Protection from cytomegalovirus after transplantation is correlated with immediate early 1-specific CD8 T cells

Abstract

T cells are crucial for the control of cytomegalovirus (CMV) in infected individuals. Although CMV-specific T cells can be quantified by various methods, clear correlates of protection from CMV disease have not been defined. However, responses to the pp65 protein are believed to play an important role. Here, the proportions of interferon gamma-producing T cells following ex vivo activation with pools of overlapping peptides representing the pp65 and immediate early (IE)-1 proteins were determined at multiple time points and related to the development of CMV disease in 27 heart and lung transplant recipients. Frequencies of IE-1-specific CD8 T cells above 0.2 and 0.4% at day 0 and 2 wk, respectively, or 0.4% at any time during the first months discriminated patients who did not develop CMV disease from patients at risk, 50-60% of whom developed CMV disease. No similar distinction between risk groups was possible based on pp65-specific CD8 or CD4 T cell responses. Remarkably, CMV disease developed exclusively in patients with a dominant pp65-specific CD8 T cell response. In conclusion, high frequencies of IE-1 but not pp65-specific CD8 T cells correlate with protection from CMV disease. These results have important implications for monitoring T cell responses, adoptive cell therapy, and vaccine design.

Figure 1.

High frequencies of IE-1–specific CD8 T cells are associated with protection from CMV disease. Dot plots show responses to the CMV pp65 and IE-1 peptide pools in two representative patients, one of whom developed CMV disease on day 39 after transplantation (left). CD8 T cells are shown (IFN-γ⁺ events highlighted in black). The relative frequencies of IFN-γ¹ events are indicated. Axes show log fluorescence.

Figure 2.

Median frequencies of IE-1–specific CD8 T cells early after transplantation are higher in patients who do not develop CMV disease. CD4 and CD8 T cell responses to the CMV IE-1 and pp65 peptide pools were measured in 27 transplant recipients at specific time points using intracellular IFN-γ staining. (A) The results for IE-1–specific CD8 T cells, (B) the results for pp65-specific CD8 T cells, and (C) the results for pp65-specific CD4 T cells. In each panel, the results are divided by clinical group (CMV-disease or not). Box plots show the responses at the indicated time points (median, 25th and 75th percentiles, and extreme values). Nonparametric longitudinal analysis was performed using SAS software (p-values are given for differences between the groups). A global significance level of 0.05 is maintained if P ≤ 0.0166 for each of three tested end points.

Figure 3.

The magnitude of the CD8/IE-1 response identifies patients who will not develop CMV disease. ROC analysis was performed to define optimum thresholds of the CD8/IE-1 response (relative frequency) that would discriminate between patients who did or did not develop CMV disease. Panels show ROC curves for the response at day 0 (A), 2 wk (B), and for the maximum response during the first month (C). The area under the curve (AUC) for the CD8/IE-1 response graph is indicated. Graphs for the CD8/pp65 and CD4/pp65 responses are shown for reference.