Real-world outcomes of nivolumab plus ipilimumab and pembrolizumab with platinum-based chemotherapy in advanced non-small cell lung cancer: a multicenter retrospective comparative study.

INTRODUCTION: Nivolumab plus ipilimumab with chemotherapy (NICT) and pembrolizumab with chemotherapy (PCT) are commonly used in patients with advanced non-small cell lung cancer (NSCLC). Compared with immune checkpoint inhibitor (ICI) monotherapy, ICI combination therapy can increase immune-related toxicity instead of prolonging survival. This study aimed to compare the efficacy and safety of NICT and PCT to decide on the favorable treatment. METHODS: We conducted a multi-center retrospective cohort study on patients who underwent NICT or PCT between December 2018 and May 2022. Propensity score matching (PSM) was performed with the variables age, sex, smoking status, performance status, stage, histology, and programmed cell death ligand-1 (PD-L1). The Kaplan-Meier method was used to compare survival for the matched patients. RESULTS: Six hundred consecutive patients were included. After PSM, 81 and 162 patients were enrolled in the NICT and PCT groups, respectively. The baseline characteristics were well-balanced. The median progression-free survival was equivalent (11.6 vs. 7.4 months; P = 0.582); however, the median overall survival (OS) was significantly longer in the NICT group than in the PCT group (26.0 vs. 16.8 months; P = 0.005). Furthermore, OS was better in PD-L1-negative patients who underwent NICT than in those who underwent PCT (26.0 vs. 16.8 months; P = 0.045). Safety profiles did not differ significantly in terms of severe adverse event and treatment-related death rates (P = 0.560, and 0.722, respectively). CONCLUSIONS: Real-world data suggests that NICT could be a favorable treatment option compared with PCT for patients with advanced NSCLC. Further follow-up is needed to determine the long-term prognostic benefit.

Pneumonitis During Durvalumab Consolidation Therapy Affects Survival in Stage III NSCLC.

Introduction: Durvalumab consolidation therapy is the standard of care after concurrent chemoradiotherapy (CRT) for stage III NSCLC. Immune-related pneumonitis during durvalumab treatment is potentially fatal; however, information is lacking regarding the impact of pneumonitis on patient survival. This study investigates the effect of pulmonary and nonpulmonary immune-related adverse events (irAEs) on the efficacy of durvalumab treatment in patients with stage III NSCLC. Methods: We retrospectively assessed 158 patients who received durvalumab after CRT at nine Japanese institutions between July 2018 and March 2020. Survival outcomes were compared between patients who developed pneumonitis with those who developed irAEs other than pneumonitis. Patients who survived for less than 3 months were excluded to reduce immortal time bias. Results: Among 158 evaluated patients, 76 (48%) experienced grade less than or equal to one irAEs, whereas 82 (52%) experienced grade greater than or equal to two irAEs. Among the patients with grade greater than or equal to two irAEs, those with grade greater than or equal to two pneumonitis (n = 55) were compared with those with grade greater than or equal to two irAEs other than pneumonitis (n = 27). Patients with grade greater than or equal to two pneumonitis exhibited a significantly worse overall survival than those with grade greater than or equal to two irAEs that excluded pneumonitis. Multivariate analysis revealed that grade greater than or equal to two pneumonitis (hazard ratio = 3.71; 95% confidence interval, 1.85-7.45; p < 0.001) and squamous histology (hazard ratio = 2.64; 95% confidence interval, 1.29-5.42; p = 0.008) were independently associated with worse overall survival. Conclusions: After minimizing immortal time bias, pneumonitis grade two or greater and squamous histology were poor prognostic factors in patients who received consolidation durvalumab after CRT.

Impact of Lymphopenia Recovery After Chemoradiotherapy on Durvalumab Consolidation Therapy in Stage III NSCLC.

