Tet2 deletion in CD4+ T cells disrupts Th1 lineage commitment in memory cells and enhances T follicular helper cell recall responses to viral rechallenge.

Following viral clearance, antigen-specific CD4+ T cells contract and form a pool of distinct Th1 and Tfh memory cells that possess unique epigenetic programs, allowing them to rapidly recall their specific effector functions upon rechallenge. DNA methylation programing mediated by the methylcytosine dioxygenase Tet2 contributes to balancing Th1 and Tfh cell differentiation during acute viral infection; however, the role of Tet2 in CD4+ T cell memory formation and recall is unclear. Using adoptive transfer models of antigen-specific wild type and Tet2 knockout CD4+ T cells, we find that Tet2 is required for full commitment of CD4+ T cells to the Th1 lineage and that in the absence of Tet2, memory cells preferentially recall a Tfh like phenotype with enhanced expansion upon secondary challenge. These findings demonstrate an important role for Tet2 in enforcing lineage commitment and programing proliferation potential, and highlight the potential of targeting epigenetic programing to enhance adaptive immune responses.

Protein Immunization Induces Memory CD4+ T Cells That Lack Th Lineage Commitment.

Acute viral infection generates lineage-committed Th1 and T follicular helper (Tfh) memory cells that recall their lineage-specific functions following secondary challenge with virus. However, the lineage commitment of effector and memory Th cells in vivo following protein vaccination is poorly understood. In this study, we analyzed effector and memory CD4+ T cell differentiation in mice (Mus musculus) following adjuvanted glycoprotein immunization compared with acute lymphocytic choriomeningitis virus infection. Glycoprotein immunization induced CXCR5- non-Tfh effector and memory CD4+ T cells that surprisingly had not undergone polarization toward any particular Th cell lineage but had undergone memory differentiation. However, upon challenge with virus, these Th lineage-nonpolarized memory CD4+ T cells were able to generate Th1 secondary effector cells, demonstrating their lineage plasticity. In addition, Tfh and memory Tfh cells were generated in response to protein immunization, and these cells differed from infection-induced Tfh cells by their lack of the transcription factor Tbet. Rechallenge experiments demonstrated that viral infection, but not protein immunization, during either the primary or secondary immune response, restricts the recall of Bcl6 expression and the generation of germinal center Tfh cells. Together, these data demonstrate that protein immunization generates a combination of nonpolarized memory cells that are highly plastic and memory Tfh cells that can undergo further Th1-like modulation during a secondary response to viral infection.

Tet2 coordinates with Foxo1 and Runx1 to balance T follicular helper cell and T helper 1 cell differentiation.

In response to various types of infection, naïve CD4+ T cells differentiate into diverse helper T cell subsets; however, the epigenetic programs that regulate differentiation in response to viral infection remain poorly understood. Demethylation of CpG dinucleotides by Tet methylcytosine dioxygenases is a key component of epigenetic programing that promotes specific gene expression, cellular differentiation, and function. We report that following viral infection, Tet2-deficient CD4+ T cells preferentially differentiate into highly functional germinal center T follicular helper (TFH) cells that provide enhanced help for B cells. Using genome-wide DNA methylation and transcription factor binding analyses, we find that Tet2 coordinates with multiple transcription factors, including Foxo1 and Runx1, to mediate the demethylation and expression of target genes, including genes encoding repressors of TFH differentiation. Our findings establish Tet2 as an important regulator of TFH cell differentiation and reveal pathways that could be targeted to enhance immune responses against infectious disease.

Exocyst inactivation in urothelial cells disrupts autophagy and activates non-canonical NF-κB signaling.

Ureter obstruction is a highly prevalent event during embryonic development and is a major cause of pediatric kidney disease. We have previously reported that ureteric bud-specific ablation of the gene expressing the exocyst subunit EXOC5 in late murine gestation results in failure of urothelial stratification, cell death and complete ureter obstruction. However, the mechanistic connection between disrupted exocyst activity, urothelial cell death and subsequent ureter obstruction was unclear. Here, we report that inhibited urothelial stratification does not drive cell death during ureter development. Instead, we demonstrate that the exocyst plays a critical role in autophagy in urothelial cells, and that disruption of autophagy activates a urothelial NF-κB stress response. Impaired autophagy first provokes canonical NF-κB activity, which is progressively followed by increasing levels of non-canonical NF-κB activity and cell death if the stress remains unresolved. Furthermore, we demonstrate that ureter obstructions can be completely rescued in Exoc5 conditional knockout mice by administering a single dose of the pan-caspase inhibitor z-VAD-FMK at embryonic day 16.5 prior to urothelial cell death. Taken together, ablation of Exoc5 disrupts autophagic stress response and activates progressive NF-κB signaling, which promotes obstructive uropathy.