AD-HIES patients have decreased numbers of central memory T cells due in part to an intrinsic defect in their ability to proliferate and differentiate from naïve precursors. Central memory CD8
+ T cells from AD-HIES patients had a more effector-like transcriptional profile and both CD4
+ and CD8
+ central memory T cells had lower expression of CD127. The partial effacement of the central memory compartment in AD-HIES patients is associated with a failure to control VZV and EBV, but appears to largely confer sufficient protection against other viruses, including CMV, which is seen only in more severe settings of T cell compromise such as bone marrow transplant, severe combined immunodeficiency, and advanced HIV (
Kost and Straus, 1996;
Steininger, 2007). Other congenital immune deficiencies characterized by mature B cell (
Faulkner et al., 1999;
Winkelstein et al., 2006), or Th17 cell defects (
Ferwerda et al., 2009;
Glocker et al., 2009;
Puel et al., 2011) are not associated with abnormal VZV or EBV responses, arguing against a role for those defects which are normally observed in AD-HIES as a cause for the diminished capacity to control chronic viruses. Additionally, the relatively intact naïve and effector memory pools may explain the failure to observe pathology from primary and recurrent viral infections in AD-HIES patients. This finding in AD-HIES appears unique in that no other known human immune deficiencies present from birth are characterized by increased rates of VZV reactivation in the absence of significant pathology when encountering primary VZV.
Our studies have revealed a role for STAT3 in CD4
+ and CD8
+ T cell memory separate from its role in T helper cell functional differentiation.
STAT3 mutations in AD-HIES patients demonstrate a critical role for STAT3 and STAT3-dependent transcription factors in the development of central memory in CD8
+ T cells and a previously unappreciated role for STAT3 in CD4
+ T cell central memory development. Of note, LCMV infected
GzmbCre/+ Stat3LoxP/LoxP mice or mice with
Socs3 silenced in naïve CD8
+ T cells have dramatically reduced frequencies of LCMV-specific central memory CD8
+ T cells memory (Cui and Kaech, submitted). This work suggests that STAT3 signaling and
SOCS3 expression within naïve T cells are key in steering CD8
+ differentiation away from an effector phenotype and towards long-term central memory. The proliferation defect observed in AD-HIES naïve T cells could reflect a requirement for STAT3 pathway genes for normal naïve T cell division (
Durant et al., 2010) or the failure of STAT3 genes to counter antiproliferative effects of other STAT pathways such as the IL-27-STAT1 pathway (
Liu and Rohowsky-Kochan, 2011). The variability in the capacity for different patients’ naïve cells to proliferate may stem from the fact that STAT3 mutations in AD-HIES are hypomorphic, as opposed to null mutations. This diminished, but not absent function can lead to a wider clinical variability, as well as unstable cellular phenotypes such as the defects in neutrophil chemotaxis which can at times even vary within an individual patient (
Donabedian and Gallin, 1983).
These newly observed clinical findings in AD-HIES may have other implications as well. Given that atopic dermatitis is a cardinal feature of AD-HIES, STAT3 pathway defects may also help explain an observed increased frequency of VZV reactivation in patients with severe atopic dermatitis (
Rystedt et al., 1986;
Veenstra et al., 1995). Additionally, the lower frequency of EBV-specific central memory T cells in AD-HIES may explain the observed increase in the number of EBV
+ cells in the blood. While activation of STAT3 is associated with lymphomagenesis (
Bromberg et al., 1999;
Migone et al., 1995;
Yu et al., 1995), the paradoxical increase in risk for B cell lymphomas in these patients with a loss of STAT3 function now may be understood as resulting from poor immune control of latently infected cells. This loss of immune control may explain the EBV
+ lymphomas in AD-HIES and also may have effects on the overall control of tumorigenesis, which has been shown to be partially dependent on central memory T cells (
Klebanoff et al., 2005). Patients with dysfunctional STAT3 signaling may need to be more closely monitored for control of VZV and EBV, and they may benefit clinically from early and perhaps frequently boosted VZV vaccination.
The specific defect in T cell central memory formation and associated loss of control of certain chronic viral infections we observed in AD-HIES illuminates our understanding of central memory T cell differentiation and the role of central memory T cells in immune responses. These insights may aid in the development of new monitoring and vaccination strategies for long-term control of chronic viral infections.