**Core Concept**
Islet cell transplants are not relevant here; the key concept is grafting between genetically identical individuals, which does not typically involve immunosuppression. In this scenario, we're dealing with a specific type of graft that occurs between identical twins.

**Why the Correct Answer is Right**
Since the donor and recipient are identical twins, they share the same genetic makeup. This means the graft will not be rejected by the immune system, as there is no genetic disparity. The ovary transplant in this case is an example of an **isograft** or **syngeneic graft**, where the donor and recipient have the same genetic profile.

**Why Each Wrong Option is Incorrect**
* **Option A:** Allograft - This is incorrect because an allograft is a graft between genetically different individuals, which would require immunosuppression to prevent rejection.
* **Option B:** Autograft - This is incorrect because an autograft involves transplanting tissue from one part of the body to another within the same individual.
* **Option C:** Xenograft - This is incorrect because a xenograft involves transplanting tissue from a different species, which is not relevant in this scenario.

**Clinical Pearl / High-Yield Fact**
Identical twins (monozygotic twins) share 100% of their genetic material, making them ideal candidates for syngeneic grafting. This concept is crucial in organ transplantation and understanding graft rejection mechanisms.

**Correct Answer:** C. Isograft