In vivo electroporation restores the low effectiveness of DNA vaccination against HER-2/neu in aging

Nucleic acid vaccines: innovations, efficacy, and applications in at-risk populations

For more than two centuries, the field of vaccine development has progressed through the adaptation of novel platforms in parallel with technological developments. Building off the advantages and shortcomings of first and second-generation vaccine platforms, the advent of third-generation nucleic acid vaccines has enabled new approaches to tackle emerging infectious diseases, cancers, and pathogens where vaccines remain unavailable. Unlike traditional vaccine platforms, nucleic acid vaccines offer several new advantages, including their lower cost and rapid production, which was widely demonstrated during the COVID-19 pandemic. Beyond production, DNA and mRNA vaccines can elicit unique and targeted responses through specialized design and delivery approaches. Considering the growth of nucleic acid vaccine research over the past two decades, the evaluation of their efficacy in at-risk populations is paramount for refining and improving vaccine design. Importantly, the aging population represents a significant portion of individuals highly susceptible to infection and disease. This review seeks to outline the major impairments in vaccine-induced responses due to aging that may be targeted for improvement with design and delivery components encompassing mRNA and DNA vaccine formulations. Results of pre-clinical and clinical applications of these vaccines in aged animal models and humans will also be evaluated to outline current successes and limitations observed in these platforms.

A novel cancer therapeutic using thrombospondin 1 in dendritic cells

Induction of thrombospondin 1 (TSP-1) is generally assumed to suppress tumor growth through inhibiting angiogenesis; however, it is less clear how TSP-1 in dendritic cells (DCs) influences tumor progression. We investigated tumor growth and immune mechanism by downregulation of TSP-1 in dendritic cells. Administration of TSP-1 small hairpin RNA (shRNA) through the skin produced anticancer therapeutic effects. Tumor-infiltrating CD4(+) and CD8(+) T cells were increased after the administration of TSP-1 shRNA. The expression of interleukin-12 and interferon-γ in the lymph nodes was enhanced by injection of TSP-1 shRNA. Lymphocytes from the mice injected with TSP-1 shRNA selectively killed the tumor cells, and the cytotoxicity of lymphocytes was abolished by depletion of CD8(+) T cells. Injection of CD11c(+) TSP-1-knockout (TSP-1-KO) bone marrow-derived DCs (BMDCs) delayed tumor growth in tumor-bearing mice. Similarly, antitumor activity induced by TSP-1-KO BMDCs was abrogated by depletion of CD8(+) T cells. In contrast, the administration of shRNAs targeting TSP-2, another TSP family member, did not extend the survival of tumor-bearing mice. Finally, TSP-1 shRNA functioned as an immunotherapeutic adjuvant to augment the therapeutic efficacy of Neu DNA vaccination. Collectively, the downregulation of TSP-1 in DCs produces an effective antitumor response that is opposite to the protumor effects by silencing of TSP-1 within tumor cells.

Myeloid-derived suppressor cells have a central role in attenuated Listeria monocytogenes-based immunotherapy against metastatic breast cancer in young and old mice

Background:

Myeloid-derived suppressor cells (MDSCs) are present in large numbers in blood of mice and humans with cancer, and they strongly inhibit T-cell and natural killer (NK) cell responses, at young and old age. We found that a highly attenuated bacterium Listeria monocytogenes (Listeria^at)-infected MDSC and altered the immune-suppressing function of MDSC.

Methods:

Young (3 months) and old (18 months) BALB/cByJ mice with metastatic breast cancer (4T1 model) were immunised with Listeria^at semi-therapeutically (once before and twice after tumour development), and analysed for growth of metastases and primary tumour, in relation to MDSC-, CD8 T-cell and NK cell responses.

Results:

We found that Listeria^at-infected MDSC, which delivered Listeria^at predominantly to the microenvironment of metastases and primary tumours, where they spread from MDSC into tumour cells (infected tumour cells will ultimately become a target for Listeria-activated immune cells). Immunotherapy with Listeria^at significantly reduced the population of MDSC in blood and primary tumours, and converted a remaining subpopulation of MDSC into an immune-stimulating phenotype producing IL-12, in correlation with significantly improved T-cell and NK cell responses to Listeria^at at both ages. This was accompanied with a dramatic reduction in the number of metastases and tumour growth at young and old age.

Conclusions:

Although preclinical studies show that immunotherapy is less effective at old than at young age, our study demonstrates that Listeria^at-based immunotherapy can be equally effective against metastatic breast cancer at both young and old age by targeting MDSC.

A single electroporation delivery of a DNA vaccine containing the hemagglutinin gene of Asian H5N1 avian influenza virus generated a protective antibody response in chickens against a North American virus strain

Protection against the avian influenza (AI) H5N1 virus is suspected to be mainly conferred by the presence of antibodies directed against the hemagglutinin (HA) protein of the virus. A single electroporation delivery of 100 or 250 μg of a DNA vaccine construct, pCAG-HA, carrying the HA gene of strain A/Hanoi/30408/2005 (H5N1), in chickens led to the development of anti-HA antibody response in 16 of 17 immunized birds, as measured by a hemagglutination inhibition (HI) test, competitive enzyme-linked immunosorbent assay (cELISA), and an indirect ELISA. Birds vaccinated by electroporation (n = 11) were protected from experimental AI challenge with strain A/chicken/Pennsylvania/1370/1/1983 (H5N2) as judged by low viral load, absence of clinical symptoms, and absence of mortality (n = 11). In contrast, only two out of 10 birds vaccinated with the same vaccine dose (100 or 250 μg) but without electroporation developed antibodies. These birds showed high viral loads and significant morbidity and mortality after the challenge. Seroconversion was reduced in birds electroporated with a low vaccine dose (10 μg), but the antibody-positive birds were protected against virus challenge. Nonelectroporation delivery of a low-dose vaccine did not result in seroconversion, and the birds were as susceptible as those in the control groups that received the control pCAG vector. Electroporation delivery of the DNA vaccine led to enhanced antibody responses and to protection against the AI virus challenge. The HI test, cELISA, or indirect ELISA for anti-H5 antibodies might serve as a good predictor of the potency and efficacy of a DNA immunization strategy against AI in chickens.