We examined the immune microenvironment of primary colorectal cancer (CRC) using immunohistochemistry, laser capture microdissection/qRT-PCR, flow cytometry and functional analysis of tumor infiltrating lymphocytes. A subset of CRC displayed high infiltration with activated CD8+ CTL as well as activated Th1 cells characterized by IFN-γ production and the Th1 transcription factor Tbet. Parallel analysis of tumor genotypes revealed that virtually all of the tumors with this active Th1/CTL microenvironment had defects in mismatch repair, as evidenced by microsatellite instability (MSI). Counterbalancing this active Th1/CTL microenvironment, MSI tumors selectively demonstrated highly up-regulated expression of multiple immune checkpoints, including five – PD-1, PD-L1, CTLA-4, LAG-3 and IDO – currently being targeted clinically with inhibitors. These findings link tumor genotype with the immune microenvironment, and explain why MSI tumors are not naturally eliminated despite a hostile Th1/CTL microenvironment. They further suggest that blockade of specific checkpoints may be selectively efficacious in the MSI subset of CRC.

The metabolic characteristics of tumors present considerable hurdles to immune cell function and cancer immunotherapy. Using a glutamine antagonist, we metabolically dismantled the immunosuppressive microenvironment of tumors. We demonstrate that glutamine blockade in tumor-bearing mice suppresses oxidative and glycolytic metabolism of cancer cells, leading to decreased hypoxia, acidosis, and nutrient depletion. By contrast, effector T cells responded to glutamine antagonism by markedly up-regulating oxidative metabolism and adopting a long-lived, highly activated phenotype. These divergent changes in cellular metabolism and programming form the basis for potent antitumor responses. Glutamine antagonism therefore exposes a previously undefined difference in metabolic plasticity between cancer cells and effector T cells that can be exploited as a “metabolic checkpoint” for tumor immunotherapy.

Immune-mediated tissue regeneration driven by a biomaterial scaffold is emerging as an innovative regenerative strategy to repair damaged tissues. We investigated how biomaterial scaffolds shape the immune microenvironment in traumatic muscle wounds to improve tissue regeneration. The scaffolds induced a pro-regenerative response, characterized by an mTOR/Rictor-dependent T helper 2 pathway that guides interleukin-4–dependent macrophage polarization, which is critical for functional muscle recovery. Manipulating the adaptive immune system using biomaterials engineering may support the development of therapies that promote both systemic and local pro-regenerative immune responses, ultimately stimulating tissue repair.

Myeloid-derived suppressor cells (MDSC) play a key immunosuppressive role in various types

Impressive responses have been observed in patients treated with checkpoint inhibitory anti-programmed cell death-1 (PD-1) or anticytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) antibodies. However, immunotherapy against poorly immunogenic cancers remains a challenge. Here we report that treatment with both anti-PD-1 and anti-CTLA-4 antibodies was unable to eradicate large, modestly immunogenic CT26 tumors or metastatic 4T1 tumors. Cotreatment with epigenetic-modulating drugs and checkpoint inhibitors markedly improved treatment outcomes, curing more than 80% of the tumor-bearing mice. Functional studies revealed that the primary targets of the epigenetic modulators were myeloid-derived suppressor cells (MDSCs). A PI3K inhibitor that reduced circulating MDSCs also eradicated 4T1 tumors in 80% of the mice when combined with immune checkpoint inhibitors. Thus, cancers resistant to immune checkpoint blockade can be cured by eliminating MDSCs.T he mammalian immune system is delicately regulated, allowing it to mount an effective attack against foreign invaders such as bacteria and viruses with minimal bystander casualties. This requires functionally redundant regulatory mechanisms to ensure safety (1-3). Cancers appear able to hijack these mechanisms to avoid immune destruction. Several of the regulatory mechanisms exploited by cancer have been identified. These include regulatory T cells (Tregs), myeloidderived suppressor cells (MDSCs), tumor-associated macrophages and neutrophils, immune checkpoint pathways, and immunosuppressive cytokines (4-8). Most recently, the checkpoints guarded by the programmed cell death-1 (PD-1) and cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) receptors have been under intense investigation because of the availability of antibodies that can inhibit their function. Recent clinical trials with anti-CTLA-4, anti-PD-1, and anti-PD-L1 monoclonal antibodies showed remarkable therapeutic responses (9-12), underscoring the idea that disruption of immune checkpoints can be therapeutically useful. However, the objective responses were observed in a minority of the treated patients and tumor types, and the reasons why certain tumors respond and others do not are mysterious. CT26 and 4T1 are among the most popular syngeneic tumor models used for assessing novel therapeutic approaches. CT26 was derived from an undifferentiated colorectal carcinoma induced in a BALB/c mouse by repeated intrarectal instillations of N-nitroso-N-methylurethan and shown to be modestly immunogenic (13,14), whereas 4T1 originated from a spontaneous mammary tumor in a BALB/c mouse (15). 4T1 is poorly immunogenic and highly metastatic, characteristics shared with advanced human cancers (16). Despite the extensive use of these tumor cell lines in cancer research, little genetic characterization is available for either of them.In the current study, we evaluated both models with respect to their responses to the immune checkpoint inhibitors alone and combined with other agents. We also determined the sequences of th...

