial using this approach in patients with relapsed indolent B-NHL is planned.

Kinetics of tumor destruction by chimeric antigen receptor-modified T cells

The use of chimeric antigen receptor (CAR)-modified T cells as a therapy for hematologic malignancies and solid tumors is becoming more widespread. However, the infusion of a T-cell product targeting a single tumor-associated antigen may lead to target antigen modulation under this selective pressure, with subsequent tumor immune escape. With the purpose of preventing this phenomenon, we have studied the impact of simultaneously targeting two distinct antigens present on tumor cells: namely mucin 1 and prostate stem cell antigen, both of which are expressed in a variety of solid tumors, including pancreatic and prostate cancer. When used individually, CAR T cells directed against either tumor antigen were able to kill target-expressing cancer cells, but tumor heterogeneity led to immune escape. As a combination therapy, we demonstrate superior antitumor effects using both CARs simultaneously, but this was nevertheless insufficient to achieve a complete response. To understand the mechanism of escape, we studied the kinetics of T-cell killing and found that the magnitude of tumor destruction depended not only on the presence of target antigens but also on the intensity of expression-a feature that could be altered by administering epigenetic modulators that upregulated target expression and enhanced CAR T-cell potency.

Engineered T cells for cancer treatment

Adoptively transferred T cells have the capacity to traffic to distant tumor sites, infiltrate fibrotic tissue and kill antigen-expressing tumor cells. Various groups have investigated different genetic engineering strategies designed to enhance tumor specificity, increase T cell potency, improve proliferation, persistence or migratory capacity and increase safety. This review focuses on recent developments in T cell engineering, discusses the clinical application of these engineered cell products and outlines future prospects for this therapeutic modality.

Chimeric antigen receptor therapy for chronic lymphocytic leukemia: what are the challenges?

Chimeric antigen receptor (CAR)-modified T cells targeting CD19 expressed by normal and malignant B cells is a unique therapy for patients with chronic lymphocytic leukemia (CLL); recent results highlight the potential of this therapy for patients with relapsed CLL. Because adoptive transfer of CAR-modified T cells is a novel approach, there are issues for the medical oncologist to consider when evaluating current and future clinical trials for CLL patients. This article reviews the impact of CAR design, T-cell production, T-cell dose, conditioning regimens, and tumor burden at the time of CAR-modified T-cell infusion on the efficacy of this therapy.

CARs in chronic lymphocytic leukemia -- ready to drive

Adoptive transfer of antigen-specific T cells has been adapted by investigators for treatment of chronic lymphocytic leukemia (CLL). To overcome issues of immune tolerance which limits the endogenous adaptive immune response to tumor-associated antigens (TAAs), robust systems for the genetic modification and characterization of T cells expressing chimeric antigen receptors (CARs) to redirect specificity have been produced. Refinements with regards to persistence and trafficking of the genetically modified T cells are underway to help improve potency. Clinical trials utilizing this technology demonstrate feasibility, and increasingly, these early-phase trials are demonstrating impressive anti-tumor effects, particularly for CLL patients, paving the way for multi-center trials to establish the efficacy of CAR(+) T cell therapy.

CD19 CAR-targeted T cells induce long-term remission and B Cell Aplasia in an immunocompetent mouse model of B cell acute lymphoblastic leukemia

Although many adults with B cell acute lymphoblastic leukemia (B-ALL) are induced into remission, most will relapse, underscoring the dire need for novel therapies for this disease. We developed murine CD19-specific chimeric antigen receptors (CARs) and an immunocompetent mouse model of B-ALL that recapitulates the disease at genetic, cellular, and pathologic levels. Mouse T cells transduced with an all-murine CD3ζ/CD28-based CAR that is equivalent to the one being used in our clinical trials, eradicate B-ALL in mice and mediate long-term B cell aplasias. In this model, we find that increasing conditioning chemotherapy increases tumor eradication, B cell aplasia, and CAR-modified T cell persistence. Quantification of recipient B lineage cells allowed us to estimate an in vivo effector to endogenous target ratio for B cell aplasia maintenance. In mice exhibiting a dramatic B cell reduction we identified a small population of progenitor B cells in the bone marrow that may serve as a reservoir for long-term CAR-modified T cell stimulation. Lastly, we determine that infusion of CD8+ CAR-modified T cells alone is sufficient to maintain long-term B cell eradication. The mouse model we report here should prove valuable for investigating CAR-based and other therapies for adult B-ALL.

