We developed a SARS-CoV-2 vaccine candidate (CoV-RBD121-NP) comprised of a tobacco mosaic virus-like nanoparticle conjugated to the receptor-binding domain of the spike glycoprotein of SARS-CoV-2 fused to a human IgG1 Fc domain. CoV-RBD121-NP elicits strong antibody responses in C57BL/6 mice and is stable for up to 12 months at 2-8 or 22-28 °C. Here, we showed that this vaccine induces a strong neutralizing antibody response in K18-hACE2 mice. Furthermore, we demonstrated that immunization protects mice from virus-associated mortality and symptomatic disease. Our data indicated that a sufficient pre-existing pool of neutralizing antibodies is required to restrict SARS-CoV-2 replication upon exposure and prevent induction of inflammatory mediators associated with severe disease. Finally, we identified a potential role for CXCL5 as a protective cytokine in SARS-CoV-2 infection. Our results suggested that disruption of the CXCL5 and CXCL1/2 axis may be important early components of the inflammatory dysregulation that is characteristic of severe cases of COVID-19.

Murine Kupffer cells (KCs) comprise CD11bhi and F4/80hi subsets. Tissue-resident macrophages are known to express the tyrosine kinase receptors colony-stimulating factor 1 receptor (Csf1r) and Mer. However, the expression of Csf1r and Mer on KC subsets and the importance of these tyrosine kinases during liver regeneration (LR) are unknown.
KCs from wild-type and Csf1r-GFP mice were characterized by flow cytometry. Partial hepatectomy (PH) was performed in mice treated with clodronate liposomes, a Csf1r small molecule inhibitor or depleting antibody, or a small molecule Mer inhibitor. Sera and livers were analyzed. The function of sorted KC subsets was tested in vitro.
Mer was specifically expressed on tissue-resident F4/80hi KCs, 55% of which also expressed Csf1r. Mer+Csf1r+ and Mer+Csf1r- KCs had distinct expression of macrophage markers. Csf1r inhibition in mice reduced F4/80hi KCs by approximately 50%, but did not affect CD11bhi KCs. Clodronate liposomes depleted F4/80hi KCs, but also altered levels of other intrahepatic leukocytes. Csf1r inhibition delayed LR, as demonstrated by a 20% reduction in liver-to-body weight ratios 7 days after PH. At 36h after PH, Csf1r inhibition increased serum ALT and histological liver injury, and decreased liver cell proliferation. A small molecule inhibitor of Mer did not alter the percentage of KCs or their proliferation and just modestly delayed LR. In vitro, Csf1r or Mer inhibition did not decrease KC viability, but did attenuate their cytokine response to stimulation.
F4/80hi KCs are Mer+ and can be subdivided based on Csf1r expression. Csf1r or Mer inhibition each reduces KC cytokine production and delays LR.

It is still technically difficult to collect high purity cancer cells from tumor tissues, which contain noncancerous cells. We hypothesized that xenograft models of NOG mice expressing enhanced green fluorescent protein (eGFP), referred to as NOG-EGFP mice, may be useful for obtaining such high purity cancer cells for detailed molecular and cellular analyses.
Pancreato-biliary cancer cell lines were implanted subcutaneously to compare the tumorigenicity between NOG-EGFP mice and nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. To obtain high purity cancer cells, the subcutaneous tumors were harvested from the mice and enzymatically dissociated into single-cell suspensions. Then, the cells were sorted by fluorescence-activated cell sorting (FACS) for separation of the host cells and the cancer cells. Thereafter, the contamination rate of host cells in collected cancer cells was quantified by using FACS analysis. The viability of cancer cells after FACS sorting was evaluated by cell culture and subsequent subcutaneous reimplantation in NOG-EGFP mice.
The tumorigenicity of NOG-EGFP mice was significantly better than that of NOD/SCID mice in all of the analyzed cell lines (p < 0.01). Sorting procedures enabled an almost pure collection of cancer cells with only slight contamination by host cells. Reimplantation of the sorted cancer cells formed tumors again, which demonstrated that cell viability after sorting was well maintained.
This method provides a novel cancer sampling system for molecular and cellular analysis with high accuracy and should contribute to the development of personalized medicine.