RESUMO
BACKGROUND: Immune suppression in the tumour microenvironment remains a major limitation to successful immunotherapy of cancer. In the current study, we analysed whether the natural killer T cell-activating glycolipid α-galactosylceramide could overcome immune suppression and improve vaccination against metastatic breast cancer. METHODS: Mice with metastatic breast cancer (4T1 model) were therapeutically treated with a Listeria monocytogenes-based vaccine expressing tumour-associated antigen Mage-b followed by α-galactosylceramide as separate agents, or as a complex of α-galactosylceramide stably incorporated into Listeria-Mage-b. Effects on metastases, tumour weight, toxicity and immune responses were determined. RESULTS: Sequential treatments of mice with established 4T1 breast carcinomas using Listeria-Mage-b followed by α-galactosylceramide as a separate agent was highly effective at reducing metastases, but was accompanied by severe liver toxicity. In contrast, combined therapy using Listeria-Mage-b modified by incorporation of α-galactosylceramide resulted in nearly complete elimination of metastases without toxicity. This was associated with a significant increase in the percentage of natural killer T cells in the spleen, and an increase in natural killer cell activity and in T cell responses to Mage-b. CONCLUSIONS: Our results suggest that direct incorporation of α-galactosylceramide into a live bacterial vaccine vector is a promising non-toxic new approach for the treatment of metastatic breast cancer.
Assuntos
Vacinas Anticâncer/uso terapêutico , Galactosilceramidas/metabolismo , Imunoterapia , Células Matadoras Naturais/imunologia , Listeria monocytogenes/genética , Neoplasias Mamárias Experimentais/prevenção & controle , Proteínas de Neoplasias/genética , Linfócitos T/imunologia , Animais , Antígenos de Neoplasias/imunologia , Apoptose , Western Blotting , Adesão Celular , Ciclo Celular , Movimento Celular , Proliferação de Células , Feminino , Citometria de Fluxo , Técnicas Imunoenzimáticas , Células Matadoras Naturais/metabolismo , Células Matadoras Naturais/patologia , Ativação Linfocitária , Neoplasias Mamárias Experimentais/genética , Neoplasias Mamárias Experimentais/imunologia , Neoplasias Mamárias Experimentais/patologia , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Nus , Metástase Neoplásica , RNA Mensageiro/genética , Reação em Cadeia da Polimerase em Tempo Real , Recombinação Genética , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Linfócitos T/metabolismo , Linfócitos T/patologia , Células Tumorais Cultivadas , VacinaçãoRESUMO
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.