Treating B-cell cancer with T cells expressing anti-CD19 chimeric antigen receptors

Most B-cell malignancies express CD19, and a majority of patients with B-cell malignancies are not cured by current standard therapies. Chimeric antigen receptors (CARs) are fusion proteins consisting of antigen recognition moieties and T-cell activation domains. T cells can be genetically modified to express CARs, and adoptive transfer of anti-CD19 CAR T cells is now being tested in clinical trials. Effective clinical treatment with anti-CD19 CAR T cells was first reported in 2010 after a patient with advanced-stage lymphoma treated at the NCI experienced a partial remission of lymphoma and long-term eradication of normal B cells. Additional patients have subsequently obtained long-term remissions of advanced-stage B-cell malignancies after infusions of anti-CD19 CAR T cells. Long-term eradication of normal CD19(+) B cells from patients receiving infusions of anti-CD19 CAR T cells demonstrates the potent antigen-specific activity of these T cells. Some patients treated with anti-CD19 CAR T cells have experienced acute adverse effects, which were associated with increased levels of serum inflammatory cytokines. Although anti-CD19 CAR T cells are at an early stage of development, the potent antigen-specific activity observed in patients suggests that infusions of anti-CD19 CAR T cells might become a standard therapy for some B-cell malignancies.

Immunotherapies in CLL

Chronic lymphocytic leukemia (CLL) is the most frequently diagnosed leukemia in the Western world, yet remains essentially incurable. Although initial chemotherapy response rates are high, patients invariably relapse and subsequently develop resistance to chemotherapy. For the moment, allogeneic hematopoietic stem cell transplant (allo-HSCT) remains the only potentially curative treatment for patients with CLL, but it is associated with high rates of treatment-related mortality. Immune-based treatment strategies to augment the cytotoxic potential of T cells offer exciting new treatment options for patients with CLL, and provide a unique and powerful spectrum of tools distinct from traditional chemotherapy. Among the most novel and promising of these approaches are chimeric antigen receptor (CAR)-based cell therapies that combine advances in genetic engineering and adoptive immunotherapy.

Augmentation of anti-tumor immunity by adoptive T-cell transfer after allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HCT) is currently the standard of care for most patients with high-risk acute leukemias and some other hematologic malignancies. Although HCT can be curative, many patients who undergo allogeneic HCT will later relapse. There is, therefore, a critical need for the development of novel post-HCT therapies for patients who are at high risk for disease recurrence following HCT. One potentially efficacious approach is adoptive T-cell immunotherapy, which is currently undergoing a renaissance that has been inspired by scientific insight into the key issues that impeded its previous clinical application. Translation of the next generation of adoptive T-cell therapies to the allogeneic HCT setting, using donor T cells of defined specificity and function, presents a unique set of challenges and opportunities. The challenges, progress and future of adoptive T-cell therapy following allogeneic HCT are discussed in this review.

Tumor-targeted T cells modified to secrete IL-12 eradicate systemic tumors without need for prior conditioning

Adoptive cell therapy with tumor-targeted T cells is a promising approach to cancer therapy. Enhanced clinical outcome using this approach requires conditioning regimens with total body irradiation, lymphodepleting chemotherapy, and/or additional cytokine support. However, the need for prior conditioning precludes optimal application of this approach to a significant number of cancer patients intolerant to these regimens. Herein, we present preclinical studies demonstrating that treatment with CD19-specific, chimeric antigen receptor (CAR)-modified T cells that are further modified to constitutively secrete IL-12 are able to safely eradicate established disease in the absence of prior conditioning. We demonstrate in a novel syngeneic tumor model that tumor elimination requires both CD4(+) and CD8(+) T-cell subsets, autocrine IL-12 stimulation, and subsequent IFNγ secretion by the CAR(+) T cells. Importantly, IL-12-secreting, tumor-targeted T cells acquire intrinsic resistance to T regulatory cell-mediated inhibition. Based on these preclinical data, we anticipate that adoptive therapy using CAR-targeted T cells modified to secrete IL-12 will obviate or reduce the need for potentially hazardous conditioning regimens to achieve optimal antitumor responses in cancer patients.

