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Immune checkpoint inhibitors (ICIs) are effective for various types of cancer, and their application has led to paradigm shifts in cancer treatment. While many patients can obtain clinical benefits from ICI treatment, a large number of patients are primarily resistant to such treatment or acquire resistance after an initial response. Thus, elucidating the resistance mechanisms is warranted to improve the clinical outcomes of ICI treatment. ICIs exert their antitumor effects by activating T cells in the tumor microenvironment. There are various resistance mechanisms, such as insufficient antigen recognition by T cells, impaired T‐cell migration and/or infiltration, and reduced T‐cell cytotoxicity, most of which are related to the T‐cell activation process. Thus, we classify them into three main mechanisms: resistance mechanisms related to antigen recognition, T‐cell migration and/or infiltration, and effector functions of T cells. In this review, we summarize these mechanisms of resistance to ICIs related to the T‐cell activation process and progress in the development of novel therapies that can overcome resistance. While many patients can obtain clinical benefits from immune checkpoint inhibitor treatment, a large number of patients are primarily resistant to such treatment or acquire resistance after an initial response. There are various resistance mechanisms, and we classify them into three main mechanisms related to the T‐cell activation process: resistance mechanisms related to antigen recognition, T‐cell migration and/or infiltration, and effector functions of T cells.

Combination therapy with anti‐cytotoxic T lymphocyte‐associated protein 4 (CTLA‐4) and anti‐programmed death‐1 (PD‐1) monoclonal antibodies (mAbs) has dramatically improved the prognosis of patients with multiple types of cancer, including renal cell carcinoma (RCC). However, more than half of RCC patients fail to respond to this therapy. Regulatory T cells (Treg cells) are a subset of highly immunosuppressive CD4+ T cells that promote the immune escape of tumors by suppressing effector T cells in the tumor microenvironment (TME) through various mechanisms. CTLA‐4 is constitutively expressed in Treg cells and is regarded as a key molecule for Treg‐cell‐mediated immunosuppressive functions, suppressing antigen‐presenting cells by binding to CD80/CD86. Reducing Treg cells in the TME with an anti‐CTLA‐4 mAb with antibody‐dependent cellular cytotoxicity (ADCC) activity is considered an essential mechanism to achieve tumor regression. In contrast, we demonstrated that CTLA‐4 blockade without ADCC activity enhanced CD28 costimulatory signaling pathways in Treg cells and promoted Treg‐cell proliferation in mouse models. CTLA‐4 blockade also augmented CTLA‐4‐independent immunosuppressive functions, including cytokine production, leading to insufficient antitumor effects. Similar results were also observed in human peripheral blood lymphocytes and tumor‐infiltrating lymphocytes from patients with RCC. Our findings highlight the importance of Treg‐cell depletion to achieve tumor regression in response to CTLA‐4 blockade therapies. CTLA‐4 blockade without ADCC activity augments the proliferation and CTLA‐4‐independent immunosuppressive functions of Treg cells by enhancing CD28 costimulatory signaling pathways in Treg cells, leading to insufficient tumor regression. This figure was created with BioRender.com.

Hydrogen peroxide (H 2 O 2 ) induces oxidative stress and cytotoxicity, and can be used for treating cancers in combination with radiotherapy. A product comprising H 2 O 2 and sodium hyaluronate has been developed as a radiosensitizer. However, the effects of H 2 O 2 on antitumor immunity remain unclear. To investigate the effects of H 2 O 2 , especially the abscopal effect when combined with radiotherapy (RT), we implanted murine tumor cells simultaneously in two locations in mouse models: the hind limb and back. H 2 O 2 mixed with sodium hyaluronate was injected intratumorally, followed by irradiation only at the hind limb lesion. No treatment was administered to the back lesion. The H 2 O 2 /RT combination significantly reduced tumor growth at the noninjected/nonirradiated site in the back lesion, whereas H 2 O 2 or RT individually did not reduce tumor growth. Flow cytometric analyses of the tumor‐draining lymph nodes in the injected/irradiated areas showed that the number of dendritic cells increased significantly with maturation in the H 2 O 2 /RT combination group. In addition, analyses of tumor‐infiltrating lymphocytes showed that the number of CD8 + (cluster of differentiation 8) T cells and the frequency of IFN‐γ + (interferon gamma) CD8 + T cells were higher in the noninjected/nonirradiated tumors in the H 2 O 2 /RT group compared to those in the other groups. PD‐1 (programmed death receptor 1) blockade further increased the antitumor effect against noninjected/nonirradiated tumors in the H 2 O 2 /RT group. Intratumoral injection of H 2 O 2 combined with RT therefore induces an abscopal effect by activating antitumor immunity, which can be further enhanced by PD‐1 blockade. These findings promote the development of H 2 O 2 /RT therapy combined with cancer immunotherapies, even for advanced cancers.

