Integrase-defective lentiviral vectors encoding cytokines induce differentiation of human dendritic cells and stimulate multivalent immune responses in vitro and in vivo

An Update on the HIV DNA Vaccine Strategy

In 2020, the global prevalence of human immunodeficiency virus (HIV) infection was estimated to be 38 million, and a total of 690,000 people died from acquired immunodeficiency syndrome (AIDS)–related complications. Notably, around 12.6 million people living with HIIV/AIDS did not have access to life-saving treatment. The advent of the highly active antiretroviral therapy (HAART) in the mid-1990s remarkably enhanced the life expectancy of people living with HIV/AIDS as a result of improved immune functions. However, HAART has several drawbacks, especially when it is not used properly, including a high risk for the development of drug resistance, as well as undesirable side effects such as lipodystrophy and endocrine dysfunctions, which result in HAART intolerability. HAART is also not curative. Furthermore, new HIV infections continue to occur globally at a high rate, with an estimated 1.7 million new infections occurring in 2018 alone. Therefore, there is still an urgent need for an affordable, effective, and readily available preventive vaccine against HIV/AIDS. Despite this urgent need, however, progress toward an effective HIV vaccine has been modest over the last four decades. Reasons for this slow progress are mainly associated with the unique aspects of HIV itself and its ability to rapidly mutate, targeting immune cells and escape host immune responses. Several approaches to an HIV vaccine have been undertaken. However, this review will mainly discuss progress made, including the pre-clinical and clinical trials involving vector-based HIV DNA vaccines and the use of integrating lentiviral vectors in HIV vaccine development. We concluded by recommending particularly the use of integrase-defective lentiviral vectors, owing to their safety profiles, as one of the promising vectors in HIV DNA vaccine strategies both for prophylactic and therapeutic HIV vaccines.

Induced dendritic cells co-expressing GM-CSF/IFN-α/tWT1 priming T and B cells and automated manufacturing to boost GvL

Acute myeloid leukemia (AML) patients with minimal residual disease and receiving allogeneic hematopoietic stem cell transplantation (HCT) have poor survival. Adoptive administration of dendritic cells (DCs) presenting the Wilms tumor protein 1 (WT1) leukemia-associated antigen can potentially stimulate de novo T and B cell development to harness the graft-versus-leukemia (GvL) effect after HCT. We established a simple and fast genetic modification of monocytes for simultaneous lentiviral expression of a truncated WT1 antigen (tWT1), granulocyte macrophage-colony-stimulating factor (GM-CSF), and interferon (IFN)-α, promoting their self-differentiation into potent “induced DCs” (iDCtWT1). A tricistronic integrase-defective lentiviral vector produced under good manufacturing practice (GMP)-like conditions was validated. Transduction of CD14⁺ monocytes isolated from peripheral blood, cord blood, and leukapheresis material effectively induced their self-differentiation. CD34⁺ cell-transplanted Nod.Rag.Gamma (NRG)- and Nod.Scid.Gamma (NSG) mice expressing human leukocyte antigen (HLA)-A∗0201 (NSG-A2)-immunodeficient mice were immunized with autologous iDCtWT1. Both humanized mouse models showed improved development and maturation of human T and B cells in the absence of adverse effects. Toward clinical use, manufacturing of iDCtWT1 was up scaled and streamlined using the automated CliniMACS Prodigy system. Proof-of-concept clinical-scale runs were feasible, and the 38-h process enabled standardized production and high recovery of a cryopreserved cell product with the expected identity characteristics. These results advocate for clinical trials testing iDCtWT1 to boost GvL and eradicate leukemia.

Recent Advances in Good Manufacturing Practice-Grade Generation of Dendritic Cells

Dendritic cells (DCs) are pivotal regulators of immune responses, specialized in antigen presentation and bridging the gap between the innate and adaptive immune system. Due to these key features, DCs have become a pillar of the continuously growing field of cellular therapies. Here we review recent advances in good manufacturing practice strategies and their individual specificities in relation to DC production for clinical applications. These take into account both small-scale experimental approaches as well as automated systems for patient care.

