Antigen-independent and antigen-dependent methods to numerically expand CD19-specific CD8+ T cells

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.

Feeder Cells at the Interface of Natural Killer Cell Activation, Expansion and Gene Editing

Genome engineered natural killer (NK) cell therapies are emerging as a promising cancer immunotherapy platform with potential advantages and remaining uncertainties. Feeder cells induce activation and proliferation of NK cells via cell surface receptor-ligand interactions, supported by cytokines. Feeder cell expanded NK cell products have supported several NK cell adoptive transfer clinical trials over the past decade. Genome engineered NK cell therapies, including CAR-NK cells, seek to combine innate and alloreactive NK cell anti-tumor activity with antigen specific targeting or additional modifications aimed at improving NK cell persistence, homing or effector function. The profound activating and expansion stimulus provided by feeder cells is integral to current applications of clinical-scale genome engineering approaches in donor-derived, primary NK cells. Herein we explore the complex interactions that exist between feeder cells and both viral and emerging non-viral genome editing technologies in NK cell engineering. We focus on two established clinical-grade feeder systems; Epstein-Barr virus transformed lymphoblastoid cell lines and genetically engineered K562.mbIL21.4-1BBL feeder cells.

GMP-Compliant Universal Antigen Presenting Cells (uAPC) Promote the Metabolic Fitness and Antitumor Activity of Armored Cord Blood CAR-NK Cells

Natural killer (NK) cells are innate lymphocytes recognized for their important role against tumor cells. NK cells expressing chimeric antigen receptors (CARs) have enhanced effector function against various type of cancer and are attractive contenders for the next generation of cancer immunotherapies. However, a number of factors have hindered the application of NK cells for cellular therapy, including their poor in vitro growth kinetics and relatively low starting percentages within the mononuclear cell fraction of peripheral blood or cord blood (CB). To overcome these limitations, we genetically-engineered human leukocyte antigen (HLA)-A- and HLA-B- K562 cells to enforce the expression of CD48, 4-1BBL, and membrane-bound IL-21 (mbIL21), creating a universal antigen presenting cell (uAPC) capable of stimulating their cognate receptors on NK cells. We have shown that uAPC can drive the expansion of both non-transduced (NT) and CAR-transduced CB derived NK cells by >900-fold in 2 weeks of co-culture with excellent purity (>99.9%) and without indications of senescence/exhaustion. We confirmed that uAPC-expanded research- and clinical-grade NT and CAR-transduced NK cells have higher metabolic fitness and display enhanced effector function against tumor targets compared to the corresponding cell fractions cultured without uAPCs. This novel approach allowed the expansion of highly pure GMP-grade CAR NK cells at optimal cell numbers to be used for adoptive CAR NK cell-based cancer immunotherapy.

The Role of Checkpoint Inhibitors and Cytokines in Adoptive Cell-Based Cancer Immunotherapy with Genetically Modified T Cells

This review focuses on the structure and molecular action mechanisms of chimeric antigen receptors (CARs) and major aspects of the manufacturing and clinical application of products for the CAR-T (CAR-modified T lymphocyte) therapy of hematological and solid tumors with special emphasis on the strategies for combined use of CAR-T therapy with immuno-oncological monoclonal antibodies (checkpoint inhibitors) and cytokines to boost survival, persistence, and antitumor efficacy of CAR-T therapy. The review also summarizes preclinical and clinical data on the additive effects of the combined use of CAR-T therapy with interleukins and monoclonal antibodies targeting immune checkpoints.

CD137 (4-1BB) Engagement Fine-Tunes Synergistic IL-15- and IL-21-Driven NK Cell Proliferation

