Evidence of STAT5-dependent and -independent routes to CD8 memory formation and a preferential role for IL-7 over IL-15 in STAT5 activation

Aging of Antiviral CD8+ Memory T Cells Fosters Increased Survival, Metabolic Adaptations, and Lymphoid Tissue Homing

Aging of established antiviral T cell memory can foster a series of progressive adaptations that paradoxically improve rather than compromise protective CD8⁺ T cell immunity. We now provide evidence that this gradual evolution, the pace of which is contingent on the precise context of the primary response, also impinges on the molecular mechanisms that regulate CD8⁺ memory T cell (T_M) homeostasis. Over time, CD8⁺ T_M generated in the wake of an acute infection with the natural murine pathogen lymphocytic choriomeningitis virus become more resistant to apoptosis and acquire enhanced cytokine responsiveness without adjusting their homeostatic proliferation rates; concurrent metabolic adaptations promote increased CD8⁺ T_M quiescence and fitness but also impart the reacquisition of a partial effector-like metabolic profile; and a gradual redistribution of aging CD8⁺ T_M from blood and nonlymphoid tissues to lymphatic organs results in CD8⁺ T_M accumulations in bone marrow, splenic white pulp, and, particularly, lymph nodes. Altogether, these data demonstrate how temporal alterations of fundamental homeostatic determinants converge to render aged CD8⁺ T_M poised for greater recall responses.

Interleukin-7 and -15 maintain pathogenic memory Th17 cells in autoimmunity

Th17 cells are principal mediators of many autoimmune conditions. Recently, memory Th17 cells have been revealed as crucial in mediating the chronicity of various refractory autoimmune disorders; however, the underlying mechanisms maintaining memory Th17 cells have remained elusive. Here, using a preclinical model of ocular autoimmune disease we show that both IL-7 and IL-15 are critical for maintaining pathogenic memory Th17 cells. Neutralization of these cytokines leads to substantial reduction of memory Th17 cells; both IL-7 and IL-15 provide survival signals via activating STAT5, and IL-15 provides additional proliferation signals via activating both STAT5 and Akt. Topical neutralization of ocular IL-7 or IL-15 effectively reduces memory Th17 cells at the inflammatory site and draining lymphoid tissues, while topical neutralization of IL-17 alone, the major pathogenic cytokine secreted by Th17 cells, does not diminish memory Th17 cells at the draining lymphoid tissues. Our results suggest that the effective removal of pathogenic memory Th17 cells via abolishing environmental IL-7 or IL-15 is likely to be a novel strategy in the treatment of autoimmune diseases.

Zap70 is essential for long-term survival of naive CD8 T cells

Survival of naive T cells requires engagement of TCR with self-peptide major histocompatibility Ags. The signaling pathways required to transmit this survival signal are poorly understood. In this study, we asked whether the tyrosine kinase Zap70 is required to transmit survival signals in naive CD8 T cells. In the absence of Zap70 expression, thymic development is completely blocked. Using a tetracycline-inducible Zap70 transgene (TetZap70), thymic development of Zap70-deficient TCR transgenic F5 mice was restored. Feeding mice doxycycline to induce Zap70 expression resulted in repopulation of the peripheral naive compartment. Zap70 transgene expression was then ablated by withdrawal of doxycycline. Survival of Zap70-deficient naive CD8 T cells depended on host environment. In hosts with a replete T cell compartment, naive T cells died rapidly in the absence of Zap70 expression. In lymphopenic hosts, Zap70-deficient T cells survived far longer, in an IL-7-dependent manner, but failed to undergo lymphopenia-induced proliferation. Analyzing mixed bone marrow chimeras revealed that intact Zap70-dependent signaling was important for integration of recent thymic emigrants into the mature naive compartment. Finally, we asked whether adaptor function conferred by Zap70 tyrosines 315 and 319 was necessary for transmission of homeostatic TCR signals. This was done by analyzing F5 mice expressing mutant Zap70 in which these residues had been mutated to alanines (Zap70(YYAA)). Inducible Zap70 expression rescued thymic development in F5 TetZap70 Zap70(YYAA) mice. However, in the absence of wild-type Zap70 expression, the Zap70(YYAA) mutant failed to transmit either survival or proliferative homeostatic signals.

