EBV-infected CD4⁺ T cells are resistant to conventional treatment regimens for CAEBV and HLH. (A) FlowRNA was performed on patient PBMCs to monitor outcome following treatment; both pre- and posttreatment samples are shown for patients 3 and 4. The percentage of EBER^POS CD4⁺ T cells is shown in the upper right quadrant. The analyses revealed an increase in the number of EBV-infected CD4⁺ T cells following treatment. (B) FlowRNA performed on PBMCs from patient 3, 1 month before HSCT (−1 month) and 16 months post-HSCT, shows a sustained loss of EBER^POS lymphocytes. However, analysis at 23 months post-HSCT revealed a significant population of EBER^POS CD4⁺ T cells. The percentage of EBER^POS CD4⁺ T cells is shown in the upper right quadrant. (C) Analysis of the EBER^POS CD4⁺ T cells identified at 23 months revealed the reappearance of the EBV-infected TCR-BV8 clone originally identified in the first sample.