The Old and the New: Prospects for Non-Integrating Lentiviral Vector Technology

Lentiviral vectors have been developed and used in multiple gene and cell therapy applications. One of their main advantages over other vectors is the ability to integrate the genetic material into the genome of the host. However, this can also be a disadvantage as it may lead to insertional mutagenesis. To address this, non-integrating lentiviral vectors (NILVs) were developed. To generate NILVs, it is possible to introduce mutations in the viral enzyme integrase and/or mutations on the viral DNA recognised by integrase (the attachment sites). NILVs are able to stably express transgenes from episomal DNA in non-dividing cells or transiently if the target cells divide. It has been shown that these vectors are able to transduce multiple cell types and tissues. These characteristics make NILVs ideal vectors to use in vaccination and immunotherapies, among other applications. They also open future prospects for NILVs as tools for the delivery of CRISPR/Cas9 components, a recent revolutionary technology now widely used for gene editing and repair.

Monocytes reprogrammed with lentiviral vectors co-expressing GM-CSF, IFN-α2 and antigens for personalized immune therapy of acute leukemia pre- or post-stem cell transplantation

Acute myeloid leukemia (AML) is the most common acute leukemia in adults and overall survival remains poor. Chemotherapy is the standard of care for intensive induction therapy. Patients who achieve a complete remission require post-remission therapies to prevent relapse. There is no standard of care for patients with minimal residual disease (MRD), and stem cell transplantation is a salvage therapy. Considering the AML genetic heterogeneity and the leukemia immune-suppressive properties, novel cellular immune therapies to effectively harness immunological responses to prevent relapse are needed. We developed a novel modality of immune therapy consisting of monocytes reprogrammed with lentiviral vectors expressing GM-CSF, IFN-α and antigens. Preclinical studies in humanized mice showed that the reprogrammed monocytes self-differentiated into highly viable induced dendritic cells (iDCs) in vivo which migrated effectively to lymph nodes, producing remarkable effects in the de novo regeneration of T and B cell responses. For the first-in-man clinical trial, the patient’s monocytes will be transduced with an integrase-defective tricistronic lentiviral vector expressing GM-CSF, IFN-α and a truncated WT1 antigen. For transplanted patients, pre-clinical development of iDCs co-expressing cytomegalovirus antigens is ongoing. To simplify the product chain for a de-centralized supply model, we are currently exploring a closed automated system for a short two-day manufacturing of iDCs. A phase I clinical trial study is in preparation for immune therapy of AML patients with MRD. The proposed cell therapy can fill an important gap in the current and foreseeable future immunotherapies of AML.

Signatures of T and B Cell Development, Functional Responses and PD-1 Upregulation After HCMV Latent Infections and Reactivations in Nod.Rag.Gamma Mice Humanized With Cord Blood CD34+ Cells

Human cytomegalovirus (HCMV) latency is typically harmless but reactivation can be largely detrimental to immune compromised hosts. We modeled latency and reactivation using a traceable HCMV laboratory strain expressing the Gaussia luciferase reporter gene (HCMV/GLuc) in order to interrogate the viral modulatory effects on the human adaptive immunity. Humanized mice with long-term (more than 17 weeks) steady human T and B cell immune reconstitutions were infected with HCMV/GLuc and 7 weeks later were further treated with granulocyte-colony stimulating factor (G-CSF) to induce viral reactivations. Whole body bio-luminescence imaging analyses clearly differentiated mice with latent viral infections vs. reactivations. Foci of vigorous viral reactivations were detectable in liver, lymph nodes and salivary glands. The number of viral genome copies in various tissues increased upon reactivations and were detectable in sorted human CD14⁺, CD169⁺, and CD34⁺ cells. Compared with non-infected controls, mice after infections and reactivations showed higher thymopoiesis, systemic expansion of Th, CTL, Treg, and Tfh cells and functional antiviral T cell responses. Latent infections promoted vast development of memory CD4⁺ T cells while reactivations triggered a shift toward effector T cells expressing PD-1. Further, reactivations prompted a marked development of B cells, maturation of IgG⁺ plasma cells, and HCMV-specific antibody responses. Multivariate statistical methods were employed using T and B cell immune phenotypic profiles obtained with cells from several tissues of individual mice. The data was used to identify combinations of markers that could predict an HCMV infection vs. reactivation status. In spleen, but not in lymph nodes, higher frequencies of effector CD4⁺ T cells expressing PD-1 were among the factors most suited to distinguish HCMV reactivations from infections. These results suggest a shift from a T cell dominated immune response during latent infections toward an exhausted T cell phenotype and active humoral immune response upon reactivations. In sum, this novel in vivo humanized model combined with advanced analyses highlights a dynamic system clearly specifying the immunological spatial signatures of HCMV latency and reactivations. These signatures can be merged as predictive biomarker clusters that can be applied in the clinical translation of new therapies for the control of HCMV reactivation.

