Integrins are cell surface receptors that mediate the interactions of cells with their surroundings and play essential roles in cell adhesion, migration, and homeostasis. Eight of the 24 integrins bind to the tripeptide Arg-Gly-Asp (RGD) motif in their extracellular ligands, comprising the RGD-binding integrin subfamily. Despite similarity in recognizing the RGD motif and some redundancy, these integrins can selectively recognize RGD-containing ligands to fulfill specific functions in cellular processes. Antibodies against individual RGD-binding integrins are desirable for investigating their specific functions, and were selected here from a synthetic yeast-displayed Fab library. We discovered 11 antibodies that exhibit high specificity and affinity toward their target integrins, i.e. αVβ3, αVβ5, αVβ6, αVβ8, and α5β1. Of these, six are function-blocking antibodies and contain a ligand-mimetic R(G/L/T)D motif in their CDR3 sequences. We report antibody-binding specificity, kinetics, and binding affinity for purified integrin ectodomains, as well as intact integrins on the cell surface. We further used these antibodies to reveal binding preferences of the αV subunit for its 5 β-subunit partners: β6 = β8 > β3 > β1 = β5.

During embryogenesis, waves of hematopoietic progenitors develop from hemogenic endothelium (HE) prior to the emergence of self-renewing hematopoietic stem cells (HSCs). Although previous studies have shown that yolk-sac-derived erythromyeloid progenitors and HSCs emerge from distinct populations of HE, it remains unknown whether the earliest lymphoid-competent progenitors, multipotent progenitors, and HSCs originate from common HE. In this study, we demonstrate by clonal assays and single-cell transcriptomics that rare HE with functional HSC potential in the early murine embryo are distinct from more abundant HE with multilineage hematopoietic potential that fail to generate HSCs. Specifically, HSC-competent HE are characterized by expression of CXCR4 surface marker and by higher expression of genes tied to arterial programs regulating HSC dormancy and self-renewal. Taken together, these findings suggest a revised model of developmental hematopoiesis in which the initial populations of multipotent progenitors and HSCs arise independently from HE with distinct phenotypic and transcriptional properties.Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.

CD279 is a cell surface protein predominantly expressed on T cells. Its ligands CD273 and CD274 are expressed on antigen-presenting cells and tumors. CD279 has been shown to act as an important immune check point by inhibiting CD8 T cell activation, and antibodies against CD279 enhance T cell-mediated cytotoxic function. However, whether CD279 has other functions in CD4 T cell homeostasis or in mediating T cell interactions with antigen-presenting cells remains unclear. In the present study, we show that antibody-mediated inhibition of CD279 reduces T cell survival in bone marrow in vivo. Unexpectedly, CD279 blockade also compromised regulatory T cell and macrophage interactions by reducing their contact time. The observation that the CD273 antagonist had little effect suggests that CD274 (the second ligand of CD279) plays a more central role in contact between conventional T cells (Tcon) and macrophages. The results of the present study suggest that both CD279 ligands contribute to the interaction length between T cells and macrophages as a mechanism of maintaining Treg homeostasis. Furthermore, CD273 and CD274 are not redundant ligands because CD274 may have unique effects on Tcon in this complex immune axis. Therefore, ligand selection for check point blockade as a tool for cancer immunotherapy has important implications with respect to anti-tumor T cell activation and the avoidance of side effects.
© 2020 The Authors. Published by FEBS Press and John Wiley & Sons Ltd.

Dendritic cells (DCs) are professional antigen-presenting cells that are pivotal in the generation and sustainability of antitumor immune responses. Whole tumor cell lysates (TCLs) have been used as sources of tumor antigens for the development of DC vaccines. However, the clinical outcomes of the use of TCL-based DC vaccines have so far been unsatisfactory because of the weak immunogenicity of tumor cells. To improve the efficacy of TCL-based DC vaccines, viruses have been used to enhance the immunity of TCLs and to further enhance the antigen delivery and antigen-presenting ability of DCs. The aim of the present study was to improve the antigen-presenting ability of DCs and to use them to effectively activate T lymphocytes. The present study demonstrated that DCs loaded with the lysate of Newcastle Disease Virus (NDV)-infected tumor cells (NDV-TCL) have increased levels of cluster of differentiation 80 (CD80), CD86, CD83 and human leukocyte antigen-antigen D-associated expression, compared with those loaded with TCL alone. The DCs loaded with the NDV-TCL promoted T-cell proliferation and antitumor cytokine secretion from T cells. These results indicated that loading DCs with NDV-TCL could enhance the antigen-presenting ability of the DCs. On the basis of the results of the present study, we hypothesize that this method of loading DCs with NDV-TCL can be used to develop novel DC vaccines for tumor immunotherapy in the future.