Introduction: Durvalumab maintenance therapy after definitive concurrent chemoradiotherapy (CRT) is the standard treatment modality for stage III NSCLC. Although severe treatment-related lymphopenia (TRL) during CRT may impair the efficacy of subsequent durvalumab therapy, data on the effect of TRL recovery on consolidation durvalumab therapy are lacking. Methods: This retrospective study evaluated patients with unresectable stage III NSCLC treated with durvalumab after concurrent CRT. The patients were enrolled across nine institutes throughout Japan between August 2018 and March 2020. The effect of TRL recovery on survival was evaluated. The patients were divided into two groups on the basis of their lymphocyte recovery status: the recovery group involved patients who did not experience severe TRL or experienced TRL but exhibited lymphocyte count recovery at durvalumab initiation, and the nonrecovery group involved patients who experienced severe TRL and did not exhibit lymphocyte count recovery on durvalumab initiation. Results: Among the 151 patients evaluated, 41 (27%) and 110 (73%) patients were classified into the recovery and the nonrecovery groups, respectively. The nonrecovery group had significantly worse progression-free survival than the recovery group (21.9 mo versus not reached, p = 0.018). Recovery from TRL (p = 0.027) and high pre-CRT lymphocyte count (p = 0.028) independently influenced progression-free survival. Conclusions: Baseline lymphocyte count and recovery from TRL at the start of durvalumab therapy were predictive factors for survival outcomes in patients with NSCLC treated with durvalumab consolidation after concurrent CRT.

Candida Pneumonia in a Young Vegan Man with Diabetic Ketoacidosis.

A 39-year-old vegan man was admitted with diabetic ketoacidosis. He had also developed pneumonia that was unresponsive to antibiotics. Based on bronchoscopy findings, the diagnosis of Candida pneumonia was made, and the pulmonary shadow disappeared rapidly after antifungal therapy. Candida pneumonia has been mostly reported in severely immunocompromised patients. This is a rare case of Candida pneumonia that was found in a young vegan man with diabetes mellitus (DM). Although malnutrition caused by DM or an unbalanced diet is often underestimated as a cause of immunodeficiency, these conditions can be risk factors for serious opportunistic infections, including Candida pneumonia.

Metastatic Lung Tumors from Colorectal Cancer with EGFR Mutations That Responded to Osimertinib.

A 50-year-old woman who had previously undergone right hemicolectomy and chemotherapy for colorectal cancer was hospitalized with respiratory failure. Chest computed tomography showed reticulonodular opacities and enlarged lymph nodes. A transbronchial biopsy revealed adenocarcinoma with epidermal growth factor receptor (EGFR) mutations T790M and L861Q. Treatment with the EGFR-tyrosine kinase inhibitor (TKI) osimertinib was started, and she achieved a partial response. We diagnosed her with metastatic lung tumors from colorectal cancer based on additional immunohistochemical staining and the EGFR mutation status (L861Q) of the specimens. Although cases with EGFR mutations have been rarely reported, an EGFR-TKI can be an effective treatment option for colorectal cancer.

In silico evaluation of particle transport and deposition in the airways of individual patients with chronic obstructive pulmonary disease.

Inhalation therapy can effectively treat chronic obstructive pulmonary disease (COPD), but the physical factors determining the appropriate aerosol delivery into the targeted airways remain unclear. The problem is nontrivial because pulmonary structures differ among individual patients with COPD and depend on the severity of the disease. In an in silico evaluation, the present study investigates the differences in particle transport and deposition in the airways of three patients with different degrees of COPD. Specific pulmonary airway models were reconstructed based on the computed tomography data of three patients with a different degree of COPD severity. The transport and deposition of inhaled particles in the airways were evaluated in a computational fluid dynamics simulation and a Lagrangian multiphase model. The sizes of the inhaled particles (1.0, 2.5, 5.5, 8.5, and 10.0 µm) were representative of drug particles delivered from inhalation devices, including dry powder inhalers (DPIs). The deposition behaviors of the inhaled particles strongly depended on the individual geometrical structure of the airways. The largest inhaled particles (10.0 µm) were most strongly affected by inertia and were deposited mostly in the oropharynx; consequently, they were rare in the bronchi. In contrast, the smallest inhaled particles (1.0 µm) were effectively delivered distally with the airflow. The spatial distributions and amounts of deposited particles in the airways obviously differed among the three COPD patients. Small particles are preferred as they can penetrate the inner lung regions. The results can assist the design and development of powder formulations and DPIs for patients with various severities of COPD.

Inflammatory Thoracic Aortic Aneurysm in a Patient with Advanced Lung Adenocarcinoma Treated with Pembrolizumab.

A 57-year-old man with lung adenocarcinoma was treated with chemotherapy and immune checkpoint blockade. After two cycles of carboplatin, pemetrexed, and pembrolizumab, he developed a persistent fever. Chest computed tomography (CT) suggested inflammation of the aortic wall. We treated the patient with corticosteroids. After four cycles of carboplatin, pemetrexed, and pembrolizumab, chest CT showed an aneurysm in the ascending aorta. We diagnosed him with inflammatory thoracic aortic aneurysm induced by pembrolizumab and performed surgical replacement of the ascending aorta. Although this might be a very rare case, we should be aware of aortitis as a potential adverse effect of pembrolizumab.

