Asymmetric anti-CLL-1×CD3 bispecific antibody, ABL602 2+1, with attenuated CD3 affinity endows potent antitumor activity but limited cytokine release.

BACKGROUND: Acute myeloid leukemia (AML) is a type of leukemia in adults with a high mortality rate and poor prognosis. Although targeted therapeutics, chemotherapy, and hematopoietic stem cell transplantation can improve the prognosis, the recurrence rate is still high, with a 5-year survival rate of approximately 40%. This study aimed to develop an IgG-based asymmetric bispecific antibody that targets CLL-1 and CD3 for treating AML. METHODS: ABL602 candidates were compared in terms of binding activity, T-cell activation, and tumor-killing activities. ABL602-mediated T-cell activation and tumor-killing activities were determined by measuring the expression of activation markers, cytokines, cytolytic proteins, and the proportion of dead cells. We evaluated in vivo tumor growth inhibitory activity in two mouse models bearing subcutaneously and orthotopically engrafted human AML. Direct tumor-killing activity and T-cell activation in patient-derived AML blasts were also evaluated. RESULTS: ABL602 2+1 showed a limited CD3 binding in the absence of CLL-1, suggesting that steric hindrance on the CD3 binding arm could reduce CLL-1 expression-independent CD3 binding. Although the CD3 binding activity was attenuated compared with that of 1+1, ABL602 2+1 exhibited much stronger T-cell activation and potent tumor-killing activities in AML cell lines. ABL602 2+1 efficiently inhibited tumor progression in subcutaneously and orthotopically engrafted AML mouse models. In the orthotopic mouse model, tumor growth inhibition was observed by gross measurement of luciferase activity, as well as a reduced proportion of AML blasts in the bone marrow, as determined by flow cytometry and immunohistochemistry (IHC) staining. ABL602 2+1 efficiently activated T cells and induced the lysis of AML blasts, even at very low effector:target (E:T) ratios (eg, 1:50). Compared with the reference 1+1 antibody, ABL602 did not induce the release of cytokines including interleukin-6 and tumor necrosis factor-α in the healthy donor-derived peripheral blood mononuclear cell. CONCLUSIONS: With its potent tumor-killing activity and reduced cytokine release, ABL602 2+1 is a promising candidate for treating patients with AML and warrants further study.

Tumor-Infiltrating Regulatory T-cell Accumulation in the Tumor Microenvironment Is Mediated by IL33/ST2 Signaling.

Regulatory T cells (Treg) are enriched in the tumor microenvironment (TME) and suppress antitumor immunity; however, the molecular mechanism underlying the accumulation of Tregs in the TME is poorly understood. In various tumor models, tumor-infiltrating Tregs were highly enriched in the TME and had significantly higher expression of immune checkpoint molecules. To characterize tumor-infiltrating Tregs, we performed bulk RNA sequencing (RNA-seq) and found that proliferation-related genes, immune suppression-related genes, and cytokine/chemokine receptor genes were upregulated in tumor-infiltrating Tregs compared with tumor-infiltrating CD4+Foxp3- conventional T cells or splenic Tregs from the same tumor-bearing mice. Single-cell RNA-seq and T-cell receptor sequencing also revealed active proliferation of tumor infiltrating Tregs by clonal expansion. One of these genes, ST2, an IL33 receptor, was identified as a potential factor driving Treg accumulation in the TME. Indeed, IL33-directed ST2 signaling induced the preferential proliferation of tumor-infiltrating Tregs and enhanced tumor progression, whereas genetic deletion of ST2 in Tregs limited their TME accumulation and delayed tumor growth. These data demonstrated the IL33/ST2 axis in Tregs as one of the critical pathways for the preferential accumulation of Tregs in the TME and suggests that the IL33/ST2 axis may be a potential therapeutic target for cancer immunotherapy.

Peripheral natural killer cells and myeloid-derived suppressor cells correlate with anti-PD-1 responses in non-small cell lung cancer.

