Herpes simplex thymidine kinase gene–transduced donor lymphocyte infusions

Fate control engagement augments NK cell responses in LV/hu-IL-12 transduced sarcoma

INTRODUCTION

NK cells are an untapped resource for cancer therapy. Sarcomas transduced with lentiviruses to express human IL-12 are only cleared in mice bearing mature human NK cells. However, systemic inflammation limits IL-12 utilization. Fate control a.k.a. "suicide mechanisms" regulate unchecked systemic inflammation caused by cellular immunotherapies. Despite increasing utilization, there remains limited data on immune consequences or tumor-directed effects of fate control.

OBJECTIVES

We sought to engage the mutant thymidylate kinase (mTMPK) metabolic fate control system to regulate systemic inflammation and assess the impact on NK cell effector functions.

METHODS

Primary human sarcoma short-passage samples and cell lines were transduced with LV/hu-IL-12_mTMPK engineering expression of IL-12 and an AZT-associated fate control enzyme. We assessed transduced sarcoma responses to AZT engagement and subsequent modulation of NK cell functions as measured by inflammatory cytokine production and cytotoxicity.

RESULTS

AZT administration to transduced (LV/hu-IL-12_mTMPK) short-passage primary human sarcomas and human Ewing sarcoma, osteosarcoma, and rhabdomyosarcoma cell lines, abrogated the robust expression of human IL-12. Fate control activation elicited a specific dose-dependent cytotoxic effect measured by metabolic activity (WST-1) and cell death (Incucyte). NK effector functions of IFN-γ and cytotoxic granule release were significantly augmented despite IL-12 abrogation. This correlated with preferentially induced expression of NK cell activation ligands.

CONCLUSIONS

mTMPK fate control engagement terminates transduced sarcoma IL-12 production and triggers cell death, but also augments an NK cell-mediated response coinciding with metabolic stress activating surface ligand induction. Fate control engagement could offer a novel immune activation method for NK cell-mediated cancer clearance.

The Development of Methods for the Production of New Molecular Vaccines and Appropriate RNA Fragments to Counteract Unwanted Genes: A Pilot Study

The potential of viruses as appropriate vectors for the development of new therapeutic strategies, as well as for the design of molecular (DNA, RNA, and/or protein) vaccines via substitution of nucleotide sequences, has been proven. Among the most appropriate DNA and/or RNA fragments, members belonging to families Parvoviridae (particularly adeno-associated virus, AAV) and Poxviridae have frequently been suggested for this purpose. In previous studies, the vaccine avipoxvirus strains FK (fowl) and Dessau (pigeon) have been proven able to infect mammalian cells (as well as avian cells), and to replicate productively in a small number of them; thus, we may be able to adapt them using incubation, and in these conditions. Additionally, we have previously proved, based on AAV recombinant DNA vectors, that it is possible to transfer appropriate genes of interest via mouse embryonic stem cells (mESCs). In the current study, we develop methods for the application of the same vaccine avipoxviral strains, based on the AAV DNA genome recombinant constructs, to be used for gene transfer in cells, for the transfer of DNA and/or RNA fragments (for the suppression of unwanted viral and/or cellular genes), and for the production of molecular (DNA, RNA, and/or protein) anti-cancer and anti-viral vaccines. To this end, sub-populations of embryonic mammalian cells infected with the two forms of both vaccine avipoxviral strains were frozen in the presence of cryo-protector dimethylsulfoxide (DMSO), subsequently thawed, and re-incubated. In most cases, the titers of the intra-cellular forms of the two strains were higher than those of their extra-cellular forms. These data were explained by the probable existence of the intra-cellular forms as different sub-forms, including those integrated in the cellular genome proviruses at a given stage of the cellular infection, and suggest the possibility of transferring nucleotide (DNA and/or RNA) fragments between cellular and viral genomes; this is due to the influence of activated fusion processes on DMSO, as well as drastic temperature variations.

