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Adoptive cellular therapy based on chimeric antigen receptor (CAR)-engineered T (CAR-T) cells is a powerful form of cancer immunotherapy. CAR-T cells can be redirected to specifically recognize tumor-associated antigens (TAAs) and induce high levels of antitumor activity. However, they may also display “on-target off-tumor” toxicities, resulting from low-level expression of TAAs in healthy tissues. These adverse effects have raised considerable safety concerns and limited the clinical application of this otherwise promising therapeutic modality. To minimize such side effects, we have designed an epidermal growth factor receptor (EGFR)-specific masked CAR (mCAR), which consists of a masking peptide that blocks the antigen-binding site and a protease-sensitive linker. Proteases commonly active in the tumor microenvironment can cleave the linker and disengage the masking peptide, thereby enabling CAR-T cells to recognize target antigens only at the tumor site. In vitro mCAR showed dramatically reduced antigen binding and antigen-specific activation in the absence of proteases, but normal levels of binding and activity upon treatment with certain proteases. Masked CAR-T cells also showed antitumor efficacy in vivo comparable to that of unmasked CAR. Our study demonstrates the feasibility of improving the safety profile of conventional CARs and may also inspire future design of CAR molecules targeting broadly expressed TAAs.

Breast cancer immunotherapy is a potent treatment option, with antibody therapies such as trastuzumab increasing 2-year survival rates by 50%. However, active immunotherapy through vaccination has generally been clinically ineffective. One potential means of improving vaccine therapy is by delivering breast cancer antigens to dendritic cells (DCs) for enhanced antigen presentation. To accomplish this in vivo, we pseudotyped lentiviral vector (LV) vaccines with a modified Sindbis Virus glycoprotein so that they could deliver genes encoding the breast cancer antigen alpha-lactalbumin (Lalba) or erb-b2 receptor tyrosine kinase 2 (ERBB2 or HER2) directly to resident DCs. We hypothesized that utilizing these DC-targeting lentiviral vectors as a breast cancer vaccine could lead to an improved immune response against self-antigens found in breast cancer tumors. Indeed, single injections of the vaccine vectors were able to amplify antigen-specific CD8 T cells 4–6 fold over naïve mice, similar to the best published vaccine regimens. Immunization of these mice completely inhibited tumor growth in a foreign antigen environment (LV-ERBB2 in wildtype mice), and it reduced the rate of tumor growth in a self-antigen environment (LV-Lalba in wildtype or LV-ERBB2 in MMTV-huHER2 transgenic). These results show that a single injection with targeted lentiviral vectors can be an effective immunotherapy for breast cancer. Furthermore, they could be combined with other immunotherapeutic regimens to improve outcomes for patients with breast cancer.

The therapeutic limitations of conventional chemotherapeutic drugs include chemo-resistance, tumor recurrence, and metastasis. Numerous nanoparticle-based active targeting approaches have emerged to enhance the intracellular concentration of drugs in tumor cells; however, efficient delivery of these systems to the tumor site while sparing healthy tissue remains elusive. Recently, much attention has been given to human immune-cell-directed nanoparticle drug delivery, because immune cells can traffic to the tumor and inflammatory sites. Natural killer cells are a subset of cytotoxic lymphocytes that play critical roles in cancer immunosurveillance. Engineering of the human natural killer cell line, NK92, to express chimeric antigen receptors to redirect their antitumor specificity has shown significant promise. We demonstrate that the efficacy of chemotherapy can be enhanced in vitro and in vivo while reducing off-target toxicity by using chimeric antigen receptor-engineered NK92 cells as carriers to direct drug-loaded nanoparticles to the target site.

