The Expression of Indoleamine 2, 3-Dioxygenase in New Zealand Melanoma Cell Lines and Melanoma Infiltrated Lymph Nodes

Abstract

Indoleamine 2,3-dioxygenase, or IDO1, has been identified as another possible immune escape mechanism used by tumours to confer a microenvironment that is immunosuppressive by depletion of the essential amino acid tryptophan and, the production of toxic metabolites. It has been found to cause a decrease in proliferation, confer of anergy, decrease in function and even sensitise to apoptosis of T cells, natural killer cells and B cells; preventing efficacious immunotherapy. Many methods of silencing IDO1 expression such as through 1-MT and siRNA have shown to be of possibility, not as a monotherapeutic cancer drug, but candidates to be used in combination with more conventional chemotherapy agents to greatly impact tumour therapy. As part of a larger program at the ACSRC to develop an IDO inhibitor, this thesis is to determine whether or not melanoma, one of the most prevalent cancers in New Zealand and Australia will be amenable to treatment with IDO1 inhibitors. The expression of the enzymes IDO1 and related enzymes IDO2 and TDO were first investigated in 49 primary tumour derived New Zealand melanoma cell lines, 84% of which whilst showing no constitutive IDO1 and IDO2 expression were able to be induced by IFN-γ. This was comparable to peripheral blood leucocytes of 12 healthy individuals, where upon identical induction 100% of the samples showed IDO1 and IDO2 expression. 13 lymph nodes from eight melanoma patients, of varying disease infiltration were then investigated to gain more clinical understanding. All 13 lymph nodes showed positive IDO1 expression in DAB immunohistochemistry. The enzyme’s presence in both infiltrated and non-infiltrated nodes indicated there were host cells capable of expressing IDO1 and this was investigate further with serial sections of the same lymph nodes by multi-coloured immunofluorescence. Whilst overlap could be seen, presence of IDO1+CD3+ subset were rejected, few IDO1+CD21+ B cells were observed, and IDO1+CD209+ DC cells were also present in large numbers. The presence of IDO1 protein expression in nearly all of the samples used in the experiments of this thesis suggests IDO1 inhibition to be promising as a therapeutic agent to be used in combination with conventional chemotherapy agents.