SUMMARY CD8+ T cells recognizing tumor-specific antigens are detected in cancer patients but are dysfunctional. Here we developed a tamoxifen-inducible liver cancer mouse model with a defined oncogenic driver antigen (SV40 large T-antigen) to follow the activation and differentiation of naive tumor-specific CD8+ T (TST) cells after tumor initiation. Early during the pre-malignant phase of tumorigenesis, TST cells became dysfunctional, exhibiting phenotypic, functional, and transcriptional features similar to dysfunctional T cells isolated from late-stage human tumors. Thus, T cell dysfunction seen in advanced human cancers may already be established early during tumorigenesis. Although the TST cell dysfunctional state was initially therapeutically reversible, it ultimately evolved into a fixed state. Persistent antigen exposure rather than factors associated with the tumor microenvironment drove dysfunction. Moreover, the TST cell differentiation and dysfunction program exhibited features distinct from T cell exhaustion in chronic infections. Strategies to overcome this antigen-driven, cell-intrinsic dysfunction may be required to improve cancer immunotherapy.

Purpose: T-cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif (ITIM) domain (TIGIT) is a recently identified T-cell coinhibitory receptor. In this study, we aimed to determine the clinical impact of TIGIT in patients with acute myelogenous leukemia (AML) and dissect the role of TIGIT in the pathogenesis of leukemia progression.Experimental Design: TIGIT expression on T cells from peripheral blood collected from patients with AML was examined by flow cytometry. The correlation of TIGIT expression to clinical outcomes, including rate of complete remission and relapse post-allogeneic stem cell transplantation (alloSCT) in AML patients, was analyzed. Phenotypic and functional study (cytokine release, proliferation, killing, and apoptosis) of TIGIT-expressing T cells were performed. Using siRNA to silence TIGIT, we further elucidated the regulatory role of TIGIT in the T-cell immune response by dissecting the effect of TIGIT knockdown on cytokine release and apoptosis of T cells from AML patients.Results: TIGIT expression on CD8 þ T cells is elevated in AML patients and high-TIGIT correlates with primary refractory disease and leukemia relapse post-alloSCT. TIGIT þ CD8 þ T cells display phenotypic features of exhaustion and exhibit functional impairment manifested by low production of cytokines and high susceptibility to apoptosis. Importantly, their functional defects are reversed by TIGIT knockdown. Conclusions: TIGIT contributes to functional T-cell impairment and associates with poor clinical outcome in AML. Our study suggests that blockade of TIGIT to restore T-cell function and antitumor immunity may represent a novel effective leukemia therapeutic.

