Technology

Of course it needs to be controlled and regulated. Like any other drugs. One of the reasons drugs are expensive is because there is so many regulatory hurdles that drug makes have to deal with before they can touch a patient.

I get your hypothetical, but it has two shortcomings. Firstly, training the immune system against cancer mutations is fairly easy, because the mutations are not present during the process of T and B cell maturation, so in the population of circulating naive T and B cells in a patient, there are likely to exist ones that are going to recognise the cancer antigen. Whatever proteins drive the dark pigmentation of skin or green eye colour will be used to drive the negative selection of T and B cells in the person with dark skin or brown eyes. And so, even if you administer a "vaccine" encoding these proteins, their immune systems will not be able to mount a response against them.

Secondly, what about the practicalities. Say you made the anti-green eye vaccine - how do you administer it to people? I'm assuming we're not talking about some dystopian future where forcing people to receive injections that contain biologicals killing them is legal. It's not the kind of "vaccine" that you could just spread in the air or add to drinking water for it to take effect.