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A hypothesis predicting that increase in the rate of synthesis of host messenger RNA would be associated with antiviral activity was examined. Biochemically, Isoprinosine or NPT-10381 (methisoprinol) increased the rate of rapid labeling of polyribosomal RNA and protein in uninfected monkey kidney cells in tissue culture. In tissue-culture systems, Isoprinosine exerted antiviral effects against influenza virus, PR-8 and A2 strains; herpes virus, LU strain; polio virus 3; and adenovirus 10. In in vivo mortality studies, Isoprinosine was observed to exert therapeutic antiviral effects against the A2 strain of influenza and, as well, against a herpes infection of newborn mice. Experiments were carried out which demonstrated a correlation between the in vivo anti-influenza (PR-8) effects of Isoprinosine and reduction in the virus titer in lungs of infected mice.

Various physicochemical characteristics and the biological activity of two murine lymphoma viruses (S-63 and GC), originally isolated in this laboratory and previously reported as sharing common antigenic properties with human and bovine lymphomas, are defined. These viruses are stable at temperature ranges from −70 °C to +4 °C and are inactivated after incubation at +56 °C for 30 min. They withstand lyophilization and are inactivated by treatment with ethanol, acetone, ethyl ether, formalin, and phenol. Both agents are of the ribonucleic acid, double-membraned viruses, similar to myxoviruses, and are approximately 100 mμ in size.

Attempts were successful to develop tissue culture cell lines of murine origin capable of supporting the GC and S63 murine viruses. Viruses from this source were used as antigens to prepare antisera in rabbits. These sera cross-reacted with Moloney, Friend, and Rauscher antigens prepared similarly; however, dilution techniques disclosed that the S63 and GC viruses contain a specific antigen not related to the Rauscher, Friend, Moloney agent. Attempts to grow these two agents (S63 and GC) on J111 cells (a human leukemia) failed.