Background: Cytomegalovirus (CMV) reactivation is associated with increased morbidity and mortality in transplant recipients. CMV establishes latency for the host's lifetime and frequently reactivates. Immunosuppression, while protecting the graft from rejection, impairs immune responses to CMV. We previously found that the frequency of CD8 T cells producing cytokine in response to CMV increased over the first year after transplantation in CMV seropositive (CMV+) heart and kidney recipients in the absence of detected viremia, likely as a result of subclinical reactivation. These T cells may not be protective, as CMV is known to induce expansion of dysfunctional T cells with age in non-immunosuppressed populations.

Methods: Blood was obtained from healthy volunteers and from heart and kidney transplant recipients pre and up to a year post transplant. Patients received standard of care treatment, including anti-viral prophylaxis and immunosuppression (steroid, calcineurin inhibitor, and anti-metabolite). Kidney recipients also received T cell depleting induction therapy with rabbit ATG. Blood mononuclear cells were cryopreserved for analysis. Here we analyze T cell receptors (TCR) and functions in T cells that secrete IFNγ in response to CMV peptide antigen using a novel approach coupling paired single cell TCR sequencing to gene expression analysis.

Results: Preliminary analysis indicates that CMV-responsive CD8 T cells are clonally expanded in CMV+ healthy volunteers. IFNγ protein levels by capture correlate with mRNA levels. 1 to 25% of CMV-responsive T cells are clonally expanded. Production of multiple cytokines and effector proteins, or polyfunctionality, has previously been shown to protect against CMV. Polyfunctionality varies between clones. Specifically, expression of cytokines (IL2, TNFα and TGFβ), cytolytic molecules (granzyme B and perforin), and transcription factors (GATA3 and T-bet) varied between and within IFNγ+ clones. Preliminary analyses indicate that CMV-responsive T cells become more terminally differentiated after transplantation in CMV+ recipients, based on loss of CD27.

Conclusions: CMV may be associated with altered T cell function in transplant recipients. Our single cell approach sensitively detects clonal expansion and function. We will measure changes post-transplant and determine if the T cell response post-transplant is dysfunctional.

CITATION INFORMATION: Higdon L., Trofe-Clark J., Liu S., Saligrama N., Margulies K., Davis M., Maltzman J. Altered Function of Cytomegalovirus Specific T Cells in Transplant Recipients Am J Transplant. 2017;17 (suppl 3).

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