Tumor gene therapy by MVA-mediated expression of T-cell-stimulating antibodies

Viro-antibody therapy: engineering oncolytic viruses for genetic delivery of diverse antibody-based biotherapeutics

Cancer therapeutics approved for clinical application include oncolytic viruses and antibodies, which evolved by nature, but were improved by molecular engineering. Both facilitate outstanding tumor selectivity and pleiotropic activities, but also face challenges, such as tumor heterogeneity and limited tumor penetration. An innovative strategy to address these challenges combines both agents in a single, multitasking therapeutic, i.e., an oncolytic virus engineered to express therapeutic antibodies. Such viro-antibody therapies genetically deliver antibodies to tumors from amplified virus genomes, thereby complementing viral oncolysis with antibody-defined therapeutic action. Here, we review the strategies of viro-antibody therapy that have been pursued exploiting diverse virus platforms, antibody formats, and antibody-mediated modes of action. We provide a comprehensive overview of reported antibody-encoding oncolytic viruses and highlight the achievements of 13 years of viro-antibody research. It has been shown that functional therapeutic antibodies of different formats can be expressed in and released from cancer cells infected with different oncolytic viruses. Virus-encoded antibodies have implemented direct tumor cell killing, anti-angiogenesis, or activation of adaptive immune responses to kill tumor cells, tumor stroma cells or inhibitory immune cells. Importantly, numerous reports have shown therapeutic activity complementary to viral oncolysis for these modalities. Also, challenges for future research have been revealed. Established engineering technologies for both oncolytic viruses and antibodies will enable researchers to address these challenges, facilitating the development of effective viro-antibody therapeutics.

Current strategies in engaging oncolytic viruses with antitumor immunity

Oncolytic virotherapy has produced promising yet limited results in preclinical and clinical studies. Besides direct oncolytic activity, a significant therapeutic mechanism of oncolytic virotherapy is the induction of tumor-specific immunity. Consequently, the efficacy of oncolytic viruses can be improved by the insertion of immune stimulator genes and rational combinatorial therapy with other immunotherapies. This article reviews recent efforts on arming oncolytic viruses with a variety of immune stimulator molecules, immune cell engagers, and other immune potentiating molecules. We outline what is known about the mechanisms of action and the corresponding results. The review also discusses recent preclinical and clinical studies of combining oncolytic virotherapy with immune-checkpoint inhibitors and the role of oncolytic virotherapy in changing the tumor microenvironment.

Gene delivery based on macrocyclic amphiphiles

Gene therapy, with an important role in biomedicine, often requires vectors for gene condensation in order to avoid degradation, improve membrane permeation, and achieve targeted delivery. Macrocyclic molecules are a family of artificial receptors that can selectively bind a variety of guest species. Amphiphilic macrocycles, particularly those bearing cationic charges and their various assemblies represent a new class of promising non-viral vectors with intrinsic advantages in gene condensation and delivery. The most prominent examples include amphiphilic cyclodextrins, calixarenes and pillararenes. Herein, we systemically reviewed reported assemblies of amphiphilic macrocycles for gene delivery and therapy. The advantages and disadvantages of each type of macrocyclic amphiphiles for gene delivery, as well as the perspectives on the future development of this area are discussed.

Oncolytic viruses as engineering platforms for combination immunotherapy

To effectively build on the recent successes of immune checkpoint blockade, adoptive T cell therapy and cancer vaccines, it is critical to rationally design combination strategies that will increase and extend efficacy to a larger proportion of patients. For example, the combination of anti-cytotoxic T lymphocyte-associated antigen 4 (CTLA4) and anti-programmed cell death protein 1 (PD1) immune checkpoint inhibitors essentially doubles the response rate in certain patients with metastatic melanoma. However, given the heterogeneity of cancer, it seems likely that even more complex combinations of immunomodulatory agents may be required to obtain consistent, durable therapeutic responses against a broad spectrum of cancers. This carries serious implications in terms of toxicities for patients, feasibility for care providers and costs for health-care systems. A compelling solution is offered by oncolytic viruses (OVs), which can be engineered to selectively replicate within and destroy tumour tissue while simultaneously augmenting antitumour immunity. In this Opinion article, we argue that the future of immunotherapy will include OVs that function as multiplexed immune-modulating platforms expressing factors such as immune checkpoint inhibitors, tumour antigens, cytokines and T cell engagers. We illustrate this concept by following the trials and tribulations of tumour-reactive T cells from their initial priming through to the execution of cytotoxic effector function in the tumour bed. We highlight the myriad opportunities for OVs to help overcome critical barriers in the T cell journey, leading to new synergistic mechanisms in the battle against cancer.

