Class II transactivator expression in melanoma cells facilitates T-cell engulfment

Melanoma cells express high levels of HLA class II, cell surface antigen-presenting proteins, which is an anomalous phenotype among solid tumors. There has never been a satisfying explanation for how this HLA class II-positive phenotype is related to tumor development. Lugini and colleagues demonstrated that melanoma cells have the capacity to engulf T-cells. We considered the possibility that this capacity could be dependent on HLA class II expression.

We co-cultured melanoma and CD4-positive, labeled, Jurkat-C T-cells. The melanoma cells were transformed with an expression vector for CIITA, the obligate HLA class II gene transactivator. We then assayed for the transfer of label to the melanoma cells.

CIITA expression facilitated engulfment of the T-cell material but not material from B-cells.

The results suggest a possible mechanism for HLA class II-positive melanoma cells in blunting an anti-tumor response and suggest a possible target for melanoma therapy.