The spike protein the mRNA tells your body to produce, binds to the ACE2 receptor blocking the reuptake of angiotensin 2 disrupting the hormonal chain that happens from angiotensin 1 through angiotensin 9. That is the disease caused by the virus, and what the gene manipulation does to you. In essence it causes a hormonal change in your body, and your body creates an immune response by destroying the spike protein so it can't bind to the ACE 2 receptors, however there's a lot of molecules that bind to that receptor. The kicker is that the ACE 2 receptor is a shitty lock, it takes any sort of similar key. The spike protein is just one, another is angiotensin 2, another is reproductive hormones, etc. If the body learns to destroy the spike protein, what if it learns to destroy some sort of similar protein?