Suicide gene therapy of graft-versus-host disease: immune reconstitution with transplanted mature T cells

Mechanisms of Tolerance Induction by Hematopoietic Chimerism: The Immune Perspective

Hematopoietic chimerism is one of the effective approaches to induce tolerance to donor‐derived tissue and organ grafts without administration of life‐long immunosuppressive therapy. Although experimental efforts to develop such regimens have been ongoing for decades, substantial cumulative toxicity of combined hematopoietic and tissue transplants precludes wide clinical implementation. Tolerance is an active immunological process that includes both peripheral and central mechanisms of mutual education of coresident donor and host immune systems. The major stages include sequential suppression of early alloreactivity, establishment of hematopoietic chimerism and suppressor cells that sustain the state of tolerance, with significant mechanistic and temporal overlap along the tolerization process. Efforts to devise less toxic transplant strategies by reduction of preparatory conditioning focus on modulation rather than deletion of residual host immunity and early reinstitution of regulatory subsets at the central and peripheral levels. Stem Cells Translational Medicine2017;6:700–712

Control of mouse graft-versus-host disease following allogeneic bone marrow transplantation by blocking the CD28/B7 signaling pathway with lentiviral vector-mediated RNA interference

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an effective way to cure hematological malignancies. However, graft-versus-host disease (GVHD) following transplantation limits the clinical application to some extent. The donor T lymphocytes play a central role in the occurrence and development of GVHD. Control of GVHD by inhibition of T cell proliferation by blocking the CD28/B7 signaling pathway with RNA interference has not been examined. In this study, we constructed a lentiviral vector carrying CD28 shRNA and generated genetically engineered splenocytes through transduction in a murine allogeneic bone marrow transplantation model. The survival and the occurrence of GVHD in transplanted mice were monitored every day. Liver, intestine, skin, and other tissues from the mice in each group were used for histological examination. We also determined plasma concentrations of interleukin (IL)-2, IL-4, IL-5, IL-10, IL-13, and interferon gamma (IFN-γ). Recipient bone marrow from mice that had survived for an extended period was examined to detect chimerism. We succeeded in suppressing the expression of CD28 gene and controlling mouse GVHD following allogeneic bone marrow transplantation in the engineered spleen cell group. These suggest that blocking the CD28/B7 signal transduction pathway with lentiviral vector-mediated RNA interference effectively controlled the occurrence of mouse GVHD following allogeneic bone marrow transplantation. Its mechanism could be due to the inhibition of T cell proliferation and, simultaneously, the promotion of the differentiation of TH0 to TH2 cells, thereby reducing GVHD in the mouse transplantation model.

Depletion of Host Reactive T Cells by Photodynamic Cell Purging and Prevention of Graft Versus Host Disease

Graft versus Host Disease (GVHD) is the principal cause of morbidity and mortality in patients undergoing allogeneic stem cell transplant. T cell depletion has been recognized as a method of reducing the incidence of GVHD in allogeneic transplants. Until recently, most T cell depletion methods were non-selective in reducing lymphocytes. Rhodamine purging is one method, which selectively reduces alloreactive T cells preventing GVHD. We review here the methods of non-selective and selective T cell depletion, particularly the newer method of photodynamic purging utilizing rhodamine.

Coexpression of the Uracil Phosphoribosyltransferase Gene with a Chimeric Human Nerve Growth Factor Receptor/Cytosine Deaminase Fusion Gene, Using a Single Retroviral Vector, Augments Cytotoxicity of Transduced Human T Cells Exposed to 5-Fluorocytosine

