Asymmetric cell division safeguards memory CD8 T cell development.

The strength of T cell receptor (TCR) stimulation and asymmetric distribution of fate determinants are both implied to affect T cell differentiation. Here, we uncover asymmetric cell division (ACD) as a safeguard mechanism for memory CD8 T cell generation specifically upon strong TCR stimulation. Using live imaging approaches, we find that strong TCR stimulation induces elevated ACD rates, and subsequent single-cell-derived colonies comprise both effector and memory precursor cells. The abundance of memory precursor cells emerging from a single activated T cell positively correlates with first mitosis ACD. Accordingly, preventing ACD by inhibition of protein kinase Cζ (PKCζ) during the first mitosis upon strong TCR stimulation markedly curtails the formation of memory precursor cells. Conversely, no effect of ACD on fate commitment is observed upon weak TCR stimulation. Our data provide relevant mechanistic insights into the role of ACD for CD8 T cell fate regulation upon different activation conditions.

Light-mediated discovery of surfaceome nanoscale organization and intercellular receptor interaction networks.

The molecular nanoscale organization of the surfaceome is a fundamental regulator of cellular signaling in health and disease. Technologies for mapping the spatial relationships of cell surface receptors and their extracellular signaling synapses would unlock theranostic opportunities to target protein communities and the possibility to engineer extracellular signaling. Here, we develop an optoproteomic technology termed LUX-MS that enables the targeted elucidation of acute protein interactions on and in between living cells using light-controlled singlet oxygen generators (SOG). By using SOG-coupled antibodies, small molecule drugs, biologics and intact viral particles, we demonstrate the ability of LUX-MS to decode ligand receptor interactions across organisms and to discover surfaceome receptor nanoscale organization with direct implications for drug action. Furthermore, by coupling SOG to antigens we achieved light-controlled molecular mapping of intercellular signaling within functional immune synapses between antigen-presenting cells and CD8+ T cells providing insights into T cell activation with spatiotemporal specificity. LUX-MS based decoding of surfaceome signaling architectures thereby provides a molecular framework for the rational development of theranostic strategies.

Protective role of the Arabidopsis leaf microbiota against a bacterial pathogen.

The aerial parts of plants are host to taxonomically structured bacterial communities. Members of the core phyllosphere microbiota can protect Arabidopsis thaliana against foliar pathogens. However, whether plant protection is widespread and to what extent the modes of protection differ among phyllosphere microorganisms are not clear. Here, we present a systematic analysis of plant protection capabilities of the At-LSPHERE, which is a collection of >200 bacterial isolates from A. thaliana, against the bacterial pathogen Pseudomonas syringae pv. tomato DC3000. In total, 224 bacterial leaf isolates were individually assessed for plant protection in a gnotobiotic system. Protection against the pathogen varied, with ~10% of leaf microbiota strains providing full protection, ~10% showing intermediate levels of protection and the remaining ~80% not markedly reducing disease phenotypes upon infection. The most protective strains were distributed across different taxonomic groups. Synthetic community experiments revealed additive effects of strains but also that a single strain can confer full protection in a community context. We also identify different mechanisms that contribute to plant protection. Although pattern-triggered immunity coreceptor signalling is involved in protection by a subset of strains, other strains protected in the absence of functional plant immunity receptors BAK1 and BKK1. Using a comparative genomics approach combined with mutagenesis, we reveal that direct bacteria-pathogen interactions contribute to plant protection by Rhizobium Leaf202. This shows that a computational approach based on the data provided can be used to identify genes of the microbiota that are important for plant protection.

Asymmetric cell division shapes naive and virtual memory T-cell immunity during ageing.

Efficient immune responses rely on heterogeneity, which in CD8+ T cells, amongst other mechanisms, is achieved by asymmetric cell division (ACD). Here we find that ageing, known to negatively impact immune responses, impairs ACD in murine CD8+ T cells, and that this phenotype can be rescued by transient mTOR inhibition. Increased ACD rates in mitotic cells from aged mice restore the expansion and memory potential of their cellular progenies. Further characterization of the composition of CD8+ T cells reveals that virtual memory cells (TVM cells), which accumulate during ageing, have a unique proliferation and metabolic profile, and retain their ability to divide asymmetrically, which correlates with increased memory potential. The opposite is observed for naive CD8+ T cells from aged mice. Our data provide evidence on how ACD modulation contributes to long-term survival and function of T cells during ageing, offering new insights into how the immune system adapts to ageing.

Modulation of asymmetric cell division as a mechanism to boost CD8+ T cell memory.

Asymmetric partitioning of fate determinants is a mechanism that contributes to T cell differentiation. However, it remains unclear whether the ability of T cells to divide asymmetrically is influenced by their differentiation state, as well as whether enforcing asymmetric cell division (ACD) rates would have an impact on T cell differentiation and memory formation. Using the murine LCMV infection model, we established a correlation between cell stemness and the ability of CD8+ T cells to undergo ACD. Transient mTOR inhibition was proven to increase ACD rates in naïve and memory cells and to install this ability in exhausted CD8+ T cells. Functionally, enforced ACD correlated with increased memory potential, leading to more efficient recall response and viral control upon acute or chronic LCMV infection. Moreover, transient mTOR inhibition also increased ACD rates in human CD8+ T cells. Transcriptional profiling revealed that progenies emerging from enforced ACD exhibited more pronounced early memory signatures, which functionally endowed these cells with better survival in the absence of antigen exposure and more robust homing to secondary lymphoid organs, providing critical access to survival niches. Our data provide important insights into how ACD can improve long-term survival and function of T cells and open new perspectives for vaccination and adoptive T cell transfer therapies.