Post-transplant lymphoproliferative disorder

Post-transplant lymphoproliferative disorder (PTLD) is the name given to a B-cell proliferation due to therapeutic immunosuppression after organ transplantation. These patients may develop infectious mononucleosis-like lesions or polyclonal polymorphic B-cell hyperplasia. Some of these B-cells may undergo mutations which will render them malignant, giving rise to a lymphoma.

In some patients, the malignant cell clone can become the dominant proliferating cell type, leading to frank lymphoma, a group of B cell lymphomas occurring in immunosuppressed patients following organ transplant.

Causes

The disease is an uncontrolled proliferation of B cell lymphocytes following infection with Epstein-Barr virus.^[1][2] Production of an interleukin-10, an endogenous, pro-regulatory cytokine, has also been implicated.

In immunocompetent patients, Epstein-Barr virus causes infectious mononucleosis, characterised by a proliferation of B-lymphocytes which is controlled by Suppressor T cells.

However, calcineurin inhibitors (tacrolimus and cyclosporine), used as immunosuppressants in organ transplantation inhibit T cell function, and can prevent the control of the B cell proliferation.

Depletion of T cells by use of anti-T cell antibodies in the prevention or treatment of transplant rejection further increases the risk of developing post-transplant lymphoproliferative disorder. Such antibodies include ATG, ALG and OKT3.

Polyclonal PTLD may form tumor masses and present with symptoms due to a mass effect, e.g. symptoms of bowel obstruction. Monoclonal forms of PTLD tend to form a disseminated malignant lymphoma.

Treatment

PTLD may spontaneously regress on reduction or cessation of immunosuppressant medication,^[3] and can also be treated with addition of anti-viral therapy. In some cases it will progress to non-Hodgkin's lymphoma and may be fatal. A phase 2 study of adoptively transferred EBV-specific T cells demonstrated high efficacy with minimal toxicity.^[4]

References