Abstract
Cytomegalovirus (CMV) infection/reactivation remains among the most important complications of immunosuppression after transplantation. However, recent clinical observations indicate that mammalian target of rapamycin (mTOR) inhibition with sirolimus may improve the outcome of CMV complications. Underlying mechanisms of this observation, particularly the effect of sirolimus on naïve- and CMV-specific cytotoxic CD8+ T-cell (CMV-CTL) functionality is still undiscovered. Here, the influence of sirolimus on naïve and memory CMV-CTLs was determined by CD3/CD28 crosslinking and alloreactivity assays. After stimulating CMV-CTL with HLA-A*02:01-restricted CMVpp65-peptide loaded artificial antigen-presenting cells (aAPCs), we measured the effect of sirolimus on T-cell proliferation, phenotype, and functionality. Sirolimus significantly improved CMV-specific effector memory T-cell function and negatively influenced naïve T cells. This unique mechanism of action was further characterized by increased secretion of interferon-gamma (IFN-γ), granzyme B (GzB) and enhanced target-cell-dependent cytotoxic capacity of activated CMV-CTLs. Next-generation-sequencing (NGS) was applied to monitor T-cell receptor (TCR)-repertoire dynamics and to verify, that the increased functionality was not related to sirolimus-resistant CTL-clones. Instead, modulation of environmental cues during CMV-CTL development via IL-2 receptor (IL-2R)-driven signal transducer and activator of transcription-5 (STAT-5) signaling under mTOR inhibition allowed fine-tuning of T-cell programming for enhanced antiviral response with stable TCR-repertoire dynamics. We show for the first time that sirolimus acts selectively on human naïve and memory T cells and improves CMV-specific T-cell function via modulation of the environmental milieu. The data emphasize the importance to extend immune monitoring including cytokine levels and T-cell functionality which will help to identify patients who may benefit from individually tailored immunosuppression.
Highlights
Immunosuppressive therapy to deplete T cells, redirect T-cell trafficking, or terminate T-cell response pathways after solid organ (SOT) and hematopoietic stem cell transplantation (HSCT) is mainly used to prevent graft rejection or severe graftvs.-host disease (GvHD) [1,2,3]
As the purpose of immunosuppression is to prevent complications like graft rejection and GvHD, which are mainly caused by alloreactive naïve T cells, the selective effect of sirolimus was investigated on human naïve and memory CD8+ T-cell populations
These results imply that the immunosuppressive effects of sirolimus on memory T cells in the allogeneic T-cell receptor (TCR)-dependent alloreactivity assay were overcome by IL-2
Summary
Immunosuppressive therapy to deplete T cells, redirect T-cell trafficking, or terminate T-cell response pathways after solid organ (SOT) and hematopoietic stem cell transplantation (HSCT) is mainly used to prevent graft rejection or severe graftvs.-host disease (GvHD) [1,2,3]. Further studies demonstrated the link between the unique metabolic requirements of T cells and the ability of mTORC1 to integrate environmental cues involved in direct T-cell differentiation and function during sirolimus treatment [26,27,28] These results indicate that the drug functions as a signaling component downstream of T-cell receptor (TCR)/CD3-mediated activation. The modulation of environmental cues during antiviral memory Tcell development through the activation of IL-2R driven STAT5 signaling under the cover of mTORC1 inhibition allows the fine-tuning of antiviral T-cell programming for improved CMVspecific T-cell response These results suggest a need to optimize the monitoring of immunosuppressed patients with an elevated risk of pathogen infection or reactivation by determining serum IL-2 or IL2R subunit-sharing cytokine levels and antigen-specific T-cell functionality for further individualization of immunosuppressive therapy
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