Inhibition of immune checkpoint proteins like programmed death 1 (PD-1) is a promising therapeutic approach for several cancers, including non-small cell lung cancer (NSCLC). Although PD-1 ligand (PD-L1) expression is used to predict anti-PD-1 therapy responses in NSCLC, its accuracy is relatively less. Therefore, we sought to identify a more accurate predictive blood biomarker for evaluating anti-PD-1 response. We evaluated the frequencies of T cells, B cells, natural killer (NK) cells, polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs), mononuclear myeloid-derived suppressor cells (M-MDSCs), and Lox-1+ PMN-MDSCs in peripheral blood samples of 62 NSCLC patients before and after nivolumab treatment. Correlation of immune-cell population frequencies with treatment response, progression-free survival, and overall survival was also determined. After the first treatment, the median NK cell percentage was significantly higher in responders than in non-responders, while the median Lox-1+ PMN-MDSC percentage showed the opposite trend. NK cell frequencies significantly increased in responders but not in non-responders. NK cell frequency inversely correlated with that of Lox-1+ PMN-MDSCs after the first treatment cycle. The NK cell-to-Lox-1+ PMN-MDSC ratio (NMR) was significantly higher in responders than in non-responders. Patients with NMRs ≥ 5.75 after the first cycle had significantly higher objective response rates and longer progression-free and overall survival than those with NMRs <5.75. NMR shows promise as an early predictor of response to further anti-PD-1 therapy.

Role of myeloid-derived suppressor cells in immune checkpoint inhibitor therapy in cancer.

Over the past decade, immune checkpoint inhibitor (ICI) therapy has demonstrated improved therapeutic efficacy in a wide range of cancers. However, the benefits are restricted to a small population of patients. Therefore, studies on understanding the mechanisms resistant to ICI therapy and for finding predictive biomarkers for ICI therapy are being actively conducted. Recent studies have demonstrated that myeloid-derived suppressor cells (MDSC) inhibit ICI therapy by various mechanisms, and that the response to ICI therapy can be improved by blocking MDSC activity. Moreover, low level of MDSC in patients with cancer has been shown to be correlated with their good prognosis after ICI treatment, thereby suggesting MDSC as a predictive biomarker in this regard. This review focuses on the roles of MDSC in ICI therapy and their relevant applications.

TIGIT and PD-1 dual checkpoint blockade enhances antitumor immunity and survival in GBM.

The use of inhibitory checkpoint blockade in the management of glioblastoma has been studied in both preclinical and clinical settings. TIGIT is a novel checkpoint inhibitor recently discovered to play a role in cancer immunity. In this study, we sought to determine the effect of anti-PD-1 and anti-TIGIT combination therapy on survival in a murine glioblastoma (GBM) model, and to elucidate the underlying immune mechanisms. Using mice with intracranial GL261-luc+ tumors, we found that TIGIT expression was upregulated on CD8+ and regulatory T cells (Tregs) in the brain compared to draining cervical lymph nodes (CLN) and spleen. We then demonstrated that treatment using anti-PD-1 and anti-TIGIT dual therapy significantly improved survival compared to control and monotherapy groups. The therapeutic effect was correlated with both increased effector T cell function and downregulation of suppressive Tregs and tumor-infiltrating dendritic cells (TIDCs). Clinically, TIGIT expression on tumor-infiltrating lymphocytes was shown to be elevated in patient GBM samples, suggesting that the TIGIT pathway may be a valuable therapeutic target. Expression of the TIGIT ligand, PVR, further portended a poor survival outcome in patients with low-grade glioma. We conclude that anti-TIGIT is an effective treatment strategy against murine GBM when used in combination with anti-PD-1, improving overall survival via modifications of both the T cell and myeloid compartments. Given evidence of PVR expression on human GBM cells, TIGIT presents as a promising immune therapeutic target in the management of these patients.