Preclinical studies are being conducted based on some problematic principals. That most experimental animals are inbred and housed in aseptic conditions might account for some differences seen between preclinical findings and clinical outcomes. Using outbred animals kept in more natural conditions could generate results that better recapitulate those seen in clinical settings.
Immunological studies investigating cancer treatments are usually performed in healthy animals transplanted with tumors. Once the immune response rejects the tumor, follow-up studies to determine whether it might relapse are not typically conducted. In humans, tumors develop spontaneously, and recurrence is a major issue. Thus, transgenic animals that develop cancer spontaneously are more suitable for testing cancer vaccines or other immunotherapeutic strategies. Follow-up studies should also be performed to determine whether the tumor returns after a therapeutic appears to be initially successful.
Xenogeneic animal models are often used as theoretical test tubes to determine the efficacy of drugs or immunotherapies. Results derived from xenogeneic models, which are immune-deficient to allow engraftment of human tumor cells, don’t always carry over into clinical studies because they focus on a single factor while ignoring the involvement of complex genes and endogenous elements in immune-competent hosts. While preclinical models used to date have generated useful data in basic research, particularly where understanding the mechanism of function of certain molecules is important, translational research requires new approaches.