Purpose Checkpoint molecules like programmed death-1 (PD-1) and T-cell immunoglobulin mucin-3 (TIM-3) are negative immune regulators that may be upregulated in the setting of glioblastoma multiforme. Combined PD-1 blockade and stereotactic radiosurgery (SRS) have been shown to improve antitumor immunity and produce long-term survivors in a murine glioma model. However, tumor-infiltrating lymphocytes (TIL) can express multiple checkpoints, and expression of ≥2 checkpoints corresponds to a more exhausted T-cell phenotype. We investigate TIM-3 expression in a glioma model and the antitumor efficacy of TIM-3 blockade alone and in combination with anti-PD-1 and SRS. Experimental Design C57BL/6 mice were implanted with murine glioma cell line GL261-luc2 and randomized into 8 treatment arms: (i) control, (ii) SRS, (iii) anti-PD-1 antibody, (iv) anti-TIM-3 antibody, (v) anti-PD-1 + SRS, (vi) anti-TIM-3 + SRS, (vii) anti-PD-1 + anti-TIM-3, and (viii) anti-PD-1 + anti-TIM-3 + SRS. Survival and immune activation were assessed. Results Dual therapy with anti-TIM-3 antibody + SRS or anti-TIM-3 + anti-PD-1 improved survival compared with anti- TIM-3 antibody alone. Triple therapy resulted in 100% overall survival (P < 0.05), a significant improvement compared with other arms. Long-term survivors demonstrated increased immune cell infiltration and activity and immune memory. Finally, positive staining for TIM-3 was detected in 7 of 8 human GBM samples. Conclusions This is the first preclinical investigation on the effects of dual PD-1 and TIM-3 blockade with radiation. We also demonstrate the presence of TIM-3 in human glioblastoma multiforme and provide preclinical evidence for a novel treatment combination that can potentially result in long-term glioma survival and constitutes a novel immunotherapeutic strategy for the treatment of glioblastoma multiforme.

We report that angiotensin-converting enzyme (ACE), a critical physiologic regulator of blood pressure, angiogenesis, and inflammation, is a novel marker for identifying hemangioblasts differentiating from human embryonic stem cells (hESC). We demonstrate that ACE ؉ CD45 ؊ CD34 ؉/؊ hemangioblasts are common yolk sac (YS)-like progenitors for not only endothelium but also both primitive and definitive human lymphohematopoietic cells. Thrombopoietin and basic fibroblast growth factor are identified as critical factors for the proliferation of human hemangioblasts.The developmental sequence of human embryoid body hematopoiesis is remarkably congruent to the timeline of normal human YS development, which occurs during weeks 2 to 6 of human gestation. Furthermore, ACE and the reninangiotensin system (RAS) directly regulate hemangioblast expansion and differentiation via signaling through the angiotensin II receptors AGTR1 and AGTR2. ACE enzymatic activity is required for hemangioblast expansion, and differentiation toward either endothelium or multipotent hematopoietic progenitors is dramatically augmented after manipulation of angiotensin II signaling with either AGTR1-or AGTR2-specific inhibitors. The RAS can therefore be exploited to direct the hematopoietic or endothelial fate of hESC-derived hemangioblasts, thus providing novel opportunities for human tissue engineering. Moreover, the initial events of human hematoendotheliogenesis can be delineated in a manner previously impossible because of inaccessibility to early human embryonic tissues. IntroductionHuman hematopoiesis initiates during the third week of development with formation of yolk sac (YS) blood islands derived from extraembryonic mesoderm. 1,2 The YS generates primarily nucleated primitive erythroblasts that express predominantly embryonic hemoglobins (eg, ε 2 2 , Gower I; ␣ 2 ε 2 , Gower II; and 2 ␥ 2 , Portland), and primitive macrophages. 3 After the onset of circulation at approximately 21 days of embryonic development, YS blood cells continue to circulate in embryonic blood, but the fetal liver (FL) eventually replaces the YS as the main hematopoietic organ beginning at 5 to 6 weeks. FL hematopoiesis is dominated by adult-type definitive erythrocytes (enucleated, macrocytic) expressing abundant fetal (HbF; ␣ 2 ␥ 2 ), adult (HbA; ␣ 2 ␤ 2 ) hemoglobins, but limited embryonic hemoglobins. [4][5][6] The FL also produces rare megakaryocytes, granulocytes, macrophages, lymphocytes, and blast cells. 7 Definitive erythroid, myeloid, megakaryocytic, natural killer-B (NK-B) lymphoid, and multipotent progenitors, with limited long-term engraftment potential, are briefly detected during the late YS (eg, 4-5 weeks) stage, before fetal liver hematopoiesis, in both mice and humans. 2,[8][9] The ephemeral nature of definitivetype YS hematopoiesis suggests a gradual yolk sac-fetal liver transition. 1 Indeed, the classic embryonic 3 fetal 3 adult globin switch in early erythrocytes occurs sequentially over time and probably in the same clonal lineage. For examp...

The asymmetric partitioning of fate determining proteins has been shown to contribute to the generation of effector and memory CD8+ T cell precursors. Here, we demonstrate the asymmetric partitioning of mTORC1 activity upon activation of naïve CD8+ T cells. This results in the generation of one daughter T cell with increased mTORC1 activity, increased glycolytic activity and increased expression of effector molecules. The other daughter T cell inherits relatively low levels of mTORC1 activity, possesses increased lipid metabolism, expresses increased anti-apoptotic molecules and subsequently displays enhanced long-term survival. Mechanistically, we demonstrate a link between TCR-induced asymmetric expression of amino acid transporters and RagC-mediated translocation of mTOR to the lysosomes. Overall, our data provide important insight into how mTORC1-mediated metabolic reprogramming affects the fate decisions of T cells.