After ingestion, oral antigens distribute systemically and provoke T cell stimulation outside the gastrointestinal tract. Within the liver, scavenger liver sinusoidal endothelial cells (LSEC) eliminate blood‐borne antigens and induce T cell tolerance. Here we investigated whether LSEC contribute to oral tolerance. Oral antigens were efficiently cross‐presented on H‐2K^b by LSEC to naive CD8 T cells. Cross‐presentation efficiency in LSEC but not dendritic cells was increased by antigen‐exposure to heat or low pH. Mechanistically, cross‐presentation in LSEC requires endosomal maturation, involves hsc73 and proteasomal degradation. H‐2K^b‐restricted cross‐presentation of oral antigens by LSEC in vivo induced CD8 T cell priming and led to development of CD8 T cell tolerance in two independent experimental systems. Adoptive transfer of LSEC from mice fed with antigen (ovalbumin) into RAG2^–/– knockout mice, previously reconstituted with naive ovalbumin‐specific CD8 T cells, prevented development of specific cytotoxicity and expression of IFN‐γ in CD8 T cells. Using a new transgenic mouse line expressing H‐2K^b only on endothelial cells, we have demonstrated that oral antigen administration leads to tolerance in H‐2K^b‐restricted CD8 T cells. Collectively, our data demonstrate a participation of the liver, in particular scavenger LSEC, in development of CD8 T cell tolerance towards oral antigens.

Although T cell-recruiting CD3-binding bispecific antibodies (BiMAb) have been proven to be clinically effective for hematologic malignancies, the success of BiMAb targeting solid tumor-associated antigens (TAA) in carcinomas so far remains poor. We reasoned that provision of co-stimulatory BiMAb in combination with αTAA–αCD3 BiMAb would boost T cell activation and proliferative capacity, and thereby facilitate the targeting of weakly or heterogeneously expressed tumor antigens. Various αTAA–αCD3 and αTAA–αCD28 BiMAb in a tetravalent IgG1-Fc based format have been analyzed, targeting multiple breast cancer antigens including HER2, EGFR, CEA, and EpCAM. Moreover, bifunctional fusion proteins of αTAA–tumor necrosis factor ligand (TNFL) superfamily members including 4-1BBL, OX40L, CD70 and TL1A have been tested. The functional activity of BiMAb was assessed using co-cultures of tumor cell lines and purified T cells in monolayer and tumor spheroid models. Only in the presence of tumor cells, αTAA–αCD3 BiMAb activated T cells and induced cytotoxicity in vitro, indicating a strict dependence on cross-linking. Combination treatment of αTAA–αCD3 BiMAb and co-stimulatory αTAA–αCD28 or αTAA–TNFL fusion proteins drastically enhanced T cell activation in terms of proliferation, activation marker expression, cytokine secretion and tumor cytotoxicity. Furthermore, BiMAb providing co-stimulation were shown to reduce the minimally required dose to achieve T cell activation by at least tenfold. Immuno-suppressive effects of TGF-β and IL-10 on T cell activation and memory cell formation could be overcome by co-stimulation. BiMAb-mediated co-stimulation was further augmented by immune checkpoint-inhibiting antibodies. Effective co-stimulation could be achieved by targeting a second breast cancer antigen, or by targeting fibroblast activation protein (FAP) expressed on another target cell. In tumor spheroids derived from pleural effusions of breast cancer patients, co-stimulatory BiMAb were essential for the activation tumor-infiltrating lymphocytes and cytotoxic anti-tumor responses against breast cancer cells. Taken together we showed that co-stimulation significantly potentiated the tumoricidal activity of T cell-activating BiMAb while preserving the dependence on TAA recognition. This approach could provide for a more localized activation of the immune system with higher efficacy and reduced peripheral toxicities.

