A Comparative Analysis of Human T Cell Responses To Adenoviral Early And Late Proteins
A detailed understanding of adenovirus (Ad) specific immune responses is needed to develop immunotherapy options for the treatment of invasive Ad disease in Hematopoetic Stem Cell Transplant (HSCT) patients. Most healthy adults exhibit memory T cell responses to the Ad Hexon, a capsid protein synthesized late after infection. Several groups are investigating the efficacy of Hexon-specific donor T cells in treatment of invasive Ad disease. However, the fact that the Ad E3-19k down regulates MHC class I molecules suggests that cytotoxic T cells (CTLs) targeted to early viral proteins may be more effective in limiting Ad replication in vivo. We propose that CTLs targeted to adenoviral early proteins would be more efficient than Hexon specific CTLs, as they would recognize virally infected cells prior to E3-19k mediated down regulation of MHC class I molecules and before the onset of viral replication. Here we show that several adenoviral early proteins are recognized by human Ad specific CD8 T cells and bear cross reactive epitopes that are well conserved amongst several Ad serotypes. We identify HLA A2 restricted epitopes from adenoviral early region 2 (E2) proteins: DNA polymerase (Pol) and DNA binding protein (DBP). We detect interferon-γ (IFN-γ) responses to HLA A2-binding motif peptides from Pol and DBP in PBMC from a recently infected normal donor as well as 3 SCT patients recovering from invasive Ad disease. Interestingly Pol epitope specific T cells are found in higher frequency than Hexon (or DBP) epitope specific T cells from PBMC in three SCT patients. Subsequently we compare human memory CD8 T cell responses to early protein Pol (P-977) and late capsid protein Hexon (H-892) CD8 T cells in peripheral blood (PB) and lymphoid (tonsils) compartments, using epitope specific pentamers. We show that in tonsils, epitope-specific pentamers detect a significantly higher frequency of P-977+CD8+ T cells compared to H-892+CD8+ T cells, although this trend gets reversed in PB. Tonsil epitope –specific CD8 T cells express IFN-γ and IL-2 but not perforin or TNF-α, whereas PB CD8 T cells are positive for IFN-γ, TNF-α, and perforin. Tonsil epitope-specific CD8 T cells express lymphoid homing marker CCR7 and exhibit lower levels of the activation marker CD25 but higher proliferative potential than PB CD8 T cells. Finally, in parallel with the kinetics of mRNA expression, P-977-specific CTLs lyse targets as early as 8 hrs post infection. In contrast, H-892-specific CTLs do not kill unless infected fibroblasts are pretreated with IFN-γ to up regulate HLA class I antigens, and cytotoxicity is delayed until 16 -24 hours. These data show that while both Ad early (Pol) and late (Hexon) proteins are recognized in humans, central memory type DNA polymerase CTLs dominate the lymphoid compartment and kill fibroblasts earlier after infection without requiring exogenous IFN-γ. Thus, use of CTLs targeted to early Ad proteins may improve the efficacy of immunotherapy for life-threatening Ad disease in SCT recipients.
Joshi, Amita, "A Comparative Analysis of Human T Cell Responses To Adenoviral Early And Late Proteins" (2011). ETD Collection for Thomas Jefferson University. AAI3450837.