Melanoma is the most aggressive form of
skin cancer with an estimated 106,110 newly diagnosed cases in the United States of America in 2021 leading to an approximated 7180
melanoma-induced deaths.
Cancer typically arises from an accumulation of somatic mutations and can be associated with mutagenic or carcinogenic exposure. A key characteristic of
melanoma is the extensive somatic mutation rate of 16.8 mutations/Mb, which is largely attributed to UV exposure. Bearing the highest mutational load, many of them occur in key driver pathways, most commonly the BRAFV600E in the
mitogen-activated protein kinase (MAPK) pathway. This driver mutation is targeted clinically with FDA-approved
therapies using small molecule inhibitors of oncogenic BRAFV600E and
MEK, which has greatly expanded therapeutic intervention following a
melanoma diagnosis. Up until 2011, therapeutic options for metastatic
melanoma were limited, and treatment typically fell under the spectrum of surgery,
radiotherapy, and
chemotherapy.Attributed to the extensive mutation rate, as well as having the highest number of neoepitopes,
melanoma is deemed to be extremely immunogenic. However, despite this highly immunogenic nature,
melanoma is notorious for inducing an immunosuppressive microenvironment which can be relieved by checkpoint inhibitor
therapy. The two molecules currently approved clinically are
ipilimumab and
nivolumab, which target the molecules CTLA-4 and PD-1, respectively.A plethora of immunomodulatory molecules exist, many with redundant functions. Additionally, these molecules are expressed not only by immune cells but also by
tumor cells within the tumor microenvironment.
Tumor profiling of these cell surface checkpoint molecules is necessary to optimize a clinical response. The presence of immunomodulatory molecules in
melanoma, using data from The
Cancer Genome Atlas and validation of expression in two model systems, human
melanoma tissues and patient-derived
melanoma cells, revealed that the expression levels of B and T lymphocyte attenuator (BTLA), TIM1, and CD226, concurrently with the BRAFV600E mutation status, significantly dictated overall survival in
melanoma patients. These molecules, along with
herpesvirus entry mediator (HVEM) and CD160, two molecules that are a part of the HVEM/BTLA/CD160 axis, had a higher expression in human
melanoma tissues when compared to normal skin melanocytes and have unique roles to play in T cell activation. New links are being uncovered between the expression of immunomodulatory molecules and the BRAFV600E genetic lesion in
melanoma. Small molecule inhibitors of the MAPK pathway regulate the surface expression of this multifaceted molecule, making BTLA a promising target for immuno-oncology to be targeted in combination with small molecule inhibitors, potentially alleviating T regulatory cell activation and improving patient prognosis.