PIM-2 protein kinase negatively regulates T cell responses in transplantation and tumor immunity

PIM kinase family members play a crucial role in promoting cell survival and proliferation via phosphorylation of their target substrates. In this study, we investigated the role of the PIM kinases with respect to T cell responses in transplantation and tumor immunity. We found that the PIM-2 isoform negatively regulated T cell responses to alloantigen, in contrast to the PIM-1 and PIM-3 isoforms, which acted as positive regulators. T cells deficient in PIM-2 demonstrated increased T cell differentiation toward Th1 subset, proliferation, and migration to target organs after allogeneic bone marrow transplantation, resulting in dramatically accelerated graft-versus-host disease (GVHD) severity. Restoration of PIM-2 expression markedly attenuated the pathogenicity of PIM-2-deficient T cells to induce GVHD. On the other hand, mice deficient in PIM-2 readily rejected syngeneic tumor, which was primarily dependent on CD8+ T cells. Furthermore, silencing PIM-2 in polyclonal or antigen-specific CD8+ T cells substantially enhanced their antitumor response in adoptive T cell immunotherapy. We conclude that PIM-2 kinase plays a prominent role in suppressing T cell responses, and provide a strong rationale to target PIM-2 for cancer immunotherapy.

Human Effector Memory T Helper Cells Engage with Mouse Macrophages and Cause Graft-versus-Host-Like Pathology in Skin of Humanized Mice Used in a Nonclinical Immunization Study

Humanized mice engrafted with human hematopoietic stem cells and developing functional human T-cell adaptive responses are in critical demand to test human-specific therapeutics. We previously showed that humanized mice immunized with long-lived induced-dendritic cells loaded with the pp65 viral antigen (iDCpp65) exhibited a faster development and maturation of T cells. Herein, we evaluated these effects in a long-term (36 weeks) nonclinical model using two stem cell donors to assess efficacy and safety. Relative to baseline, iDCpp65 immunization boosted the output of effector memory CD4⁺ T cells in peripheral blood and lymph nodes. No weight loss, human malignancies, or systemic graft-versus-host (GVH) disease were observed. However, for one reconstitution cohort, some mice immunized with iDCpp65 showed GVH-like signs on the skin. Histopathology analyses of the inflamed skin revealed intrafollicular and perifollicular human CD4⁺ cells near F4/80⁺ mouse macrophages around hair follicles. In spleen, CD4⁺ cells formed large clusters surrounded by mouse macrophages. In plasma, high levels of human T helper 2-type inflammatory cytokines were detectable, which activated in vitro the STAT5 pathway of murine macrophages. Despite this inflammatory pattern, human CD8⁺ T cells from mice with GVH reacted against the pp65 antigen in vitro. These results uncover a dynamic cross-species interaction between human memory T cells and mouse macrophages in the skin and lymphatic tissues of humanized mice.

Recent Advances in Lentiviral Vaccines for HIV-1 Infection

The development of an effective HIV vaccine to prevent and/or cure HIV remains a global health priority. Given their central role in the initiation of adaptive immune responses, dendritic cell (DC)-based vaccines are being increasingly explored as immunotherapeutic strategies to enhance HIV-specific T cells in infected individuals and, thus, promote immune responses that may help facilitate a functional cure. HIV-1-based lentiviral (LV) vectors have inherent advantages as DC vaccine vectors due to their ability to transduce non-dividing cells and integrate into the target cell genomic DNA, allowing for expression of encoded antigens over the lifespan of the cell. Moreover, LV vectors may express additional immunostimulatory and immunoregulatory proteins that enhance DC function and direct antigen-specific T cells responses. Recent basic and clinical research efforts have broadened our understanding of LV vectors as DC-based vaccines. In this review, we provide an overview of the pre-clinical and clinical LV vector vaccine studies for treating HIV to date. We also discuss advances in LV vector designs that have enhanced DC transduction efficiency, target cell specificity, and immunogenicity, and address potential safety concerns regarding LV vector-based vaccines.

