Metformin synergizes with PD-1 blockade to promote normalization of tumor vessels via CD8T cells and IFNγ.

Tumor blood vessels are highly leaky in structure and have poor blood perfusion, which hampers infiltration and function of CD8T cells within tumor. Normalizing tumor vessels is thus thought to be important in promoting the flux of immune T cells and enhancing ant-tumor immunity. However, how tumor vasculature is normalized is poorly understood. Metformin (Met) combined with ant-PD-1 therapy is known to stimulate proliferation of and to produce large amounts of IFNγ from tumor-infiltrating CD8T lymphocytes (CD8TILs). We found that the combination therapy promotes the pericyte coverage of tumor vascular endothelial cells (ECs) to improve blood perfusion and that it suppresses the hyperpermeability through the increase of VE-cadherin. Peripheral node addressin(PNAd) and vascular cell adhesion molecule (VCAM)-1, both implicated to promote tumor infiltration of CD8T cells, were also increased. Importantly, tumor vessel normalization, characterized as the reduced 70-kDa dextran leakage and the enhancement of VE-cadherin and VCAM-1, were canceled by anti-CD8 Ab or anti-IFNγ Ab injection to mice. The increased CD8TILs were also abrogated by anti-IFNγ Ab injection. In vascular ECs, flow cytometry analysis revealed that pSTAT1 expression was found to be associated with VE-cadherin expression. Moreover, in vitro treatment with Met and IFNγ enhanced VE-cadherin and VCAM-1 on human umbilical vein endothelial cells (HUVECs). The Kaplan-Meier method revealed a correlation of VE-cadherin or VCAM-1 levels with overall survival in patients treated with immune checkpoint inhibitors. These data indicate that IFNγ-mediated cross talk of CD8TILs with tumor vessels is important for creating a better tumor microenvironment and maintaining sustained antitumor immunity.

Estrogen contributes to the sex difference in the occurrence of senescence-related T cells during the development of visceral adipose tissue inflammation.

It remains unclear whether sex differences exist during the development of visceral adipose tissue (VAT) inflammation associated with obesity. The purpose of this study was to clarify sex differences in the occurrence of senescence-related T cells (CD44high PD-1+ CD4+), which play a key role in the progression of VAT inflammation associated with high-fat diet (HFD)-induced obesity. Phase 1: C57BL/6N mice were fed either a control diet (HFC) or HFD for 5 wk. The area under the curve of the oral glucose-tolerance test (oGTT) was maximal at 15 wk in HFD-fed males and at 21 wk in females. At 17 wk, VAT weights were similar, but an increase in the number of macrophages in the VAT was observed only in HFD-fed males. In addition, the numbers of regulatory and senescence-related T cells were consistently higher in males than in females. Phases 2 and 3: 6-wk-old female mice were randomly divided into sham operation and bilateral ovariectomy (OVX) groups and fed either an HFC or HFD from 7 wk. OVX mice were subjected to 17ß-estradiol releasing or placebo pellet implantation and fed an HFC. Body and VAT weights were higher in the OVX group than in the sham. The number of macrophages did not change in the OVX group with either diet. HFC-fed OVX mice exhibited high senescence-related T cells in the VAT, resembling HFC-fed male mice. This change was abolished by 17ß-estradiol replacement. Thus, we demonstrated different accumulation patterns of VAT immune cells between the sexes, revealing a role for estrogen in the appearance of senescence-related T cells.NEW & NOTEWORTHY The accumulation pattern of adipose tissue differs between the sexes; however, it is unclear whether sex differences exist during the development of adipose tissue inflammation and whether estrogen plays a role. We demonstrated sex differences in immune cells' subpopulation of visceral adipose tissue. The proinflammatory environment appeared earlier in males than in females. In addition, our results suggest that estrogen plays a role in visceral adipose tissue inflammation, particularly by regulating the appearance of senescence-related T cells.

The effect of caloric restriction on the increase in senescence-associated T cells and metabolic disorders in aged mice.

Aging is associated with functional decline in the immune system and increases the risk of chronic diseases owing to smoldering inflammation. In the present study, we demonstrated an age-related increase in the accumulation of Programmed Death-1 (PD-1)+ memory-phenotype T cells that are considered "senescence-associated T cells" in both the visceral adipose tissue and spleen. As caloric restriction is an established intervention scientifically proven to exert anti-aging effects and greatly affects physiological and pathophysiological alterations with advanced age, we evaluated the effect of caloric restriction on the increase in this T-cell subpopulation and glucose tolerance in aged mice. Long-term caloric restriction significantly decreased the number of PD-1+ memory-phenotype cluster of differentiation (CD) 4+ and CD8+ T cells in the spleen and visceral adipose tissue, decreased M1-type macrophage accumulation in visceral adipose tissue, and improved insulin resistance in aged mice. Furthermore, the immunological depletion of PD-1+ T cells reduced adipose inflammation and improved insulin resistance in aged mice. Taken together with our previous report, these results indicate that senescence-related T-cell subpopulations are involved in the development of chronic inflammation and insulin resistance in the context of chronological aging and obesity. Thus, long-term caloric restriction and specific deletion of senescence-related T cells are promising interventions to regulate age-related chronic diseases.