Immune checkpoint therapy has transformed cancer treatment, yet efficacy and safety challenges persist. Selectively inhibiting tumor-infiltrating regulatory T cells (Ti-Tregs) while enhancing CD8+ T cell function are complementary strategies in cancer immunotherapy. Here, we engineered a bispecific antibody, FRP303, targeting 4-1BB and CCR8, which are co-expressed on a highly immunosuppressive subset of Ti-Tregs. In vivo, FRP303 outperformed monoclonal antibodies in CT26 and MC38 colorectal tumors and poorly immunogenic B16F10 melanoma. Treatment with FRP303 reduced Ti-Treg frequency, increased CD8+ T cell infiltration, and elevated antitumor cytokines IFN-γ and TNF-α. Safety assessments showed FRP303 does not disrupt immune homeostasis in peripheral tissues or induce significant hepatotoxicity. Moreover, FRP303 demonstrated strong synergistic effects when combined with a PD-1 antibody. In summary, FRP303 mediated anti-tumor activity through a dual mechanism involving the selective depletion of Ti-Tregs and the enhancement of CD8+ T cell function, offering a promising strategy for cancer immunotherapy.
© 2025 The Authors.

Transmembrane 4 L six family member 1 (TM4SF1) is highly expressed and contributes to the progression of various malignancies. However, how it modulates hepatocellular carcinoma (HCC) progression and senescence remains to be elucidated.
TM4SF1 expression in HCC samples was evaluated using immunohistochemistry and flow cytometry. Cellular senescence was assessed through SA-β-gal activity assays and Western blot analysis. TM4SF1-related protein interactions were investigated using immunoprecipitation-mass spectrometry, co-immunoprecipitation, bimolecular fluorescence complementation, and immunofluorescence. Tumor-infiltrating immune cells were analyzed by flow cytometry. The HCC mouse model was established via hydrodynamic tail vein injection.
TM4SF1 was highly expressed in human HCC samples and murine models. Knockdown of TM4SF1 suppressed HCC proliferation both in vitro and in vivo, inducing non-secretory senescence through upregulation of p16 and p21. TM4SF1 enhanced the interaction between AKT1 and PDPK1, thereby promoting AKT phosphorylation, which subsequently downregulated p16 and p21. Meanwhile, TM4SF1-mediated AKT phosphorylation enhanced PD-L1 expression while reducing major histocompatibility complex class I level on tumor cells, leading to impaired cytotoxic function of CD8+ T cells and an increased proportion of exhausted CD8+ T cells. In clinical HCC samples, elevated TM4SF1 expression was associated with resistance to anti-PD-1 immunotherapy. Targeting TM4SF1 via adeno-associated virus induced tumor senescence, reduced tumor burden and synergistically enhanced the efficacy of anti-PD-1 therapy.
Our results revealed that TM4SF1 regulated tumor cell senescence and immune evasion through the AKT pathway, highlighting its potential as a therapeutic target in HCC, particularly in combination with first-line immunotherapy.

Elucidating the detailed features of emerging SARS-CoV-2 strains both in vitro and in vivo is indispensable for the development of effective vaccines or drugs against viral infection. We thoroughly characterized the virological and pathogenic features of eight different pandemic SARS-CoV-2 strains, from the WT strain to current circulating sublineage EG.5.1, both in vitro and in vivo. Besides detailed virological features observed in Vero E6 cells, the Omicron variants, from BA.1 to EG.5.1, exhibited enhanced infectious effects to upper respiratory tract in K18 human angiotensin-converting enzyme (ACE2) (K18 hACE2) transgenic mice. Both XBB.1.9.1 and EG.5.1 presented stronger tropism to brain, which could be the main reason for the increased lethal effects on mice. In addition, the pathogenesis comparisons among all these viruses in C57BL/6JGpt mice indicated that Omicron variant BA.1 and two new sublineages XBB.1.9.1 and EG.5.1 possessed dual tropisms to both human and mice, which were further confirmed by subsequent bioinformatic analyses and actual affinity comparison between viral RBDs and mouse or human receptor ACE2. Furthermore, the immunocompromised BKS-db mice were found to be more susceptible to Omicron strains compared to C57BL/6JGpt mice, which revealed that viral infectivity was determined by both its affinity to the host receptor and host immunocompetence. Thus, this study not only contributes to a systematic understanding of the pathogenic features of SARS-CoV-2 in mice, but also provides new insights to combat potential future surges of new SARS-CoV-2 variants.
© 2024 Wiley Periodicals LLC.