Vectorization in an oncolytic vaccinia virus of an antibody, a Fab and a scFv against programmed cell death -1 (PD-1) allows their intratumoral delivery and an improved tumor-growth inhibition

We report here the successful vectorization of a hamster monoclonal IgG (namely J43) recognizing the murine Programmed cell death-1 (mPD-1) in Western Reserve (WR) oncolytic vaccinia virus. Three forms of mPD-1 binders have been inserted into the virus: whole antibody (mAb), Fragment antigen-binding (Fab) or single-chain variable fragment (scFv). MAb, Fab and scFv were produced and assembled with the expected patterns in supernatants of cells infected by the recombinant viruses. The three purified mPD-1 binders were able to block the binding of mPD-1 ligand to mPD-1 in vitro. Moreover, mAb was detected in tumor and in serum of C57BL/6 mice when the recombinant WR-mAb was injected intratumorally (IT) in B16F10 and MCA 205 tumors. The concentration of circulating mAb detected after IT injection was up to 1,900-fold higher than the level obtained after a subcutaneous (SC) injection (i.e., without tumor) confirming the virus tropism for tumoral cells and/or microenvironment. Moreover, the overall tumoral accumulation of the mAb was higher and lasted longer after IT injection of WR-mAb1, than after IT administration of 10 µg of J43. The IT injection of viruses induced a massive infiltration of immune cells including activated lymphocytes (CD8⁺ and CD4⁺). Interestingly, in the MCA 205 tumor model, WR-mAb1 and WR-scFv induced a therapeutic control of tumor growth similar to unarmed WR combined to systemically administered J43 and superior to that obtained with an unarmed WR. These results pave the way for next generation of oncolytic vaccinia armed with immunomodulatory therapeutic proteins such as mAbs.

Adenovirus-mediated intratumoral expression of immunostimulatory proteins in combination with systemic Treg inactivation induces tumor-destructive immune responses in mouse models

Tumor-associated antigens (TAAs) include overexpressed self-antigens (e.g. Her2/neu) and tumor-virus antigens (e.g. HPV-16 E6/E7). Although in cancer patients, TAA-specific CD4+ and CD8+ cells are often present, they are not able to control tumor growth. In recent studies it became apparent that tumor-site located immune-evasion mechanisms contribute to this phenomenon and that regulatory T-cells play a major role. We tested in Her2/neu+ breast cancer and HPV-16 E6/E7+ cervical cancer mouse models, whether intratumoral expression of immunostimulatory proteins (ISPs), e.g. recombinant antibodies (αCTLA-4, αCD137, αCD3), cyto/chemokines (IL-15, LIGHT, mda-7), and costimulatory ligands (CD80), via adenovirus(Ad)-mediated gene transfer would overcome resistance. In both the breast and cervical cancer model, none of the Ad.ISP vectors displayed a significant therapeutic effect when compared with an Ad vector that lacked a transgene (Ad.zero). However, the combination of Ad.ISP vectors with systemic Treg depletion, using anti-CD25 mAb (breast cancer model) or low-dose cyclophosphamide (cervical cancer model) resulted in a significant delay of tumor growth in mice treated with Ad.αCTLA4. In the cervical cancer model we also demonstrated the induction of a systemic anti-tumor immune response that was able to delay the growth of distant tumors. Ad.αCTLA4 mediated tumor-destructive immune responses involved NKT- and CD8+ T-cells. In both models no auto-immune reactions were observed. The study shows that Ad.αCTLA4 in combination with systemic Treg depletion has potentials in the immunotherapy of cancer.