Current status of ex vivo gene therapy for hematological disorders: a review of clinical trials in Japan around the world

Gene therapies are classified into two major categories, namely, in vivo and ex vivo. Clinical trials of human gene therapy began with the ex vivo techniques. Based on the initial successes of gene-therapy clinical trials, these approaches have spread worldwide. The number of gene therapy trials approved worldwide increased gradually starting in 1989, reaching 116 protocols per year in 1999, and a total of 2210 protocols had been approved by 2015. Accumulating clinical evidence has demonstrated the safety and benefits of several types of gene therapy, with the exception of serious adverse events in several clinical trials. These painful experiences were translated backward to basic science, resulting in the development of several new technologies that have influenced the recent development of ex vivo gene therapy in this field. To date, six gene therapies have been approved in a limited number of countries worldwide. In Japan, clinical trials of gene therapy have developed under the strong influence of trials in the US and Europe. Since the initial stages, 50 clinical trials have been approved by the Japanese government. In this review, the history and current status of clinical trials of ex vivo gene therapy for hematological disorders are introduced and discussed.

Haploidentical HSCT: a 15-year experience at San Raffaele

Hematopoietic SCT (HSCT) from HLA haploidentical family donors is a promising therapy for high-risk hematological malignancies. In the past 15 years at San Raffaele Scientific Institute, we investigated several transplant platforms and post transplant cellular-based interventions. We showed that T cell-depleted haploidentical transplantation followed by the infusion of genetically modified donor T cells (TK007 study, Eudract-2005-003587-34) promotes fast and wide immune reconstitution and GvHD control. This approach is currently tested in a phase III multicenter randomized trial (TK008 study, NCT00914628). We targeted patients with advanced leukemia with a sirolimus-based, calcineurin inhibitor-free prophylaxis of GvHD to allow the safe infusion of unmanipulated PBSCs from haploidentical family donors (TrRaMM study, Eudract 2007-5477-54). Results of these approaches are summarized and discussed.

Engineered T cell therapies

Alongside advancements in gene therapy for inherited immune disorders, the need for effective alternative therapeutic options for other conditions has resulted in an expansion in the field of research for T cell gene therapy. T cells are easily obtained and can be induced to divide robustly ex vivo, a characteristic that allows them to be highly permissible to viral vector-mediated introduction of transgenes. Pioneering clinical trials targeting cancers and infectious diseases have provided safety and feasibility data and important information about persistence of engineered cells in vivo. Here, we review clinical experiences with γ-retroviral and lentiviral vectors and consider the potential of integrating transposon-based vectors as well as specific genome editing with designer nucleases in engineered T cell therapies.

Infusion of donor lymphocytes expressing the herpes simplex virus thymidine kinase suicide gene for recurrent hematologic malignancies after allogeneic hematopoietic stem cell transplantation

The infusion of donor lymphocytes expressing the herpes simplex virus thymidine kinase suicide gene (TK-cells) is a promising strategy for the treatment of hematologic malignancies relapsing after allogeneic hematopoietic stem cell transplantation. Here we report the results of a phase I clinical trial designed to examine the feasibility, safety, and efficacy of donor lymphocyte infusion (DLI) of TK-cells. Three patients (two with malignant lymphomas, one with acute myeloid leukemia) were enrolled in the trial and received a single DLI of 1 × 10(7) or 5 × 10(7) TK-cells/kg. No local or systemic toxicity related to the gene-transfer procedure was observed. Two patients achieved stable disease. No patient had severe graft-versus-host disease requiring systemic steroid and/or ganciclovir administration. TK-cells were detected in the peripheral blood of all three patients by PCR, but did not persist longer than 28 days. Analysis of cytotoxic T lymphocyte activity detected no immune response against TK-cells by the recipient's own T cells. Flow cytometric analysis showed low proliferative activity and cytotoxic function of TK-cells. In conclusion, DLI of TK-cells was safely performed in all three patients. Our analysis suggests the probable cause of rapid disappearance of TK-cells to be insufficient in vivo expansion of TK-cells in these patients.

