In 2005, a Phase 1 clinical trial was conducted to evaluate the immunogenicity and safety of V3526 in human volunteers. The findings from this trial showed robust immune responses in virtually all vaccine recipients [12
]. However, a significant number of the vaccine recipients demonstrated mild to moderate adverse events including headache, fever, malaise and sore throat. Nonclinical studies performed prior to the clinical trial revealed lymphopenia and viral shedding in vaccinated NHP; however, febrile responses were not evident [9
]. Following the clinical trial, temperature data in NHP were re-evaluated and showed changes in approximately 50% of NHP that may be indicative of a febrile response (). It is our belief that the febrile response in PCM-inoculated NHP were due to non-specific inflammatory responses to the components of the PCM while the febrile response to V3526 were due to viral replication and specific inflammatory/immune responses to V3526 replication. Re-evaluation of the NHP data highlighted the importance of examining individual animal responses visually in addition to reporting averaged group data. Mouse data from earlier nonclinical safety and efficacy testing were not re-evaluated as the original results were based on daily cage-side observations and would not have provided additional insight into whether mice also experienced mild adverse events.
In the current study, mice were implanted with telemeters and vaccinated with V3526 to determine if telemetric data collection would make the mouse more predictive of clinical symptoms in humans, and therefore a useful tool in early stages of vaccine development. These studies are the first indication that vaccination with V3526 produced a mild febrile reaction in mice.
We conducted these studies in BALB/c mice to build upon the analyses conducted during the early stages of nonclinical development of V3526 [3
]. Neither changes in temperature nor changes in activity were detected in BALB/c mice following vaccination with V3526. These results are supported by the general good health of these mice (weight gain, lack of signs of illness) observed in this study and reported in the literature [3
]. In follow-on studies, we evaluated two outbred mouse strains, NIH-Swiss and CF-1, as they may be more predictive of the heterogeneity in the human and NHP populations. In these studies, an increase in temperature post-inoculation with V3526 compared to baseline temperature was observed in approximately 25% of NIH-Swiss mice and 30% of CF-1 mice and a large percentage of CF-1 mice showed increased activity for a few days duration post-vaccination. It is important to note that the percentage of outbred mice with changes in temperature and activity are similar to the percentage of human, NHP and equines with febrile responses following vaccination with V3526. Approximately 30% of humans [12
], 50% of NHP and 20% of equines [11
] developed a fever of short duration following V3526 vaccination. From this study we conclude the use of telemetry in outbred mouse strains is sufficiently sensitive to detect subtle changes in temperature and activity that may be reflective of the febrile response induced by vaccination in large animal models and humans. However, from these studies it is clear that analysis of changes in individual animals is essential for predicting responses in humans as analysis of group means did not reveal physiological changes in individual mice that were in fact predictive of outcomes in larger species and humans.
To date, evaluation of safety and efficacy in V3526-vaccinated mice has been limited to clinical observations (ruffled fur, hunched back, etc.) and resistance to challenge following immunization [3
]. In the current study, we evaluated temperature and activity in V3526-vaccinated mice following VEEV TrD challenge. All vaccinated mice survived challenge and the daily observations suggested all mice remained healthy during the post-challenge period demonstrating the effectiveness of V3526 in preventing overt disease. However, telemetry data collected from V3526-vaccinated CF-1 mice revealed a remarkable change in daily temperature fluctuations and increased activity following VEEV TrD challenge suggesting that the vaccinated CF-1 mice experience a transient febrile response following challenge.
The results described in this report demonstrate the utility of telemetry in mice, not only for evaluating vaccine safety but also efficacy. Procurement of a telemetry system has a substantial up-front cost, however studies can be planned to take advantage of the long battery life, as telemeters can be reused in multiple, short duration studies. Alternatives to implantable telemeters are available but are often associated with a myriad of disadvantages including the restraint stress induced in animals, aberrant responses due to frequent handling [18
] and limited data sets. The effect of limited data sets on the sensitivity of the outbred mouse model described in this report was evaluated by extracting temperature data that would reflect periodic monitoring following V3526 vaccination and following challenge with VEEV TrD. The results of this analysis suggested a minimum of four data collection time points would be required to identify statistically significant changes during the post-exposure period compared to baseline. Although periodic monitoring may have utility, the collection of data would be labor intensive and data analysis would likely lack the statistical power associated with continuous data collection. Further, periodic monitoring would likely require a longer duration of baseline data collection for establishment of a baseline diurnal pattern as slight variations in baseline temperature readings would likely have a profound effect on detecting differences post-exposure.
Although the current study monitored the responses to V3526 vaccination and VEEV TrD challenge in mice, the use of telemetry holds great promise for advancing our understanding of disease progression and amelioration of disease (vaccination or immunotherapy) in other infectious disease models. In January 2009, the U.S. Food and Drug Administration released draft guidance on addressing efficacy under the Animal Rule [28
]. The application of telemetry was suggested as a method to gain information of disease manifestations that may otherwise be difficult to obtain through clinical observations. Importantly, continuous data collection in natural history studies may reveal physiological parameters that are predictors of mortality that could be used as euthanasia criteria in vaccine and therapeutic efficacy studies to prevent unnecessary suffering of animals or to accurately identify triggers of intervention in therapeutic studies.
As with pharmacologic and toxicologic studies, the use of telemetry in studies of infectious diseases has historically been limited to larger species [13
]. The data presented in this report demonstrate that the addition of telemetric analysis in mice, particularly outbred mice, increases the sensitivity of the mouse model and demonstrates its utility in predicting responses in larger animals and humans. The use of outbred mouse strains appears to be important in predicting responses in heterogeneous populations as individual mice within the inbred mouse strain were found to respond similarly in these studies. Further, analysis of data on an individual basis appears to be critical to detecting febrile responses that may be subtle or of short duration. In conclusion, the data presented in this report demonstrate the utility of telemetry in outbred mice to assess safety and efficacy of a live-attenuated vaccine which may be applicable to testing of vaccines developed on other platforms.