The cytotoxic T-lymphocyte response to wild-type simian virus 40 large tumor antigen (Tag) in C57BL/6 (H2 b ) mice is directed against three H2-D b -restricted epitopes, I, II/III, and V, and one H2-K b -restricted epitope, IV. Epitopes I, II/III, and IV are immunodominant, while epitope V is immunorecessive. We investigated whether this hierarchical response was established in vivo or was due to differential expansion in vitro by using direct enumeration of CD8 ؉ T lymphocytes with Tag epitope/major histocompatibility complex class I tetramers and intracellular gamma interferon staining. The results demonstrate that epitope IV-specific CD8 ؉ T cells dominated the Tag-specific response in vivo following immunization with full-length Tag while CD8 ؉ T cells specific for epitopes I and II/III were detected at less than one-third of this level. The immunorecessive nature of epitope V was apparent in vivo, since epitope V-specific CD8 ؉ T cells were undetectable following immunization with full-length Tag. In contrast, high levels of epitope V-specific CD8 ؉ T lymphocytes were recruited in vivo following immunization and boosting with a Tag variant in which epitopes I, II/III, and IV had been inactivated. In addition, analysis of the T-cell receptor ␤ (TCR␤) repertoire of Tag epitope-specific CD8 ؉ cells revealed that multiple TCR␤ variable regions were utilized for each epitope except Tag epitope II/III, which was limited to TCR␤10 usage. These results indicate that the hierarchy of Tag epitope-specific CD8 ؉ T-cell responses is established in vivo.Immunity to the large tumor antigen (Tag) of simian virus 40 (SV40) in C57BL/6 mice is characterized by the development of CD8 (23,34,50,52). An immunological hierarchy has been demonstrated among these four epitopes within Tag. Immunization of C57BL/6 mice with SV40, SV40 Tagtransformed cells, or a recombinant vaccinia virus (rVV) which encodes the full-length Tag leads to the induction of cytotoxic T lymphocytes (CTL) specific for epitopes I, II/III, and IV (26, 41, 51). Frequency estimates from limiting-dilution analysis of splenic lymphocytes obtained 9 days after immunization with SV40 Tag-transformed cells revealed that epitope IV-specific CTL represent 1 in 14,000 splenocytes while epitope I and II/III-specific CTL were less abundant (1 in 67,000) and epitope V-specific CTL were undetectable (41).Although epitope V-specific CTL are not detected following immunization with full-length SV40 Tag, immunization with syngeneic cells carrying inactivating mutations or deletions in Tag epitopes I, II/III, and IV leads to the induction of epitope V-specific CTL (41, 50). Accordingly, epitope V has been characterized as immunorecessive. Additional strategies which enhance the immunogenicity of epitope V include immunization with rVVs which express epitope V as a minigene linked to a secretory signal sequence (ES) or in which the epitope V sequence is inserted into a nonimmunogenic murine self protein, dihydrofolate reductase (26). Precise mechanisms which control the immun...

Protein complexes of the 28-kDa proteasome activator (PA28) family activate the proteasome and may alter proteasome cleavage specificity. Initial investigations have demonstrated a role for the IFN-γ-inducible PA28α/β complex in Ag processing. Although the noninducible and predominantly nuclear PA28γ complex has been implicated in affecting proteasome-dependent signaling pathways, such as control of the mitotic cell cycle, there is no previous evidence demonstrating a role for this structure in Ag processing. We therefore generated PA28γ-deficient mice and investigated their immune function. PA28γ−/− mice display a slight reduction in CD8+ T cell numbers and do not effectively clear a pulmonary fungal infection. However, T cell responses in two viral infection models appear normal in both magnitude and the hierarchy of antigenic epitopes recognized. We conclude that PA28γ−/− mice, like PA28α−/−/β−/− mice, are deficient in the processing of only specific Ags.

Prognosis of leukemia relapse post allogeneic stem cell transplantation (alloSCT) is poor and effective new treatments are urgently needed. T cells are pivotal in eradicating leukemia through a graft versus leukemia (GVL) effect and leukemia relapse is considered a failure of GVL. T-cell exhaustion is a state of T-cell dysfunction mediated by inhibitory molecules including programmed cell death protein 1 (PD-1) and T-cell immunoglobulin domain and mucin domain 3 (TIM-3). To evaluate whether T-cell exhaustion and inhibitory pathways are involved in leukemia relapse post alloSCT, we performed phenotypic and functional studies on T cells from peripheral blood of acute myeloid leukemia patients receiving alloSCT. Here we report that PD-1hiTIM-3+ cells are strongly associated with leukemia relapse post transplantation. Consistent with exhaustion, PD-1hiTIM-3+ T cells are functionally deficient manifested by reduced production of interleukin 2 (IL-2), tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ). In addition, these cells demonstrate a phenotype consistent with exhausted antigen-experienced T cells by losing TN and TEMRA subsets. Importantly, increase of PD-1hiTIM-3+ cells occurs before clinical diagnosis of leukemia relapse, suggesting their predictive value. Results of our study provide an early diagnostic approach and a therapeutic target for leukemia relapse post transplantation.

