RELA and neoplasm: A newly attenuated strain, HCS1, was developed based on VNP20009 by knocking out relA and spoT. HCS1 exhibited comparable in vitro growth to VNP20009 but significantly lower cytotoxicity and invasiveness In the MC38 tumor-bearing mouse model, HCS1 induced abundant immune cell infiltration and released high levels of antitumor inflammatory cytokines TNF-α and IL-1β and anti-inflammatory factor IL-10.