Donor T lymphocytes genetically engineered to express a "suicide gene" to facilitate negative selection represent a promising strategy for the management of graft-versus-host disease occurring after allogeneic hematopoietic cell transplantation (HCT). For this purpose, the herpes simplex virus thymidine kinase (HSV-tk) gene, although well studied, has limitations. Cytosine deaminase (CD), an alternative gene for negative selection, converts 5-fluorocytosine (5-FC) to the toxic metabolite 5-fluorouracil (5-FU). Sensitivity of cells to 5-FU can be further increased by expression of uracil phosphoribosyltransferase (UPRT), which catalyzes the conversion of 5-FU to 5-fluorouridine monophosphate. By using a chimeric gene (NG/CD) expressing the truncated human nerve growth factor receptor (NGFR) for positive selection fused to the Saccharomyces cerevisiae CD gene, we investigated strategies to achieve optimal T cell eradication by CD and UPRT expression, utilizing a single retroviral vector. Three vector strategies were compared on the basis of NGFR expression by flow cytometry, western analysis, and enzymatic activity. A construct (NG/CDiU) expressing UPRT and NG/CD, using a bicistronic message, provided the greatest UPRT activity and killing, reducing the lethal dose of 5-FC sufficient to eradicate 90% of cells from 38.7 microg/ml (300 microM) (NG/CD expression alone) to 0.13 microg/ml (1 microM). This approach provides an effective alternative to the HSV-tk system for eradication of donor T lymphocytes after allogeneic HCT.

Angiogenic Gene Cell Therapy using Suicide Gene System Regulates the Effect of Angiogenesis in Infarcted Rat Heart

BACKGROUND

Although angiogenic gene therapy has been reported to be effective in restoring ischemic heart function, there are several obstacles to its clinical application, such as unreliable efficiency of transfection and uncontrollable expression. We developed human HGF (hHGF)-producing cells that regulated hHGF production using the thymidine kinase gene of Herpes Simplex Virus (TK) and the Ganciclovir (GCV) system. We tested whether these cells induced and regulated angiogenic effects in infarcted myocardium.

METHODS

NIH3T3 cells were stably transfected with an hHGF cDNA expression plasmid (NIH/HGF). Next, the NIH/HGF cells were stably transfected with TK (NIH/HGF/TK). The left anterior descending artery was ligated in the heart of severe combined immunodeficiency rats, and four materials were transplanted: 1) NIH/HGF (n=10), 2) NIH/HGF/TK, with orally administered GCV (n=10), 3) NIH3T3 (n=10), and 4) culture medium (n=10).

RESULTS

In vitro, the proliferation of NIH/HGF/TK cells was suppressed by GCV. In vivo, significant increases in cardiac performance and angiogenesis were observed in the NIH/HGF and NIH/HGF/TK groups 4 weeks after transplantation. Although tumorous lesions were detected in the NIH/HGF group, their growth was completely controlled in the NIH/HGF/TK group.

CONCLUSIONS

Angiogenic gene cell therapy using the TK-GCV suicide gene system induces and regulates angiogenesis under the control of cell growth, suggesting it as a promising system for therapeutic angiogenesis.

Severe combined immunodeficiency. A model disease for molecular immunology and therapy

Severe combined immunodeficiencies (SCIDs) consist of genetically determined arrest of T-cell differentiation. Ten different molecular defects have now been identified, which all lead to early death in the absence of therapy. Transplantation of allogeneic hematopoietic stem cells (HSCT) can restore T-cell development, thus saving the lives of SCID patients. In this review, the different characteristics of HSCT are discussed along with the available data regarding the long-term outcome. Transient thymopoiesis caused by an exhaustion of donor progenitor cells and possibly a progressive loss of thymus function can lead to a progressive decline in T-cell functions. The preliminary results of gene therapy show the correction of two SCID conditions. Based on the assumption that long-lasting pluripotent progenitor cells are transduced, these data suggest that gene therapy could overcome the long-term recurrence of the T-cell immunodeficiency. SCID is thus a disease model for experimental therapy in the hematopoietic system.