IL-33 Induces Sema4A Expression in Dendritic Cells and Exerts Antitumor Immunity.

Cancer immunotherapy has shown great promise as a new standard therapeutic strategy against cancer. However, the response rate and survival benefit remain unsatisfactory because most current approaches, such as the use of immune checkpoint inhibitors, depend on spontaneous antitumor immune responses. One possibility for improving the efficacy of immunotherapy is to promote antitumor immunity using adjuvants or specific cytokines actively. IL-33 has been a candidate for such cytokine therapies, but it remains unclear how and in which situations IL-33 exerts antitumor immune effects. In this study, we demonstrate the potent antitumor effects of IL-33 using syngeneic mouse models, which included marked inhibition of tumor growth and upregulation of IFN-γ production by tumor-infiltrating CD8+ T cells. Of note, IL-33 induced dendritic cells to express semaphorin 4A (Sema4A), and the absence of Sema4A abolished the antitumor activity of IL-33, indicating that Sema4A is intrinsically required for the antitumor effects of IL-33 in mice. Collectively, these results not only present IL-33 and Sema4A as potential therapeutic targets but also shed light on the potential use of Sema4A as a biomarker for dendritic cell activation status, which has great value in various fields of cancer research, including vaccine development.

Successful continuous nivolumab therapy for metastatic non-small cell lung cancer after local treatment of oligometastatic lesions.

The patient in this report was a 57-year-old man with metastatic non-small cell lung cancer (NSCLC). After no response to two lines of systemic chemotherapy, he was treated with nivolumab as third-line therapy, which resulted in a partial response. After 17 months of nivolumab treatment, he developed bone metastasis in his left femur which was treated with radiation therapy. Nivolumab was restarted after radiation therapy. Four months after radiation therapy, he developed another metastatic lesion in the small intestine which was surgically resected. Because there were no recurrent NSCLC lesions after surgical resection, nivolumab was restarted again. At 18 months after surgery, there were no recurrent NSCLC lesions. Immunohistochemical analysis of peritumoral T lymphocytes showed higher expression of T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3) and lymphocyte activation gene 3 (LAG-3) in recurrent lesions of bone and small intestine than in primary lesions. Upregulation of TIM-3 and LAG-3 could be associated with mechanisms of adaptive resistance to nivolumab in this case. Here, we report a successful case of continued nivolumab therapy with remission after local treatments consisting of radiation therapy and surgical resection for oligometastases. Continuation of immune checkpoint inhibitor (ICI) treatment may be worth considering if oligometastases can be controlled. KEY POINTS: Significant findings of the study We report a successful case of continued nivolumab treatment with remission after local treatment (radiation therapy and surgical resection) for oligometastases. What this study adds Upregulation of T cell immunoglobulin and mucin domain-containing protein 3 and lymphocyte-activation gene 3 could be associated with mechanisms of adaptive resistance to nivolumab.

Neuropsychiatric Immune-related Adverse Events Induced by Pembrolizumab in a Patient with Lung Adenocarcinoma and Systemic Lupus Erythematosus.

The patient was a 73-year-old woman with lung adenocarcinoma and systemic lupus erythematosus (SLE) who was treated with pembrolizumab. After six cycles of pembrolizumab, she developed symptoms suggestive of neuropsychiatric SLE, such as resting tremor, confusional state, depression, mood disorder, and anxiety disorder. In addition, her cerebrospinal fluid level of interleukin-6 was elevated. Her symptoms resolved one month after the discontinuation of pembrolizumab. This is the first report of neuropsychiatric symptoms in a patient with lung cancer and SLE on immune checkpoint blockade therapy.

Efficient Differentiation of Mouse Induced Pluripotent Stem Cells into Alveolar Epithelium Type II with a BRD4 Inhibitor.

