Cytomegalovirus‐Specific Regulatory and Effector T Cells Share TCR Clonality—Possible Relation to Repetitive CMV Infections

Cytomegalovirus (CMV) infections have a major impact on morbidity and mortality of transplant patients. Among the complex antiviral T‐cell response, CMV‐IE‐1 antigen‐specific CD8+ cells are crucial for preventing CMV disease but do not protect from recurring/lasting CMV reactivation. Recently, we confirmed that adoptive transfer of autologous IE‐1/pp65‐specific T‐cell lines was able to combat severe CMV disease; however, the control of CMV infection was only temporary. We hypothesized that CMV‐induced regulatory T cells (iTreg) might be related to recurring/lasting CMV infection. In fact, kidney transplant patients with recurring CMV infections expressed enhanced suppression on CMV response. Analysis of in vitro expanded CD4+ epitope‐specific cells revealed that CMV‐specific CD4+CD25high Treg cells functionally suppress CD25low effector T cells (Teff) upon epitope‐specific reactivation. Their phenotype is similar to iTreg – CD39high/Helios‐/IL‐2low/IFNγhigh/IL‐10±/TGFß‐LAP±/FOXP3+ and methylated foxp3 locus. Remarkably, in vitro expanded CD4+CD25high iTreg share the same dominant TCR‐Vβ‐CDR3 clones with functionally distinct CD4+CD25low Teff. Moreover, the same clones were present in freshly isolated CD4+CD25high and CD4+CD25low T cells suggesting their in vivo generation. These findings directly demonstrate that Teff and iTreg can differentiate from one “mother” clone with specificity to the same viral epitope and indicate that peripheral iTreg generation is related to frequent antigen appearance. This study relates the impact of cytomegalovirus (CMV)‐specific regulatory T cells on the quality of CMV‐specific T cell responses to frequent antigen appearance.