Improving the safety of cell therapy with the TK-suicide gene

While opening new frontiers for the cure of malignant and non-malignant diseases, the increasing use of cell therapy poses also several new challenges related to the safety of a living drug. The most effective and consolidated cell therapy approach is allogeneic hematopoietic stem cell transplantation (HSCT), the only cure for several patients with high-risk hematological malignancies. The potential of allogeneic HSCT is strictly dependent on the donor immune system, particularly on alloreactive T lymphocytes, that promote the beneficial graft-versus-tumor effect (GvT), but may also trigger the detrimental graft-versus-host-disease (GvHD). Gene transfer technologies allow to manipulate donor T-cells to enforce GvT and foster immune reconstitution, while avoiding or controlling GvHD. The suicide gene approach is based on the transfer of a suicide gene into donor lymphocytes, for a safe infusion of a wide T-cell repertoire, that might be selectively controlled in vivo in case of GvHD. The herpes simplex virus thymidine kinase (HSV-TK) is the suicide gene most extensively tested in humans. Expression of HSV-TK in donor lymphocytes confers lethal sensitivity to the anti-herpes drug, ganciclovir. Progressive improvements in suicide genes, vector technology and transduction protocols have allowed to overcome the toxicity of GvHD while preserving the antitumor efficacy of allogeneic HSCT. Several phase I-II clinical trials in the last 20 years document the safety and the efficacy of HSV-TK approach, able to maintain its clear value over the last decades, in the rapidly progressing horizon of cancer cellular therapy.

Adoptive immunotherapy with genetically modified lymphocytes in allogeneic stem cell transplantation

Hematopoietic stem cell transplantation from a healthy donor (allo-HSCT) represents the most potent form of cellular adoptive immunotherapy to treat malignancies. In allo-HSCT, donor T cells are double edge-swords: highly potent against residual tumor cells, but potentially highly toxic, and responsible for graft versus host disease (GVHD), a major clinical complication of transplantation. Gene transfer technologies coupled with current knowledge on cancer immunology have generated a wide range of approaches aimed at fostering the immunological response to cancer cells, while avoiding or controlling GVHD. In this review, we discuss cell and gene therapy approaches currently tested in preclinical models and in clinical trials.

Progress and prospects for engineered T cell therapies

Proof-of-concept studies have demonstrated the therapeutic potential of engineered T cells. Transfer of recombinant antigen-specific T cell receptors (TCR) and chimaeric antigen receptors (CARs) against tumour and viral antigens are under investigation by multiple approaches, including viral- and nonviral-mediated gene transfer into both autologous and allogeneic T cell populations. There have been notable successes recently using viral vector-mediated transfer of CARs specific for B cell antigens, but also reports of anticipated and unanticipated complications in these and other studies. We review progress in this promising area of cellular therapy, and consider developments in antigen receptor therapies including the application of emerging gene-editing technologies.

Production and first-in-man use of T cells engineered to express a HSVTK-CD34 sort-suicide gene

Suicide gene modified donor T cells can improve immune reconstitution after allogeneic haematopoietic stem cell transplantation (SCT), but can be eliminated in the event of graft versus host disease (GVHD) through the administration of prodrug. Here we report the production and first-in-man use of mismatched donor T cells modified with a gamma-retroviral vector expressing a herpes simplex thymidine kinase (HSVTK):truncated CD34 (tCD34) suicide gene/magnetic selection marker protein. A stable packaging cell line was established to produce clinical grade vector pseudotyped with the Gibbon Ape Leukaemia Virus (GALV). T cells were transduced in a closed bag system following activation with anti-CD3/CD28 beads, and enriched on the basis of CD34 expression. Engineered cells were administered in two escalating doses to three children receiving T-depleted, CD34 stem cell selected, mismatched allogeneic grafts. All patients had pre-existing viral infections and received chemotherapy conditioning without serotherapy. In all three subjects cell therapy was tolerated without acute toxicity or the development of acute GVHD. Circulating gene modified T cells were detectable by flow cytometry and by molecular tracking in all three subjects. There was resolution of virus infections, concordant with detectable antigen-specific T cell responses and gene modified cells persisted for over 12 months. These findings highlight the suitability of tCD34 as a GMP compliant selection marker and demonstrate the feasibility, safety and immunological potential of HSVTK-tCD34 suicide gene modified donor T cells.

Trial Registration

ClinicalTrials.gov NCT01204502 <NCT01204502>

Retrovolution: HIV-driven evolution of cellular genes and improvement of anticancer drug activation

