Inflammatory monocytes -- but not the non-inflammatory subset -- depend on the chemokine receptor CCR2 for distribution to injured tissue and stimulate disease progression. Precise therapeutic targeting of this inflammatory monocyte subset could spare innate immunity's essential functions for maintenance of homeostasis and thus limit unwanted effects. Here we developed siRNA nanoparticles targeting CCR2 expression in inflammatory monocytes. We identified an optimized lipid nanoparticle and silencing siRNA sequence that when administered systemically, had rapid blood clearance, accumulated in spleen and bone marrow and showed high cellular localization of fluorescently tagged siRNA inside monocytes. Efficient degradation of CCR2 mRNA in monocytes prevented their accumulation in sites of inflammation. Specifically, the treatment attenuated their number in atherosclerotic plaques, reduced infarct size following coronary artery occlusion, prolonged normoglycemia in diabetic mice after pancreatic islet transplantation and resulted in reduced tumor volumes and lower numbers of tumor-associated macrophages. Taken together, siRNA nanoparticle-mediated CCR2 gene silencing in leukocytes selectively modulates functions of innate immune cell subtypes and may allow for the development of specific anti-inflammatory therapy.

The ability to mount protective immune responses depends on the diversity of T cells. T cell diversity may be compromised by the declining thymic output of new T cells. The aging process imposes a threat to diversity, because thymic function deteriorates. In this study we have examined the relationship between thymic production, homeostatic T cell proliferation and TCR β-chain diversity in young (∼25 years), middle-aged (∼60 years), and elderly adults (∼75 years). TCR excision circles (TREC) as a marker of thymic output exponentially decreased by >95% between 25 and 60 years of age. The frequency of Ki67+ cycling CD4 T cells remained steady, and surprisingly, the diversity of the naive CD4 T cell repertoire was maintained at ∼2 × 107 different TCR β-chains. After the age of 70 years, TRECs only slightly declined, but homeostatic proliferation doubled. The diversity of the T cell pool drastically contracted to 200,000 TCR β-chains. Also, the phenotypic distinction between naive and memory CD4 T cells became fuzzy. The collapse in CD4 T cell diversity during the seventh and eighth decades indicates substantial T cell loss and implies that therapeutic measures to improve vaccine responses will have to include strategies for T cell replenishment.

IL-1b signaling augments continued splenic monocyte supply during acute inflammation.