**Question:** Post-transplant lymphoma occurs due to proliferation of which of the following cells -

A. B cells
B. T cells
C. Plasma cells
D. Natural killer (NK) cells

**Core Concept:** Post-transplant lymphoma is a specific type of lymphoma that develops in patients who have undergone organ transplantation. It is characterized by the uncontrolled growth of lymphocytes, which are a type of white blood cell.

**Why the Correct Answer is Right:** Post-transplant lymphoma is primarily caused by the proliferation of T cells (option B). In organ transplantation, the recipient's immune system is suppressed to prevent organ rejection, but this suppression also allows for the growth of cancerous cells, such as T cells, which can lead to the development of post-transplant lymphoma.

**Why Each Wrong Option is Incorrect:**

A. B cells (option A) are not the primary cause of post-transplant lymphoma, although they can contribute to the disease in some cases.

C. Plasma cells (option C) are not directly involved in post-transplant lymphoma. They are a different type of lymphocyte involved in producing antibodies.

D. Natural killer (NK) cells (option D) are not the primary cause of post-transplant lymphoma, although they can contribute to the disease in some cases.

**Clinical Pearl:** Post-transplant lymphomas are typically low-grade lymphomas and are associated with a better prognosis compared to de novo lymphomas. However, it is crucial for transplant physicians and oncologists to monitor patients for signs of lymphoma and initiate timely treatment to improve outcomes.

In summary, post-transplant lymphoma is primarily caused by the uncontrolled proliferation of T cells, making option B the correct answer. B cells, plasma cells, and NK cells can contribute to the disease but are not the primary cause.