The transduction pattern of IL-12-encoding lentiviral vectors shapes the immunological outcome

In situ modification of antigen-presenting cells garnered interest in cancer immunotherapy. Therefore, we developed APC-targeted lentiviral vectors (LVs). Unexpectedly, these LVs were inferior vaccines to broad tropism LVs. Since IL-12 is a potent mediator of antitumor immunity, we evaluated whether this proinflammatory cytokine could enhance antitumor immunity of an APC-targeted LV-based vaccine. Therefore, we compared subcutaneous administration of broad tropism LVs (VSV-G-LV) with APC-targeted LVs (DC2.1-LV)-encoding enhanced GFP and ovalbumin, or IL-12 and ovalbumin in mice. We show that codelivery of IL-12 by VSV-G-LVs or DC2.1-LVs augments CD4(+) or CD8(+) T-cell proliferation, respectively. Furthermore, we demonstrate that codelivery of IL-12 enhances the CD4(+) TH 1 profile irrespective of its delivery mode, while an increase in cytotoxic and therapeutic CD8(+) T cells was only induced upon VSV-G-LV injection. While codelivery of IL-12 by DC2.1-LVs did not enhance CD8(+) T-cell performance, it increased expression of inhibitory checkpoint markers Lag3, Tim3, and PD-1. Finally, the discrepancy between CD4(+) T-cell stimulation with and without functional CD8(+) T-cell stimulation by VSV-G- and DC2.1-LVs is partly explained by the observation that IL-12 relieves CD8(+) T cells from CD4(+) T-cell help, implying that a T(H)1 profile is of minor importance for antitumor immunotherapy if IL-12 is exogenously delivered.

Murine granulocyte-macrophage colony-stimulating factor expressed from a bicistronic simian immunodeficiency virus-based integrase-defective lentiviral vector does not enhance T-cell responses in mice

As a prelude to immunization studies in nonhuman primates, we compared in mice the immunogenicity of a simian immunodeficiency virus (SIV)-based integrase (IN)-defective lentiviral vector (IDLV) encoding the model antigen-enhanced green fluorescence protein (eGFP) in the presence or absence of the murine granulocyte-macrophage colony-stimulating factor (mGM-CSF) expressed from an internal ribosomal entry site (IRES) sequence. BALB/c mice were immunized once intramuscularly with IDLV expressing eGFP alone or eGFP and mGM-CSF and immune responses were evaluated up to 90 days from the single intramuscular immunization. Results indicated that the mGM-CSF was unable to improve the magnitude and quality of the immune response against the eGFP transgene in the context of the SIV-based IDLV, as evaluated by enzyme-linked immunosorbent spot (ELISPOT) assays for interferon-γ (IFN-γ) and by intracellular cytokine staining for IFN-γ, interleukin-2 (IL-2), and tumor necrosis factor-alpha (TNF-α). These findings suggest that for vaccination purposes, the presence of mGM-CSF expressed after the IRES in a SIV-based IDLV system does not favor the improvement of the immunological response against the transgene of interest. Further studies should investigate whether the selection of a different cytokine gene might improve the immune response against the transgene.

Generation of lentivirus-induced dendritic cells under GMP-compliant conditions for adaptive immune reconstitution against cytomegalovirus after stem cell transplantation

Background

Reactivation of latent viruses such as human cytomegalovirus (HCMV) after allogeneic hematopoietic stem cell transplantation (HSCT) results in high morbidity and mortality. Effective immunization against HCMV shortly after allo-HSCT is an unmet clinical need due to delayed adaptive T cell development. Donor-derived dendritic cells (DCs) have a critical participation in stimulation of naïve T cells and immune reconstitution, and therefore adoptive DC therapy could be used to protect patients after HSCT. However, previous methods for ex vivo generation of adoptive donor-derived DCs were complex and inconsistent, particularly regarding cell viability and potency after thawing. We have previously demonstrated in humanized mouse models of HSCT the proof-of-concept of a novel modality of lentivirus-induced DCs (“SmyleDCpp65”) that accelerated antigen-specific T cell development.

