Epstein-Barr virus: general factors, virus-related diseases and measurement of viral load after transplant A recent review showed that a single dose of rituximab was efficient to prevent PTLD.(24) Although many studies certify the efficiency and safe administration of this therapy,(33) it is important to say that one of the limitations of anti-CD20 is its specificity for B cells (infected or not), causing a systemic reduction in this cell population(5) and hypogammaglobulinemia.(34) Prophylactic use of antiviral agents has been discouraged due to the lack of efficiency.(35) Ganciclovir and aciclovir can reduce EBV replication, but these are not active in PTLD.(24) The role of passive immunization with the intravenous anti-CMV antibody remains uncertain.(7) In a study involving renal transplant patients, the use of anti- CMV IV was beneficial in the first year after transplant.(36) A promising treatment is the use of EBV-specific cytotoxic T lymphocyte infusions cultivated from samples of the recipient in SOT(23,33) and from the donor in HSCT(37) to prevent and treat PTLD.(37,38) The confirmation of the disease requires biopsy tests and histological analysis.(24) Notwithstanding, viral load analysis is paramount for post-transplant monitoring. Besides the measurement of virus load, the demand for alternative assays to evaluate PTLD risk increases every year. Tests to quantify EBV-specific T lymphocytes are proving promising.(5) It is important to remember, however, that there are EBV- negative PTLD cases. These are rare and common in late onset cases (50 months post-transplant on average). In such situations, viral load assays for EBV will not detect PTLD.(39) According to Muti et al.(40) around 30% of late onset cases present a pattern of EBV-negative lymphoma. Nasopharyngeal carcinoma This disease has its highest incidence in the south of China, where it represents around 20% of all cancer cases in adults.(41) It is also found in northeast Africa and among the indigenous peoples of Alaska. In Europe and North America incidence rates are lower than 1/100,000 inhabitants.(42) Over 99% of the cases are EBV-related and the viral genome is found in modified epithelial cells.(43) Tests on DNA extracted from these cells revealed that all the cases in areas of high, intermediate and low incidence were consistently EBV-positive.(44) The varied percentages of EBV-positive cases in some associated pathologies are listed in Table 1. Post-transplant Epstein-Barr virus viral load measurement Qualitative and quantitative PCR methods are precise, highly sensitive and specific techniques. However, the simple detection of EBV does not offer the clinician an overview of the patient's real condition.(2) The technique of quantitative real-time PCR for EBV is becoming an essential part of Rev Bras Hematol Hemoter. 2011;33(5):383-8 monitoring protocols of transplant patients, as well as a predictive parameter for PTLD.(45,46) Moreover, the relation between viral load increase and PTLD has not been properly elucidated.(1) In high-risk patients submitted to HSCT and SOT, it is recommended to quantify EBV once a week for at least three months after the transplant. After this period, it is suggested a follow-up only for patients with reactivation or diseases related to EBV.(6) There is no consensus on the best sample type, extraction method, viral target gene, qPCR platforms and tools and measurement units to evaluate EBV-related complications. In fact, there is not yet a standard method (commercial or in-house) of EBV detection.(6) Standards of preventive interventions for PTLD have been defined in transplant centers (HSCT and SOT) according to the population studied and local experience. It is important to say, however, that these cut-off levels have not been validated by multicentric studies.(47) A recent review confirms that there is not yet an indicative limit for the beginning of preventive interventions.(48) Kimura et al.(2) in another recent review affirm that whole blood (WB) is the best option to test for PTLD although the authors believe that further studies are necessary to clarify the question. Another study compared EBV viral load measurement using WB, peripheral blood mononuclear cells (PBMC) and plasma. The sensitivity of qPCR was similar between WB and PBMC but lower in plasma.(49) A multicentric comparison opted for WB sampling, based on studies that showed better sensitivity using this material and also because this option was more commonly used amongst participating laboratories.(49-51) Gulley et al.(25) argue that it is not appropriate to affirm that WB sampling for PTLD is more informative than plasma. In this disease, there can be relatively few circulating cells and other models of latency, lytic replication and virion production may occur. These factors, without doubt, lead to 385