In vitro and in vivo immunomodulatory activity of ST 789 on two human lymphoblastic T cell lines.

The immunomodulatory activity of the synthetic derivative, N-alpha-5(1,6-dihydro-6-oxo-9-purinyl) pentyloxy-carbonyl-L-arginine (ST 789) has been evaluated by using two human T-cell lines stabilized in our laboratory from the pleural effusion fluid of a patient with acute T lymphoblastic leukemia and from the lymph node biopsy of a child with convoluted T-cell lymphoma, respectively. In vitro, ST 789 did not substantially modify the expression of membrane antigens and the proliferation of both lines, whereas their growth in immunosuppressed nude mice was hampered by the local injection of 0.1 microgram/mouse ST 789 for ten days. The combined administration of ST 789 with human peripheral blood polymorphonuclear cells completely inhibited the in vivo tumorigenicity of the T lymphoma. These in vivo findings show that the antitumor action displayed by ST 789 is probably due to its boosting of natural mechanisms.