A composition for human and animal use as a therapy for the treatment of tumors, acquired immunodeficiency syndrome and leukemias is described. The composition, for human and animal use as an antitumor agent, has a strain of bacteria Lactobacillus reuteri LRE 03 DSM 23879 which is able to strongly stimulate the production of pro-inflammatory cytokines (Th1) interferon INF-gamma, the cytokines exhibiting a marked antitumor activity, and/or a strain of bacteria Lactobacillus salivarius LSO6 DSM 26037 which is able to strongly stimulate the production of dendritic cells, the dendritic cells also exhibiting a marked antitumor activity.
