No you cannot make that up because the body can naturaly fight it as it's naturaly designed for that: but when you artificaly induce something in the body there

No you cannot make that up because the body can naturaly fight it as it's naturaly designed for that: but when you artificaly induce something in the body there is no guarantee that you won't just break the natural protection. And no modern medicine cannot predict anything on a global level of the body: if it could then we could've simulate billion of virtual humans using supercomputers and go for real human trials only after that. But such simulations would be innacurate just like how weather prediction is innacurate for more than a few days in the future: the problem is that the body (just like the weather) is a complex system where the butterfly effects becaomes a real thing. So it's not a question of "models" or "compute power": even the slightest devition in the model will break all predictions results in a cascading manner over time.