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The availability of l-arginine in tumours is a key determinant of an efficient anti-tumour T cell response.sup.1-4. Consequently, increases of typically low l-arginine concentrations within the tumour may greatly potentiate the anti-tumour responses of immune checkpoint inhibitors, such as programmed death-ligand 1 (PD-L1)-blocking antibodies.sup.5. However, currently no means are available to locally increase intratumoural l-arginine levels. Here we used a synthetic biology approach to develop an engineered probiotic Escherichia coli Nissle 1917 strain that colonizes tumours and continuously converts ammonia, a metabolic waste product that accumulates in tumours.sup.6, to l-arginine. Colonization of tumours with these bacteria increased intratumoural l-arginine concentrations, increased the number of tumour-infiltrating T cells and had marked synergistic effects with PD-L1 blocking antibodies in the clearance of tumours. The anti-tumour effect of these bacteria was mediated by l-arginine and was dependent on T cells. These results show that engineered microbial therapies enable metabolic modulation of the tumour microenvironment leading to enhanced efficacy of immunotherapies. Injection of engineered bacteria that convert ammonia to l-arginine into tumours enhance the anti-tumour response in a mouse model and synergize with anti-PD-L1 treatment to clear tumours., Author(s): Fernando P. Canale [sup.1] , Camilla Basso [sup.1] [sup.5] , Gaia Antonini [sup.1] , Michela Perotti [sup.1] [sup.2] , Ning Li [sup.3] , Anna Sokolovska [sup.3] , Julia Neumann [...]

The optimal use of many biotherapeutics is restricted by Anti-drug antibodies (ADAs) and hypersensitivity responses which can affect potency and ability to administer a treatment. Here we demonstrate that Re-surfacing can be utilized as a generalizable approach to engineer proteins with extensive surface residue modifications in order to avoid binding by pre-existing ADAs. This technique was applied to E. coli Asparaginase (ASN) to produce functional mutants with up to 58 substitutions resulting in direct modification of 35% of surface residues. Re-surfaced ASNs exhibited significantly reduced binding to murine, rabbit and human polyclonal ADAs, with a negative correlation observed between binding and mutational distance from the native protein. Reductions in ADA binding correlated with diminished hypersensitivity responses in an in vivo mouse model. By using computational design approaches to traverse extended distances in mutational space while maintaining function, protein Re-surfacing may provide a means to generate novel or second line therapies for life-saving drugs with limited therapeutic alternatives. [ABSTRACT FROM AUTHOR]

Deletion of CD8+ T cells by dendritic cells (DCs) is recognized as a critical mechanism of immune tolerance to self-antigens. Although DC-mediated peripheral deletion of autoreactive CD8+ T cells has been demonstrated using T cells reactive to model Ags, its role in shaping the naturally occurring polyclonal CD8+ T cell repertoire has not been defined. Using Batf3-/- mice lacking cross-presenting CD8α+ and CD103+ DCs (also known as type 1 conventional [cDC1]), we demonstrate that peripheral deletion of CD8+ T cells reactive to a model tissue Ag is dependent on cDC1. However, endogenous CD8+ T cells from the periphery of Batf3-/- mice do not exhibit heightened self-reactivity, and deep TCR sequencing of CD8+ T cells from Batf3-/-and Batf3+/+ mice reveals that cDC1 have a minimal impact on shaping the peripheral CD8+ T cell repertoire. Thus, although evident in reductionist systems, deletion of polyclonal self-specific CD8+ T cells by cDC1 plays a negligible role in enforcing tolerance to natural self-ligands. [ABSTRACT FROM AUTHOR]

Deletion of CD8 + T cells by dendritic cells (DCs) is recognized as a critical mechanism of immune tolerance to self-antigens. Although DC-mediated peripheral deletion of autoreactive CD8 + T cells has been demonstrated using T cells reactive to model Ags, its role in shaping the naturally occurring polyclonal CD8 + T cell repertoire has not been defined. Using Batf3 -/- mice lacking cross-presenting CD8α + and CD103 + DCs (also known as type 1 conventional [cDC1]), we demonstrate that peripheral deletion of CD8 + T cells reactive to a model tissue Ag is dependent on cDC1. However, endogenous CD8 + T cells from the periphery of Batf3 -/- mice do not exhibit heightened self-reactivity, and deep TCR sequencing of CD8 + T cells from Batf3 -/- and Batf3 +/+ mice reveals that cDC1 have a minimal impact on shaping the peripheral CD8 + T cell repertoire. Thus, although evident in reductionist systems, deletion of polyclonal self-specific CD8 + T cells by cDC1 plays a negligible role in enforcing tolerance to natural self-ligands., (Copyright © 2019 by The American Association of Immunologists, Inc.)