To understand and dissect the mechanisms driving human NK cell proliferation, we exploited the methodology used in cell therapy to numerically expand NK cells in the presence of K562-derived artificial APC (aAPCs) and cytokines. For four consecutive weeks, high expression of CD137L by a K562-derived aAPC cell line could sustain NK cell expansion by 3 × 10⁵-fold, whereas low expression of CD137L by the parental K562 cell line only supported the expansion by 2 × 10³-fold. The level of expression of CD137L, however, did not modulate the sensitivity of K562 cells to the intrinsic cytotoxicity of NK cells. Similarly, the low NK cell proliferation in the presence of the parental K562 cell line and cytokines was increased by adding agonistic anti-CD137 Abs to levels similar to CD137L-expressing K562-derived aAPCs. Finally, synergy between IL-15 and IL-21 was observed only upon CD137 engagement and the presence of aAPCs. Therefore, we conclude that NK cell proliferation requires cell-to-cell contact, activation of the CD137 axis, and presence of IL-15 (or its membranous form) and IL-21. By analogy with the three-signal model required to activate T cells, we speculate that the cell-to-cell contact represents "signal 1," CD137 represents "signal 2," and cytokines represent "signal 3." The precise nature of signal 1 remains to be defined.

Cell death in cancer in the era of precision medicine

Tumors constitute a large class of diseases that affect different organs and cell lineages. The molecular characterization of cancers of a given type has revealed an extraordinary heterogeneity in terms of genetic alterations and DNA mutations; heterogeneity that is further highlighted by single-cell DNA sequencing of individual patients. To address these issues, drugs that specifically target genes or altered pathways in cancer cells are continuously developed. Indeed, the genetic fingerprint of individual tumors can direct the modern therapeutic approaches to selectively hit the tumor cells while sparing the healthy ones. In this context, the concept of precision medicine finds a vast field of application. In this review, we will briefly list some classes of target drugs (Bcl-2 family modulators, Tyrosine Kinase modulators, PARP inhibitors, and growth factors inhibitors) and discuss the application of immunotherapy in tumors (T cell-mediated immunotherapy and CAR-T cells) that in recent years has drastically changed the prognostic outlook of aggressive cancers. We will also consider how apoptosis could represent a primary end point in modern cancer therapy and how "classic" chemotherapeutic drugs that induce apoptosis are still utilized in therapeutic schedules that involve the use of target drugs or immunotherapy to optimize the antitumor response.

Manufacture of T cells using the Sleeping Beauty system to enforce expression of a CD19-specific chimeric antigen receptor

T cells can be reprogrammed to redirect specificity to tumor-associated antigens (TAAs) through the enforced expression of chimeric antigen receptors (CARs). The prototypical CAR is a single-chain molecule that docks with TAA expressed on the cell surface and, in contrast to the T-cell receptor complex, recognizes target cells independent of human leukocyte antigen. The bioprocessing to generate CAR(+) T cells has been reduced to clinical practice based on two common steps that are accomplished in compliance with current good manufacturing practice. These are (1) gene transfer to stably integrate the CAR using viral and nonviral approaches and (2) activating the T cells for proliferation by crosslinking CD3 or antigen-driven numeric expansion using activating and propagating cells (AaPCs). Here, we outline our approach to nonviral gene transfer using the Sleeping Beauty system and the selective propagation of CD19-specific CAR(+) T cells on AaPCs.

Universal artificial antigen presenting cells to selectively propagate T cells expressing chimeric antigen receptor independent of specificity

T cells genetically modified to stably express immunoreceptors are being assessed for therapeutic potential in clinical trials. T cells expressing a chimeric antigen receptor (CAR) are endowed with a new specificity to target tumor-associated antigen (TAA) independent of major histocompatibility complex. Our approach to nonviral gene transfer in T cells uses ex vivo numeric expansion of CAR T cells on irradiated artificial antigen presenting cells (aAPC) bearing the targeted TAA. The requirement for aAPC to express a desired TAA limits the human application of CARs with multiple specificities when selective expansion through coculture with feeder cells is sought. As an alternative to expressing individual TAAs on aAPC, we expressed 1 ligand that could activate CAR T cells for sustained proliferation independent of specificity. We expressed a CAR ligand (designated CARL) that binds the conserved IgG4 extracellular domain of CAR and demonstrated that CARL aAPC propagate CAR T cells of multiple specificities. CARL avoids technical issues and costs associated with deploying clinical-grade aAPC for each TAA targeted by a given CAR. Using CARL enables 1 aAPC to numerically expand all CAR T cells containing the IgG4 domain, and simplifies expansion, testing, and clinical translation of CAR T cells of any specificity.

