The role of αβ T-cells in spontaneous regression of melanoma tumors in swine.

Using a porcine model, we describe Melanoma-Associated CD4CD8 T-lymphocytes (MATL) in peripheral blood that increase during melanoma regression. These MATL possess the CD4CD8 phenotype and they have their direct counterparts in Tumor Infiltrating Lymphocytes (TIL) isolated from melanoma loci. Both MATL and CD4CD8 TIL have a similar expression of selected markers indicating that they represent effector/memory αβ T-cell subset. Moreover, although TIL also contain CD4CD8 T-cells, only CD4CD8 TIL expand during melanoma regression. Importantly, TIL isolated from different pigs and different melanoma loci among the same pig have similar composition of CD4/CD8 subsets, indicating that the composition of the MATL and TIL compartment is identical. Analysis of sorted cells from regressing pigs revealed a unique MATL subpopulation with mono-specific T-cell receptor that was further analyzed by sequencing. These results indicate that pigs regressing melanomas possess a characteristic population of recirculating T-cells playing a role in tumor control and regression.