An immunotherapeutic agent utilizing mRNA to encode the cytokines interleukin-12sc (IL-12sc), interleukin-15sushi (IL-15sushi), interferon alpha (IFNa) and granulocyte-macrophage colony-stimulating factor (GM-CSF), with potential immunomodulating and antineoplastic activities. Upon intratumoral administration of IL-12sc, IL-15sushi, IFNa and GM-CSF mRNA-based immunotherapeutic agent SAR441000, mRNA is picked up by nearby cells, translated and released into the local tumor microenvironment (TME). Secretion of these cytokines activate the immune system by promoting the activation of natural killer cells (NKs) and inducing cytotoxic T-lymphocyte (CTL) responses, which may result in an immune-mediated destruction of tumor cells.