|dc.description.abstract||Adoptive cell therapy (ACT) with tumour-reactive T cells has been shown to be one of the most effective cancer treatments. However, there are many consensus questions that need to be answered so that ACT can deliver a more effective cancer treatment. By using a murine model of melanoma, we attempt to elucidate several strategies to augment the anti-tumour responses mediated by ACT. The traditional ACT focuses only on using the classical killer cell - CD8 cytotoxic T lymphocyte (CTL). CD4 T helper (Th) cells have been gradually shown to be crucial for enhancing CD8 CTL response and inducing complete tumour regression. However, the difficulties in obtaining adequate numbers of CD4 Th cells with desired phenotype through in vitro expansion limits the application of CD4 Th cells in ACT.
By using mice with transgenic CD4 Th cells, the methodology for antigen-specific expansion of murine CD4 Th1-like cells in tissue culture has been optimised in this study. This optimal cell expansion utilises 1 ng/ml IL-2 and 5 ng/ml IL-7 and the CD4 Th cells were cultured in advanced-DMEM/F12 medium. Greater than 10,000 fold expansion can be generated in 20-day period with this method; and the majority of these cells were found to express an early effector cell phenotype as CD27+/CD28+/CD44+/CD62L-/IL-7Rg+/PD-1-/CTLA-4-. These CD4 Th1-like cells were not generated under the Th1 polarised conditions, but expressed multiple Th1- cytokines and Th cell transcriptional factors. Cytolytic activity was also identified in these CD4 Th1-like cells, suggesting they may be a unique subset of cytotoxic Th cells.
These CD4 Th1-like cells were found to be able to persist in the lymph nodes and spleen of the naïve recipient mice and remained functionally active for at least 30 days, without challenge with the target antigen. In addition, both in vitro expanded CD4 and CD8 CTL were able to persist for at least 150 days in mice challenged with subcutaneous tumours that expressed the target antigens
To investigate the factors associated with the efficacy of ACT, a series of ACT with these in vitro expanded CD4 Th1-like and CD8 CTL, with or without Dacarbazine and VLP-OVA vaccine treatments, was performed in a subcutaneous mouse model of melanoma. The VLP-OVA vaccine is derived from Rabbit Haemorrhagic disease virus (RHDV) Virus-like particles that express Ovalbumin. By themselves, CD4 Th1-like cells were not as good as CD8 CTL in controlling tumour growth. However, co-transfer of CD4 Th1-like cells and CD8 CTL significantly enhanced tumour regression, leading to complete cure in 80% of the mice. A combination of ACT and VLP-OVA vaccine treatment induced similar anti-tumour response to the primary B16-OVA tumour challenge. However, this combination treatments enhanced memory and endogenous immune response to tumour re-challenge with a mixture of B16-OVA and B16-gp33 cells. Addition of the Dacarbazine treatment to the ACT did not enhance immune response to the primary B16-OVA tumour or the generation of an endogenous immune response to the tumour re-challenge with B16-gp33 cells. However, DTIC was found to synergise with VLP-OVA vaccine to delay the growth of B16-OVA tumour.
These data clearly demonstrate the ability of these in vitro expanded CD4 Th1-like cells in enhancing tumour regression mediated by CD8 CTL, and inducing durable memory response to tumour recurrence. Therefore cancer immunotherapies that include targeting of CD4 Th1-like cells are promising for inducing complete, durable anti-tumour rejection.||