Hello everyone, and welcome to another installment of Put the Sci in your Fi! I’m sure any sci-fi enthusiast has come across this trope, whether it’s in video games or books or TV show/movies, and that is: If you have a disease, plus an immune (usually human) character, that person will be sacrificed by the end to provide a cure and save the rest of humanity from the dastardly plague.
As a writer and reader, of course I understand why this approach is often taken. It’s dramatic, it creates tension and an ethical dilemma, and if a beloved character is sacrificed for “the greater good,” it pulls the reader’s heartstrings. But the scientist in me always whines that this isn’t scientifically sound, that it’s a huge waste of a valuable and limited resource, that there are other, more creative (and perhaps less obvious) ways where you can save the character and generate a cure, and be much smarter and more efficient in the process.
But how are you supposed to use the immune character (henceforth referred to as the IC) to generate a panacea serum if you don’t bleed them dry or scoop out their entire brain? How to science this?
Well…by not bleeding them dry. And also by not removing their brains.
The adaptive immune system is what vertebrates build up over their lifetimes to combat infections. This little biological army learns (hence, “adaptive”) during each exposure to the same pathogen how to fight that particular bug more effectively. And, assuming a vaccine is unavailable, it is statistically probable for a very small percentage of the population that is naturally immune to a particular pathogen.
Assuming your IC is the Chosen One, the one and only Golden Child that will save the world, what is the scientific downside of sacrificing them, and how can you generate a cure without killing them?
This post will gloss over only a couple of facets of immunology (because let’s face it, this is a blog post, not a textbook, and I’d rather not have anyone die of boredom.) We’ll start with…
Antibodies are generated by the adaptive immune system, specifically by B-cells. These molecules can actually convey a passive immunity to others, in that if antibodies are isolated from your IC’s blood, vialed up and injected into other people, those antibodies can pass on immunity to those other people for a few weeks or months. While these antibodies will need to be administered constantly to maintain immunity, it can help protect your other non-immune characters within hours or days.
Not only can these antibodies potentially immunize, they can itself be a cure for someone who’s already infected, as shown by Shibasaburo Kitasato and Emil von Behring in 1890 when they cured diphtheria and tetanus in infected animals by injecting them with the blood products of an immunized animal. So, not only can they pre-empt infection in a character who’s been exposed to the infective agent, antibody-containing blood products can help cure a character after symptoms start to show.
From this standpoint, killing your IC is a bad move just because if they’re dead, guess what, they’re no longer making that magic elixir in their blood. You need their immune system alive and kicking to make antibodies. Not to mention, in reality, you’d need a lot of ICs to produce sufficient quantities of the antibody, so by sacrificing them, you’re just stacking the odds against the rest of the world that much more.
Sometimes, though, it isn’t quite just the antibody that’s doing all the heavy lifting. Sometimes, an IC can be immune simply because for whatever reason, the pathogen has lost its potency or The Thing that makes it potentially dangerous, whether due to mutation or an alternate strain. In other words, the bug is attenuated.
A lot of real-life vaccines (particularly for viral infections) rely on attenuated pathogens. Basically, the virus is alive, but contains mutations that make it non-virulent, which makes it unable to cause disease but still bear the antigens necessary for your immune system to build up an immunity. Generally, this effect is artificially produced in the lab in a systematic and selective manner.
However, every once in a while, nature is able to create this effect as well, since random mutations can occur at any time. Given all the variables found in nature, the stars must align—your unexposed IC must come into contact with a version of the virus that has adapted to live in a different host (while that other host is still alive or at least able to spread the infection) but still be able to infect humans without causing disease. This, in effect, inoculates your IC with a mutated virus that likely doesn’t grow very well and doesn’t cause disease, but still carries viral antigens that your IC’s immune system can learn to recognize and combat.
In other words, if the virus can withstand the IC’s immune system long enough (keep in mind there is very likely a time limit here), you have a walking, talking incubator for an attenuated virus that can be collected and cultured in a lab. But a virus needs a living host to reproduce (assuming it can even do so in a host it’s not well adapted to), so if your IC dies, so does your vaccine.
This same logic can be applied to bacterial/fungal infections too. Some species of bacteria can sequester themselves, hiding from the immune system. This usually causes a problem since the body isn’t able to fight the infection, but if the bacteria is no longer virulent, this could be a gold mine for isolation and culture of a non-pathogenic strain of something that would normally be deadly.
However, mutations in infective agents aren’t always what conveys immunity. While much, much slower, human genomes can mutate too.
Host mutation and immunity
This right here is essentially why 10% of the European population is immune to HIV. These individuals have a mutation in the receptor that the virus uses to enter immune cells. This bars entry, and effectively prevents HIV from reproducing. As mentioned earlier, a virus requires a living host to reproduce. This is because a virus itself lacks the molecular machinery to replicate its DNA. It must hijack its host’s DNA-replication tools, but if it can’t access the toolbox, it won’t be able to grow, and the host’s immune system will eventually catch up with it and eradicate the infection.
But guess what didn’t happen? Researchers did not murder those immune to HIV! No, people like Stephen Crohn, upon realizing that they were immune when those around them succumbed, volunteered to be studied, and the discovery of the mutated receptor became the foundation for the development of anti-viral drug maraviroc. Similarly, by not sacrificing your IC, the science in your story world can move forward.
Thank you for reading! As always, if you have any questions/feedback, please leave them as comments below, I would love to hear your thoughts or address any concerns you may have.