Peril in perishing pericytes

Angiogenesis regulates tumor growth and metastatic dissemination, and developmental alteration of blood vessels in malignant tissues has opened dramatic therapeutic perspectives (1). In the current issue of the Journal, as proof for a novel involvement of vascular cells in cancer spread, Hong and collaborators uncover an indirect a role for pericytes in the control of antitumor immunity (2). Pericytes, aka mural cells, are perivascular cells that ensheath capillaries and microvessels in all tissues, playing essential roles in the development by secretion of proangiogenic factors and physical stabilization of microvascular networks, in addition to regulating blood pressure via contractile properties (3). Hong et al. grew B16 melanomas and Lewis lung carcinoma xenografts in pdgfb ret/ret mice, in which absence of the PDGF-B retention motif causes severe abnormalities in microvessel coverage by pericytes, and observed in these pericyte-deficient tumors a higher frequency—as compared with the same tumors grown in control mice—of myeloid-derived suppressor cells (MDSC), typified as Gr1+ CD11b+ and known to inhibit T-cell–mediated antitumor immunity (4). Interestingly, pericyte-deficient lung carcinomas and melanomas also exhibited larger size and higher propensity to metastasis, respectively. Accordingly, pericyte-deficient tumors displayed lower expression of genes involved in T-cell cytotoxicity …