Membrane-tethered proteins for basic research, imaging, and therapy

Secreted and intracellular proteins including antibodies, cytokines, major histocompatibility complex molecules, antigens, and enzymes can be redirected to and anchored on the surface of mammalian cells to reveal novel functions and properties such as reducing systemic toxicity, altering the in vivo distribution of drugs and extending the range of useful drugs, creating novel, specific signaling receptors and reshaping protein immunogenicity. The present review highlights progress in designing vectors to target and retain chimeric proteins on the surface of mammalian cells. Comparison of chimeric proteins indicates that selection of the proper cytoplasmic domain and introduction of oligiosaccharides near the cell surface can dramatically enhance surface expression, especially for single-chain antibodies. We also describe progress and limitations of employing surface-tethered proteins for preferential activation of prodrugs at cancer cells, imaging gene expression in living animals, performing high-throughput screening, selectively activating immune cells in tumors, producing new adhesion molecules, creating local immune privileged sites, limiting the distribution of soluble factors such as cytokines, and enhancing polypeptide immunogenicity. Surface-anchored chimeric proteins represent a rich source for developing new techniques and creating novel therapeutics.

Fusokine Interleukin-2/Interleukin-18, a Novel Potent Innate and Adaptive Immune Stimulator with Decreased Toxicity

To redress the immune imbalances created by pathologies such as cancer, it would be beneficial to create novel cytokine molecules, which combine desired cytokine activities with reduced toxicities. Due to their divergent but complementary activities, it is of interest to combine interleukin-2 (IL-2) and IL-18 into one recombinant molecule for immunotherapy. Evaluation of a fusokine protein that combines murine IL-2/IL-18 shows that it is stable, maintains IL-2 and IL-18 bioactivities, has notably reduced IL-2 associated toxicities, and has a novel lymphocyte-stimulating activity. An adeno-viral expression system was used to explore the biology of this "fusokine". Inclusion of the IL-18 prosequence (proIL-18) increases the expression, secretion, and potency of this fusokine. In vivo gene transfer experiments show that Ad-IL-2/proIL-18 dramatically outdoes Ad-IL-2, Ad-proIL-18, or the combination of both, by inducing high rates of tumor rejection in several murine models. Both innate and adaptive effector mechanisms are required for this antitumor activity.

Secretomers as a new tool for the monitoring of CTL responses

Efforts to follow tumor-specific immune responses in patients are often thwarted by lack of knowledge of the appropriate tumor antigens and the CTL epitopes of those antigens. There is, therefore, a growing need for techniques to monitor tumor-specific immune responses in settings where tumor antigens, and antigenic epitopes, remain unidentified. Here we describe a novel system to follow tumor-specific CTL immune responses. A truncated, soluble murine class I MHC (H-2Db) molecule was fused with a rat IgG2a Fc, in order to allow secretion of the complex. Tumor-specific CTL could then be detected as a result of the complex fastening to specific T cell receptors (TCR). These constructs were inserted into the genome of a recombinant adenovirus vector. Infection of tumor cells with these adenovirus constructs results in the secretion of the complexes into the culture supernatant. These soluble divalent class I MHC molecules were used to detect and activate specific CTL populations.

Fighting Cancer with Vaccinia Virus: Teaching New Tricks to an Old Dog

Vaccinia virus has played a huge part in human beings' victory over smallpox. With smallpox being eradicated and large-scale vaccination stopped worldwide, vaccinia has assumed a new role in our fight against another serious threat to human health: cancer. Recent advances in molecular biology, virology, immunology, and cancer genetics have led to the design of novel cancer therapeutics based on vaccinia virus backbones. With the ability to infect efficiently a wide range of host cells, a genome that can accommodate large DNA inserts and express multiple genes, high immunogenicity, and cytoplasmic replication without the possibility of chromosomal integration, vaccinia virus has become the platform of many exploratory approaches to treat cancer. Vaccinia virus has been used as (1) a delivery vehicle for anti-cancer transgenes, (2) a vaccine carrier for tumor-associated antigens and immunoregulatory molecules in cancer immunotherapy, and (3) an oncolytic agent that selectively replicates in and lyses cancer cells.