A new approach to gene therapy using Sleeping Beauty to genetically modify clinical-grade T cells to target CD19

The advent of efficient approaches to the genetic modification of T cells has provided investigators with clinically appealing methods to improve the potency of tumor-specific clinical grade T cells. For example, gene therapy has been successfully used to enforce expression of chimeric antigen receptors (CARs) that provide T cells with ability to directly recognize tumor-associated antigens without the need for presentation by human leukocyte antigen. Gene transfer of CARs can be undertaken using viral-based and non-viral approaches. We have advanced DNA vectors derived from the Sleeping Beauty (SB) system to avoid the expense and manufacturing difficulty associated with transducing T cells with recombinant viral vectors. After electroporation, the transposon/transposase improves the efficiency of integration of plasmids used to express CAR and other transgenes in T cells. The SB system combined with artificial antigen-presenting cells (aAPC) can selectively propagate and thus retrieve CAR(+) T cells suitable for human application. This review describes the translation of the SB system and aAPC for use in clinical trials and highlights how a nimble and cost-effective approach to developing genetically modified T cells can be used to implement clinical trials infusing next-generation T cells with improved therapeutic potential.

Adoptive immunotherapy for cancer

Recent clinical success has underscored the potential for immunotherapy based on the adoptive cell transfer (ACT) of engineered T lymphocytes to mediate dramatic, potent, and durable clinical responses. This success has led to the broader evaluation of engineered T-lymphocyte-based adoptive cell therapy to treat a broad range of malignancies. In this review, we summarize concepts, successes, and challenges for the broader development of this promising field, focusing principally on lessons gleaned from immunological principles and clinical thought. We present ACT in the context of integrating T-cell and tumor biology and the broader systemic immune response.

Human cell-based artificial antigen-presenting cells for cancer immunotherapy

Adoptive T-cell therapy, where anti-tumor T cells are first prepared in vitro, is attractive since it facilitates the delivery of essential signals to selected subsets of anti-tumor T cells without unfavorable immunoregulatory issues that exist in tumor-bearing hosts. Recent clinical trials have demonstrated that anti-tumor adoptive T-cell therapy, i.e. infusion of tumor-specific T cells, can induce clinically relevant and sustained responses in patients with advanced cancer. The goal of adoptive cell therapy is to establish anti-tumor immunologic memory, which can result in life-long rejection of tumor cells in patients. To achieve this goal, during the process of in vitro expansion, T-cell grafts used in adoptive T-cell therapy must be appropriately educated and equipped with the capacity to accomplish multiple, essential tasks. Adoptively transferred T cells must be endowed, prior to infusion, with the ability to efficiently engraft, expand, persist, and traffic to tumor in vivo. As a strategy to consistently generate T-cell grafts with these capabilities, artificial antigen-presenting cells have been developed to deliver the proper signals necessary to T cells to enable optimal adoptive cell therapy.

Activating and propagating polyclonal gamma delta T cells with broad specificity for malignancies

PURPOSE

To activate and propagate populations of γδ T cells expressing polyclonal repertoire of γ and δ T-cell receptor (TCR) chains for adoptive immunotherapy of cancer, which has yet to be achieved.

EXPERIMENTAL DESIGN

Clinical-grade artificial antigen-presenting cells (aAPC) derived from K562 tumor cells were used as irradiated feeders to activate and expand human γδ T cells to clinical scale. These cells were tested for proliferation, TCR expression, memory phenotype, cytokine secretion, and tumor killing.

RESULTS

γδ T-cell proliferation was dependent upon CD137L expression on aAPC and addition of exogenous IL2 and IL21. Propagated γδ T cells were polyclonal as they expressed TRDV1, TRDV2-2, TRDV3, TRDV5, TRDV7, and TRDV8 with TRGV2, TRGV3F, TRGV7, TRGV8, TRGV9*A1, TRGV10*A1, and TRGV11 TCR chains. IFNγ production by Vδ1, Vδ2, and Vδ1(neg)Vδ2(neg) subsets was inhibited by pan-TCRγδ antibody when added to cocultures of polyclonal γδ T cells and tumor cell lines. Polyclonal γδ T cells killed acute and chronic leukemia, colon, pancreatic, and ovarian cancer cell lines, but not healthy autologous or allogeneic normal B cells. Blocking antibodies demonstrated that polyclonal γδ T cells mediated tumor cell lysis through combination of DNAM1, NKG2D, and TCRγδ. The adoptive transfer of activated and propagated γδ T cells expressing polyclonal versus defined Vδ TCR chains imparted a hierarchy (polyclonal>Vδ1>Vδ1(neg)Vδ2(neg)>Vδ2) of survival of mice with ovarian cancer xenografts.