Methods

Here we demonstrate the feasibility of good manufacturing practices (GMP) for production of donor-derived DCs consisting of monocytes from peripheral blood transduced with an integrase-defective lentiviral vector (IDLV, co-expressing GM-CSF, IFN-α and the cytomegalovirus antigen pp65) that were cryopreserved and thawed.

Results

Upscaling and standardized production of one lot of IDLV and three lots of SmyleDCpp65 under GMP-compliant conditions were feasible. Analytical parameters for quality control of SmyleDCpp65 identity after thawing and potency after culture were defined. Cell recovery, uniformity, efficacy of gene transfer, purity and viability were high and consistent. SmyleDCpp65 showed only residual and polyclonal IDLV integration, unbiased to proto-oncogenic hot-spots. Stimulation of autologous T cells by GMP-grade SmyleDCpp65 was validated.

Conclusion

These results underscore further developments of this individualized donor-derived cell vaccine to accelerate immune reconstitution against HCMV after HSCT in clinical trials.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0599-5) contains supplementary material, which is available to authorized users.

Lentivirus-induced 'Smart' dendritic cells: Pharmacodynamics and GMP-compliant production for immunotherapy against TRP2-positive melanoma

Monocyte-derived conventional dendritic cells (ConvDCs) loaded with melanoma antigens showed modest responses in clinical trials. Efficacy studies were hampered by difficulties in ConvDC manufacturing and low potency. Overcoming these issues, we demonstrated higher potency of lentiviral vector (LV)-programmed DCs. Monocytes were directly induced to self-differentiate into DCs (SmartDC-TRP2) upon transduction with a tricistronic LV encoding for cytokines (granulocyte macrophage colony stimulating factor (GM-CSF) and interleukin-4 (IL-4)) and a melanoma antigen (tyrosinase-related protein 2 (TRP2)). Here, SmartDC-TRP2 generated with monocytes from five advanced melanoma patients were tested in autologous DC:T cell stimulation assays, validating the activation of functional TRP2-specific cytotoxic T lymphocytes (CTLs) for all patients. We described methods compliant to good manufacturing practices (GMP) to produce LV and SmartDC-TRP2. Feasibility of monocyte transduction in a bag system and cryopreservation following a 24-h standard operating procedure were achieved. After thawing, 50% of the initial monocyte input was recovered and SmartDC-TRP2 self-differentiated in vitro, showing uniform expression of DC markers, detectable LV copies and a polyclonal LV integration pattern not biased to oncogenic loci. GMP-grade SmartDC-TRP2 expanded TRP2-specific autologous CTLs in vitro. These results demonstrated a simpler GMP-compliant method of manufacturing an effective individualized DC vaccine. Such DC vaccine, when in combination with checkpoint inhibition therapies, might provide higher specificity against melanoma.

Engineered dendritic cells from cord blood and adult blood accelerate effector T cell immune reconstitution against HCMV

Human cytomegalovirus (HCMV) harmfully impacts survival after peripheral blood hematopoietic stem cell transplantation (PB-HSCT). Delayed immune reconstitution after cord blood (CB)-HSCT leads to even higher HCMV-related morbidity and mortality. Towards a feasible dendritic cell therapy to accelerate de novo immunity against HCMV, we validated a tricistronic integrase-defective lentiviral vector (coexpressing GM-CSF, IFN-α, and HCMV pp65 antigen) capable to directly induce self-differentiation of PB and CB monocytes into dendritic cells processing pp65 (“SmyleDCpp65”). In vitro, SmyleDCpp65 resisted HCMV infection, activated CD4⁺ and CD8⁺ T cells and expanded functional pp65-specific memory cytotoxic T lymphocytes (CTLs). CD34⁺ cells obtained from PB and CB were transplanted into irradiated NOD.Rag1^−/−.IL2γc^−/− mice. Donor-derived SmyleDCpp65 administration after PB-HSCT stimulated peripheral immune effects: lymph node remodeling, expansion of polyclonal effector memory CD8⁺ T cells in blood, spleen and bone marrow, and pp65-reactive CTL and IgG responses. SmyleDCpp65 administration after CB-HSCT significantly stimulated thymopoiesis. Expanded frequencies of CD4⁺/CD8⁺ T cell precursors containing increased levels of T-cell receptor excision circles in thymus correlated with peripheral expansion of effector memory CTL responses against pp65. The comparative in vivo modeling for PB and CB-HSCT provided dynamic and spatial information regarding human T and B cell reconstitution. In vivo potency supports future clinical development of SmyleDCpp65.

