To the editor:
It is with great interest that we read the article by Gautier-Vargas and colleagues that reported a favorable clinical response with tocilizumab in a kidney transplant recipient with severe coronavirus disease 2019 (COVID-19).1 Our clinical experience has also been similar.2 The authors reported a dramatic decrease of serum interleukin 6 (IL-6) levels from 430.8 pg/ml to 3.4 pg/ml within 2 days after the administration of tocilizumab. However, as previously published,3 , 4 and in our own experience, IL-6 levels generally increase after the administration of tocilizumab. In our published case report,2 the IL-6 level was 241 pg/ml before tocilizumab and increased to 1259 pg/ml after the administration of tocilizumab. Given that tocilizumab functions by acting as a competitive inhibitor of the IL-6 receptor (IL-6R), increased serum IL-6 levels after its administration are likely caused by inhibition of IL-6R–mediated clearance as well as the endogenous production of IL-6 with ongoing disease activity. Hence, we wonder if the rapid decline of serum IL-6 level after tocilizumab in the case reported by Gautier-Vargas and colleagues was due to spontaneous improvement of disease activity or factors not related to tocilizumab. Randomized controlled studies are necessary to confirm the benefit of tocilizumab in transplant recipients with COVID-19.
References
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