Salmonella-induced immune response reduces recurrence and tumor dissemination in preclinical melanoma model

Localized melanoma is easy to remove by surgery, resulting in a high five-year relative survival rate. However, when disseminated the disease management is challenging. The use of immunotherapies, such as anti-checkpoint monoclonal antibodies, has improved treatment options but still only a small percentage of patients responds to these expensive treatments. In this work, we apply a bacteria-based immunotherapy using LVR01, an attenuated Salmonella enterica serovar Typhimurium, as neoadjuvant therapy one week before surgery in a preclinical disseminated murine melanoma model. LVR01 administration resulted in tumor growth retardation prior to tumor resection, due to a rapid upregulation of inflammatory genes in the tumor microenvironment. As a consequence, cell infiltration increased, particularly neutrophils, macrophages and NK cells, being the latter involved in Salmonella anti-tumor activity. Besides, tumor-draining lymph node infiltration is characterized by reinvigorated CD4(+) and CD8(+) lymphocytes. Induced immune response could account for the prevention or delay of tumor recurrence and appearance of metastasis, resulting in a prolonged overall survival after surgery. Furthermore, upon rechallenge mice show partial protection, suggesting the existence of specific memory against melanoma. We propose that neoadjuvant LVR01 treatment could represent an interesting inexpensive alternative that may ease tumor resection, while preventing tumor recurrence in patients with melanoma.