In evolution strategies aimed at isolating molecules with new functions, screening for the desired phenotype is generally performed in vitro or in bacteria. When the final goal of the strategy is the modification of the human cell, the mutants selected with these preliminary screenings may fail to confer the desired phenotype, due to the complex networks that regulate gene expression in higher eukaryotes. We developed a system where, by mimicking successive infection cycles with HIV-1 derived vectors containing the gene target of the evolution in their genome, libraries of gene mutants are generated in the human cell, where they can be directly screened. As a proof of concept we created a library of mutants of the human deoxycytidine kinase (dCK) gene, involved in the activation of nucleoside analogues used in cancer treatment, with the aim of isolating a variant sensitizing cancer cells to the chemotherapy compound Gemcitabine, to be used in gene therapy for anti-cancer approaches or as a poorly immunogenic negative selection marker for cell transplantation approaches. We describe the isolation of a dCK mutant, G12, inducing a 300-fold sensitization to Gemcitabine in cells originally resistant to the prodrug (Messa 10K), an effect 60 times stronger than the one induced by the wt enzyme. The phenotype is observed in different tumour cell lines irrespective of the insertion site of the transgene and is due to a change in specificity of the mutated kinase in favour of the nucleoside analogue. The mutations characterizing G12 are distant from the active site of the enzyme and are unpredictable on a rational basis, fully validating the pragmatic approach followed. Besides the potential interest of the G12 dCK variant for therapeutic purposes, the methodology developed is of interest for a large panel of applications in biotechnology and basic research.

We exploited the error-prone replication machinery of HIV-1 and its ability to stably introduce transgenes in human cells to develop a novel system, Retrovolution, to generate libraries of mutants of cellular genes. When libraries are screened to isolate variants that modify the phenotype of the human cell for biomedical applications or basic research, false positives often arise from the classical screening procedures performed in vitro or in bacteria. Retrovolution allows an easy screening of the libraries directly in the human cell, where they are generated. We describe the creation and screening of a library of the hdCK (a human kinase activating several anticancer compounds) gene, to identify variants increasing the sensitivity of cancer cells to treatment with low, poorly toxic doses of the anticancer drug Gemcitabine. We isolated a dCK variant inducing death in tumour cells at doses up to 300 times lower than those required for killing non-engineered cells. The mutant presents mutations unpredictable on structural basis and revealed a change in enzymatic properties that accounts for the observed cellular effect. Besides the intrinsic interest of the mutant identified, these results fully validate Retrovolution as a mutagenesis system with broad applications in applied and basic research.

Gene-modified T lymphocytes in the setting of hematopoietic cell transplantation: potential benefits and possible risks

INTRODUCTION

Allogeneic hematopoietic cell transplantation (HCT) is a consolidated treatment for several hematologic malignancies. Donor T lymphocytes can mediate a graft versus tumor (GVT) effect and control opportunistic infections but can also cause severe graft versus host disease (GVHD). Gene-transfer strategies are appealing tools to modulate T cell functions when infused after HCT.

AREAS COVERED

The current and potential future applications of T cell gene-transfer approaches to HCT. This review is not limited to GVHD control but covers the issues of GVT and immune reconstitution. Clinical data are used to discuss more general issues, perspectives and concerns common to gene-modification of T cells. An overview of the results and limitations emerging from clinical trials with herpes simplex virus-thymidine kinase (HSV-TK) engineered lymphocytes is provided. The review provides perspectives on additional gene-transfer strategies, currently at preclinical level or that have just entered clinical trials, to increase the efficacy and safety of HCT.

EXPERT OPINION

Gene-transfer can positively interfere with T cell functions after HCT. TK-lymphocytes have proven effective in controlling GVHD while retaining an acceptable GVT effect. Strategies exploiting new suicide molecules or engineered T cell receptors (TCRs) should be further explored to address current limitations with TK-lymphocytes and augment the efficacy and specificity of GVT and antiviral activity.

TK.007: A novel, codon-optimized HSVtk(A168H) mutant for suicide gene therapy

Conditional elimination of infused gene-modified alloreactive T cells, using suicide gene activation, has been shown to be an efficient strategy to abrogate severe graft-versus-host disease (GvHD) in the context of adoptive immunotherapy. To overcome shortcomings of the most widely used suicide gene, wild-type (splice-corrected) herpes simplex virus thymidine kinase (scHSVtk), we generated two new variants: the codon-optimized coHSVtk and, by introducing an additional mutation (A168H), the novel TK.007. We transduced human hematopoietic cell lines and primary T cells with retroviral "sort-suicide vectors" encoding combinations of selection markers (tCD34 and OuaSelect) with one of three HSVtk variants. In vitro we observed higher expression levels and sustained long-term expression of TK.007, indicating lower nonspecific toxicity. Also, we noted significantly improved kinetics of ganciclovir (GCV)-mediated killing for TK.007-transduced cells. In an experimental (murine) allogeneic transplantation model, TK.007-transduced T cells mediated severe GvHD, which was readily abrogated by application of GCV (10 mg/kg). Last, we established a modified allotransplantation model that allowed quantitative comparison of the in vivo activities of TK.007 versus scHSVtk. We found that TK.007 mediates both significantly faster and higher absolute killing at low GCV concentrations (10 and 25 mg/kg). In summary, we demonstrate that the novel TK.007 suicide gene combines better killing performance with reduced nonspecific toxicity (as compared with the frequently used splice-corrected wild-type scHSVtk gene), thus representing a promising alternative for suicide gene therapy.

