Macrophage morphology correlates with single-cell diversity and prognosis in colorectal liver metastasis

Abstract

It has long been known that in vitro polarized macrophages differ in morphology. Stemming from a conventional immunohistology observation, we set out to test the hypothesis that morphology of tumor-associated macrophages (TAMs) in colorectal liver metastasis (CLM) represents a correlate of functional diversity with prognostic significance. Density and morphological metrics of TAMs were measured and correlated with clinicopathological variables. While density of TAMs did not correlate with survival of CLM patients, the cell area identified small (S-TAM) and large (L-TAM) macrophages that were associated with 5-yr disease-free survival rates of 27.8% and 0.2%, respectively (P < 0.0001). RNA sequencing of morphologically distinct macrophages identified LXR/RXR as the most enriched pathway in large macrophages, with up-regulation of genes involved in cholesterol metabolism, scavenger receptors, MERTK, and complement. In single-cell analysis of mononuclear phagocytes from CLM tissues, S-TAM and L-TAM signatures were differentially enriched in individual clusters. These results suggest that morphometric characterization can serve as a simple readout of TAM diversity with strong prognostic significance.

Macrophage imaging and subset analysis using single-cell RNA sequencing

“…Aside from abundance, altered TAM distribution in the tumor and neighboring tissue can be predictive of treatment response 201 . Macrophage shape 94 ; 202 and transcriptional phenotype 203 also represent potential pathological parameters that can inform patient stratification or serve as companion markers of surrogate endpoints in clinical trials. Practical, logistic, and economic considerations all are challenges in successfully moving such applications from research into practice.…”

Tissue-Resident and Recruited Macrophages in Primary Tumor and Metastatic Microenvironments: Potential Targets in Cancer Therapy

“…In that study, the authors proposed that differences in cell area delineate resident versus recruited cells such that large macrophages are resident Kupffer cells whereas small macrophages are recruited TAMs. Interestingly, the presence of small macrophages in patient samples was associated with prolonged disease-free survival when compared with patient samples exhibiting a preponderance of large macrophages [93].…”

“…While many of the studies described above point to an inverse relationship between TAM density and prognosis, recent work evaluating morphological characteristics of macrophages in colorectal liver metastasis found cell size to be an indicator of TAM diversity that also tracked with prognosis [93]. In that study, the authors proposed that differences in cell area delineate resident versus recruited cells such that large macrophages are resident Kupffer cells whereas small macrophages are recruited TAMs.…”

Histopathological and Immune Prognostic Factors in Colo-Rectal Liver Metastases

“…These systems are based on the identification of relevant immune features to be combined in the profiling. Recently, macrophage morphology has gained attention, as an additional parameter capturing distinct macrophage populations with prognostic functions [ 66 ]. Immunologists are trained to detect subtle differences in cell morphological features and attribute them to variations in activation states of the cells analyzed, thus using cell morphology as a proxy of their activation.…”

“…This hypothesis has been tested in a recent study on colo-rectal liver metastasis, in which morphology of macrophages has been systematically quantified and correlated to prognosis. Distinct populations of small and large macrophages were identified ( Figure 2 ), with very different transcriptional profiles [ 66 ] and when tested as a prognostic tool, they showed opposite correlation with clinical outcome. Ongoing studies aimed at evaluating macrophage features as prognostic or predictive markers would benefit from digital tools and machine-learning based approaches.…”