Controlling for Immunosuppressive Therapy in Studies of BK Virus Disease


To the Editor:

I read with interest the study by Theodoropoulos et al. on BK virus replication and nephropathy in altemtuzumab-induced kidney transplantation [1]. As alemtuzumab becomes more widely used for induction, it is important to ascertain the risk of infectious complications such as BK virus disease. Reassuringly, their study did not find an increased risk of BK viremia or BK virus nephropathy with the use of alemtuzumab compared to less potent induction. Their conclusions are strengthened by their large sample size and use of BK virus nephropathy as a primary outcome.

To further enhance our understanding of the primary relationship of interest, it would be insightful to control for tacrolimus trough levels after induction, in the multivariate analysis. It is well understood that the incidence of BK virus disease is related to the intensity of immunosuppression [2]. A prior study showed that even modest reductions in tacrolimus trough levels of 15% resulted in a 72% lower incidence of BK virus nephropathy [3].

Although the authors report that tacrolimus trough levels were similar in the study participants, small variation in these levels could have an important impact on the outcomes of BK virus disease. Controlling for this variable would help to isolate the effect of alemtuzumab on BK virus disease and provide further reassurance about the safety profile of this induction agent.


The author of this manuscript has no conflicts of interest to disclose as described by the American Journal of Transplantation.