No abstract

Five rhesus monkeys were injected multiple times over several months with two different human IgG1 monoclonal antibodies, both directed against human cytomegalovirus. Three monkeys each injected four times with monoclonal antibody EV2-7 for over 200 days showed no response other than a normal decay in antibody level. The in vivo half life of this antibody was substantially longer when measured with an idiotype-specific two site immunoassay than with radiolabeled antibody, indicating that the iodination procedure greatly affected the stability of the antibody. Although there was considerable individual variation in the half-life of EV2-7, from 8.9 to 30.5 days, the half-life was fairly long, especially considering the size of the monkeys. Two monkeys were injected with monoclonal antibody EV1-15. One monkey has responded in a similar manner to the EV2-7-injected monkeys. However, the other monkey has produced an anti-idiotypic antibody (or antibodies) of high affinity. It is possible that this response was triggered by the unusual physical nature of antibody EV1-15 or the effect of the species difference between human and rhesus monkey. In any case, the results from these five monkeys indicate that human monoclonal antibodies should have a significant advantage over mouse monoclonal antibodies for in vivo therapeutic applications.

We have shown previously that human monoclonal antibodies are not very immunogenic in rhesus monkeys, with only one monkey out of five mounting an anti-monoclonal antibody response. Two additional monkeys have been injected multiple times with much larger amounts of one human monoclonal antibody. No anti-antibody response has been detected in these monkeys. Structural changes that occur in the monoclonal antibodies over time in vivo have been investigated by Western Blots using anti-idiotypic antisera. Sodium dodecyl sulfate gel electrophoresis reveals that very little antibody has altered molecular weight. Isoelectric focusing patterns change more dramatically. Forms of the antibodies with lower isoelectric points appear in the serum. These forms have a similar in vivo half-life as the freshly prepared antibody. Very low pI forms of the monoclonal antibodies are not detected in the serum. Isoelectric focusing can be used to determine the in vivo or in vitro condition of a monoclonal antibody preparation. Finally, the monkey anti-human IgG that arose in the single monkey studied previously has been further characterized.