Breakthroughs in gene synthesis has allowed synthetic biologists the ability to design any DNA sequence of interest, enabling the possibility to create complex systems inside cells with novel functions to tackle problems in immunology. Synthetic immunology of mammalian cells expressing natural or synthetic genes can guide and induce immune responses in patients. Through recent developments in engineering chimeric receptors, it is now feasible to customize control over engineered cells to target the disease sites with specificity. These cells can avoid immune rejection if derived from expandable cell types (e.g., stem cells or T cells) and then can be grown in abundance before implantation. However, safety concerns of engineered cells in circulation necessitates the development of a wide range of mechanisms to kill cells after their therapeutic life ends. This therapeutic effect is still predominantly the secretion of therapeutic proteins, but novel therapeutic interventions have been explored by synthetic biologists. In the pursuit of engineering new cell functions for synthetic immunology, it is possible that many problems previously thought intractable may actually be possible.