- Depending on the type of experiment you are doing, the process of optimization is different. 

For example, in our experiment we wanted to know what was the minimal number of cells required to form tumors in immunocompromised mice. This was a process of optimization. We wanted to know this because this will significantly lower the variability in the size of the tumors that you obtain in those mice, and not only that, will allow us to do the experiment faster in terms that we will need to grow less cells in the lab to be injected into mice. 

So the way that we did that is by injecting a small number of mice with different number of cells. So we just went ahead and prepared the cells and inject five million cells in some mice, two million cells in another mice, and even one million cells in other mice. And we were just monitoring the growth, the tumor growth in these mice to assess which one was the minimal number that we needed to form those tumors. 

And from an ethical point of view when we are talking about animals it's very important that the conditions are as good as possible before starting the experiment.