Suicide gene therapy for graft-versus-host disease

In allogeneic hematopoietic stem cell transplantation, donor-derived T cells are key players for early immune reconstitution and efficient engraftment, as well as the graft-versus-leukemia and graft-versus-infection effects. However, a severe and quite common life-threatening complication is the development of graft-versus-host disease, during which the alloreactive donor T cells attack the host. Controlling graft-versus-host disease while preserving the benefits of graft-versus-leukemia still constitutes a challenge. A promising approach for the control of graft-versus-host disease is suicide gene therapy, which involves the ex vivo genetic modification of donor T cells with a suicide gene that allows for the selective elimination of the cells in vivo if graft-versus-host disease occurs. This article presents an overview of such approaches with special reference to lessons learned from previous clinical experiences, as well as a discussion of critical factors in suicide gene therapy.

Clinical impact of suicide gene therapy in allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (allo-SCT) from an HLA-matched related or unrelated donor is a curative option for patients with high-risk hematological diseases. In the absence of a matched donor, patients have been offered investigational transplantation strategies such as umbilical cord blood SCT or family haploidentical SCT. Besides the activity of the conditioning regimen, most of the antileukemic potential of allo-SCT relies on alloreactivity, promoted by donor lymphocytes reacting against patient-specific antigens, such as minor and major histocompatibility antigens, ultimately translating into cancer immunotherapy. Unfortunately, alloreactivity is also responsible for the most serious and frequent complication of allo-SCT: graft-versus-host-disease (GvHD). The risk of GvHD increases with the level of HLA disparity between host and donor, and leads to impaired quality of life and reduced survival expectancy, particularly among patients receiving transplants from HLA-mismatched donors. Gene transfer technologies are promising tools to manipulate donor T cell immunity to enforce the graft-versus-tumor effect, to promote functional immune reconstitution (graft vs. infection), and to prevent or control GvHD. To this purpose, several cell and gene transfer approaches have been investigated at the preclinical level, and are being implemented in clinical trials. Suicide gene therapy is to date the most extensive clinical application of T cell-based gene therapy. In several phase I-II clinical studies conducted worldwide this approach proved highly feasible, safe, and effective in promoting a dynamic and patient-specific modulation of alloreactivity. This review focuses on this approach.

Adoptive T-cell immunotherapy of cancer using chimeric antigen receptor-grafted T cells

Harnessing the power of the immune system to target cancer has long been a goal of tumor immunologists. One avenue under investigation is the modification of T cells to express a chimeric antigen receptor (CAR). Expression of such a receptor enables T-cell specificity to be redirected against a chosen tumor antigen. Substantial research in this field has been carried out, incorporating a wide variety of malignancies and tumor-associated antigens. Ongoing investigations will ensure this area continues to expand at a rapid pace. This review will explain the evolution of CAR technology over the last two decades in addition to detailing the associated benefits and disadvantages. The outcome of recent phase I clinical trials and the impact that these have had upon the direction of future research in this field will also be addressed.

Early immune response against retrovirally transduced herpes simplex virus thymidine kinase-expressing gene-modified T cells coinfused with a T cell-depleted marrow graft: an altered immune response?

