FUNCTIONAL CHARACTERIZATION OF CMV-SPECIFIC CD8 T LYMPHOCYTES IN HUMAN LUNG TRANSPLANT RECIPIENTS

Abstract

P1017 Aims: Human cytomegalovirus (CMV) continues to be a significant cause of morbidity in immunosuppressed lung transplant recipients (LTR), this despite the routine use of prophylactic antiviral therapies. Given the importance of an intact effector immune system to suppress CMV reactivation in normal individuals, we studied the impact of immunosuppression on the frequencies, function and phenotype of CMV-specific CD8+ T cells in a cohort of LTR. Methods: LTR, with known donor/recipient (D/R) CMV serostatus, were cross-sectionally studied before and following (1, 2, and 3 months post) lung transplantation. The frequency and functional characteristics of circulating CMV-specific CD8+ T lymphocytes was assessed by binding of specific tetrameric peptide/HLA complexes and peptide-induced interferon-γ (IFN-γ) production, respectively. HLA-A2, -B7, and –B8 CMV-specific epitopes were used as CD8+ antigenic stimulants. Phenotypic classification of CD8+ T cells into naïve, memory and effector subsets was based on the expression of the four T cell surface markers, CD27, CD28, CD45RA and CCR7. CMV viral load measurements were made in the plasma and bronchoalveolar lavage (BAL) using the COBAS Amplicor CMV monitor test. Results: The frequencies of CMV-specific CD8+ T cells varied considerably between CMV-seropositive LTR (range 0.1-8.1% of all CD8+ T cells), but remained relatively stable over time in any one individual, and were not significantly reduced compared to pre-transplant levels. In those “at-risk” LTR (CMV serostatus D+/R+, D+/R- and D-/R+) who did not demonstrate CMV reactivation during the study period, there was no evidence of any functional impairment in their CMV-specific CD8+ T cell subset (50-70% of tetramer positive CD8+ T cells produced IFN-γ following specific CMV peptide stimulation). In those LTR who were mismatched for CMV (D+/R-) the appearance of CMV-specific immunity (circulating tetramer positive CD8+ T cells) was often not associated with either a clinical CMV syndrome or measurable CMV DNA (viral load <400 copies) in the blood or BAL. Following primary CMV infection, CMV-specific CD8+ T cells were skewed predominantly towards an effector phenotype, CD45RA+/−CCR7- or CD27+/−CD28-. Conclusions: The maintenance of CMV latency in immunosuppressed CMV seropositive lung transplant recipients is associated with the persistence of functionally active circulating CMV-specific CD8+ T cells. Combining the measurement of CMV viral load with a detailed analysis of the frequency, function and phenotype of CMV-specific CD8+ T lymphocytes offers insights into the dynamic relationship that exists between host immunity and viral replication, particularly in the transplant setting.