Background Epidermal growth factor receptor ( EGFR ) mutations represent one of the most frequent oncogenic driver in non-small cell lung cancer (NSCLC). Amivantamab, a bispecific antibody targeting EGFR and MET proto-oncogene, receptor tyrosine kinase (MET), has demonstrated clinical benefit in EGFR -mutant NSCLC through dual blockade, but its immunological role in human clinical specimens, especially tumor-infiltrating lymphocytes (TILs), has not been directly evaluated. Methods We analyzed surgically resected tumor samples from 40 patients with NSCLC to investigate immune responses and their associations with EGFR and MET expression. TILs were characterized by flow cytometry (FCM) and immunohistochemistry (IHC). To assess the immunomodulatory potential of amivantamab, fresh tumor digests containing live tumor cells and TILs were cultured ex vivo with CD3 and CD28 stimulation in the absence or presence of amivantamab, followed by FCM. EGFR and MET expression were also evaluated by IHC. Results EGFR mutations and high EGFR protein expression were associated with a trend toward reduced CD8⁺ T-cell and dendritic cell (DC) infiltration. In ex vivo TIL assays, exposure to amivantamab significantly activated CD8⁺ T cells, such as programmed cell death-1 expression and cytokine production, and promoted DC maturation. These effects were most pronounced in tumors with high EGFR or MET protein expression rather than EGFR mutations. Conclusions This study provides the first direct evidence from ex vivo fresh TIL assays using human NSCLC clinical specimens that amivantamab can activate immune responses. EGFR and MET expression may serve as potential biomarkers for amivantamab-induced immune responses.

Regulatory T (Treg) cells have an immunosuppressive function, and programmed death‐1 (PD‐1)‐expressing Treg cells reportedly induce resistance to PD‐1 blockade therapies through their reactivation. However, the effects of antigenicity on PD‐1 expression in Treg cells and the resistance to PD‐1 blockade therapy remain unclear. Here, we show that Treg cells gain high PD‐1 expression through an antigen with high antigenicity. Additionally, tumors with high antigenicity for Treg cells were resistant to PD‐1 blockade in vivo due to PD‐1+ Treg‐cell infiltration. Because such PD‐1+ Treg cells have high cytotoxic T lymphocyte antigen (CTLA)‐4 expression, resistance could be overcome by combination with an anti‐CTLA‐4 monoclonal antibody (mAb). Patients who responded to combination therapy with anti‐PD‐1 and anti‐CTLA‐4 mAbs sequentially after primary resistance to PD‐1 blockade monotherapy showed high Treg cell infiltration. We propose that the high antigenicity of Treg cells confers resistance to PD‐1 blockade therapy via high PD‐1 expression in Treg cells, which can be overcome by combination therapy with an anti‐CTLA‐4 mAb. High antigenicity of Treg cells confers resistance to anti‐PD‐1 mAb monotherapy via high PD‐1 expression in Treg cells. Resistance to anti‐PD‐1 mAb monotherapy via high PD‐1 expression in Treg cells can be overcome by combination therapy with an anti‐CTLA‐4 mAb. PD‐1+ Treg cells in the TME and Treg cell antigens may be predictive biomarkers for combination therapy with anti‐PD‐1 and anti‐CTLA‐4 mAbs.

BackgroundPatients with cancer benefit from treatment with immune checkpoint inhibitors (ICIs), and those with an inflamed tumor microenvironment (TME) and/or high tumor mutation burden (TMB), particularly, tend to respond to ICIs; however, some patients fail, whereas others acquire resistance after initial response despite the inflamed TME and/or high TMB. We assessed the detailed biological mechanisms of resistance to ICIs such as programmed death 1 and/or cytotoxic T-lymphocyte-associated protein 4 blockade therapies using clinical samples.MethodsWe established four pairs of autologous tumor cell lines and tumor-infiltrating lymphocytes (TILs) from patients with melanoma treated with ICIs. These tumor cell lines and TILs were subjected to comprehensive analyses and in vitro functional assays. We assessed tumor volume and TILs in vivo mouse models to validate identified mechanism. Furthermore, we analyzed additional clinical samples from another large melanoma cohort.ResultsTwo patients were super-responders, and the others acquired resistance: the first patient had a non-inflamed TME and acquired resistance due to the loss of the beta-2 microglobulin gene, and the other acquired resistance despite having inflamed TME and extremely high TMB which are reportedly predictive biomarkers. Tumor cell line and paired TIL analyses showed high CD155, TIGIT ligand, and TIGIT expression in the tumor cell line and tumor-infiltrating T cells, respectively. TIGIT blockade or CD155-deletion activated T cells in a functional assay using an autologous cell line and paired TILs from this patient. CD155 expression increased in surviving tumor cells after coculturing with TILs from a responder, which suppressed TIGIT+ T-cell activation. Consistently, TIGIT blockade or CD155-deletion could aid in overcoming resistance to ICIs in vivo mouse models. In clinical samples, CD155 was related to resistance to ICIs in patients with melanoma with an inflamed TME, including both primary and acquired resistance.ConclusionsThe TIGIT/CD155 axis mediates resistance to ICIs in patients with melanoma with an inflamed TME, promoting the development of TIGIT blockade therapies in such patients with cancer.

