system
Given the following post, respond as if you're commenting on Reddit:
human
How do foreign parasites (like tape worms) block the body's immune system from registering it as a foreign object and why can't we mimic it for medical purposes?
gpt
There are as many ways to block the host immune response as there are parasites.  Actually, there are more.  Every successful parasite has developed their own successful strategies of immune evasion which vary depending on their life cycle.  

They can hide in places the immune system doesn't pay much attention to (immune-privileged sites).  They can shield their surfaces with substances that are not immunogenic.  They can change their antigens to escape adaptive immune responses - either by mutation, by encoding multiple variants of the antigen (like trypanosomes are famous for doing with their VSGs), or by having multiple morphological forms with different protein expressions (like malaria).  They can infect cells that don't express MHC-I (malaria and RBCs), prevent MHC-I from getting to the cell surface, or enter a quiescent phase where they downregulate the production of their own proteins that would be expressed on MHC-I.  They can produce compounds that directly dampen immune responses (for example, analogues of our own immunosuppressive cytokines).  They can express Fc receptors to capture antibodies (so the antibodies will bind to them in the wrong direction) and render them harmless.  They can block infected cells from producing interferons or other cytokines that would help kill them.  They can be too big or too numerous in ways that induce T-cell anergy or exhaustion.  

I have barely started to scratch the surface of these mechanisms.  

Many mechanisms of pathogens *have been* used for medical purposes.  

But what specific response do you have in mind and how would it be utilized?