CONCLUSIONS

Polyclonal γδ T cells can be activated and propagated with clinical-grade aAPCs and demonstrate broad antitumor activities, which will facilitate the implementation of γδ T-cell cancer immunotherapies in humans.

Simplified process for the production of anti-CD19-CAR-engineered T cells

BACKGROUND AIMS

Adoptive immunotherapy with the use of chimeric antigen receptor (CAR)-engineered T cells specific for CD19 has shown promising results for the treatment of B-cell lymphomas and leukemia. This therapy involves the transduction of autologous T cells with a viral vector and the subsequent cell expansion. We describe a new, simplified method to produce anti-CD19-CAR T cells.

METHODS

T cells were isolated from peripheral blood mononuclear cell (PBMC) with anti-CD3/anti-CD28 paramagnetic beads. After 2 days, the T cells were added to culture bags pre-treated with RetroNectin and loaded with the retroviral anti-CD19 CAR vector. The cells, beads and vector were incubated for 24 h, and a second transduction was then performed. No spinoculation was used. Cells were then expanded for an additional 9 days.

RESULTS

The method was validated through the use of two PBMC products from a patient with B-cell chronic lymphoblastic leukemia and one PBMC product from a healthy subject. The two PBMC products from the patient with B-cell chronic lymphoblastic leukemia contained 11.4% and 12.9% T cells. The manufacturing process led to final products highly enriched in T cells with a mean CD3+ cell content of 98%, a mean expansion of 10.6-fold and a mean transduction efficiency of 68%. Similar results were obtained from the PBMCs of the first four patients with acute lymphoblastic leukemia treated at our institution.

CONCLUSIONS

We developed a simplified, semi-closed system for the initial selection, activation, transduction and expansion of T cells with the use of anti-CD3/anti-CD28 beads and bags to produce autologous anti-CD19 CAR-transduced T cells to support an ongoing clinical trial.

Bayesian continual reassessment method for dose-finding trials infusing T cells with limited sample size

We consider the design of dose-finding trials for patients with malignancies when only a limited sample size is available. The small sample size may be necessary because (1) the modality of treatment is very expensive, and/or (2) the disease under investigation is rare, requiring a lengthy period to enroll a target patient population. Both of these are common in the field of adoptive immunotherapy, in which T cells are infused to prevent and treat infections and malignancies. The clinical trial described in this paper investigates a novel therapy to adoptively transfer genetically modified T cells in small pilot protocols enrolling patients with B-lineage malignancies. Due to the constraints of cost and infrastructure, the maximum sample size for this trial is fixed at 12 patients distributed among four doses of T cells. Given these limitations, an innovative statistical design has been developed to efficiently evaluate the safety, feasibility, persistence, and toxicity profiles of the trial doses. The proposed statistical design is specifically tailored for trials with small sample sizes in that it uses the toxicity outcomes from patients treated at different doses to make dose-finding decisions. Supplementary materials including an R function and a movie demo can be downloaded in the websites mentioned in the paper.

A foundation for universal T-cell based immunotherapy: T cells engineered to express a CD19-specific chimeric-antigen-receptor and eliminate expression of endogenous TCR

Clinical-grade T cells are genetically modified ex vivo to express a chimeric antigen receptor (CAR) to redirect specificity to a tumor associated antigen (TAA) thereby conferring antitumor activity in vivo. T cells expressing a CD19-specific CAR recognize B-cell malignancies in multiple recipients independent of major histocompatibility complex (MHC) because the specificity domains are cloned from the variable chains of a CD19 monoclonal antibody. We now report a major step toward eliminating the need to generate patient-specific T cells by generating universal allogeneic TAA-specific T cells from one donor that might be administered to multiple recipients. This was achieved by genetically editing CD19-specific CAR(+) T cells to eliminate expression of the endogenous αβ T-cell receptor (TCR) to prevent a graft-versus-host response without compromising CAR-dependent effector functions. Genetically modified T cells were generated using the Sleeping Beauty system to stably introduce the CD19-specific CAR with subsequent permanent deletion of α or β TCR chains with designer zinc finger nucleases. We show that these engineered T cells display the expected property of having redirected specificity for CD19 without responding to TCR stimulation. CAR(+)TCR(neg) T cells of this type may potentially have efficacy as an off-the-shelf therapy for investigational treatment of B-lineage malignancies.