Lentivirus-Induced Dendritic Cells (iDC) for Immune-Regenerative Therapies in Cancer and Stem Cell Transplantation

Conventional dendritic cells (cDC) are ex vivo differentiated professional antigen presenting cells capable of potently stimulating naïve T cells and with vast potential for immunotherapeutic applications. The manufacture of clinical-grade cDC is relatively complex and requires several days for completion. Clinical trials showed poor trafficking of cDC from subcutaneous injection sites to lymph nodes (LN), where DC can optimally stimulate naïve lymphocytes for long-lasting memory responses. We demonstrated in mouse and human systems that a single overnight ex vivo lentiviral (LV) gene transfer into DC precursors for production of combination of cytokines and antigens was capable to induce autonomous self-differentiation of antigen-loaded DC in vitro and in vivo. These highly viable induced DC (iDC) effectively migrated from the injected skin to LN, where they effectively activated de novo antigen-specific effector memory T cells. Two iDC modalities were validated in relevant animal models and are now in clinical development: Self-differentiated Myeloid-derived Antigen-presenting-cells Reactive against Tumors co-expressing GM-CSF/IL-4/TRP2 for melanoma immunotherapy in the autologous setting (SmartDCtrp2), and Self-differentiated Myeloid-derived Lentivirus-induced against human cytomegalovirus as an allogeneic matched adoptive cell after stem cell transplantation (SmyleDCpp65). The lentiviral vector design and packaging methodology has “evolved” continuously in order to simplify and optimize function and biosafety of in vitro and in vivo genetic reprogramming of iDC. Here, we address the challenges seeking for new creations of genetically programmed iDC and integrase-defective LV vaccines for immune regeneration.

Design and Potential of Non-Integrating Lentiviral Vectors

Lentiviral vectors have demonstrated promising results in clinical trials that target cells of the hematopoietic system. For these applications, they are the vectors of choice since they provide stable integration into cells that will undergo extensive expansion in vivo. Unfortunately, integration can have unintended consequences including dysregulated cell growth. Therefore, lentiviral vectors that do not integrate are predicted to have a safer profile compared to integrating vectors and should be considered for applications where transient expression is required or for sustained episomal expression such as in quiescent cells. In this review, the system for generating lentiviral vectors will be described and used to illustrate how alterations in the viral integrase or vector Long Terminal Repeats have been used to generate vectors that lack the ability to integrate. In addition to their safety advantages, these non-integrating lentiviral vectors can be used when persistent expression would have adverse consequences. Vectors are currently in development for use in vaccinations, cancer therapy, site-directed gene insertions, gene disruption strategies, and cell reprogramming. Preclinical work will be described that illustrates the potential of this unique vector system in human gene therapy.

Advances in homology directed genetic engineering of human pluripotent and adult stem cells

The ability to introduce precise genomic modifications in human cells has profound implications for both basic and applied research in stem cells, ranging from identification of genes regulating stem cell self-renewal and multilineage differentiation to therapeutic gene correction and creation of in vitro models of human diseases. However, the overall efficiency of this process is challenged by several factors including inefficient gene delivery into stem cells and low rates of homology directed site-specific targeting. Recent studies report the development of novel techniques to improve gene targeting efficiencies in human stem cells; these methods include molecular engineering of viral vectors to efficiently deliver episomal genetic sequences that can participate in homology directed targeting, as well as the design of synthetic proteins that can introduce double-stranded breaks in DNA to initiate such recombination events. This review focuses on the potential of these new technologies to precisely alter the human stem cell genome and also highlights the possibilities offered by the combination of these complementary strategies.