What is a major concern associated with using embryonic stem cells?

Using embryonic stem cells raises significant concerns regarding immunosuppression issues. This stems from the fact that these cells are derived from embryos and are genetically distinct from the recipient’s own body. When transplanted into a patient, the immune system may recognize the embryonic stem cells as foreign invaders, leading to an immune response that could potentially reject the transplanted cells. This necessitates the use of immunosuppressive drugs to prevent rejection, which can increase the risk of infections and other complications for the patient.

In the context of the other options, while short lifespan and cost can be relevant factors in stem cell research and therapy, they are not as critical as the immunological challenges posed when using embryonic stem cells. Availability of embryonic stem cells can also be a concern, but it is primarily the issue of immune rejection that is of major concern in terms of patient safety and treatment efficacy.