Adoptive T-cell therapy improves treatment of canine non-Hodgkin lymphoma post chemotherapy

Clinical observations reveal that an augmented pace of T-cell recovery after chemotherapy correlates with improved tumor-free survival, suggesting the add-back of T cells after chemotherapy may improve outcomes. To evaluate adoptive immunotherapy treatment for B-lineage non-Hodgkin lymphoma (NHL), we expanded T cells from client-owned canines diagnosed with NHL on artificial antigen presenting cells (aAPC) in the presence of human interleukin (IL)-2 and IL-21. Graded doses of autologous T cells were infused after CHOP chemotherapy and persisted for 49 days, homed to tumor, and significantly improved survival. Serum thymidine kinase changes predicted T-cell engraftment, while anti-tumor effects correlated with neutrophil-to-lymphocyte ratios and granzyme B expression in manufactured T cells. Therefore, chemotherapy can be used to modulate infused T-cell responses to enhance anti-tumor effects. The companion canine model has translational implications for human immunotherapy which can be readily exploited since clinical-grade canine and human T cells are propagated using identical approaches.

Highlights of the second international conference on "Immunotherapy in Pediatric Oncology"

The Second International Conference on Immunotherapy in Pediatric Oncology was held in Houston, Texas, USA, October 11-12, 2010, to discuss the progress and challenges that have occurred in cutting edge immunotherapeutic strategies currently being developed for pediatric oncology. Major topics included immune targeting of acute lymphoblastic leukemia and pediatric solid tumors, chimeric antigen receptors (CARs) for hematologic malignancies and solid tumors, enhancing graft-versus-leukemia for pediatric cancers, overcoming hurdles of immunotherapy, strategies to active the innate immune system, and moving immunotherapy beyond phase I studies. Significant progress has been made in the last 2 years both in the development of novel immunobiologics such as CARs, and in establishing survival benefits of an anti-GD2 monoclonal antibody in randomized studies. Although there is much excitement going forward, a great deal of laboratory and regulatory challenges lie ahead in improving the efficacy of each of these modalities as well as getting them to patients in a timely and cost-effective fashion. The resulting discussions will hopefully lead to new collaborations and insight for further translational and clinical studies.

Engineered T cells for the adoptive therapy of B-cell chronic lymphocytic leukaemia

B-cell chronic lymphocytic leukaemia (B-CLL) remains an incurable disease due to the high risk of relapse, even after complete remission, raising the need to control and eliminate residual tumor cells in long term. Adoptive T cell therapy with genetically engineered specificity is thought to fulfil expectations, and clinical trials for the treatment of CLL are initiated. Cytolytic T cells from patients are redirected towards CLL cells by ex vivo engineering with a chimeric antigen receptor (CAR) which binds to CD19 on CLL cells through an antibody-derived domain and triggers T cell activation through CD3ζ upon tumor cell engagement. Redirected T cells thereby target CLL cells in an MHC-unrestricted fashion, secret proinflammatory cytokines, and eliminate CD19(+) leukaemia cells with high efficiency. Cytolysis of autologous CLL cells by patient's engineered T cells is effective, however, accompanied by lasting elimination of healthy CD19(+) B-cells. In this paper we discuss the potential of the strategy in the treatment of CLL, the currently ongoing trials, and the future challenges in the adoptive therapy with CAR-engineered T cells.