CD20-specific adoptive immunotherapy for lymphoma using a chimeric antigen receptor with both CD28 and 4-1BB domains: pilot clinical trial results

Cellular immune responses have the potential to elicit dramatic and sustained clinical remissions in lymphoma patients. Recent clinical trial data demonstrate that modification of T cells with chimeric antigen receptors (CARs) is a promising strategy. T cells containing CARs with costimulatory domains exhibit improved activity against tumors. We conducted a pilot clinical trial testing a "third-generation" CD20-specific CAR with CD28 and 4-1BB costimulatory domains in patients with relapsed indolent B-cell and mantle cell lymphomas. Four patients were enrolled, and 3 received T-cell infusions after cyclophosphamide lymphodepletion. Treatment was well tolerated, although one patient developed transient infusional symptoms. Two patients without evaluable disease remained progression-free for 12 and 24 months. The third patient had an objective partial remission and relapsed at 12 months after infusions. Modified T cells were detected by quantitative PCR at tumor sites and up to 1 year in peripheral blood, albeit at low levels. No evidence of host immune responses against infused cells was detected. In conclusion, adoptive immunotherapy with CD20-specific T cells was well tolerated and was associated with antitumor activity. We will pursue alternative gene transfer technologies and culture conditions in future studies to improve CAR expression and cell production efficiency.

Chimeric antibody receptors (CARs): driving T-cell specificity to enhance anti-tumor immunity

Adoptive transfer of antigen-specific T cells is a compelling tool to treat cancer. To overcome issues of immune tolerance which limits the endogenous adaptive immune response to tumor-associated antigens, robust systems for the genetic modification and characterization of T cells expressing chimeric antigen receptors (CARs) to redirect specificity have been produced. Refinements with regards to persistence and trafficking of the genetically modified T cells are underway to help improve the potency of genetically modified T cells. Clinical trials utilizing this technology demonstrate feasibility, and increasingly, antitumor activity, paving the way for multi-center trials to establish the efficacy of this novel T-cell therapy.

B-cell depletion and remissions of malignancy along with cytokine-associated toxicity in a clinical trial of anti-CD19 chimeric-antigen-receptor-transduced T cells

We conducted a clinical trial to assess adoptive transfer of T cells genetically modified to express an anti-CD19 chimeric Ag receptor (CAR). Our clinical protocol consisted of chemotherapy followed by an infusion of anti-CD19-CAR-transduced T cells and a course of IL-2. Six of the 8 patients treated on our protocol obtained remissions of their advanced, progressive B-cell malignancies. Four of the 8 patients treated on the protocol had long-term depletion of normal polyclonal CD19(+) B-lineage cells. Cells containing the anti-CD19 CAR gene were detected in the blood of all patients. Four of the 8 treated patients had prominent elevations in serum levels of the inflammatory cytokines IFNγ and TNF. The severity of acute toxicities experienced by the patients correlated with serum IFNγ and TNF levels. The infused anti-CD19-CAR-transduced T cells were a possible source of these inflammatory cytokines because we demonstrated peripheral blood T cells that produced TNF and IFNγ ex vivo in a CD19-specific manner after anti-CD19-CAR-transduced T-cell infusions. Anti-CD19-CAR-transduced T cells have great promise to improve the treatment of B-cell malignancies because of a potent ability to eradicate CD19(+) cells in vivo; however, reversible cytokine-associated toxicities occurred after CAR-transduced T-cell infusions.

Regulatory B cell production of IL-10 inhibits lymphoma depletion during CD20 immunotherapy in mice

Current therapies for non-Hodgkin lymphoma commonly include CD20 mAb to deplete tumor cells. However, the response is not durable in a substantial proportion of patients. Herein, we report our studies in mice testing the hypothesis that heterogeneity in endogenous tissue CD20+ B cell depletion influences in vivo lymphoma therapy. Using highly effective CD20 mAbs that efficiently deplete endogenous mature B cells and homologous CD20+ primary lymphoma cells through monocyte- and antibody-dependent mechanisms, we found that lymphoma depletion and survival were reduced when endogenous host B cells were not depleted, particularly a rare IL-10-producing B cell subset (B10 cells) known to regulate inflammation and autoimmunity. Even small numbers of adoptively transferred B10 cells dramatically suppressed CD20 mAb-mediated lymphoma depletion by inhibiting mAb-mediated monocyte activation and effector function through IL-10-dependent mechanisms. However, the activation of innate effector cells using a TLR3 agonist that did not activate B10 cells overcame the negative regulatory effects of endogenous B10 cells and enhanced lymphoma depletion during CD20 immunotherapy in vivo. Thus, we conclude that endogenous B10 cells are potent negative regulators of innate immunity, with even small numbers of residual B10 cells able to inhibit lymphoma depletion by CD20 mAbs. Consequently, B10 cell removal could provide a way to optimize CD20 mAb-mediated clearance of malignant B cells in patients with non-Hodgkin lymphoma.

