CAR T-Cell Therapy Side Effects

If you’ve read about CAR T-cell therapy, you’ll know it's providing a lot of hope for treatment and even cures for blood cancer. But what are the risks and the side effects?

I personally had CAR T-cell therapy as part of a trial from a company called Juno Therapeutics, one of the pioneers in the treatment. When I first met the trial doctor, I asked about side effects and he informed me that there is a risk, of course, and that in fact, two patients had died from the side effects of the treatment about a year earlier. Clearly, this was pretty sobering news, but the pharma company had immediately stopped the trial and looked into the causes of the deaths and had learned a lot. They’d made changes to the treatment since then in response.

It reinforced to me though, that no trial is without risk.

In some ways, the main possible side effects of CAR T-cell therapy are a consequence of the treatment working, perhaps too well. Essentially the modified T-cells coming back into the body means the immune system is now aware of the cancer, and swings into action. Similar to a condition like sepsis, the immune response can be so extreme that the body struggles to handle it.

Cytokine release storm

When T-cells communicate with each other, they do so using chemicals called cytokines. When the body’s immune system goes into overdrive, it can trigger a cycle of the release of lots of these cytokines, which in turn can activate more white blood components. This can be severe, causing headaches, respiratory issues, fevers, and even (if unchecked) death. The good news is that this consequence is now relatively well understood, and the new CAR T-cell therapies seem to have far less impact like this – and even if they do, there is a well-understood treatment for it, which dampens down the immune response.

Tumor lysis

Again, tumor lysis is a side effect showing that the CAR T-cell treatment is working, perhaps too well. When the modified T-cells kill the tumor cells, these then break into component parts and all the leftover gunk can be floating in your bloodstream. If there were a lot of tumor cells, that can mean the body can’t process all the waste components, and essentially the blood is poisoned. The most common minor symptom here is gout, caused by the increased levels of uric acid, and that is why you’re likely to get prescribed some anti-gout medication like allopurinol.

Neurological impacts

When the doctor warned me and my wife about the side effects, he told her that one day I might just stop making sense. That caused all sorts of jokes of course, about how she’d be able to tell – but apparently, if a patient does have a severe neurological side effect, it’s very obvious. They suddenly (within a few minutes) may get confused, have difficulty writing or speaking, and may get drowsy or agitated. People who have witnessed this say it can be very unsettling to see their loved ones suddenly lose their minds. The good news is that this is fairly rare and only lasts a few days typically. There doesn’t seem to be any long term impact from it, but in the short term, it’s alarming.

The most common side effect – a flu

By far the most common side effect, which is a perverse way you want to see, is the patient gets the flu - sort of. That’s the only side effect I had – a mild flu. It started on day 8 after the infusion and lasted about a week, and it was an outward sign that inside me there was a battle going on. The symptoms we commonly associate with the flu (fever/chills, sniffly nose, achy joints, etc.) are actually that cytokine response again, this time a more mild version of it. So getting flu-like symptoms is a great indicator that the CAR T-cells are working.

Other effects

There are some other possible side effects too (eg. losing some of your B cells, lowering your immune resistance, diarrhea, vomiting, etc.), but on the whole, these seem to be less severe and if you’ve had chemotherapy or other ‘standard’ treatments, you’re well used to them!

So CAR T-cell therapy isn’t without risks, and side effects, but researchers and doctors are learning more and more all the time about what causes there, and making adjustments to the therapies to lessen the risk and impact. Talk to your doctor if you’re really worried, but my personal advice is that nothing is risk-free, and the benefits of the therapy outstrip the possible side effects.

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