Reduced IL-7 responsiveness defined by signal transducer and activator of transcription 5 phosphorylation in T cells may be a marker for increased risk of developing cytomegalovirus disease in patients after hematopoietic stem cell transplantation

Cytomegalovirus (CMV) reactivation may lead to CMV disease associated with high morbidity and mortality in patients after hematopoietic stem cell transplantation (HSCT); the identification of clinically relevant markers may aid in the identification of patients at increased risk for developing CMV-associated complications. We evaluated the phosphorylation of signal transducer and activator of transcription 5 (STAT5) in CD4(+) T cells, CD8(+) T cells, and TCRγδ T cells in response to stimulation with IL-7 or IL-2 after HSCT by analyzing blood samples taken monthly 1 to 6 months after HSCT. Patients were monitored weekly with a quantitative PCR from the time of engraftment for CMV viral load in whole blood until at least day 100 after HSCT. We identified a correlation between clinical outcome regarding CMV replication and the ability to respond to IL-7 and IL-2 defined by STAT5 phosphorylation (pSTAT5). Patients with recurrent or prolonged CMV replications had significantly lower pSTAT5 upon stimulation of T cells with either IL-7 or IL-2 at time points 1 through 3 than those without CMV replication (P < .05). This was also found after stimulation of CD8(+) T cells at time point 2 (P < .05). We conclude that reduced responses to IL-7, reflected by pSTAT5, may represent a clinically relevant functional biomarker for individuals at increased risk for CMV reactivation; our data may also aid in designing better strategies to improve anti-CMV immune responses without increasing the risk of developing graft-versus-host disease.

Disparate roles for STAT5 in primary and secondary CTL responses

IL-2 signals during the primary response to infection are essential in shaping CD8(+) T cell fate decisions. How CD8(+) T cells integrate IL-2 signals in the development of functional memory is not well understood. Because IL-2 induces potent activation of the STAT5 transcription factor, we tested the role of STAT5 in CD8(+) memory T cell differentiation and function using a model system in which STAT5 activity is inducibly abrogated upon CD8(+) T cell activation. We report that STAT5 activity is broadly important for the expansion and effector function of all effector CTL subsets. After pathogen clearance, STAT5 was required for the survival of effector phenotype memory CTLs during the contraction phase. However, despite its role in supporting full primary CD8(+) T cell expansion, and unlike IL-2, STAT5 activity is not required for the development of memory CD8(+) T cells capable of robust secondary expansion upon rechallenge. Our findings highlight differential requirements for survival signals between primary and secondary effector CTL, and demonstrate that IL-2-dependent programming of memory CD8(+) T cells capable of secondary expansion and secondary effector differentiation is largely STAT5 independent.

Constitutive STAT5 activation correlates with better survival in cervical cancer patients treated with radiation therapy

PURPOSE

Constitutively activated signal transducers and activators of transcription (STAT) factors, in particular STAT1, STAT3, and STAT5, have been detected in a wide variety of human primary tumors and have been demonstrated to directly contribute to oncogenesis. However, the expression pattern of these STATs in cervical carcinoma is still unknown, as is whether or not they have prognostic significance. This study investigated the expression patterns of STAT1, STAT3, and STAT5 in cervical cancer and their associations with clinical outcomes in patients treated with radical radiation therapy.

METHODS AND MATERIALS

A total of 165 consecutive patients with International Federation of Gynecology and Obstetrics (FIGO) Stages IB to IVA cervical cancer underwent radical radiation therapy, including external beam and/or high-dose-rate brachytherapy between 1989 and 2002. Immunohistochemical studies of their formalin-fixed, paraffin-embedded tissues were performed. Univariate and multivariate analyses were performed to identify and to evaluate the effects of these factors affecting patient survival.

RESULTS

Constitutive activations of STAT1, STAT3, and STAT5 were observed in 11%, 22%, and 61% of the participants, respectively. While STAT5 activation was associated with significantly better metastasis-free survival (p < 0.01) and overall survival (p = 0.04), STAT1 and STAT3 activation were not. Multivariate analyses showed that STAT5 activation, bulky tumor (≥ 4 cm), advanced stage (FIGO Stages III and IV), and brachytherapy (yes vs. no) were independent prognostic factors for cause-specific overall survival. None of the STATs was associated with local relapse. STAT5 activation (odds ratio = 0.29, 95% confidence interval = 0.13-0.63) and advanced stage (odds ratio = 2.54; 95% confidence interval = 1.03-6.26) were independent predictors of distant metastasis.

CONCLUSIONS

This is the first report to provide the overall expression patterns and prognostic significance of specific STATs in cervical carcinoma. Our results indicate that constitutive STAT5 activation correlates with better metastasis-free survival and overall survival in cervical cancer patients who have received radiation therapy.