Although ropeginterferon alfa‐2b has recently been clinically applied to myeloproliferative neoplasms with promising results, its antitumor mechanism has not been thoroughly investigated. Using a leukemia model developed in immunocompetent mice, we evaluated the direct cytotoxic effects and indirect effects induced by ropeginterferon alfa‐2b in tumor cells. Ropeginterferon alfa‐2b therapy significantly prolonged the survival of mice bearing leukemia cells and led to long‐term remission in some mice. Alternatively, conventional interferon‐alpha treatment slightly extended the survival and all mice died. When ropeginterferon alfa‐2b was administered to interferon‐alpha receptor 1–knockout mice after the development of leukemia to verify the direct effect on the tumor, the survival of these mice was slightly prolonged; nevertheless, all of them died. In vivo CD4+ or CD8+ T‐cell depletion resulted in a significant loss of therapeutic efficacy in mice. These results indicate that the host adoptive immunostimulatory effect of ropeginterferon alfa‐2b is the dominant mechanism through which tumor cells are suppressed. Moreover, mice in long‐term remission did not develop leukemia, even after tumor rechallenge. Rejection of rechallenge tumors was canceled only when both CD4+ and CD8+ T cells were removed in vivo, which indicates that each T‐cell group functions independently in immunological memory. We show that ropeginterferon alfa‐2b induces excellent antitumor immunomodulation in hosts. Our finding serves in devising therapeutic strategies with ropeginterferon alfa‐2b. Although ropeginterferon alfa‐2b has recently been clinically applied to hematological malignancies, the antitumor mechanism of ropeginterferon alfa‐2b has not been fully examined. The results of experiments in mouse models of leukemia suggest that the antitumor effect of ropeginterferon alfa‐2b is mainly mediated by immunomodulation. Furthermore, T‐cells may play a crucial role in this function.

Cancer cells in the tumour microenvironment use various mechanisms to evade the immune system, particularly T cell attack 1 . For example, metabolic reprogramming in the tumour microenvironment and mitochondrial dysfunction in tumour-infiltrating lymphocytes (TILs) impair antitumour immune responses 2 , 3 – 4 . However, detailed mechanisms of such processes remain unclear. Here we analyse clinical specimens and identify mitochondrial DNA (mtDNA) mutations in TILs that are shared with cancer cells. Moreover, mitochondria with mtDNA mutations from cancer cells are able to transfer to TILs. Typically, mitochondria in TILs readily undergo mitophagy through reactive oxygen species. However, mitochondria transferred from cancer cells do not undergo mitophagy, which we find is due to mitophagy-inhibitory molecules. These molecules attach to mitochondria and together are transferred to TILs, which results in homoplasmic replacement. T cells that acquire mtDNA mutations from cancer cells exhibit metabolic abnormalities and senescence, with defects in effector functions and memory formation. This in turn leads to impaired antitumour immunity both in vitro and in vivo. Accordingly, the presence of an mtDNA mutation in tumour tissue is a poor prognostic factor for immune checkpoint inhibitors in patients with melanoma or non-small-cell lung cancer. These findings reveal a previously unknown mechanism of cancer immune evasion through mitochondrial transfer and can contribute to the development of future cancer immunotherapies. Mitochondria with mutations in their DNA from cancer cells can be transferred to T cells in the tumour microenvironment, which leads to T cell dysfunction and impaired antitumour immunity.

The etiologies of secondary idiopathic thrombocytopenic purpura (ITP) include infection, autoimmune disease, and immunodeficiency. We report the cases of three elderly patients who developed ITP after receiving influenza vaccinations. The platelet count of an 81-year-old woman fell to 27,000/μL after she received an influenza vaccination. A 75-year-old woman developed thrombocytopenia (5,000 platelets/μL) after receiving an influenza vaccination. An 87-year-old woman whose laboratory test values included a platelet count of 2,000/μL experienced genital bleeding after receiving an influenza vaccination. After Helicobacter pylori (HP) eradication or corticosteroid treatment, all of the patients’ platelet counts increased. Influenza vaccination is an underlying etiology of ITP in elderly patients. HP eradication or corticosteroid treatment is effective for these patients. Clinicians should be aware of the association between ITP and influenza vaccinations.