Evaluation of current cancer immunotherapy: hemato-oncology

Hematologic malignancies were the first diseases in clinical oncology for which the potential of harnessing the immune system as targeted therapy was unequivocally demonstrated. Unfortunately, the use of this highly efficacious modality has been limited to only a subset of patients and diseases because of immune-mediated toxicities resulting from incomplete specificity, and disease-specific determinants of sensitivity versus resistance to immune effector mechanisms. Recent studies, however, have begun to elucidate the molecular basis of the observed clinical effects allowing the rational development of next generation of immunotherapeutic combinations. We discuss here cancer antigen targets in hematologic malignancies and the specific approaches to induce immunity being pursued, the importance of modulating the host immunoregulatory environment, and the special features of immunological monitoring in clinical investigation. The hematologic malignancies represent an ideal setting for the development of immunotherapy due to logistical, clinical monitoring, and disease biology factors and may represent an exemplar for immune-based treatment in other cancer types.

Safety and persistence of adoptively transferred autologous CD19-targeted T cells in patients with relapsed or chemotherapy refractory B-cell leukemias

We report the findings from the first 10 patients with chemotherapy-refractory chronic lymphocytic leukemia (CLL) or relapsed B-cell acute lymphoblastic leukemia (ALL) we have enrolled for treatment with autologous T cells modified to express 19-28z, a second-generation chimeric antigen (Ag) receptor specific to the B-cell lineage Ag CD19. Eight of the 9 treated patients tolerated 19-28z(+) T-cell infusions well. Three of 4 evaluable patients with bulky CLL who received prior conditioning with cyclophosphamide exhibited either a significant reduction or a mixed response in lymphadenopathy without concomitant development of B-cell aplasia. In contrast, one patient with relapsed ALL who was treated in remission with a similar T-cell dose developed a predicted B-cell aplasia. The short-term persistence of infused T cells was enhanced by prior cyclophosphamide administration and inversely proportional to the peripheral blood tumor burden. Further analyses showed rapid trafficking of modified T cells to tumor and retained ex vivo cytotoxic potential of CD19-targeted T cells retrieved 8 days after infusion. We conclude that this adoptive T-cell approach is promising and more likely to show clinical benefit in the setting of prior conditioning chemotherapy and low tumor burden or minimal residual disease. These studies are registered at www.clinicaltrials.org as #NCT00466531 (CLL protocol) and #NCT01044069 (B-ALL protocol).

T cells raised against allogeneic HLA-A2/CD20 kill primary follicular lymphoma and acute lymphoblastic leukemia cells

T cells mediating a graft-versus-leukemia/lymphoma effects without causing graft-versus-host disease would greatly improve the safety and applicability of hematopoietic stem cell transplantation. We recently demonstrated that highly peptide- and HLA-specific T cells can readily be generated against allogeneic HLA-A*02:01 in complex with a peptide from the B cell-restricted protein CD20. Here, we show that such CD20-specific T cells can easily be induced from naïve precursors in cord blood, demonstrating that they do not represent cross-reactive memory cells. The cells displayed high avidity and mediated potent cytotoxic effects on cells from patients with the CD20(pos) B cell malignancies follicular lymphoma (FL) and acute lymphoblastic leukemia (ALL). However, the cytotoxicity was consistently lower for cells from two of the ALL patients. The ALL cells that were less efficiently killed did not display lower surface expression of CD20 or HLA-A*02:01, or mutations in the CD20 sequence. Peptide pulsing fully restored the levels of cytotoxicity, indicating that they are indeed susceptible to T cell-mediated killing. Adoptive transfer of CD20-specific T cells to an HLA-A*02:01(pos) patient requires an HLA-A*02:01(neg) , but otherwise HLA identical, donor. A search clarified that donors meeting these criteria can be readily identified even for patients with rare haplotypes. The results bear further promise for the clinical utility of CD20-specific T cells in B cell malignancies.

