A microbial metabolite and dipeptide with potential immunomodulatory and antitumor activities. Ubenimex competitively inhibits many aminopeptidases, including B, N and leucine aminopeptidases. Aminopeptidases has been implicated in the process of cell adhesion and invasion of tumor cells. Therefore, inhibiting aminopeptidases may partially attribute to the antitumor effect of ubenimex. This agent also activates T lymphocyte, macrophage and bone marrow stem cell as well as stimulates release of interleukin-1 and -2, thus further enhances its antitumor activity.