Bone marrow ablation is routinely performed before hematopoietic stem cell transplantation (HSCT). Hematopoietic stem and progenitor cells (HSPCs) require a stable bone marrow microenvironment to expand and refill the peripheral blood cell pool after ablation. Roundabout guidance receptor 4 (Robo4) is a transmembrane protein exclusive to endothelial cells and is vital in preserving vascular integrity. Hence, the hypothesis is that Robo4 maintains the integrity of bone marrow endothelial cells following radiotherapy. We created an endothelial cell injury model with γ-radiation before Robo4 gene manipulation using lentiviral-mediated RNAi and gene overexpression techniques. We demonstrate that Robo4 and specific mesenchymal proteins (Fibronectin, Vimentin, αSma, and S100A4) are upregulated in endothelial cells exposed to irradiation (IR). We found that Robo4 depletion increases the expression of endoglin (CD105), an auxiliary receptor for the transforming growth factor (TGF-β) family of proteins, and promotes endothelial-to-mesenchymal transition (End-MT) through activation of both the canonical (Smad) and non-canonical (AKT/NF-κB) signaling pathways to facilitate Snail1 activation and its nuclear translocation. Endothelial Robo4 overexpression stimulates the expression of immunoglobulin-like adhesion molecules (ICAM-1 and VCAM-1) and alleviates irradiation-induced End-MT. Our coculture model showed that transcriptional downregulation of endothelial Robo4 reduces HSPC proliferation and increases HSC quiescence and apoptosis. However, Robo4 overexpression mitigated the damaged endothelium's suppressive effects on HSC proliferation and differentiation. These findings indicate that by controlling End-MT, Robo4 preserves microvascular integrity after radiation preconditioning, protects endothelial function, and lessens the inhibitory effect of damaged endothelium on hematopoietic reconstitution.
© 2024. The Author(s).

Rac GTPases are required for neutrophil adhesion and migration, and for the neutrophil effector responses that kill pathogens. These Rac-dependent functions are impaired when neutrophils lack the activators of Rac, Rac-GEFs from the Prex, Vav, and Dock families. In this study, we demonstrate that Tiam1 is also expressed in neutrophils, governing focal complexes, actin cytoskeletal dynamics, polarisation, and migration, in a manner depending on the integrin ligand to which the cells adhere. Tiam1 is dispensable for the generation of reactive oxygen species but mediates degranulation and NETs release in adherent neutrophils, as well as the killing of bacteria. In vivo, Tiam1 is required for neutrophil recruitment during aseptic peritonitis and for the clearance of Streptococcus pneumoniae during pulmonary infection. However, Tiam1 functions differently to other Rac-GEFs. Instead of promoting neutrophil adhesion to ICAM1 and stimulating β2 integrin activity as could be expected, Tiam1 restricts these processes. In accordance with these paradoxical inhibitory roles, Tiam1 limits the fMLP-stimulated activation of Rac1 and Rac2 in adherent neutrophils, rather than activating Rac as expected. Tiam1 promotes the expression of several regulators of small GTPases and cytoskeletal dynamics, including αPix, Psd4, Rasa3, and Tiam2. It also controls the association of Rasa3, and potentially αPix, Git2, Psd4, and 14-3-3ζ/δ, with Rac. We propose these latter roles of Tiam1 underlie its effects on Rac and β2 integrin activity and on cell responses. Hence, Tiam1 is a novel regulator of Rac-dependent neutrophil responses that functions differently to other known neutrophil Rac-GEFs.
Copyright © 2023 Hornigold, Baker, Machin, Chetwynd, Johnsson, Pantarelli, Islam, Stammers, Crossland, Oxley, Okkenhaug, Walker, Walker, Segonds-Pichon, Fukui, Malliri and Welch.