In vivo inhibition of human CD19-targeted effector T cells by natural T regulatory cells in a xenotransplant murine model of B cell malignancy

Human T cells genetically modified to express chimeric antigen receptors (CAR) specific to the B cell tumor antigen CD19 can successfully eradicate systemic human CD19(+) tumors in immunocompromised SCID (severe combined immunodeficient)-Beige mice. However, in the clinical setting, CD4(+) CD25(hi) T regulatory cells (Treg) present within the tumor microenvironment may be potent suppressors of tumor-targeted effector T cells. In order to assess the impact of Tregs on CAR-modified T cells in the SCID-Beige xenotransplant model, we isolated, genetically targeted and expanded natural T regulatory cells (nTreg). In vitro nTregs modified to express CD19-targeted CARs efficiently inhibited the proliferation of activated human T cells, as well as the capacity of CD19-targeted 19-28z(+) effector T cells to lyse CD19(+) Raji tumor cells. Intravenous infusion of CD19-targeted nTregs into SCID-Beige mice with systemic Raji tumors traffic to sites of tumor and recapitulate a clinically relevant hostile tumor microenvironment. Antitumor efficacy of subsequently infused 19-28z(+) effector T cells was fully abrogated as assessed by long-term survival of treated mice. Optimal suppression by genetically targeted nTregs was dependent on nTreg to effector T-cell ratios and in vivo nTreg activation. Prior infusion of cyclophosphamide in the setting of this nTreg-mediated hostile microenvironment was able to restore the antitumor activity of subsequently infused 19-28z(+) effector T cells through the eradication of tumor-targeted nTregs. These findings have significant implications for the design of future clinical trials utilizing CAR-based adoptive T-cell therapies of cancer.

Adoptive transfer of syngeneic T cells transduced with a chimeric antigen receptor that recognizes murine CD19 can eradicate lymphoma and normal B cells

Adoptive T-cell therapy with anti-CD19 chimeric antigen receptor (CAR)-expressing T cells is a new approach for treating advanced B-cell malignancies. To evaluate anti-CD19-CAR-transduced T cells in a murine model of adoptive T-cell therapy, we developed a CAR that specifically recognized murine CD19. We used T cells that were retrovirally transduced with this CAR to treat mice bearing a syngeneic lymphoma that naturally expressed the self-antigen murine CD19. One infusion of anti-CD19-CAR-transduced T cells completely eliminated normal B cells from mice for at least 143 days. Anti-CD19-CAR-transduced T cells eradicated intraperitoneally injected lymphoma cells and large subcutaneous lymphoma masses. The antilymphoma efficacy of anti-CD19-CAR-transduced T cells was critically dependent on irradiation of mice before anti-CD19-CAR-transduced T-cell infusion. Anti-CD19-CAR-transduced T cells had superior antilymphoma efficacy compared with the anti-CD19 monoclonal antibody from which the anti-CD19 CAR was derived. Our results demonstrated impressive antilymphoma activity and profound destruction of normal B cells caused by anti-CD19-CAR-transduced T cells in a clinically relevant murine model.

Synergistic and persistent effect of T-cell immunotherapy with anti-CD19 or anti-CD38 chimeric receptor in conjunction with rituximab on B-cell non-Hodgkin lymphoma

Using artificial receptors, it is possible to redirect the specificity of immune cells to tumour-associated antigens, which is expected to provide a useful strategy for cancer immunotherapy. Given that B-cell non-Hodgkin lymphoma (B-NHL) cells invariably express CD19 and CD38, these antigens may be suitable molecular candidates for such immunotherapy. We transduced human peripheral T cells or a T-cell line with either anti-CD19-chimeric receptor (CAR) or anti-CD38-CAR, which contained an anti-CD19 or anti-CD38 antibody-derived single-chain variable domain respectively. Retroviral transduction led to anti-CD19-CAR or anti-CD38-CAR expression in T cells with high efficiency (>60%). The T cell line, Hut78, when transduced with anti-CD19-CAR or anti-CD38-CAR, exerted strong cytotoxicity against the B-NHL cell lines, HT and RL, and lymphoma cells isolated from patients. Interestingly, use of both CARs had an additive cytotoxic effect on HT cells in vitro. In conjunction with rituximab, human peripheral T cells expressing either anti-CD19-CAR or anti-CD38-CAR enhanced cytotoxicity against HT-luciferase cells in xenografted mice. Moreover, the synergistic tumour-suppressing activity was persistent in vivo for over 2 months. These results provide a powerful rationale for clinical testing of the combination of rituximab with autologous T cells carrying either CAR on aggressive or relapsed B-NHLs.

