Cancer research has demonstrated that immunization with homologous xenogeneic proteins (such as vaccines contaminated with animal proteins that resemble human proteins) results in autoimmunity. Bioinformatics analysis demonstrates that animal proteins have occasional amino acids differences compared to equivalent human proteins. So mutated human protein epitopes can be identical to animal protein derived epitopes. Low affinity self reactive T cells suited for detection of mutated human epitopes will be activated by animal derived epitopes. CD8+ T cells involved in numerous autoimmune disorders express the CCR4 skin homing receptor. This is evidence that the site of priming was the skin. This is consistent with subcutaneous or intramuscular injection of animal protein contaminated vaccines. Taken together, we have strong mechanistic evidence of animal protein contaminated vaccines causing numerous autoimmune disorders.