MVA as a vector for vaccines against HIV-1

A vaccine against HIV Type 1 (HIV-1) is urgently needed. Modified vaccinia virus Ankara is an attenuated smallpox vaccine which can be adapted to express HIV-1 antigens. In this review, we discuss the features which make modified vaccinia virus Ankara an attractive vector for genetic vaccines and have put it, together with several other recombinant viral vectors, at the forefront of HIV-1 vaccine development. Many candidate vaccines including those vectored by modified vaccinia virus Ankara are now entering human trials, the results of which will become available in the coming years.

Stable expression of chimeric anti-CD3 receptors on mammalian cells for stimulation of antitumor immunity

Expression of CD80 or CD86 costimulatory molecules on tumor cells can produce rejection of immunogenic but not poorly immunogenic tumors. We have previously shown that anti-CD3 single-chain antibodies expressed on the surface of cells can directly activate T cells. We therefore investigated whether anti-CD3 "receptors" could enhance CD86-mediated rejection of poorly immunogenic tumors. Expression of anti-CD3 receptors on cells was increased by introduction of membrane-proximal "spacer" domains containing glycosylation sites between the single-chain antibody and the transmembrane domain of the chimeric receptors. Removal of glycosylation sites in the spacer reduced surface expression due to increased shedding of chimeric receptors from the cell surface. Induction of T-cell proliferation by anti-CD3 receptors did not correlate with the expression level of chimeric protein, but rather depended on the physical properties of the spacer. Anti-CD3 receptors effectively induced T-cell cytotoxicity, whereas coexpression with CD80 or CD86 was required for generating T-cell proliferation and IL-2 secretion. Although expression of CD86 did not significantly delay the growth of poorly immunogenic B16-F1 tumors, expression of anti-CD3 receptors with CD86 produced complete tumor rejections in 50% of mice and induced significant protection against wild-type B16-F1 tumor cells. Our results show that spacer domains can dramatically influence the surface expression and the biological activity of chimeric antibody receptors. The strong antitumor activity produced by anti-CD3 receptors and CD86 on tumor cells indicates that this strategy may be beneficial for the gene-mediated therapy of poorly immunogenic tumors.

Cancer gene therapy: an awkward adolescence

At the Eleventh International Conference on Gene Therapy of Cancer (December 12-14, 2002, San Diego, CA) progress on using gene transfer technology to treat cancer was presented. Although there is as yet no cancer gene therapy being marketed, considerable progress has been made in defining likely strategies and likely targets for gene therapy of cancer. These strategies, including viral and non-viral delivery systems, and potential targets in cancer cells linked to our developing knowledge of cancer cell biology, are reviewed in this paper. Use of gene therapy to sensitize tumors to radiation and chemotherapy is one promising area of investigation. Some of the ancillary benefits of research on cancer gene therapy, including the development of public-private partnerships, recruitment of laboratory scientists into clinical research, and credentialing of potential cancer cell targets for therapies other than gene therapy, are noted.

Gene Therapy Applications to Cancer Treatment

Over the past ten years significant advances have been made in the fields of gene therapy and tumour immunology, such that there now exists a considerable body of evidence validating the proof in the principle of gene therapy based cancer vaccines. While clinical benefit has so far been marginal, data from preclinical and early clinical trials of gene therapy combined with standard therapies are strongly suggestive of additional benefit. Many reasons have been proposed to explain the paucity of clinical responses to single agent vaccination strategies including the poor antigenicity of tumour cells and the development of tolerance through down-regulation of MHC, costimulatory, signal transduction, and other molecules essential for the generation of strong immune responses. In addition, there is now evidence from animal models that the growing tumour may actively inhibit the host immune response. Removal of the primary tumour prior to T cell transfer from the spleen of cancer bearing animals, led to effective tumour cell line specific immunity in the recipient mouse suggesting that there is an ongoing tumour-host interaction. This model also illustrates the potential difficulties of clinical vaccine trials in patients with advanced stage disease.