Immunotherapy has expanded treatment options for cancers with historically poor outcomes, yet a significant proportion of patients still fail to achieve durable clinical benefit. We defined the contribution of β-adrenergic receptor (βAR) signaling, a component of the stress response, on success of immunotherapy for melanoma since the use of antagonists (β-blockers) is associated with improved clinical outcomes in some cancers. We show that metastatic melanoma patients who received immunotherapy had improved overall survival if they also received pan β-blockers. This retrospective analysis is reinforced by results showing that βAR blockade enhances the control of murine melanoma growth by anti-(α)PD-1 checkpoint blockade. However, this effect was most significant when β-blocker was combined with dual αPD-1 + high dose interleukin-2 therapy and was reproduced by selective blockade of βARs. These results identify a novel strategy that can be quickly introduced to potentially increase the number of patients who benefit from immune-based therapies.

Circulating tumor cells (CTCs) are of recognized importance for diagnosis and prognosis of cancer patients. With melanoma, most studies do not show any clear relationship between CTC levels and stage of disease. Here, CTCs were enriched (∼400X) from blood of melanoma patients using a simple centrifugation device (OncoQuick), and 4 melanocyte target RNAs (TYR, MLANA, MITF, and MIF) were quantified using QPCR. Approximately one-third of melanoma patients had elevated MIF and MLANA transcripts (p<0.0001 and p<0.001, respectively) compared with healthy controls. In contrast, healthy controls had uniformly higher levels of TYR and MITF than melanoma patients (p<0.0001). There was a marked shift of leukocytes into the CTC-enriched fractions (a 430% increase in RNA recovery, p<0.001), and no relationship between CTC levels and stage of disease was found. CTCs were captured on microfabricated filters and cultured. Captured melanoma CTCs were large cells, and consisted of 2 subpopulations, based on immunoreactivity. One subpopulation (∼50%) stained for both pan-cytokeratin (KRT) markers and the common leukocyte marker CD-45, whereas the second subpopulation stained for only KRT. Since similar cells are described in many cancers, we also examined blood from colorectal and pancreatic cancer patients. We observed analogous results, with most captured CTCs staining for both CD-45/KRT markers (and for the monocyte differentiation marker CD-14). Our results suggest that immature melanocyte-related cells (expressing TYR and MITF RNA) may circulate in healthy controls, although they are not readily detectable without considerable enrichment. Further, as early-stage melanomas develop, immature melanocyte migration into the blood is somehow curtailed, whereas a significant proportion of patients develop elevated CTC levels (based on MIF and MLANA RNAs). The nature of the captured CTCs is consistent with literature describing leukocyte/macrophage-tumor cell fusion hybrids, and their role in metastatic progression.

There is a growing body of evidence supporting the synergistic roles of radiotherapy and immunotherapy in the treatment of malignancy. Published case studies of the abscopal effect have been reported with the use of ipilimumab and radiotherapy in metastatic melanoma, but evidence supporting the routine use of this combination of therapy is limited. We conducted a retrospective analysis to evaluate patients treated with ipilimumab for advanced melanoma at a single institution from May 2011 to June 2015. Patients were grouped into those who had received concurrent radiotherapy while on ipilimumab (Ipi-RT), and those who did not. We then evaluated the treatment response following completion of ipilimumab. A total of 101 patients received ipilimumab in the prespecified time frame. 70 received Ipi-RT and 31 received ipilimumab without concurrent radiotherapy. Median overall survival (OS) was significantly increased in the concurrent Ipi-RT arm at 19 months vs. 10 months for ipilimumab alone (p = 0.01). Median progression free survival (PFS) was marginally increased in the Ipi-RT group compare with the ipilimumab alone group (5 months vs. 3 months, p = 0.20). Rates of complete response (CR) were significantly increased in the Ipi-RT group vs. ipilimumab alone (25.7% vs. 6.5%; p = 0.04), and rates of overall response (OR) in the groups were 37.1% vs. 19.4% (p = 0.11). No increase in toxicities was observed in the Ipi-RT group compare with ipilimumab alone. Prospective trials are needed to further clarify the role of radiotherapy with ipilimumab, but these encouraging preliminary observations suggest that this combination can induce more durable responses to immunotherapy.