A Population of TIM4+FOLR2+ Macrophages Localized in Tertiary Lymphoid Structures Correlates to an Active Immune Infiltrate Across Several Cancer Types

TIM4 has previously been associated with antitumor immu-nity, yet the pattern of expression and the function of this receptor across human cancer tissues remain poorly explored. Here we combined extensive immunolabeling of human tissues with in silico analysis of pan-cancer transcriptomic data sets to explore the clinical significance of TIM4 expression. Our results unveil that TIM4 is expressed on a fraction of cavity macrophages (CATIM4(+)M Phi) of carcinoma patients. Moreover, we uncover a high expression of TIM4 on macrophages of the T-cell zone of the carcinoma-associated tertiary lymphoid structures ((TLS)TIM4(+)M Phi). In silico analysis of a pan-cancer data set revealed a positive correlation between TIM4 expression and markers of B cells, effector CD8(+) T cells, and a 12-chemokine signa-ture defining tertiary lymphoid structure. In addition, (TLS)TIM4(+)M Phi were enriched in cancers displaying microsatellite instability and high CD8(+) T-cell infiltration, confirming their associa-tion with immune-reactive tumors. Both CATIM4(+)M Phi and (TLS)TIM4(+)M Phi express FOLR2, a marker of tissue-resident M Phi. However, CATIM4(+)M Phi had a higher expression of the immu-nosuppressive molecules TREM2, IL10, and TGFI3 as compared with (TLS)TIM4(+)M Phi. By analyzing a scRNA sequence data set of tumor-associated myeloid cells, we identified two TIM4(+)FOLR2(+) clusters coherent with CATIM4(+)M Phi and (TLS)TIM4(+)M Phi. We de-fined specific gene signatures for each subset and found that the CATIM4(+) M Phi signature was associated with worse patient survival. In contrast, (TLS)TIM4(+)M Phi gene signature positively correlates with a better prognosis. Together, these data illustrate that TIM4 marks two distinct macrophage populations with distinct pheno-types and tissue localization and that may have opposing roles in tumor immunity.

Automated summary

This study reveals the expression of TIM4 on cavity macrophages and macrophages of carcinoma-associated tertiary lymphoid structures in cancer patients, indicating their association with immune-reactive tumors. The two distinct macrophage populations marked by TIM4 exhibit differences in the expression of immunosuppressive molecules and patient prognosis.