Flow cytometric analysis of T cells in hemophagocytic lymphohistiocytosis

Background: T cell immunophenotypes in patients with hemophagocytic lymphohistiocytosis (HLH) have been described. Downregulation of CD5 or CD7 on T cells has been reported in patients with Epstein-Barr virus (EBV)-positive HLH. As the utility of T cell immunophenotypes as an adjunctive diagnostic or a prognostic marker for HLH has not been evaluated, we analyzed T cell immunophenotypes in HLH patients for this purpose. Methods: We classified 45 HLH patients into three subgroups: EBV-positive HLH (N=27), EBV-negative secondary HLH (N=15), and familial HLH (N=3). We retrospectively characterized downregulation patterns of CD5 or CD7 on activated T cells, using flow cytome-try. Overall survival was estimated using Kaplan-Meier curves and compared using the log-rank test. Results: An aberrant immunophenotype, including CD5 and/or CD7 downregulation on T cells, was observed in 55.6% (15/27) of the EBV-positive HLH patients and 100% of the familial HLH (3/3). Only one (1/15, 6.7%) patient with EBV-negative secondary HLH showed an aberrant loss of CD7 antigen on CD8⁺ T cells. The presence of an aberrant T cell immunophenotype was not related to overall survival in EBV-positive HLH and EBV-negative secondary HLH patients. Conclusions: An aberrant T cell immunophenotype may assist in discriminating EBV-negative secondary HLH and EBV-positive HLH. However, it may not be useful as a prognostic marker.