13 Exploring Mechanisms of Tumour Lymphangiogenesis to Potentiate Immunotherapies in Melanoma

Introduction Tumour lymphangiogenesis correlates with poor prognosis and metastasis in melanoma and other cancers, yet its functional roles in regulating antitumor immunity have remained largely unexplored. Recently, we showed that despite its pro-metastatic effects, tumour lymphangiogenesis potentiates immunotherapies in melanoma. Here, we sought to further explore mechanisms of potentiation of immunotherapies and develop means to exploit the lymphatic growth factor VEGF-C therapeutically. Material and methods For this study, we used two mouse melanoma models: the injected B16F10 and the BrafV600E-PTEN-/- (±β-CAT-STA) autochthonous models. Lymphangiogenesis was inhibited using VEGFR-3 blocking antibodies, or promoted through either1 viral transduction of B16F10 with VEGF-C or2 intratumoral injections of a matrix-binding form of VEGF-C. Immunotherapies included PD-1 blockade, immune adjuvants (CpG-B and Poly I:C), or adoptive T cell transfer. For mechanistic studies, we used Batf3-/- mice, which lack cross-presenting dendritic cells (DCs) and fail to mount a potent antitumor CD8+ T cell response. Moreover, using gene expression analysis from The Cancer Genome Atlas (TCGA) database, we correlated VEGFC expression with the expression of genes associated with cross-presenting DCs such as BATF3, IRF8 and ZBTB46. Results and discussions In addition to reducing T cell infiltrates, VEGFR3 blockade in both models of melanoma reduced the number of cross-presenting DCs. Moreover, in tumours with low T cell infiltrates (coldtumours), and thus unresponsive to immunotherapies, the intratumoral delivery of matrix-binding VEGF-C increased T cell infiltration and restored the ability to respond to immunotherapies. Lymphangiogenic potentiation of immunotherapies was not observed in Batf3-/- mice, indicating the importance of cross-presenting dendritic cells and subsequent generation of tumor-specific endogenous CD8+ T cells. Finally, in the TCGA database, we found that VEGFC expression correlated with genes associated with cross-presenting DCs in human primary melanomas. Conclusion Our findings indicate that tumour lymphangiogenesis promotes recruitment of T cells and DCs into the microenvironment. By using an engineered variant of VEGF-C, we were able to transform the tumour microenvironment from a cold one to a hot one, thereby restoring responsiveness to immunotherapies. Further studies are needed to further develop this therapeutic approach.