Interruption of the intratumor CD8+ T cell:Treg crosstalk improves the efficacy of PD-1 immunotherapy.

PD-1 blockade unleashes potent antitumor activity in CD8+ T cells but can also promote immunosuppressive T regulatory (Treg) cells, which may worsen the response to immunotherapy. Tumor-Treg inhibition is a promising strategy to improve the efficacy of checkpoint blockade immunotherapy; however, our understanding of the mechanisms supporting tumor-Tregs during PD-1 immunotherapy is incomplete. Here, we show that PD-1 blockade increases tumor-Tregs in mouse models of melanoma and metastatic melanoma patients. Mechanistically, Treg accumulation is not caused by Treg-intrinsic inhibition of PD-1 signaling but depends on an indirect effect of activated CD8+ T cells. CD8+ T cells produce IL-2 and colocalize with Tregs in mouse and human melanomas. IL-2 upregulates the anti-apoptotic protein ICOS on tumor-Tregs, promoting their accumulation. Inhibition of ICOS signaling before PD-1 immunotherapy improves control over immunogenic melanoma. Thus, interrupting the intratumor CD8+ T cell:Treg crosstalk represents a strategy to enhance the therapeutic efficacy of PD-1 immunotherapy.

Variegate expression of Cre recombinase in hematopoietic cells in CD11c-cre transgenic mice.

In this study, we performed an in-depth analysis of Cre expression in the widely used CD11c-Cre transgenic mice generated by the group of Boris Reizis. In contrast to previous observation, using the highly sensitive Rosa-26-floxed-tdTomato reporter mouse line, we show variegated expression of Cre in multiple hematopoietic linage cells starting in hematopoietic stem cells. Indeed, we found that in the CD11c-Cre driver mice, Cre is expressed in cDC linage cells and pDC starting from the myeloid dendritic cell precursor, as expected, but also in a substantial fraction of hematopoietic stem cells and common lymphoid progenitors and, consequently, in >50% of all leukocytes. Hence, this study indicates that the reporter mice used to characterize Cre expression in Cre-driver mice should be selected with caution and considering the sensitivity of the reporter system. This study also suggests that the interpretation of some reports using this CD11c-Cre transgenic mice may need to be re-considered based on a careful evaluation of the cell type-specificity of Cre-mediated in their model.

Tissue-Specific Factors Differentially Regulate the Expression of Antigen-Processing Enzymes During Dendritic Cell Ontogeny.

Dendritic cells (DCs) form a collection of antigen-presenting cells (APCs) that are distributed throughout the body. Conventional DCs (cDCs), which include the cDC1 and cDC2 subsets, and plasmacytoid DCs (pDCs) constitute the two major ontogenically distinct DC populations. The pDCs complete their differentiation in the bone marrow (BM), whereas the cDC subsets derive from pre-committed BM precursors, the pre-cDC, that seed lymphoid and non-lymphoid tissues where they further differentiate into mature cDC1 and cDC2. Within different tissues, cDCs express distinct phenotype and function. Notably, cDCs in the thymus are exquisitely efficient at processing and presenting antigens in the class II pathway, whereas in the spleen they do so only upon maturation induced by danger signals. To appraise this functional heterogeneity, we examined the regulation of the expression of distinct antigen-processing enzymes during DC ontogeny. We analyzed the expression of cathepsin S (CTSS), cathepsin L (CTSL), and thymus-specific serine protease (TSSP), three major antigen-processing enzymes regulating class II presentation in cDC, by DC BM precursors and immature and mature cDCs from the spleen and thymus. We found that pre-cDCs in the BM express relatively high levels of these different proteases. Then, their expression is modulated in a tissue-specific and subset-specific manner with immature and mature thymic cDCs expressing overall higher levels than immature splenic cDCs. On the other hand, the TSSP expression level is selectively down-regulated in spleen pDCs, whereas CTSS and CTSL are both increased in thymic and splenic pDCs. Hence, tissue-specific factors program the expression levels of these different proteases during DC differentiation, thus conferring tissue-specific function to the different DC subsets.

Light-controlled active release of photocaged ciprofloxacin for lipopolysaccharide-targeted drug delivery using dendrimer conjugates.

We report an active delivery mechanism targeted specifically to Gram(-) bacteria based on the photochemical release of photocaged ciprofloxacin carried by a cell wall-targeted dendrimer nanoconjugate.