Before people get too ahead of themselves - the CAR-T (Chimeric Antigen Receptor T-cell) technology used here is super hot right now and works by reprogramming the immune cells (via genetically engineering a new recognition domain into them) so that they recognize and kill cancer cells. All great, the problem is that most cancers don't have a single "hey look im cancer" biomarker - except blood cancers. This therapy works because the cancer they're targeting is immune cell cancer and immune cells DO have very specific receptors on their surface that allow this therapy to be extremely targeted (and extremely effective).
Not to discount the work which is amazing and is surely great news for sufferers of myeloma, but when you see mention of technology like this don't get TOO excited that we're on the cusp of a cure for cancer UNTIL you see it happening in various solid tumors.
As a naive layperson, we can’t be very far from getting a sample of cancer from a person, doing a diff against a regular cell and then creating a specific vector that holds whatever can kill those particular cells. How far are we really?
1. To be definitely safe, you can't just sample one healthy cell, you have to sample lots and from the many different types and subtypes everywhere in your body. Imagine training a swarm of robots to attack anybody wearing a mask and wielding a knife... and then they enter a hospital surgical ward.
2. Sometimes the problem with cancers is that they are behaviorally wrong in ways that aren't easily expressed at the cell-boundary. (Your body has MHC-1 proteins that try to offer a debug-window into what the cell has been doing, but that's its own complicated topic.)
That's the right approach. But, as the other commenter pointed out, there are a number of complications which mostly center on the inability to distinguish cancer from self. Many of the mutations that make cells cancerous are not expressed at the cell surface, and the only way to probe the interior is through MHC molecules which act as little windows into the cell. More specifically, during normal metabolism the cell will chop up the proteins its making and display them on the surface for immune surveillance. The immune system can use these because its been trained against EVERYTHING SELF (in the thymus) so when something goes wrong in a cell and surface expression looks different it can usually recognize this.
Of course by the time cancer has developed something has gone wrong in this process normal process in any number of ways.
Even if the challenge was just "recognize MHC-presented cancer antigen" in therapy you have to a) determine what section of the mutated protein would be displayed in MHC, b) determine and develop an antibody (or antibody-like molecule) how to recognize specifically that (and not the non-mutated version which will be present in healthy cells), then c) either genetically engineer the patient's immune cells to recognize it, or hijack the recognition process in some other manner.
Each of these steps is very very difficult and we're only just developing the computational and experimental tools to do these for any patient, let alone every cancer patient.
I won't go into it, but you also have to think about cancer as a living organism susceptible to evolution so if you don't hit hard and fast to wipe it out all at once, you select for mutations that evade your treatment. This is made especially challenging considering that cancer usually has some mechanism gone awry that leads to increased growth and mutation rates so that they're even MORE likely to evade your treatments then a generic cell - think of it kind of like antibiotic resistance in bacteria
As another layperson who only has a college freshman-level understanding of Biology 101, I don't think that's going to be simple.
Immune cells look for -expressions- on the surface of a cell to tell them whether a cell is wonky or not. Typically, these are proteins. These proteins are encoded by DNA, yes, but it's not going to be as simple as diffing the DNA between a regular cell and a cancerous cell because a simple diff like that won't tell you what will get expressed as a key cancer cell surface protein.
DNA gets interpreted as mRNA which then acts as instructions to build long strands of amino acids. These amino acid chains then fold (in hard to calculate ways) into proteins. There's a whole set of other machinery in the cell that regulates how those proteins behave once they're constructed.
TLDR, there's multiple compilation steps to go from a DNA to protein, and then a whole host of runtime monkeypatching to get proteins from A to B.
Not to discount the work which is amazing and is surely great news for sufferers of myeloma, but when you see mention of technology like this don't get TOO excited that we're on the cusp of a cure for cancer UNTIL you see it happening in various solid tumors.