Administration of herpes simplex thymidine kinase (HSV-tk)-expressing, gene-modified T cells (GMCs) with T cell-depleted bone marrow transplantation (TCD-BMT) can allow modulation of posttransplantation alloreactivity. Twelve patients received 2 x 10(5) to 2 x 10(6) CD3+ donor GMCs per kilogram with HLA-identical sibling TCD-BMT. Despite extensive T cell depletion of bone marrow, an intensive conditioning regimen, and immunosuppressive graft-versus-host disease (GvHD) prophylaxis, infusion at the time of TCD-BMT of this low number of GMCs sufficed to induce a rapid GMC-specific immune response, as detected by interferon- enzyme- linked immunospot assay in six of eight patients, preferentially targeting HSV-tk. Maximal responses were reached early (median time, 49 [35-68] days post-BMT), with a subsequent rapid and significant decrease in five of six evaluable patients. Immune responses were negatively correlated with the maximal circulating GMC counts. However, such immune response did not result in the elimination of circulating GMCs and was not associated with measurable ex vivo cytotoxic activity against GMCs. Furthermore, alloreactive GMCs still could induce GCV-sensitive GvHD in one patient despite an ongoing immune response. Overall, infusion of HSV-tk-expressing GMCs at the time of BMT results in an early immune response. Such immune response may be altered and may not prevent persistent GCV-sensitive alloreactivity.

T cells for suicide gene therapy: activation, functionality and clinical relevance

In order to control graft-versus-host disease after donor lymphocyte infusion, T cells can be retrovirally transduced with a suicide gene. However, the immune competence of activated T cells appears compromised, responsible for reduced alloreactivity. The present study compared different activation protocols using soluble or bead-coupled antibodies regarding T-cell subtype expansion capacity and functionality. T cells were purified on a laboratory and clinical scale using both CD3 and CD4/CD8 antibodies for selection, leading to a mean purity of 96%. Transductions were performed with a GMP-grade CD34/HSV-TK vector. Activation with soluble CD3/CD28-antibodies +1000 U/ml IL-2 induced a 50-fold expansion of T cells over 14 days, whereas T cells activated with bead-coupled antibodies only expanded 2-4-fold restricted to the first week. Apart from using soluble antibodies, proliferation was highly IL-2 dependent. Expansion of CMV-specific T cells coincided with the expansion of whole CD3(+) cells. Soluble antibodies and higher IL-2 concentrations preferentially stimulated CD8(+) T cells, while bead-coupled antibodies +20 U/ml IL-2 preserved the CD4/CD8 ratio. Irrespective of the activation protocol, there was a shift from a naive to memory phenotype. When activated with soluble antibodies, mainly CD8(+) T cells were transduced. Furthermore, Th1/Th2 cytokine secretion was reduced. In contrast, CD4(+)/CD8(+) T cells activated with bead-coupled antibodies were rather homogenously transduced and cytokine secretion did not appear to be affected.

T cell therapies following hematopoietic stem cell transplantation: surely there must be a better way than DLI?

Advances in the past few years have significantly improved adoptive immunotherapy strategies available following autologous and allogeneic hematopoietic stem cell transplantation (HSCT). Minimal residual disease, relapsed disease and viral infections remain a significant cause of mortality in patients undergoing HSCT. Novel therapies are critically needed to overcome these management dilemmas, while sparing the graft-versus-tumor effect and avoiding graft-versus-host disease. This review focuses on the T-cell strategies currently available to allay disease while minimizing toxicities in patients who have undergone HSCT.

The suicide gene therapy challenge: how to improve a successful gene therapy approach

The transfer of a suicide gene into donor lymphocytes to control alloreactivity in the context of allogeneic hematopoietic stem cell transplantation (allo-HSCT) represents the widest clinical application of T-cell based gene transfer, as shown by more than 100 patients treated worldwide to date, several phase I-II studies completed, and a registrative phase III study, sponsored by a biotech firm, about to begin. In this mini-review, we will summarize the clinical results obtained to date, and attempt to identify the steps envisaged to optimize the suicide gene therapy approach.

Control of graft-versus-host disease with maintenance of the graft-versus-leukemia effect in a murine allogeneic transplant model using retrovirally transduced murine suicidal lymphocytes

OBJECTIVE

Limited clinical trials have validated the hypothesis of controlling graft-versus-host disease (GVHD) arising from stem cell transplant utilizing suicidal T-lymphocytes that have been transduced to express the HSV-TK gene. However, clinical utility has been limited by diminished T-cell function arising from the production process. To evaluate strategies for harnessing the graft-versus-leukemia (GVL) effect while improving the safety and function of suicidal lymphocytes, we have developed techniques to produce fully functional, retrovirally transduced, HSV-TK-positive murine T cells (TK+TC).