Redirecting T-cell specificity by introducing a tumor-specific chimeric antigen receptor

Infusions of antigen-specific T cells have yielded therapeutic responses in patients with pathogens and tumors. To broaden the clinical application of adoptive immunotherapy against malignancies, investigators have developed robust systems for the genetic modification and characterization of T cells expressing introduced chimeric antigen receptors (CARs) to redirect specificity. Human trials are under way in patients with aggressive malignancies to test the hypothesis that manipulating the recipient and reprogramming T cells before adoptive transfer may improve their therapeutic effect. These examples of personalized medicine infuse T cells designed to meet patients' needs by redirecting their specificity to target molecular determinants on the underlying malignancy. The generation of clinical grade CAR(+) T cells is an example of bench-to-bedside translational science that has been accomplished using investigator-initiated trials operating largely without industry support. The next-generation trials will deliver designer T cells with improved homing, CAR-mediated signaling, and replicative potential, as investigators move from the bedside to the bench and back again.

Adoptive immunotherapy for B-cell malignancies with autologous chimeric antigen receptor modified tumor targeted T cells

Chemotherapy-resistant B-cell hematologic malignancies may be cured with allogeneic hematopoietic stem cell transplantation (HSCT), demonstrating the potential susceptibility of these tumors to donor T-cell mediated immune responses. However, high rates of transplant-related morbidity and mortality limit this approach. For this reason, there is an urgent need for less-toxic forms of immune-based cellular therapy to treat these malignancies. Adoptive transfer of autologous T cells genetically modified to express chimeric antigen receptors (CARs) targeted to specific tumor-associated antigens represents an attractive means of overcoming the limitations of conventional HSCT. To this end, investigators have generated CARs targeted to various antigens expressed by B-cell malignancies, optimized the design of these CARs to enhance receptor mediated T cell signaling, and demonstrated significant anti-tumor efficacy of the resulting CAR modified T cells both in vitro and in vivo mouse tumor models. These encouraging preclinical data have justified the translation of this approach to the clinical setting with currently 12 open clinical trials and one completed clinical trial treating various B-cell malignancies utilizing CAR modified T cells targeted to either the CD19 or CD20 B-cell specific antigens.

Mathematical modeling of chimeric TCR triggering predicts the magnitude of target lysis and its impairment by TCR downmodulation

We investigated relationships among chimeric TCR (cTCR) expression density, target Ag density, and cTCR triggering to predict lysis of target cells by cTCR(+) CD8(+) T human cells as a function of Ag density. Triggering of cTCR and canonical TCR by Ag could be quantified by the same mathematical equation, but cTCR represented a special case in which serial triggering was abrogated. The magnitude of target lysis could be predicted as a function of cTCR triggering, and the predicted minimum cTCR density required for maximal target lysis by CD20-specific cTCR was experimentally tested. cTCR density below approximately 20,000 cTCR/cell impaired target lysis, but increasing cTCR expression above this density did not improve target lysis or Ag sensitivity. cTCR downmodulation to densities below this critical minimum by interaction with Ag-expressing targets limited the sequential lysis of targets in a manner that could be predicted based on the number of cTCRs remaining. In contrast, acute inhibition of lysis of primary, intended targets (e.g., leukemic B cells) due to the presence of an excess of secondary targets (e.g., normal B cells) was dependent on the Ag density of the secondary target but occurred at Ag densities insufficient to promote significant cTCR downmodulation, suggesting a role for functional exhaustion rather than insufficient cTCR density. This suggests increasing cTCR density above a critical threshold may enhance sequential lysis of intended targets in isolation, but will not overcome the functional exhaustion of cTCR(+) T cells encountered in the presence of secondary targets with high Ag density.

Adoptive T cell therapy of cancer

Adoptive transfer of T cells specific for antigens expressed on tumor cells is an attractive strategy for producing targeted and long-lived anti-tumor activity. T cell therapies have shown activity in selected clinical applications but broader application is limited by inadequate persistence of transferred T cells and by tumor-evasion strategies. Current research focuses on defining the optimum type of cell for transfer, genetically modifying infused T cells to augment function and overcome tumor evasion strategies and modulating the host environment.