Diminished CD68+ cancer-associated fibroblasts subset induces Tregs infiltration and predicts poor prognosis of oral squamous cell carcinoma patients

Although cancer-associated fibroblasts (CAFs) are the most crucial stromal cells, characterizing their heterogeneity is far from complete. The authors report a novel subset of CAFs in oral squamous cell carcinoma (OSCC), which positively expressed CD68, the classic marker of macrophages. The spatial and temporal distribution of the CD68+ CAF subset of OSCC (n = 104) was determined by CD68/α-SMA immunohistochemistry of serial sections. The CD68+ α-SMA+ CAF subset was found to be elevated from dysplasia to OSCC. Moreover, although both the tumor center and invasive front harbor an abundant CD68+ CAF subset, patients with low-CD68+ CAFs in the tumor center showed more recurrence after operation and shorter survival time, indicating the different function of CD68+ CAFs in tumor initiation and progression. Functional analysis in the OSCC–CAF co-culture system found knockdown of CD68 did not change the phenotype of CAFs, tumor growth, or migration. Unexpectedly, low-CD68+ CAFs were associated with aberrant immune balance. A high proportion of tumor-supportive Tregs was found in patients with low-CD68+ CAFs. Mechanistically, knockdown of CD68 in CAFs contributed to the up-regulation of chemokine CCL17 and CCL22 of tumor cells to enhance Treg recruitment. Thus, up-regulated CD68+ fibroblasts participate in tumor initiation, but the low-CD68+ CAF subset in OSCC is conducive to Treg recruitment in the tumor microenvironment and contribute to poor prognosis of OSCC patients.