Regenerative medicine has continued to progress for lung biology and lung diseases. Efforts have focused on a variety of different applications for pluripotent stem cells. Several groups have reported successful methods for inducing differentiation of induced pluripotent stem cells (iPSCs) into the airway epithelium such as alveolar epithelium type II (ATII). However, differentiation efficiency varies among reports and improvements are needed. In the present paper, we propose a novel method for elimination of residual undifferentiated murine iPSCs using JQ1, a potent inhibitor of bromodomain (BRD) and extraterminal domain (BET) family proteins, for efficient differentiation into ATII. First, the murine iPSC line 20D-17 was induced to differentiate into ATII over a period of 26 days (days 0-26) using previously reported embryoid body seeding and stepwise differentiation methods. mRNA expressions of differentiation markers including surfactant protein C (Sftpc) were confirmed by real-time reverse transcription-polymerase chain reaction (RT-PCR) results, and 17% of the cells were shown positive for prosurfactant protein C (proSPC) in flow cytometry analysis. Next, those cells were cultured three-dimensionally in Matrigel for an additional 14 days (days 26-40), during which JQ1 was added for 4 days (days 28-32) to remove residual undifferentiated iPSCs. As a result, on day 40, the mRNA expression level of Sftpc in the three-dimensional culture was maintained at the same level as on day 26 and shown to be further increased by the addition of JQ1, with 39% of the cells found to express proSPC, showing that differentiation efficiency could be further increased. Three-dimensional culture with BRD4 inhibition by JQ1 improved the differentiation induction efficiency to ATII by removing residual undifferentiated murine iPSCs during the differentiation induction process.

Eosinophil-derived neurotoxin enhances airway remodeling in eosinophilic chronic rhinosinusitis and correlates with disease severity.

Eosinophilic chronic rhinosinusitis (ECRS) is a subtype of chronic rhinosinusitis (CRS) that is characterized by intractable nasal polyp formation. Eosinophil-derived neurotoxin (EDN) is an eosinophil granule protein that is closely related to allergic inflammation, but the pathological implications of EDN in ECRS remain unknown. In this study, we evaluated the function of EDN in ECRS pathogenesis and assessed its potential as a disease activity marker. Serum EDN levels were significantly higher in patients with ECRS than in those with other nasal and paranasal diseases, and were positively correlated with clinical disease activity. Production of EDN from isolated human eosinophils was induced by stimulation with IL-5 in vitro. Human nasal epithelial cells were stimulated with EDN, and the resultant changes in gene expression were detected by RNA sequencing. Pathway analysis revealed that the major canonical pathway affected by EDN stimulation was 'regulation of the epithelial-mesenchymal transition pathway'; the only gene in this pathway to be up-regulated was matrix metalloproteinase 9 (MMP-9). Consistent with this, immunostaining analysis revealed intense staining of both EDN and MMP-9 in nasal polyps from patients with ECRS. In conclusion, our data demonstrate that serum EDN level is a useful marker for the evaluation of ECRS severity. Furthermore, EDN induces production of MMP-9 from the nasal epithelium, which may be involved in the pathogenesis of ECRS.

Semaphorin 7A promotes EGFR-TKI resistance in EGFR mutant lung adenocarcinoma cells.

Although responses to EGFR tyrosine kinase inhibitors (EGFR-TKIs) are initially positive, 30%-40% of patients with EGFR-mutant tumors do not respond well to EGFR-TKIs, and most lung cancer patients harboring EGFR mutations experience relapse with resistance. Therefore, it is necessary to identify not only the mechanisms underlying EGFR-TKI resistance, but also potentially novel therapeutic targets and/or predictive biomarkers for EGFR-mutant lung adenocarcinoma. We found that the GPI-anchored protein semaphorin 7A (SEMA7A) is highly induced by the EGFR pathway, via mTOR signaling, and that expression levels of SEMA7A in human lung adenocarcinoma specimens were correlated with mTOR activation. Investigations using cell culture and animal models demonstrated that loss or overexpression of SEMA7A made cells less or more resistant to EGFR-TKIs, respectively. The resistance was due to the inhibition of apoptosis by aberrant activation of ERK. The ERK signal was suppressed by knockdown of integrin ß1 (ITGB1). Furthermore, in patients with EGFR mutant tumors, higher SEMA7A expression in clinical samples predicted poorer response to EGFR-TKI treatment. Collectively, these data show that the SEMA7A-ITGB1 axis plays pivotal roles in EGFR-TKI resistance mediated by ERK activation and apoptosis inhibition. Moreover, our results reveal the potential utility of SEMA7A not only as a predictive biomarker, but also as a potentially novel therapeutic target in EGFR-mutant lung adenocarcinoma.

Clinical implications of monitoring nivolumab immunokinetics in non-small cell lung cancer patients.

