Representative clinical response. An 18-month-old boy with XLP presented at day 87 after matched unrelated donor transplantation with pharyngeal swelling, an elevated lactate dehydrogenase level, and a rapidly increasing EBV-DNA load. (A) After receiving 2 × 10⁷ CTLs/m² on day 90, he showed rapid clinical improvement and a decrease in EBV DNA level to baseline. (B) Coincident with this response, there was an increase in EBV-specific activity, as measured with a γ-interferon EliSpot assay, whereas CMV activity remained undetectable.