The diagnosis of interstitial nephritis BKV based on the detection of viral DNA by PCR and plasma is confirmed by histological analysis of renal tissue . Plasma quantitative PCR ( qPCR) to measure the progression of the disease and therapeutic efficacy. Control of BKV viremia is the direct antiviral immune response quality based primarily on a very effective anti- T lymphocyte activity BKV reflection. In this context, the inhibition of lymphocyte activation induced by IS blocks the establishment of T-cell responses anti- BKV in most transplant, a very low presence of T lymphocytes is generally observed in these patients anti- BKV (LYT - BKV) blood .