Surface Neuritin Expression Primarily Marks a Unique Activated Subpopulation of Regulatory T Cells in The Melanoma Setting
MetadataShow full item record
The uncontrolled proliferation of a somatic cell into a tumor that is capable of invasion and metastases is a complicated process that requires the failure of multiple protective measures that have evolved over millions of years. Over the past several decades, there has been prolific data on the importance of the immune system in deterring the development of a tumor. The heterogeneous population of immune cells are in a constant surveillance for the destruction of potential precancerous cells; however, there exists a suppressive subset of T cells, called regulatory T cells (Tregs), which can undermine immune cells with anti-tumor potential. To date, there is a severe lack of reliable, targetable surface molecules that can be used to antagonize Tregs in the context of cancer; this poses a challenge to clinicians for treating patients with tumors that are highly Treg dependent. Molecules that have been proposed for targeting, such as CD25, are not exclusive to Tregs and targeting them can lead to undesirable off-target effects, such as the depletion of T cells with potential of eradicating tumors. In the search for novel surface molecules, Barbi and Pardoll have discovered a small, glycosylphosphatidylinisotol-anchored protein called Neuritin, on the surface of Tregs. Surface expression of Neuritin on Tregs has characterized these cells as more potent immunosuppressors and Neuritin may emerge as an important immunomodulatory factor, necessary for Treg-mediated suppression. However, understanding Neuritin in the biology of Treg function is a necessary hurdle in order to realize new therapies that exploit this protein for cancer therapeutics. The present study uses flow cytometric analyses in a tumor-bearing mouse model to explore which cells, in addition to Tregs, also express Neuritin. Additionally, Neuritin-expressing Tregs were further scrutinized to determine if the expression of Neuritin could be indicative of changes in naivety, memory, and activation markers. Finally, we documented the effects of acute Neuritin blockade on Treg and non-Treg populations in the context of the highly Treg-dependent, B16F10 tumorbearing mouse models. These experiments reveal the following: 1. in addition to Tregs, there is a very minor percentage of CD8s and CD4+ T conventionals (Tconvs) that are Neuritin+. 2. In all subsets of T cells, Neuritin+ T cells were more likely to express CD44 and CD62L, while Neuritin- T cells were likely to express markers of naivety. 3. Neuritin-expressing T cells also saw increased TCR activity compared to Neuritin- T cells. 4. Upon treating tumor-bearing mice with the α-Neuritin blockade, there was little effect on TCR stimulation, but an appreciable increase in CD44 among nonTreg populations and a decrease in CD44 among Tregs. These data have added a layer of understanding of the role Neuritin plays in the biology of Tregs, including the relationship between the expression of this molecule and activated Tregs. Finally, these findings may benefit further studies aimed at ultimately determining the role this protein plays in Tregs as well as inform future translational studies.