Kinetics of in vivo elimination of suicide gene-expressing T cells affects engraftment, graft-versus-host disease, and graft-versus-leukemia after allogeneic bone marrow transplantation

Suicide gene therapy is one approach being evaluated for the control of graft-vs-host disease (GVHD) after allogeneic bone marrow transplantation (BMT). We recently constructed a novel chimeric suicide gene in which the entire coding region of HSV thymidine kinase (HSV-tk) was fused in-frame to the extracellular and transmembrane domains of human CD34 (DeltaCD34-tk). DeltaCD34-tk is an attractive candidate as a suicide gene in man because of the ensured expression of HSV-tk in all selected cells and the ability to rapidly and efficiently purify gene-modified cells using clinically approved CD34 immunoselection techniques. In this study we assessed the efficacy of the DeltaCD34-tk suicide gene in the absence of extended ex vivo manipulation by generating transgenic animals that express DeltaCD34-tk in the peripheral and thymic T cell compartments using the CD2 locus control region. We found that DeltaCD34-tk-expressing T cells could be purified to near homogeneity by CD34 immunoselection and selectively eliminated ex vivo and in vivo when exposed to low concentrations of GCV. The optimal time to administer GCV after allogeneic BMT with DeltaCD34-tk-expressing transgenic T cells was dependent on the intensity of the conditioning regimen, the leukemic status of the recipient, and the dose and timing of T cell infusion. Importantly, we used a controlled graft-vs-host reaction to promote alloengraftment in sublethally irradiated mice and provide a graft-vs-leukemia effect in recipients administered a delayed infusion of DeltaCD34-tk-expressing T cells. This murine model demonstrates the potential usefulness of DeltaCD34-tk-expressing T cells to control GVHD, promote alloengraftment, and provide a graft-vs-leukemia effect in man.

Selective elimination of alloreactive donor T cells attenuates graft-versus-host disease and enhances T-cell reconstitution

Impaired T-cell immune reconstitution is a major complication after allogeneic bone marrow transplantation (BMT) and is particularly exacerbated in the setting of graft-versus-host disease (GVHD). Conventional approaches to reduce GVHD, such as T-cell depletion or pharmacologic immunosuppression, typically fail to enhance T-cell immunity and often further exacerbate this problem. An alternative strategy to mitigate GVHD severity is the selective elimination of graft-versus-host-reactive donor T cells by using an incorporated thymidine kinase suicide gene. This approach has been shown to effectively reduce GVHD, although the effect of this strategy on T-cell reconstitution is unresolved. We addressed this question in a murine BMT model (C57BL/6 [H-2(b)] --> AKR/J [H-2(k)]) in which donor and recipient differ at major and minor histocompatibility antigens. Lethally irradiated AKR recipients transplanted with T cell-depleted bone marrow plus thymidine kinase-positive T cells followed by post-BMT ganciclovir (GCV) administration had more prompt and complete normalization of the T-cell repertoire than phosphate-buffered saline-treated GVHD control animals. By 60 days after transplantation, mice administered GCV had T-cell repertoires that were virtually indistinguishable from those of mice that underwent transplantation with T cell-depleted bone marrow alone (no GVHD controls) when assayed by T-cell receptor (TCR) spectratyping. In contrast, phosphate-buffered saline-treated animals had persistent skewing in most Vbeta families. T cells obtained from GCV-treated mice also had significantly higher in vitro proliferative responses after posttransplantation inoculation with ovalbumin than GVHD animals, indicating that CD4(+) T-cell responses against a nominal antigen were better preserved in these chimeras. Finally, GCV-treated mice had augmented immune reconstitution in response to exogenous interleukin-7 administration, as evidenced by increased overall spleen cellularity and absolute numbers of T and B cells. This was in contrast to GVHD control animals, which had a blunted response to interleukin-7 administration. These data indicate that GVHD severity can be significantly reduced by selective elimination of alloreactive donor T cells without compromise of T-cell immunity. Moreover, in light of previous studies demonstrating that this strategy can reduce GVHD without loss of alloengraftment and antileukemia reactivity, further examination of this approach in humans seems warranted.

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.