Exhaustion of CD8(+) T cells and upregulation of programmed death 1 (PD-1), a negative regulator of T cell activation, are characteristic features of individuals chronically infected with human immunodeficiency virus type 1. In a previous study, we showed in mice that a dendritic cell-directed lentiviral vector (DCLV) system encoding the human immunodeficiency virus (HIV)-1 Gag protein was an efficient vaccine modality to induce a durable Gag-specific T cell immune response. In this study, we demonstrate that blocking of the PD-1/PD-1 ligand (PD-L) inhibitory signal via an anti-PD-L1 antibody generated an enhanced HIV-1 Gag-specific CD8(+) immune response following both a single round of DCLV immunization and a homologous prime/boost regimen. The prime/boost regimen combined with PD-L1 blockade generated very high levels of Gag-specific CD8(+) T cells comprising several valuable features: improved ability to produce multiple cytokines, responding to a broader range of Gag-derived epitopes, and long-lasting memory. This enhanced cellular immune response generated by DCLV immunization combined with anti-PD-L1 blockade correlated with improved viral control following challenge with Gag-expressing vaccinia virus. Taken together, our studies offer evidence to support the use of PD-1/PD-L1 blockade as an adjuvant modality to enhance antigen-specific immune responses elicited by T cell-based immunizations such as DCLV.

As a vector for gene delivery, lentiviruses based on HIV-1 are commonly used in the laboratory. These lentivectors benefit from the advantages of efficient transduction of nondividing cells, low natural antivector immunity, and a low potential for genotoxicity due to insertional mutagenesis. Numerous modifications of the lentivector have improved their safety profile and ability to elicit a strong immune response. In cancer therapy, lentivectors have been used to transduce dendritic cells with tumor-associated antigens ex vivo. When transferred back into mice, these vaccines generate a strong antigen-specific immune response, and they can slow the growth of tumors in several mouse models of human cancer. Antigen-carrying lentivectors can also be injected directly into mice, after which they also elicit a strong immune response and provide protection to tumor challenge. In the few clinical trials that have utilized lentivectors, no adverse effects from the lentivector have been observed. Future advances in the field will likely focus on improving the safety profile of these vectors and adapting them for large-scale clinical trials.

Lentiviral vectors (LVs) are a powerful means of delivering genetic material to many types of cells. Because of safety concerns associated with these HIV-1 derived vectors, producing large quantities of LVs is challenging. In this paper, we report a method for producing high titers of self-inactivating LVs. We retrovirally transduce the tet-off stable producer cell line GPR to generate a cell line, GPRS, which can express all the viral components, including a dendritic cell-specific glycoprotein, SVGmu. Then, we use concatemeric DNA transfection to transfect the LV transfer plasmid encoding a reporter gene GFP in combination with a selectable marker. Several of the resulting clones can produce LV at a titer 10-fold greater than what we achieve with transient transfection. Plus, these viruses efficiently transduce dendritic cells in vitro and generate a strong T cell immune response to our reporter antigen. This method may be a good option for producing strong LV-based vaccines for clinical studies of cancer or infectious diseases.

Breast cancer immunotherapy is a potent treatment option, with antibody therapies such as trastuzumab increasing 2-year survival rates by 50%. In contrast, active immunotherapy through therapeutic vaccination has yet to be proven clinically effective for breast cancer. One potential means of improving vaccine therapy is by delivering breast cancer antigens to dendritic cells (DCs) for enhanced antigen presentation. To achieve this in vivo, we have pseudotyped lentiviral vector vaccines with a modified Sindbis Virus glycoprotein that targets the C-type lectin DC-SIGN, which is expressed on DCs. We hypothesized that utilizing these DC-targeting lentiviral vectors as a breast cancer vaccine could lead to an improved immune response against self antigens found in breast cancer tumors. Such an improved immune response may help to prevent or slow tumor growth in breast cancer models. To test these hypotheses, we have constructed lentiviral vectors encoding each of the breast cancer antigens, human Her2 (ERBB2) and mouse alpha-lactalbumin (Lalba). Single injections were able to amplify antigen-specific CD8 T cells to 1.6% of total CD8 T cells in BALB/cJ mice and 0.7% in transgenic ERBB2 mice. This compares favorably with recently published vector vaccines, which have elicited 0.9% and Citation Format: Paul D. Bryson, Xiaolu Han, Norman Truong, Pin Wang. Dendritic cell-targeted lentiviral vector vaccines overcome tolerance to generate a protective T-cell immune response to breast cancer antigens ERBB2 and α-lactalbumin. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2888. doi:10.1158/1538-7445.AM2014-2888