BACKGROUND: The PD-1-blocking antibody nivolumab persists in patients several weeks after the last infusion. However, no study has systematically evaluated the maximum duration that the antibody persists on T cells or the association between this duration and residual therapeutic efficacy or potential adverse events. METHODS: To define the duration of binding and residual efficacy of nivolumab after discontinuation, we developed a simplified strategy for T cell monitoring and used it to analyze T cells from peripheral blood from 11 non-small cell lung cancer patients previously treated with nivolumab. To determine the suitability of our method for other applications, we compared transcriptome profiles between nivolumab-bound and nivolumab-unbound CD8 T cells. We also applied T cell monitoring in 2 nivolumab-treated patients who developed progressive lung tumors during long-term follow-up. RESULTS: Prolonged nivolumab binding was detected more than 20 weeks after the last infusion, regardless of the total number of nivolumab infusions (2-15 doses) or type of subsequent treatment, in 9 of the 11 cases in which long-term monitoring was possible. Ki-67 positivity, a proliferation marker, in T cells decreased in patients with progressive disease. Transcriptome profiling identified the signals regulating activation of nivolumab-bound T cells, which may contribute to nivolumab resistance. In 2 patients who restarted nivolumab, T cell proliferation markers exhibited the opposite trend and correlated with clinical response. CONCLUSIONS: Although only a few samples were analyzed, our strategy of monitoring both nivolumab binding and Ki-67 in T cells might help determine residual efficacy under various types of concurrent or subsequent treatment. TRIAL REGISTRATION: University Hospital Medical Information Network Clinical Trials Registry, UMIN000024623. FUNDING: This work was supported by Japan Society for the Promotion of Science KAKENHI (JP17K16045, JP18H05282, and JP15K09220), Japan Agency for Medical Research and Development (JP17cm0106310, JP18cm0106335 and JP18cm059042), and Core Research for Evolutional Science and Technology (JPMJCR16G2).

Apoptosis-derived membrane vesicles drive the cGAS-STING pathway and enhance type I IFN production in systemic lupus erythematosus.

OBJECTIVE: Despite the importance of type I interferon (IFN-I) in systemic lupus erythematosus (SLE) pathogenesis, the mechanisms of IFN-I production have not been fully elucidated. Recognition of nucleic acids by DNA sensors induces IFN-I and interferon-stimulated genes (ISGs), but the involvement of cyclic guanosine monophosphate (GMP)-AMP synthase (cGAS) and stimulator of interferon genes (STING) in SLE remains unclear. We studied the role of the cGAS-STING pathway in the IFN-I-producing cascade driven by SLE serum. METHODS: We collected sera from patients with SLE (n=64), patients with other autoimmune diseases (n=31) and healthy controls (n=35), and assayed them using a cell-based reporter system that enables highly sensitive detection of IFN-I and ISG-inducing activity. We used Toll-like receptor-specific reporter cells and reporter cells harbouring knockouts of cGAS, STING and IFNAR2 to evaluate signalling pathway-dependent ISG induction. RESULTS: IFN-I bioactivity and ISG-inducing activities of serum were higher in patients with SLE than in patients with other autoimmune diseases or healthy controls. ISG-inducing activity of SLE sera was significantly reduced in STING-knockout reporter cells, and STING-dependent ISG-inducing activity correlated with disease activity. Double-stranded DNA levels were elevated in SLE. Apoptosis-derived membrane vesicles (AdMVs) from SLE sera had high ISG-inducing activity, which was diminished in cGAS-knockout or STING-knockout reporter cells. CONCLUSIONS: AdMVs in SLE serum induce IFN-I production through activation of the cGAS-STING pathway. Thus, blockade of the cGAS-STING axis represents a promising therapeutic target for SLE. Moreover, our cell-based reporter system may be useful for stratifying patients with SLE with high ISG-inducing activity.

Semaphorin 6D reverse signaling controls macrophage lipid metabolism and anti-inflammatory polarization.

Polarization of macrophages into pro-inflammatory or anti-inflammatory states has distinct metabolic requirements, with mechanistic target of rapamycin (mTOR) kinase signaling playing a critical role. However, it remains unclear how mTOR regulates metabolic status to promote polarization of these cells. Here we show that an mTOR-Semaphorin 6D (Sema6D)-Peroxisome proliferator receptor γ (PPARγ) axis plays critical roles in macrophage polarization. Inhibition of mTOR or loss of Sema6D blocked anti-inflammatory macrophage polarization, concomitant with severe impairments in PPARγ expression, uptake of fatty acids, and lipid metabolic reprogramming. Macrophage expression of the receptor Plexin-A4 is responsible for Sema6D-mediated anti-inflammatory polarization. We found that a tyrosine kinase, c-Abl, which associates with the cytoplasmic region of Sema6D, is required for PPARγ expression. Furthermore, Sema6D is important for generation of intestinal resident CX3CR1hi macrophages and prevents development of colitis. Collectively, these findings highlight crucial roles for Sema6D reverse signaling in macrophage polarization, coupling immunity, and metabolism via PPARγ.

