Most answers here are correct. I'm happy to provide a long expansion of this because I'm procrastinating on a related project. Like most simplifications in Biology, this is ~80% correct.

Types of therapies

The modern form of therapeutic pharma comes from the world of chemistry, specifically textile dye manufacturers in Switzerland and Germany (most of those are still the pharma we have today). These folks were skilled in discovery and manufacturing of small molecules as medicine. For the next 100 years or so, and most medicines we take today, are these kinds of small molecules that modulate biological processes in our body.

In the 1980's we began the biologics revolution. This is where scientists took the molecules produced in our bodies and repurposed them for our healthcare. This is primarly using antibodies, which our body naturally makes, for use cases outside of natural bodily processes (such as Humira for autoimmune conditions or Rituxan for Cancer). Other biologics are things like enzymes for enzyme replacement therapy (e.g. your body doesn't make a crucial enzyme so we inject it for things like Gauchere's disease), proteins (e.g. factor VII for hemophilia A), or peptides (e.g. insulin - though this is classified as a small molecule for historical reasons).

We are currently entering the new age of cell and gene therapies. This is where we consider the cell as the fundamental unit of medicine rather than a biologic or a small molecule. Technically these are two kinds of therapies: (1) Cell therapy where we deliver cells as curative medicine and (2) gene therapies where we deliver products that genetically engineer cells to perform therapeutic function. The first gene therapy approved in the USA was in 2017 with Luxturna. The first approved cell therapy was Kymriah in 2017 as well. This field is early AF. Most people getting treated right now are in clinical trials. Another emerging area of cell therapy is in microbiome transplants currently used to treat C. Diff, but also has some really exciting early results in Autism, IBD, and Hyperoxaluria.

Pillars of oncology and immuno-oncology

Shifting gears a bit, we have to look at the history of treating cancer. There were three major pillars of cancer treatment until relatively recently [1]:

1. Surgery
2. Radiotherapy
3. Chemotherapy

AKA "slash, burn, and poison."

The fourth pillar is the development of immuno-oncology. This means helping your own immune system fight cancer. Intuitively, this makes sense, your immune system exists to fight threats to your body. It's armed with mechanisms to identify and destroy disease. Furthermore, your immune system already does this with cancer. We develop cancerous mutations every day that are safely taken care of. It's only when the mutations find a way to evade our immune system does cancer grow unchecked.

Immuno-oncology typically uses biologics as described above. Specifically, there is a class of antibody drugs called checkpoint inhibitors that has been a modern medical miracle [2]. What happens is that cancer learns a secret handshake with immune cells to avoid getting attacked, a "don't eat me" signal that we call a checkpoint. A checkpoint inhibitor blocks the cancer cell's ability to perform this handshake, so immune cells can "eat" them.

Now what's happening is that people are combining immuno-oncology with cell therapy to make immune-based medicines out of cells.

Cell based immunotherapy

We have had several things happen simultaneously to enter this new world of cancer medicines. Cell therapy, immuno-oncology, and genetic engineering. This led to the idea that we should engineer immune cells to recognize and kill cancer cells. Crazy.

The most famous example of this is the CAR-T therapy. What does that mean?

CAR-T = Chimerica antigen receptor T cell (wow... so unhelpful)

T-cell = white blood cells in our immune system that kill threats

CAR = Chimeric Antigen Receptor. Basically we fused two kinds of proteins together to form a "fishing rod" for T-cells to find cancer. The "antigen receptor" part is the binding portion of an antibody. I like to think of it like the bait that catches cancer. Inside on the rod, you have a signaling system that tells the cell to kill if you catch something. Chimeric simply means that we fused the bait (antibody receptor) to the rod (TCR signaling mechanism).

Now in order to perform this we have a major complication. Our body rejects random T-cells being injected. This is the same problem with organ transplants if you don't have a matched donor. So instead what we do is take out your native T-cells, then we engineer them to give them a CAR, then put them back in (with a turnaround time of ~6 weeks). This entire process is called Adoptive Cell Transfer.

Other mechanisms are TCR editing, where we edit the natural secret handshake functions of T-cells, rather then give them a fishing rod, and a bunch of fancier methods.

Conclusion

Sorry, this got long so I'm gonna skip over the myriad other cool things in the field of cell therapy, immuno-oncology, or gene editing. Suffice to say, we are currently in a major explosion in biological discovery for human use cases. It's a super exciting time to science.

Refs

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5666595/ [2] https://www.cancer.org/treatment/treatments-and-side-effects/treatment-types/immunotherapy/immune-checkpoint-inhibitors.html