A transgene-encoded cell surface polypeptide for selection, in vivo tracking, and ablation of engineered cells

An unmet need in cell engineering is the availability of a single transgene encoded, functionally inert, human polypeptide that can serve multiple purposes, including ex vivo cell selection, in vivo cell tracking, and as a target for in vivo cell ablation. Here we describe a truncated human EGFR polypeptide (huEGFRt) that is devoid of extracellular N-terminal ligand binding domains and intracellular receptor tyrosine kinase activity but retains the native amino acid sequence, type I transmembrane cell surface localization, and a conformationally intact binding epitope for pharmaceutical-grade anti-EGFR monoclonal antibody, cetuximab (Erbitux). After lentiviral transduction of human T cells with vectors that coordinately express tumor-specific chimeric antigen receptors and huEGFRt, we show that huEGFRt serves as a highly efficient selection epitope for chimeric antigen receptor(+) T cells using biotinylated cetuximab in conjunction with current good manufacturing practices (cGMP)-grade anti-biotin immunomagnetic microbeads. Moreover, huEGFRt provides a cell surface marker for in vivo tracking of adoptively transferred T cells using both flow cytometry and immunohistochemistry, and a target for cetuximab-mediated antibody-dependent cellular cytotoxicity and in vivo elimination. The versatility of huEGFRt and the availability of pharmaceutical-grade reagents for its clinical application denote huEGFRt as a significant new tool for cellular engineering.

The hyperactive Sleeping Beauty transposase SB100X improves the genetic modification of T cells to express a chimeric antigen receptor

Sleeping Beauty (SB3) transposon and transposase constitute a DNA plasmid system used for therapeutic human cell genetic engineering. Here we report a comparison of SB100X, a newly developed hyperactive SB transposase, to a previous generation SB11 transposase to achieve stable expression of a CD19-specific chimeric antigen receptor (CAR3) in primary human T cells. The electro-transfer of SB100X expressed from a DNA plasmid or as an introduced mRNA species had superior transposase activity in T cells based on the measurement of excision circles released after transposition and emergence of CAR expression on T cells selectively propagated upon CD19+ artificial antigen-presenting cells. Given that T cells modified with SB100X and SB11 integrate on average one copy of the CAR transposon in each T-cell genome, the improved transposition mediated by SB100X apparently leads to an augmented founder effect of electroporated T cells with durable integration of CAR. In aggregate, SB100X improves SB transposition in primary human T cells and can be titrated with an SB transposon plasmid to improve the generation of CD19-specific CAR+ T cells.

Artificial antigen-presenting cells for use in adoptive immunotherapy

The observation that T cells can recognize and specifically eliminate cancer cells has spurred interest in the development of efficient methods to generate large numbers of T cells with specificity for tumor antigens that can be harnessed for use in cancer therapy. Recent studies have demonstrated that during encounter with tumor antigen, the signals delivered to T cells by professional antigen-presenting cells can affect T-cell programming and their subsequent therapeutic efficacy. This has stimulated efforts to develop artificial antigen-presenting cells that allow optimal control over the signals provided to T cells. In this review, we will discuss the advantages and disadvantages of cellular and acellular artificial antigen-presenting cell systems and their use in T-cell adoptive immunotherapy for cancer.

Genetic redirection of T cells for cancer therapy

Adoptive immunotherapy can induce dramatic tumor regressions in patients with melanoma or viral-induced malignancies, but extending this approach to many common cancers has been hampered by a lack of naturally occurring tumor-specific T cells. In this review, we describe recent advances in the genetic modification of T cells using genes encoding cell-surface receptors specific for tumor-associated antigen. Using genetic modification, the many functional properties of T cells, including cytokine secretion and cytolytic capacity, are redirected from their endogenous specificity toward the elimination of tumor cells. Advances in gene design, vectors, and cell production are discussed, and details of the progress in clinical application of this approach are provided.

