Pericytes within tumour and other angiogenic microenvironments as potential targets for therapeutic viruses

Oncolytic viruses (OVs) were designed to selectively infect and kill tumour cells while simultaneously initiating antitumour immune responses. The mechanisms by which OVs engage anticancer immunity have been proposed to be initiated by infection of both cancer and non-cancer cells within the tumour. Mouse models of tumour growth, Matrigel ® implantation and ex vivo human tissue culture were studied using a mix of in vivo intravital microscopy and high-resolution confocal imaging to track OV delivery and infection. Engineered OV expressing the Cre recombinase allowed for cellular fate mapping post-infection. Application of multiplexed chemokine analysis and single-cell RNA sequencing allowed for study of the host response to OV treatment. Using high resolution in vivo imaging, we found that cancer cells are rarely infected by systemically delivered OVs, whereas perivascular cells with morphology and markers associated with pericytes are consistently infected. Pericyte infection was also observed in other models of vessel perturbation, including wound healing and neoangiogenesis, and in human pericyte cultures and tissue slices. Using genetic fate mapping, single-cell RNA sequencing, and multiplex chemokine analyses, we found that pericytes survive OV infection and mount a potent immune response that includes the secretion of T cell recruiting chemokines such as CXCL9 and CXCL10. Indeed, OV treatment leads to the deposition of CXCL9 on tumour vessels, potentially supporting the recruitment of activated T cells, and CD8 + T cell-dependent tumour regression. The observation that pericytes around perturbed vessels are infectable, may indicate these cells act as virus scavengers and immune sentinels in peripheral tissue experiencing compromised vessel integrity. Moreover, these cells may represent a new target for localized gene therapy directed at damaged or remodeling tissues.