METHODS

Utilizing a murine major histocompatibility complex-matched transplant model, we evaluated the ability of TK+TC to generate a GVL effect and the ability to control GVHD in experiments where we varied the dose of TK+TC, ganciclovir (GCV) dose, the start of GCV administration (day 4, 7, 10, 13, 15, or 19) posttransplantation, and the GCV administration route (osmotic pump versus intraperitoneal).

RESULTS

At TK+TC doses in excess of the standard lethal dose (SLD) of unmanipulated T-cells, GCV administration completely (2 x SLD) and partially (4 x SLD) controlled GVHD. Additionally, GVHD remained reversible despite delaying administration of GCV for a week after GVHD developed. Importantly, GVHD was controlled with a 1-log but not 2-log reduction in GCV dose, and this "partial suicide" preserved more circulating TK+TC compared with standard-dose GCV. Survival of leukemia-positive mice receiving TK+TC and GCV was significantly increased compared with control cohorts not receiving GCV or transplanted with unmanipulated T cells, thereby demonstrating a GVL effect.

CONCLUSION

Retrovirally transduced suicidal lymphocytes generate a potent GVL effect while simultaneously enabling control of GVHD, which results in improved leukemia and GVHD-free survival.

Lentiviral Vectors for T-cell Suicide Gene Therapy: Preservation of T-cell Effector Function After Cytokine-mediated Transduction

Retroviral transfer of the Herpes Simplex thymidine kinase (HSVTK) suicide gene to donor T cells has been used as a safety strategy against graft-versus-host disease following allogeneic stem cell transplantation. The feasibility of this strategy in human studies has been demonstrated, but a number of limitations have become apparent. Preactivation of donor lymphocytes using mitogens or monoclonal antibodies is essential for retroviral transduction, but can compromise subsequent T-cell function in vivo. We report the application of lentiviral vectors for transduction of T cells in cytokine culture, without activation through the T-cell receptor. Using vectors encoding either enhanced green fluorescent protein or a truncated CD34/mutant HSVTK fusion selection/suicide construct, we investigated the properties of T cells after gene modification. We found that following cytokine stimulation, a fraction of T cells undergoes division, and transgene expression occurred predominantly in these cells. Antiviral and alloreactive responses were preserved in these populations, and in contrast to fully activated T cells, there was minimal perturbation of regulatory T-cell numbers. We conclude that the use of interleukin-7 for lentiviral transduction offers the greatest potential for gene transfer to T cells without loss of function, and is favored for the clinical production of suicide gene modified T cells.

Rapid and massive expansion of cord blood-derived cytokine-induced killer cells: an innovative proposal for the treatment of leukemia relapse after cord blood transplantation

We have used a standardized 21-day expansion protocol to produce cytokine-induced killer (CIK) cells starting from very small amounts of nucleated cells (approximately 15 x 10(6) cells) isolated from cord blood. Mononuclear cells are stimulated with anti CD3 (OKT3) and IFNgamma and then expanded with IL-2. Moreover, we show that washouts of cord blood units bags (at the end of the infusion) may be sufficient to yield almost 500 x 10(6) CIK by the same expansion protocol. CIK cells show strong cytotoxic activity against a variety of tumor target cell lines including B and T lymphomas and myeloid leukemias. More importantly, expanded cord blood-derived CIK cells are cytotoxic against fresh leukemic blasts and express perforin, granzyme and NKG2D molecule at high levels. The same in vitro protocol has already been used to expand CIK cells from peripheral blood of adult donors under GMP conditions and therefore these observations open up the possibility of imagining a future clinical application of leukemia relapse following cord blood transplantation with CIK cells obtained from the same cord blood unit.

Current status of genetic modification of T cells for cancer treatment

Clinical studies of adoptive immunotherapy with T cells have shown activity directed at hematologic and solid malignancies and viral infections. Genetic modification of infused T cells offers the prospect of improving such therapies and has already been used to track infused T cells, insert suicide genes and redirect the immune response towards specific Ag. Pre-clinical studies are evaluating novel approaches to genetically modify T cells to confer resistance to tumor evasion mechanisms. There is also increasing interest in developing suicide gene strategies as a failsafe mechanism to eradicate genetically modified cells should adverse effects occur.