Cytokines as Adjuvants for Vaccine and Cellular Therapies for Cancer

PROBLEM STATEMENT: The development of a potent vaccine that can help treat tumors resistant to conventional cytotoxic therapies remains elusive. While part of the problem may be that trials have focused on patients with bulky residual disease, the desire to maximize responses to the vaccine remains. APPROACH: The gamma(c) family of cytokines offer a unique opportunity to support the expansion and effector potential of vaccine-responding T-cells, as well as stimulate other effectors, such as natural killer (NK) cells, to become activated. RESULTS: Combining vaccines with cytokines seems logical but can bring unwanted toxicity, as has been observed with interleukin (IL)-2. In addition, the nonspecific activation or expansion of unwanted cell subsets, such as regulatory T-cells, can contribute to global immunosuppression and limit vaccine responses. The development of IL-7 and IL-21 for the clinic offers the promise of enhancing anti-tumor responses but with far less systemic toxicity and no expansion of regulatory T cells. Preclinical studies demonstrate that IL-15 could also improve T-cell, and especially NK-cell, responses as well. CONCLUSIONS/RECOMMENDATIONS: Future work should expand the use of vaccines with IL-7, IL-21 and hopefully IL-15 in high-risk patients, and consider treatment while in a state of minimal residual disease to maximize benefit. Identifying tumors that can signal through gamma(c) cytokines will also be essential so that induction of relapse will be avoided.

Low dose IL-15 induces snap arming of CD44(low) T lymphocytes in the absence of antigen

It is widely accepted that naïve T cells require two signals, antigen recognition and co-simulation, to become cytotoxic over the course of 3-5days. However, we observed that freshly isolated murine splenocytes without exposure to antigen become cytotoxic within 24h after culture with IL-15. IL-15 is a cytokine that promotes homeostatic proliferation, maintenance and activation of memory T cells. The induced cytotoxicity, measured by anti-CD3 redirected (51)Cr release, represented the combined activity of T cells regardless of their antigen specificity, and proceeded even when CD44(hi) (memory-associated phenotype) CD8(+) T cells were depleted. Cytotoxic capacity was perforin-dependent and occurred without detectable up-regulation of granzyme B or cell division. After induction, the phenotypic markers for the memory subset and for activation remained unchanged from the expression of resting T cells. Our work suggests that T cells may gain cytotoxic potential earlier than currently thought and even without TCR stimulation.

Adjuvant effect of anti-4-1BB mAb administration in adoptive T cell therapy of cancer

Administration of anti-4-1BB mAb has been found to be a potent adjuvant when combined with other therapeutic approaches, e.g. chemotherapy, cytokine therapies, anti-OX40 therapy, and peptide or DC vaccines. However, the adjuvant effect of anti-4-1BB mAb administration in adoptive T cell therapy of cancer has not been fully evaluated. In this report, effector T cells were generated in vitro by anti-CD3/anti-CD28 activation of tumor-draining lymph node (TDLN) cells and used in an adoptive immunotherapy model. While T cells or anti-4-1BB alone showed no therapeutic efficacy in mice bearing macroscopic 10-day pulmonary metastases, T cells plus anti-4-1BB mediated significant tumor regression in an anti-4-1BB dose dependent manner. Mice bearing microscopic 3-day lung metastases treated with T cells alone demonstrated tumor regression which was significantly enhanced by anti-4-1BB administration. NK cell depletion abrogated the augmented therapeutic efficacy rendered by anti-4-1BB. Cell transfer between congenic hosts demonstrated that anti-4-1BB administration increased the survival of adoptively transferred TDLN cells. Using STAT4^-/- mice, we found that modulated IFNγ secretion in wt TDLN cells after anti-CD3/CD28/4-1BB activation in vitro was lost in similarly stimulated STAT4^-/- TDLN cells. Additionally, anti-4-1BB administration failed to augment the therapeutic efficacy of T cell therapy in STAT4^-/- mice. Together, these results indicate that administered anti-4-1BB mAb can serve as an effective adjuvant to augment the antitumor reactivity of adoptively transferred T cells by recruiting the host NK cells; increasing the persistence of infused effector T cells, and modulating the STAT4 molecular signaling pathway.

Adoptive cellular immunotherapy for childhood malignancies

Clinical trials have established that T cells have the ability to prevent and treat pathogens and tumors. This is perhaps best exemplified by engraftment of allogeneic T cells in the context of hematopoietic stem-cell transplantation (HSCT), which for over the last 50 years remains one of the best and most robust examples of cell-based therapies for the treatment of hematologic malignancies. Yet, the approach to infuse T cells for treatment of cancer, in general, and pediatric tumors, in particular, generally remains on the sidelines of cancer therapy. This review outlines the current state-of-the-art and provides a rationale for undertaking adoptive immunotherapy trials with emphasis on childhood malignancies.