Tumor cell-based vaccine contributes to local tumor irradiation by eliciting a tumor model-dependent systemic immune response

In vitro-irradiated cancer vaccine enhances anti-tumor efficacy of radiotherapy and PD-L1 blockade in a syngeneic murine breast cancer model

BACKGROUND AND PURPOSE

Local radiotherapy (RT) exerts immunostimulatory effects by inducing immunogenic cell death. However, it remains unknown whether in vitro-irradiated tumor cells can elicit anti-tumor responses and enhance the efficacy of local RT and immune checkpoint inhibitors when injected in vivo.

METHODS AND MATERIALS

We tested the "in vitro-irradiated cancer vaccine (ICV)", wherein tumor cells killed by varying doses of irradiation and their supernatants are intravenously injected. We examined the efficacy of combining local RT (24 Gy in three fractions), PD-L1 blockade, and the ICV in a murine breast cancer model. The immune cell profiles were analyzed via flow cytometry and immunohistochemistry. The cytokine levels were measured by multiplex immunoassays.

RESULTS

The ICV significantly increased the effector memory phenotype and interferon-γ production capacity in splenic CD8+ T cells. The in vitro-irradiated products contained immune response-related molecules. When combined with local RT and PD-L1 blockade, the ICV significantly delayed the growth of irradiated and non-irradiated tumors. The triple combination therapy increased the proportions of CD8+ T cells and effector memory CD8+ T cells while decreasing the proportion of CTLA-4+ exhausted CD8+ T cells within tumor microenvironment. Additionally, plasma level of interferon-γ and proliferation of effector T cells in the spleen and tumor-draining lymph nodes were significantly increased by the triple combination therapy.

CONCLUSIONS

The ICV enhanced the therapeutic efficacy of local RT and PD-L1 blockade by augmenting anti-tumor immune responses. Our findings suggest a therapeutic potential of in vitro-irradiation products of tumor cells.

The future of cancer vaccines against colorectal cancer

INTRODUCTION

Colorectal cancer (CRC) is the second most lethal malignancy worldwide. Immune checkpoint inhibitors (ICIs) benefit only 15% of patients with mismatch repair-deficient/microsatellite instability (dMMR/MSI) CRC. The majority of patients are not suitable due to insufficient immune infiltration. Cancer vaccines are a potential approach for inducing tumor-specific immunity within the solid tumor microenvironment.

AREA COVERED

In this review, we have provided an overview of the current progress in CRC vaccines over the past three years and briefly depict promising directions for further exploration.

EXPERT OPINION

Cancer vaccines are certainly a promising field for the antitumor treatment against CRC. Compared to monotherapy, cancer vaccines are more appropriate as adjuvants to standard treatment, especially in combination with ICI blockade, for microsatellite stable patients. Improved vaccine construction requires neoantigens with sufficient immunogenicity, satisfactory HLA-binding affinity, and an ideal delivery platform with perfect lymph node retention and minimal off-target effects. Prophylactic vaccines that potentially prevent CRC carcinogenesis are also worth investigating. The exploration of appropriate biomarkers for cancer vaccines may benefit prognostic prediction analysis and therapeutic response prediction in patients with CRC. Although many challenges remain, CRC vaccines represent an exciting area of research that may become an effective addition to current guidelines.

Transplantable Subcutaneous Tumor Models

Mouse tumor models are essential in cancer research, especially in elucidating malignancy, developing prevention, diagnosis, and new therapeutic approaches. Nowadays, due to standardized ways of maintaining animal colonies and the availability of mouse strains with known genetic backgrounds and approaches to reduce the variability of tumor size between animals, transplantable mouse tumor models can be widely used in translational cancer research. Here, we describe the induction of different subcutaneous tumor models in mice, in particular xenograft and syngeneic that can be used as experimental tumor models.

Immunospot Assessment of T-Cell Responses in Preclinical Tumor Models with Undefined Target Antigens

Assessment of functional tumor-specific T-cell responses in preclinical tumor models represents an important tool for successful translation of new immunotherapies to clinics. Usually, it requires a known tumor antigen target. Here, we describe the method to detect tumor-specific T cell after immunotherapies without a known antigen. Splenocytes, lymph node immune cells, or PBMCs are isolated from treated mice and stimulated with relevant tumor cells ex vivo before immunospot analysis of Granzyme B and interferon γ-positive T cells. The method is especially valuable for monitoring tumor-specific T cells after vaccination with various whole tumor vaccines or after in situ vaccination and other antigen agnostic immunotherapies, where no specific antigens are used.

What We Learned about the Feasibility of Gene Electrotransfer for Vaccination on a Model of COVID-19 Vaccine

DNA vaccination is one of the emerging approaches for a wide range of applications, including prophylactic vaccination against infectious diseases and therapeutic vaccination against cancer. The aim of this study was to evaluate the feasibility of our previously optimized protocols for gene electrotransfer (GET)-mediated delivery of plasmid DNA into skin and muscle tissues on a model of COVID-19 vaccine. Plasmids encoding the SARS-CoV-2 proteins spike (S) and nucleocapsid (N) were used as the antigen source, and a plasmid encoding interleukin 12 (IL-12) was used as an adjuvant. Vaccination was performed in the skin or muscle tissue of C57BL/6J mice on days 0 and 14 (boost). Two weeks after the boost, blood, spleen, and transfected tissues were collected to determine the expression of S, N, IL-12, serum interferon-γ, the induction of antigen-specific IgG antibodies, and cytotoxic T-cells. In accordance with prior in vitro experiments that indicated problems with proper expression of the S protein, vaccination with S did not induce S-specific antibodies, whereas significant induction of N-specific antibodies was detected after vaccination with N. Intramuscular vaccination outperformed skin vaccination and resulted in significant induction of humoral and cell-mediated immunity. Moreover, both boost and adjuvant were found to be redundant for the induction of an immune response. Overall, the study confirmed the feasibility of the GET for DNA vaccination and provided valuable insights into this approach.