Analysis of transgene-specific immune responses that limit the in vivo persistence of adoptively transferred HSV-TK-modified donor T cells after allogeneic hematopoietic cell transplantation

The introduction of an inducible suicide gene such as the herpes simplex virus thymidine kinase (HSV-TK) might allow exploitation of the antitumor activity of donor T cells after allogeneic hematopoietic cell transplantation (HCT) without graft versus host disease. However, HSV-TK is foreign, and immune responses to gene-modified T cells could lead to their premature elimination. We show that after the infusion of HSV-TK-modified donor T cells to HCT recipients, CD8+ and CD4+ T-cell responses to HSV-TK are rapidly induced and coincide with the disappearance of transferred cells. Cytokine flow cytometry using an overlapping panel of HSV-TK peptides allowed rapid detection and quantitation of HSV-TK-specific T cells in the blood and identified multiple immunogenic epitopes. Repeated infusion of modified T cells boosted the induced HSV-TK-specific T cells, which persisted as memory cells. These studies demonstrate the need for nonimmunogenic suicide genes and identify a strategy for detection of CD4+ and CD8+ T-cell responses to transgene products that should be generally applicable to monitoring patients on gene therapy trials. The potency of gene-modified T cells to elicit robust and durable immune responses imply this approach might be used for vaccination to elicit T-cell responses to viral or tumor antigens.

Temporal discordance between graft-versus-leukemia and graft-versus-host responses: A strategy for the separation of graft-versus-leukemia/graft-versus-host reactivity?

The graft-versus-leukemia (GVL) effect is often coexpressed with graft-versus-host disease (GVHD), although the temporal kinetics of these responses have not been critically examined. To evaluate this question in the absence of the confounding effects of the conditioning regimen, 23 patients who received donor lymphocyte infusions from HLA-identical siblings and subsequently developed GVHD and/or a GVL response were studied to determine whether these were temporally synchronous events. The GVL effect occurred significantly earlier than GVHD, being that 19 of 23 patients had a sustained GVL response that antedated the onset of clinical GVHD. The median difference between time to GVL and graft-versus-host (GVH) reactivity in the entire cohort was 14 days. There was no correlation between total T-cell dose and the relative onset of GVL versus GVH reactivity, indicating that temporal dissociation of GVL and GVH responses was not a function of the absolute number of infused donor T cells. These data support existing murine bone marrow transplantation studies indicating that GVL and GVH responses are not temporally synchronous events and raise the possibility that targeted elimination of alloreactive donor T cells after bone marrow transplantation may be an effective strategy for the separation of GVL/GVH reactivity.

Suicide gene therapy and the control of graft-vs-host disease

Allogeneic bone marrow transplantation as a cure for leukaemia and lymphoma is limited by the development of graft-vs-host disease (GVHD), an immunological reaction of the donor's T lymphocytes against the host's normal tissues. One therapeutic option to treat GVHD is the transfer of 'suicide' genes into the donor's T lymphocytes to render them susceptible to prodrug administration. This procedure should permit the elimination of unwanted T lymphocytes in GVHD. The main genes proposed for such a strategy will be described in this chapter, together with the advantages and limitations found during preclinical and clinical studies to date.

Cellular immunotherapy after allogeneic stem cell transplantation in hematologic malignancies

PURPOSE OF REVIEW

The chimeric state after allogeneic stem cell transplantation provides an ideal platform for adoptive immunotherapy of hematologic malignancies using donor-derived cells. The present review aims to summarize recent results of the transfusion of donor-derived cells with regard to the diseases treated, the cells used for treatment, and the origin of these cells.

RECENT FINDINGS

The transfusion of donor lymphocytes has been studied widely, not only in patients with recurrent disease, persistent disease, and mixed chimerism but also in a variety of hematologic malignancies. Donors of lymphocytes and hematopoietic stem cells have been HLA-identical siblings, HLA-matched unrelated donors, and HLA-different haploidentical family members. A variety of cells have been used for adoptive immunotherapy, including plain lymphocytes, selected T cells, T cell lines, and T cell clones. The possible therapies have been expanded by natural killer cells and natural killer T cells as well as antibodies directing the effector cells toward the malignancy.

SUMMARY

Adoptive immunotherapy in chimeras has become not only a routine form of treatment of recurrent hematologic malignancy but also a prophylactic measure in high-risk leukemia and lymphoma.