Lysosomal Protein Lamtor1 Controls Innate Immune Responses via Nuclear Translocation of Transcription Factor EB.

Amino acid metabolism plays important roles in innate immune cells, including macrophages. Recently, we reported that a lysosomal adaptor protein, Lamtor1, which serves as the scaffold for amino acid-activated mechanistic target of rapamycin complex 1 (mTORC1), is critical for the polarization of M2 macrophages. However, little is known about how Lamtor1 affects the inflammatory responses that are triggered by the stimuli for TLRs. In this article, we show that Lamtor1 controls innate immune responses by regulating the phosphorylation and nuclear translocation of transcription factor EB (TFEB), which has been known as the master regulator for lysosome and autophagosome biogenesis. Furthermore, we show that nuclear translocation of TFEB occurs in alveolar macrophages of myeloid-specific Lamtor1 conditional knockout mice and that these mice are hypersensitive to intratracheal administration of LPS and bleomycin. Our observation clarified that the amino acid-sensing pathway consisting of Lamtor1, mTORC1, and TFEB is involved in the regulation of innate immune responses.

Eukaryotic translation initiation factor 3 subunit C is associated with acquired resistance to erlotinib in non-small cell lung cancer.

The acquisition of resistance to EGFR tyrosine kinase inhibitors (EGFR-TKIs) is one of the major problems in the pharmacotherapy against non-small cell lung cancers; however, molecular mechanisms remain to be fully elucidated. Here, using a newly-established erlotinib-resistant cell line, PC9/ER, from PC9 lung cancer cells, we demonstrated that the expression of translation-related molecules, including eukaryotic translation initiation factor 3 subunit C (eIF3c), was upregulated in PC9/ER cells by proteome analyses. Immunoblot analyses confirmed that eIF3c protein increased in PC9/ER cells, compared with PC9 cells. Importantly, the knockdown of eIF3c with its siRNAs enhanced the drug sensitivity in PC9/ER cells. Mechanistically, we found that LC3B-II was upregulated in PC9/ER cells, while downregulated by the knockdown of eIF3c. Consistently, the overexpression of eIF3c increased the number of autophagosomes, proposing the causality between eIF3c expression and autophagy. Moreover, chloroquine, an autophagy inhibitor, restored the sensitivity to erlotinib. Finally, immunohistochemical analyses of biopsy samples showed that the frequency of eIF3c-positive cases was higher in the patients with EGFR-TKI resistance than those prior to EGFR-TKI treatment. Moreover, the eIF3c-positive cases exhibited poor prognosis in EGFR-TKI treatment. Collectively, the upregulation of eIF3c could impair the sensitivity to EGFR-TKI as a novel mechanism of the drug resistance.

Lamtor1 Is Critically Required for CD4+ T Cell Proliferation and Regulatory T Cell Suppressive Function.

Mechanistic target of rapamycin complex (mTORC)1 integrates intracellular sufficiency of nutrients and regulates various cellular functions. Previous studies using mice with conditional knockout of mTORC1 component proteins (i.e., mTOR, Raptor, and Rheb) gave conflicting results on the roles of mTORC1 in CD4+ T cells. Lamtor1 is the protein that is required for amino acid sensing and activation of mTORC1; however, the roles of Lamtor1 in T cells have not been investigated. In this article, we show that Lamtor1-deficient CD4+ T cells exhibited marked reductions in proliferation, IL-2 production, mTORC1 activity, and expression of purine- and lipid-synthesis genes. Polarization of Th17 cells, but not Th1 and Th2 cells, diminished following the loss of Lamtor1. Accordingly, CD4-Cre-driven Lamtor1-knockout mice exhibited reduced numbers of CD4+ and CD8+ T cells at rest, and they were completely resistant to experimental autoimmune encephalomyelitis. In contrast, genetic ablation of Lamtor1 in Foxp3+ T cells resulted in severe autoimmunity and premature death. Lamtor1-deficient regulatory T cells survived ex vivo as long as wild-type regulatory T cells; however, they exhibited a marked loss of suppressive function and expression of signature molecules, such as CTLA-4. These results indicate that Lamtor1 plays essential roles in CD4+ T cells. Our data suggest that Lamtor1 should be considered a novel therapeutic target in immune systems.