What the article unfortunately not explains: as far as I understand the medication suppresses ways the immune system can identify healthy/own cells of the body.

What the article unfortunately not explains: as far as I understand the medication suppresses ways the immune system can identify healthy/own cells of the body. If that is suppressed I'd expect more severe side effects, up to death, no less. Why isn't this the case? Imho it could work only if cancerous cells are more affected than healthy ones (like they are more affected by cytostatic drugs because they divide faster). Can anyone chime in with an explanation?