Inhibition of TNF-alpha produced by Kupffer cells protects against the nonspecific liver toxicity of immunotoxin anti-Tac(Fv)-PE38, LMB-2

LMB-2 (anti-Tac(Fv)-PE3B) is a recombinant immunotoxin composed of the Fv f ragment of the anti-Tac Ab fused to a 38-kDa form of Pseudomonas exotoxin A . Recent clinical trials showed that LMB-2 is a promising agent for the tre atment of patients with Tac-positive leukemia or lymphoma. One major side e ffect that needs to be overcome is nonspecific liver toxicity. In the curre nt study, we have analyzed the mechanism of this toxicity using a mouse mod el. Mice that were injected with a lethal dose of LMB-2 showed severe hepat ic necrosis, Immunohistochemistry revealed that LMB-2 accumulated in Kupffe r cells in the liver, suggesting that the damage to the hepatocytes was ind irect, When we examined the effects of LMB-2, on peritoneal macrophages, ce lls in the same lineage as Kupffer cells, we found that LMB-2 induced the p roduction of TNF-alpha by these cells. Following LMB-2 administration to mi ce, the levels of TNF-alpha in the liver increased to very high levels, whe reas the rise in serum levels was modest. in addition, the LMB-2-induced li ver toxicity was blocked by a specific TNF binding protein (TNFsRp55). Live r toxicity was also blocked by indomethacin, which also blocked the rise of TNF-alpha in the liver. Both TNFsRp55 and indomethacin treatment protected mice against a lethal dose of LMB-2, These data indicate that TNF-alpha pr oduced in the liver by Kupffer cells has an important causal role in the no nspecific liver toxicity of LMB-2, These findings have important clinical i mplications for the use of immunotoxins in the therapy of patients with can cer.