NKG2A has emerged as a new immunotherapy target and its blockade with the novel immune checkpoint inhibitor (ICI) monalizumab can boost both NK cell and CD8⁺ T cell responses. NKG2A forms heterodimers with CD94 and binds to the human non‐classical MHC class I molecule HLA‐E. HLA‐E forms complexes with a limited set of peptides mainly derived from the leader sequences of the classical MHC class I molecules (HLA‐A, HLA‐B and HLA‐C) and the non‐classical class I paralogue HLA‐G, and it is well established that the interaction between CD94/NKG2x receptors and its ligand HLA‐E is peptide‐sensitive. Here, we have evaluated peptide dependence of NKG2A‐mediated inhibition and the efficiency of interference by monalizumab in a transcriptional T cell reporter system. NKG2A inhibition was mediated by cell‐expressed HLA‐E molecules stably presenting disulfate‐trapped peptide ligands. We show that different HLA‐class I leader peptides mediate varying levels of inhibition. We have used NKG2A/NKG2C chimeric receptors to map the binding site of NKG2A and NKG2C blocking antibodies. Furthermore, we determined the functional EC₅₀ values of blocking NKG2A antibodies and show that they greatly depend on the HLA‐leader peptide presented by HLA‐E. Monalizumab was less effective in augmenting NK cell‐mediated killing of target cells displaying HLA‐G peptide on HLA‐E, than cells expressing HLA‐E complexed with HLA‐A, HLA‐B and HLA‐C peptides. Our results indicate that peptides displayed by HLA‐E molecules on tumour cells might influence the effectivity of NKG2A‐ICI therapy and potentially suggest novel approaches for patient stratification, for example, based on tumoral HLA‐G levels.

Angiogenesis plays an important role in both soft and hard tissue regeneration, which can be modulated by therapeutic drugs. If nanoparticles (NP) are used as vectors for drug delivery, they have to encounter endothelial cells (EC) lining the vascular lumen, if applied intravenously. Herein the interaction of unloaded polyelectrolyte complex nanoparticles (PECNP) composed of cationic poly(l-lysine) (PLL) and various anionic polysaccharides with human vascular endothelial cells (HUVEC) was analyzed. In particular PECNP were tested for their cell adhesive properties, their cellular uptake and intracellular localization considering composition and net charge. PECNP may form a platform for both cell coating and drug delivery. PECNP, composed of PLL in combination with the polysaccharides dextran sulfate (DS), cellulose sulfate (CS) or heparin (HEP), either unlabeled or labeled with fluorescein isothiocyanate (FITC) and either with positive or negative net charge were prepared. PECNP were applied to human umbilical cord vein endothelial cells (HUVEC) in both, the volume phase and immobilized phase at model substrates like tissue culture dishes. The attachment of PECNP to the cell surface, their intracellular uptake, and effects on cell proliferation and growth behavior were determined. Immobilized PECNP reduced attachment of HUVEC, most prominently the systems PLL/HEP and PLL/DS. A small percentage of immobilized PECNP was taken up by cells during adhesion. PECNP in the volume phase showed no effect of the net charge sign and only minor effects of the composition on the binding and uptake of PECNP at HUVEC. PECNP were stored in endosomal vesicles in a cumulative manner without apparent further processing. During mitosis, internalized PECNP were almost equally distributed among the dividing cells. Both, in the volume phase and immobilized at the surface, PECNP composed of PLL/HEP and PLL/DS clearly reduced cell proliferation of HUVEC, however without an apparent cytotoxic effect, while PLL/CS composition showed minor impairment. PECNP have an anti-adhesive effect on HUVEC and are taken up by endothelial cells which may negatively influence the proliferation rate of HUVEC. The negative effects were less obvious with the composition PLL/CS. Since uptake and binding for PLL/HEP was more efficient than for PLL/DS, PECNP of PLL/HEP may be used to deliver growth factors to endothelial cells during vascularization of bone reconstitution material, whereas those of PLL/CS may have an advantage for substituting biomimetic bone scaffold material.