41 × 109 bp. It is also assumed that there is only one oncogene of size 1925 contained in the canine genome. The safety factor is calculated to be 2.3 × 1011. This indicates that 230 billion doses of vaccine would need to be administered before an oncogene dosage Topoisomerase inhibitor equivalent to 9.4 μg would be reached. Safety factor for infectivity due to a single provirus is similarly calculated, substituting the following values for those in Eq. (19): Qm = 2.5 μg; E[U] < 1 ng; Med0 = 450 bp; diploid size of host genome N = 4.82 × 109 bp; J0 = 1; n1 = 7000 bp. The safety factor for a single provirus is calculated to be 8.3 × 1013

or the equivalent of 83 trillion doses to induce an infective event. We repeat the calculations of safety factors for the example given in Section 4, using Eq. (1), which is a method suggested in Refs. [7] and [8]. The safety factors of oncogenicity and infectivity are determined to be 1.2 × 1010 VE-822 mw and 1.7 × 109, respectively. These calculations overestimate risk due to oncogenicity by more than 19-fold. The overestimation issue for risk of infectivity is even more pronounced; the risk is overstated by more than 48,000 times. The overestimation stems from the fact that enzyme inactivation is not taken into

account. The method we propose in the paper clearly results in more accurate estimates of risks because of the inclusion of enzyme inactivation in its calculations. It is also worth noting that in all the calculations of safety Montelukast Sodium factors, we assume that the residual hcDNA is less than 1 ng. However, the intranasal administration of the vaccine is likely to reduce the residual hcDNA found in tissues which, if shown to be true, would further lower associated risks. Model validation is an integral part of a probabilistic method development. It ensures that a method is fit

for its intended use. The accuracy and reliability of the risk assessment approach we develop ideally should be validated by comparing its estimated values with observed events. However, before a biological product is approved for marketing and distributing, there are only a limited number of doses administered in human subjects during clinical development. Because the risks of oncogenicity and infectivity due to hcDNA are in general low, it would take many doses to observe some events. As a result, validation of the model based on empirical data can only be accomplished if one were to follow millions of doses for extended periods of time. This is one of the limitations the proposed method has. It is also worth pointing out that the quantity in Eq. (18) or (19) represents a point estimate of the safety factor. Because the parameters involved in the calculations are determined through analytical methods which have inherent variability, the accuracy and precision of the safety factor estimate are influenced by that of the analytical methods. It is advisable to conduct a sensitivity analysis of the safety factors.