Functional and phenotypic variations in human T cells subjected to retroviral-mediated gene transfer

The insertion of suicide genes in donor T lymphocytes constitutes the basis of new approaches aiming at the treatment of the graft-versus-host disease (GVHD), a frequent complication in recipients of allogeneic haematopoietic grafts. In this study we investigated the impact that the ex vivo manipulation required for the retroviral transduction of T cells had on the functionality and differentiation of these cells. Compared to fresh T cells, samples that had been subjected to standard activation (1 microg/ml of both anti-CD3i and anti-CD28i MoAbs) followed by transduction with vectors encoding for the HSV-tk and tNGFR genes maintained the proliferative response to an allogeneic stimulus. These cells, however, had a significantly lower cytotoxic response to allogeneic cells compared to fresh samples. When the concentration of anti-CD3i was reduced to up to 1000-fold (1 ng/ml), similar T-cell transductions were obtained, while the cytotoxicity of the ex vivo manipulated samples was significantly recovered, when assessed either at 7 or 14 days of culture. In all instances, a similar functionality was observed in transduced samples not subjected to immunomagnetic cell sorting, compared to purified fractions enriched in NGFR(+) and NFGR(-) cells. The analysis of CD45RA and CCR7 markers in samples transduced under standard stimulatory conditions showed a differentiation of fresh CD8(+) CD45RA(+)/CCR7(+) naive cells to cells having a predominant central CD45RA(-)/CCR7(+) and effector CD45RA(-)/CCR7(-) memory phenotype. However, when samples were activated with low doses of anti-CD3i, a significant population of naive cells became apparent. Although activation with high doses of anti-CD3i/anti-CD28i resulted in a similar phenotype in both NGFR(+) and NFGR(-) populations, the naive population observed in samples activated with low concentrations of anti-CD3i was almost restricted to the NGFR(-) population. These results show that reducing the stimulation mediated by anti-CD3i in protocols of T-cell retroviral gene transfer significantly helps to preserve the cytotoxic capacity of these cells to allogeneic cells, without affecting the susceptibility of these cells to the retroviral vector. In addition, we observed that modulating the activation of transduced T cells implies the generation of changes in the differentiation of CD8(+) cells, although we could not establish a direct relationship between the CD45RA/CCR7 phenotype of these cells and their cytotoxic reactivity to an allogeneic stimulus.

Tumor Vaccination after Allogeneic Bone Marrow Cell Reconstitution of the Nonmyeloablatively Conditioned Tumor-Bearing Murine Host

Allogeneic bone marrow cell reconstitution of the nonmyeloablatively conditioned host is supposed to provide an optimized platform for tumor vaccination. We recently showed that an allogeneic T cell-depleted graft was well accepted if the tumor-bearing host was NK depleted. Based on this finding, a vaccination protocol in tumor-bearing, nonmyeloablatively conditioned, allogeneically reconstituted mice was elaborated. Allogeneically reconstituted mice, bearing a renal cell carcinoma, received tumor-primed donor lymph node cells (LNC), which had or had not matured in the allogeneic host. Primed LNC were supported by tumor lysate-pulsed dendritic cells, which were donor or host derived. Optimal responses against the tumor were observed with host-tolerant, tumor-primed LNC in combination with host-derived dendritic cells. High frequencies of tumor-specific proliferating and CTLs were recorded; the survival time of tumor-bearing mice was significantly prolonged, and in >50% of mice the tumor was completely rejected. Notably, severe graft-vs-host disease was observed in reconstituted mice that received tumor-primed LNC, which had not matured in the allogeneic host. However, graft-vs-host was not aggravated after vaccination with tumor-primed, host-tolerant LNC. Thus, the LNC were tolerant toward the host, but not toward the tumor. The finding convincingly demonstrates the feasibility and efficacy of tumor vaccination after allogeneic reconstitution of the nonmyeloablatively conditioned host.

Functional impairment of human T-lymphocytes following PHA-induced expansion and retroviral transduction: implications for gene therapy

The immune function of retrovirus-mediated gene modified (GM) T cells is critical for a beneficial effect to follow their adoptive transfer into patients. Recent clinical data show that GM T cells expanded with PHA have reduced function in vivo. However, little functional analysis of PHA stimulation is available. Our results show that expansion of T cells with PHA impairs their ability to respond (proliferation, cytotoxicity and IFN gamma and perforin expression) to allogeneic stimulation or viral antigens in vitro. Conversely, CD3/CD28-based protocols can preserve this immune function. Retroviral transduction did not alter the functional profile induced by polyclonal stimulation. We investigated the mechanisms leading to this functional effect, and identified differential effects of PHA and CD3/CD28 on the distribution of CCR7/CD45RA T cell functional subsets, which may explain the functional differences observed. While CD3/CD28 stimulation parallels the lineage differentiation pattern induced by antigens in physiological conditions, PHA induces a skewed distribution of the CCR7/CD45RA functional T cell subsets, with near disappearance of the subpopulations that display the effector phenotype. Overall, this study demonstrates a functional disadvantage for transduction protocols based on PHA, uncovers mechanisms that may explain this functional effect, and provides us with information to design and select transduction protocols with an improved functional outcome.

