Expansion of CD8+ T cell population in Lassa virus survivors with low T cell precursor frequency reveals durable immune response in most survivors.

Despite reports of strong CD8+ T cell responses during acute Lassa virus infection, circulating Lassa virus-specific CD8+ T cells declined to undetectable levels in most Lassa fever survivors after ten years when evaluated with an 18-hour T cell stimulation. However, when Lassa virus-specific T cells were expanded prior to restimulation, a Lassa virus-specific CD8+ T cell response could be detected in many if the samples that were negative in the 18-hour stimulation assay, suggesting that prolonged cellular immunity does exist in Lassa fever survivors at low frequencies.