**Core Concept**
The patient's hyperacute rejection of the transplanted kidney is an immune response mediated by pre-existing antibodies against antigens present on the graft. This reaction occurs within minutes to hours after transplantation and is a major cause of early graft failure.

**Why the Correct Answer is Right**
The principle target for immune attack in hyperacute rejection is the ABO blood group antigens and human leukocyte antigens (HLA) present on the endothelial cells of the graft's blood vessels. These antigens trigger the activation of the complement system and the coagulation cascade, leading to thrombosis, ischemia, and eventual graft failure. The presence of pre-existing antibodies against these antigens in the recipient's plasma is the primary cause of this reaction.

**Why Each Wrong Option is Incorrect**
* **Option A:** While IgM antibodies against ABO blood group antigens can be a cause of hyperacute rejection, they are not the primary target for immune attack in this scenario.
* **Option B:** IgG antibodies against HLA class I or II antigens can also contribute to hyperacute rejection, but they are not the primary target in this case.
* **Option D:** Complement system activation is a downstream effect of the immune response, not the primary target for immune attack.

**Clinical Pearl / High-Yield Fact**
Hyperacute rejection is a major cause of early graft failure in kidney transplantation, and it is often due to pre-existing antibodies against ABO blood group antigens or HLA. Accurate ABO blood typing and HLA matching between the donor and recipient are crucial to prevent this complication.

**Correct Answer:** C. Human leukocyte antigens (HLA).