Spatially organized multicellular immune hubs in human colorectal cancer

Immune responses to cancer are highly variable, with mismatch repair-deficient (MMRd) tumors exhibiting more anti-tumor immunity than mismatch repair-proficient (MMRp) tumors. To understand the rules governing these varied responses, we transcriptionally profiled 371,223 cells from colorectal tumors and adjacent normal tissues of 28 MMRp and 34 MMRd individuals. Analysis of 88 cell subsets and their 204 associated gene expression programs revealed extensive transcriptional and spatial remodeling across tumors. To discover hubs of interacting malignant and immune cells, we identified expression programs in different cell types that co-varied across tumors from affected individuals and used spatial profiling to localize coordinated programs. We discovered a myeloid cell-attracting hub at the tumor-luminal interface associated with tissue damage and an MMRd-enriched immune hub within the tumor, with activated T cells together with malignant and myeloid cells expressing T cell-attracting chemokines. By identifying interacting cellular programs, we reveal the logic underlying spatially organized immune-malignant cell networks.

Diet-induced obesity causes visceral, but not subcutaneous, lymph node hyperplasia via increases in specific immune cell populations

OBJECTIVES

The spatial proximity of adipose depots to secondary lymph nodes allows a unique relation between the two systems. Obesity, predominately visceral adiposity, links to numerous diseases; hence, we postulate that secondary lymphatics within this region contributes to disease risk.

MATERIAL AND METHODS

Male C57BL/6 mice were fed standard CHOW (18% kcal fat) or Western diet (45% kcal fat) for 7 weeks. Visceral and subcutaneous lymph nodes and associated adipose depots they occupy were excised. Lymph node morphology and resident immune cell populations were characterized via histopathology, immunofluorescence and flow cytometry. Adipose tissue immune cell populations were also characterized.

RESULTS

Obesity caused lymph node expansion, increased viable cell number and deviations in immune cell populations. These alterations were exclusive to visceral lymph nodes. Notably, pro-inflammatory antigen presenting cells and regulatory T cells increased in number in the visceral lymph node. Obesity, however, reduced T regulatory cells in visceral lymph nodes. The visceral adipose depot also had greater reactivity towards HFD than subcutaneous, with a greater percent of macrophages, dendritic and CD8⁺ T cells. Immune cell number, in both the visceral and subcutaneous, however decreased as adipose depots enlarged.

CONCLUSION

Overall, HFD has a greater influence on visceral cavity than the subcutaneous. In the visceral lymph node, but not subcutaneous, HFD-induced obesity decreased cell populations that suppressed immune function while increasing those that regulate/activate immune response.

Inhibition of adipose tissue PPARγ prevents increased adipocyte expansion after lipectomy and exacerbates a glucose-intolerant phenotype

OBJECTIVES

Adipose tissue plays a fundamental role in glucose homeostasis. For example, fat removal (lipectomy, LipX) in lean mice, resulting in a compensatory 50% increase in total fat mass, is associated with significant improvement in glucose tolerance. This study was designed to further examine the link between fat removal, adipose tissue compensation and glucose homeostasis using a peroxisome proliferator-activated receptor γ (PPAR γ; activator of adipogenesis) knockout mouse.

MATERIAL AND METHODS

The study involved PPARγ knockout (FKOγ) or control mice (CON), subdivided into groups that received LipX or Sham surgery. We reasoned that as the ability of adipose tissue to expand in response to LipX would be compromised in FKOγ mice, so would improvements in glucose homeostasis.

RESULTS

In CON mice, LipX increased total adipose depot mass (~60%), adipocyte number (~45%) and changed adipocyte distribution to smaller cells. Glucose tolerance was improved (~30%) in LipX CON mice compared to Shams. In FKOγ mice, LipX did not result in any significant changes in adipose depot mass, adipocyte number or distribution. LipX FKOγ mice were also characterized by reduction of glucose tolerance (~30%) compared to shams.

CONCLUSIONS

Inhibition of adipose tissue PPARγ prevented LipX-induced increases in adipocyte expansion and produced a glucose-intolerant phenotype. These data support the notion that adipose tissue expansion is critical to maintain and/or improvement in glucose homeostasis.