Graft-versus-leukemia effect after suicide-gene-mediated control of graft-versus-host disease

Clinical data indicate that after allogeneic hematopoietic stem cell transplantation (HSCT) for hematological malignancies, the graft-versus-leukemia (GVL) effect is in large part mediated by the graft-versus-host reaction (GVHR), which also often leads to graft-versus-host disease (GVHD). Controlling alloreactivity to prevent GVHD while retaining GVL poses a true dilemma for the successful treatment of such malignancies. We reasoned that suicide gene therapy, which kills dividing cells expressing the thymidine kinase (TK) "suicide" gene using time-controlled administration of ganciclovir (GCV), might solve this dilemma. We have previously shown that after infusion of allogeneic TK T cells along with HSCT to an irradiated recipient, an early and short GCV treatment efficiently prevents GVHD by selectively eliminating alloreactive T cells while sparing nonalloreactive T cells, which can then contribute to immune reconstitution. Nevertheless, it remained to be established that this therapeutic strategy retained the desired GVL effect. Hypothesizing that a contained GVHR would be essential, we evaluated the GVL effect using different protocols of GCV administration. We were able to show that when the GCV treatment is initiated at, or close to, the time of grafting, GVHD is controlled but GVL is lost. In contrast, when the onset of GCV administration is delayed until day 6, a potent GVL effect is retained while GVHD is still controlled. These data emphasize that, by a time-optimized scheduling of the administration of GCV, this TK/GCV strategy can be tuned to efficiently treat malignant hemopathies.

Effect of combined cytostatic cyclosporin A and cytolytic suicide gene therapy on the prevention of experimental graft-versus-host disease

The immunosuppressive drug cyclosporin A (CsA) represents the standard preventive treatment of graft-versus-host disease (GVHD), the main complication of allogeneic hematopoietic stem cell transplantation (HSCT). However, its efficacy is only partial and many patients develop lethal GVHD despite CsA. A strategy of genetic immunosuppression based on conditional elimination of donor T cells expressing the Herpes simplex type 1 thymidine kinase (TK) suicide gene was recently developed. In this system, ganciclovir (GCV) selectively kills dividing but not quiescent TK T cells. Since CsA is known to have a cytostatic effect on T cells, it could negatively interfere with the division-dependent TK gene therapy. We thus tested whether administration of CsA would antagonize elimination of alloreactive donor TK T cells mediated by GCV in a murine model of GVHD. In vivo experiments revealed that, contrary to GCV, CsA only transiently controlled alloactivation-induced T cell proliferation, and likewise could not prevent lethal GVHD. When T cells resumed proliferation under CsA, they were however still sensitive to GCV. Survival, as well as immune reconstitution, was excellent in mice treated with GCV alone or in combination with CsA. These observations should help to design improved suicide gene therapy trials in the field of allogeneic HSCT.

Improving immune reconstitution while preventing graft-versus-host disease in allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is the treatment of choice for many hematologic malignancies or inherited disorders. Ex vivo T-cell depletion (TCD) of the graft and post-transplantation immunosuppression efficiently prevent the development of graft-versus-host disease (GVHD). However, the consequence of these nonspecific approaches is a long-lasting immunodeficiency associated with increased disease relapse, graft rejection, and reactivation of viral infections. Donor lymphocyte infusion, to treat leukemic relapse after allogeneic HSCT, can cause severe GVHD. Several strategies are being optimized to specifically inactivate anti-host T cells while preserving antileukemic or antimicrobial immunocompetence, based on ex vivo or in vivo elimination of anti-host T cells or on the modulation of their anti-host activity.