Our innate immune system distinguishes microbes from self by detecting conserved pathogen-associated molecular patterns (PAMPs) 1. However, all microbes produce PAMPs, regardless of their pathogenic potential. To distinguish virulent microbes from ones with lower disease-causing potential the innate immune system detects conserved pathogen-induced processes 2, such as the presence of microbial products in the host cytosol, by mechanisms that are not fully resolved. Here we show that Nod1 senses cytosolic microbial products by monitoring the activation state of small Rho GTPases. Activation of Rac1 and Cdc42 by bacterial delivery or ectopic expression of a Salmonella virulence factor, SopE, triggered the Nod1 signaling pathway with consequent Rip2-mediated induction of NF-κB-dependent inflammatory responses. Similarly, activation of the Nod1 signaling pathway by peptidoglycan required Rac1 activity. Furthermore, constitutively active forms of Rac1, Cdc42 and RhoA activated the Nod1 signaling pathway. Our data identify activation of small Rho GTPases as a pathogen-induced process sensed through the Nod1 signaling pathway (Fig. S1).

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Adoptive transfer of primary (unmodified) or genetically engineered antigen-specific T cells has demonstrated astonishing clinical results in the treatment of infections and some malignancies. Besides the definition of optimal targets and antigen receptors, the differentiation status of transferred T cells is emerging as a crucial parameter for generating cell products with optimal efficacy and safety profiles. Long-living memory T cells subdivide into phenotypically as well as functionally different subsets (e.g. central memory, effector memory, tissue-resident memory T cells). This diversification process is crucial for effective immune protection, with probably distinct dependencies on the presence of individual subsets dependent on the disease to which the immune response is directed as well as its organ location. Adoptive T cell therapy intends to therapeutically transfer defined T cell immunity into patients. Efficacy of this approach often requires long-term maintenance of transferred cells, which depends on the presence and persistence of memory T cells. However, engraftment and survival of highly differentiated memory T cell subsets upon adoptive transfer is still difficult to achieve. Therefore, the recent observation that a distinct subset of weakly differentiated memory T cells shows all characteristics of adult tissue stem cells and can reconstitute all types of effector and memory T cell subsets, became highly relevant. We here review our current understanding of memory subset formation and T cell subset purification, and it's implications for adoptive immunotherapy.

T cells expressing anti-CD19 chimeric antigen receptors (CARs) demonstrate impressive efficacy in the treatment of systemic B cell malignancies, including B cell lymphoma. However, their effect on primary central nervous system lymphoma (PCNSL) is unknown. Additionally, the detailed cellular dynamics of CAR T cells during their antitumor reaction remain unclear, including their intratumoral infiltration depth, mobility, and persistence. Studying these processes in detail requires repeated intravital imaging of precisely defined tumor regions during weeks of tumor growth and regression. Here, we have combined a model of PCNSL with in vivo intracerebral 2-photon microscopy. Thereby, we were able to visualize intracranial PCNSL growth and therapeutic effects of CAR T cells longitudinally in the same animal over several weeks. Intravenous (i.v.) injection resulted in poor tumor infiltration of anti-CD19 CAR T cells and could not sufficiently control tumor growth. After intracerebral injection, however, anti-CD19 CAR T cells invaded deeply into the solid tumor, reduced tumor growth, and induced regression of PCNSL, which was associated with long-term survival. Intracerebral anti-CD19 CAR T cells entered the circulation and infiltrated distant, nondraining lymph nodes more efficiently than mock CAR T cells. After complete regression of tumors, anti-CD19 CAR T cells remained detectable intracranially and intravascularly for up to 159 d. Collectively, these results demonstrate the great potential of anti-CD19 CAR T cells for the treatment of PCNSL.