While I agree in principle and I am also not an expert by any means, I think it should be possible to inject a finite amount of substances that eventually cause

While I agree in principle and I am also not an expert by any means, I think it should be possible to inject a finite amount of substances that eventually cause a change to the composition of the human body to make it functionally immortal, in theory. I think this can be reasoned from three observations: 1. That it is possible to change the DNA of the cells of a living organism by injecting substances in said organism (as evidenced by genetic advances in recent decades?). 2. That the DNA of an organism has an extreme amount of control over the composition of said organism (as evidenced by the amount of diversity in all DNA-based organisms and species and also by the known fact that changes in the DNA of an organism also change how it evolves). 3. That biologically immortal species already exist (e.g. hydras?). That said, I'm pretty sure we're extremely far away from achieving this (unless we can create superintelligent AIs soon).