Immunogenicity and safety profiles of genetic vaccines against human Her-2/neu in cynomolgus monkeys

Combination of vasculature targeting, hypofractionated radiotherapy, and immune checkpoint inhibitor elicits potent antitumor immune response and blocks tumor progression

Background

Tumor endothelial marker 1 (TEM1) is a protein expressed in the tumor-associated endothelium and/or stroma of various types of cancer. We previously demonstrated that immunization with a plasmid-DNA vaccine targeting TEM1 reduced tumor progression in three murine cancer models. Radiation therapy (RT) is an established cancer modality used in more than 50% of patients with solid tumors. RT can induce tumor-associated vasculature injury, triggering immunogenic cell death and inhibition of the irradiated tumor and distant non-irradiated tumor growth (abscopal effect). Combination treatment of RT with TEM1 immunotherapy may complement and augment established immune checkpoint blockade.

Methods

Mice bearing bilateral subcutaneous CT26 colorectal or TC1 lung tumors were treated with a novel heterologous TEM1-based vaccine, in combination with RT, and anti-programmed death-ligand 1 (PD-L1) antibody or combinations of these therapies, tumor growth of irradiated and abscopal tumors was subsequently assessed. Analysis of tumor blood perfusion was evaluated by CD31 staining and Doppler ultrasound imaging. Immunophenotyping of peripheral and tumor-infiltrating immune cells as well as functional analysis was analyzed by flow cytometry, ELISpot assay and adoptive cell transfer (ACT) experiments.

Results

We demonstrate that addition of RT to heterologous TEM1 vaccination reduces progression of CT26 and TC1 irradiated and abscopal distant tumors as compared with either single treatment. Mechanistically, RT increased major histocompatibility complex class I molecule (MHCI) expression on endothelial cells and improved immune recognition of the endothelium by anti-TEM1 T cells with subsequent severe vascular damage as measured by reduced microvascular density and tumor blood perfusion. Heterologous TEM1 vaccine and RT combination therapy boosted tumor-associated antigen (TAA) cross-priming (ie, anti-gp70) and augmented programmed cell death protein 1 (PD-1)/PD-L1 signaling within CT26 tumor. Blocking the PD-1/PD-L1 axis in combination with dual therapy further increased the antitumor effect and gp70-specific immune responses. ACT experiments show that anti-gp70 T cells are required for the antitumor effects of the combination therapy.

Conclusion

Our findings describe novel cooperative mechanisms between heterologous TEM1 vaccination and RT, highlighting the pivotal role that TAA cross-priming plays for an effective antitumor strategy. Furthermore, we provide rationale for using heterologous TEM1 vaccination and RT as an add-on to immune checkpoint blockade as triple combination therapy into early-phase clinical trials.

A phase 1 study of a heterologous prime-boost vaccination involving a truncated HER2 sequence in patients with HER2-expressing breast cancer

A phase 1 clinical trial was conducted to assess the safety, tolerability, and preliminary efficacy of a heterologous prime-boost strategy involving plasmid DNA (pHM-GM-CSF, expressing truncated human epidermal growth factor receptor 2 (HER2) and granulocyte macrophage colony-stimulation factor (GM-CSF) as a bicistronic message) and an adenoviral vector (Ad-HM, containing the same modified HER2 sequence only), in patients with stage III–IV metastatic breast cancer expressing HER2. Nine eligible subjects were divided into three cohorts based on the dosages (2, 4, and 8 mg/patient/visit) of pHM-GM-CSF used as the primer, which was intramuscularly injected three times at weeks 0, 2, and 4. It was followed by a single injection of Ad-HM (3 × 10⁹ virus particles), used as a booster, at week 6. During the 6-month follow-up period, adverse events (AEs), pharmacokinetics and pharmacodynamics, and HER2-specific cellular and humoral immune responses were evaluated. Seven cases of minor grade 1 toxicities in four of nine subjects and no serious drug-related AEs were reported. HER2-specific cell-mediated or humoral immunity was produced in all (100%) or three subjects (33%), respectively. One subject showed a partial response, and seven subjects had stable diseases. However, there were no differences in clinical tumor response and HER2-specific immune responses among the cohorts. These results showed that intramuscular injections of pHM-GM-CSF and Ad-HM were well tolerated and safe.

Enhanced antitumor immunotherapeutic effect of B-cell-based vaccine transduced with modified adenoviral vector containing type 35 fiber structures

For successful clinical tumor immunotherapy outcomes, strong immune responses against tumor antigens must be generated. Cell-based vaccines compromise one strategy with which to induce appropriate strong immune responses. Previously, we established a natural killer T-cell (NKT) ligand-loaded, adenoviral vector-transduced B-cell-based anticancer cellular vaccine. To enhance tumor antigen delivery to B cells, we established a modified adenoviral vector (Ad-k35) that encoded a truncated form of the breast cancer antigen Her2/neu (Ad-k35HM) in which fiber structure was substituted with adenovirus serotype 35. We observed increased tumor antigen expression with Ad-k35HM in both human and murine B cells. In addition, an Ad-k35HM-transduced B-cell vaccine elicited strong antigen-specific cellular and humoral immune responses that were further enhanced with the additional loading of soluble NKT ligand KBC009. An Ad-k35HM-transduced, KBC009-loaded B-cell vaccine efficiently suppressed the in vivo growth of established tumors in a mouse model. Moreover, the vaccine elicited human leukocyte antigen (HLA)-A2 epitope-specific cytotoxic T-cell responses in B6.Cg (CB)-Tg (HLA-A/H2-D) 2Enge/Jat mice. These findings indicated that the Ad-k35 could be appropriate for the preclinical and clinical development of B-cell-based anticancer immunotherapies.