Importance of treatment regimen of interferon as an antitumor agent.

A highly purified hybrid human leukocyte interferon, IFN-alpha AD, produced in Escherichia coli, has been used to define optimum treatment conditions for L1210 leukemia in mice. Treatments prior to tumor inoculation were ineffective. Treatments from the third day post-tumor inoculation were most effective, and treatments every third day were more effective than were regimens involving more frequent treatments. IFN-alpha AD was effective in vivo against tumors formed from a line of L1210 cells resistant to IFN-alpha AD in cell cultures. These and other results indicate the importance and nature of indirect mechanisms of action for efficacy of interferons against tumors.