This proposal assembles experts in tumor immunotherapy, tumor immunology, melanoma, biostatistics,
pathology and mouse models to address effects of tumor intrinsic PD-L1 signals on melanomagenesis. The
principal mechanism of action of aPD-L1 immunotherapy is thought to be protection of PD-1+ anti-tumor T cells
from negative tumor surface-expressed PD-L1. Paradigm shifting work from our lab has now defined important
immunopathogenic tumor cell-intrinsic PD-L1 signals. It is unreported whether PD-L1 in a given cancer cell of
origin contributes to carcinogenesis. Our published and preliminary data on major tumor cell-intrinsic effects of
tumor PD-L1, illuminated in this grant proposal, suggest that these signals could contribute to carcinogenesis.
We developed a novel mouse melanoma model in which PD-L1 can be deleted in the cancer cell of origin
(melanocyte). Melanomas are induced by either oncogene induction (Nras/Cdkn2a) or oncogene induction plus
DNA damage from UV irradiation. We will use this unique and clinically relevant model to test our overarching
hypothesis that melanocyte-intrinsic PD-L1 signals promote melanomagenesis by enhancing the
oncogenic effects of Nras/Cdkn2a and/or DNA damage. We address this hypothesis in the following aims:
Specific Aim 1: Define cell-intrinsic PD-L1 control of the DNA damage response (DDR) and consequent
effects on the tumor microenvironment (TME). We will induce tumors in our mouse melanoma model via
either tamoxifen-induced oncogene induction or oncogene induction plus DNA damage by UV irradiation. Tumor
cell-intrinsic PD-L1-regulated alterations in DNA repair and subsequent TME effects will be assessed using
Westerns, confocal imaging, RNA-seq, immune analyses, histologic and DNA damage studies. Our novel model
will show how appearance of melanocyte PD-L1 alters DDR and other oncogenic mediators (e.g., mTOR) sculpt
the stroma and immune microenvironment over time during early melanomagenesis. We will also treat
melanoma-bearing mice with aPD-L1 or DDR kinase inhibitors and assess tumor intrinsic PD-L1-signaling
consequence on tumor (e.g., mutational burden) and microenvironment (immune analyses).
Specific Aim 2: Test the hypothesis that PD-L1 promotes initiation of oncogene and/or UV induced
melanomagenesis through cell-intrinsic effects. To distinguish cell-intrinsic versus immune-dependent PD-
L1 signaling consequences on carcinogenesis, melanomas will be induced in mice ± immune cell depletions
with specific antibodies. Mouse experiments will be complemented with human cell studies in vitro by
transfecting Nras, Cdkn2a and other candidate genes into normal human melanocytes to test effects on
tumorigenesis and PD-L1 expression.