Overcoming T cell tolerance to tumour antigens: an evaluation of the role of helper responses.

This project aims to investigate ways of enhancing the immune system such that it is able to eradicate cancerous cells. The strategy we will adopt is to genetically alter immune cells to recognise a molecule on the surface of cancer cells. Once recognised as abnormal, the cancer cell should be targeted for killing.
However, sometimes the distinction between cancerous and normal cells is incomplete. A potential problem with immune therapy, therefore, is that modified immune cells may kill normal cells leading to ‘auto-immune‘ diseases. Conversely, they may either fail to recognise cancer cells or become over-stimulated and stop killing.
We know that there are natural mechanisms which exist to prevent immune cells becoming unresponsive in this way e.g. in the setting of infection. It may be that we can exploit these, much as childhood vaccines have enabled us to boost immunity to common viral infections
We will investigate the functioning of genetically altered immune cells within a mouse model. We will then investigate strategies to improve their recognition and killing of cancer cells with a view to improving future immune therapies for cancer.

Gene transfer of T cell receptors (TCR) specific for tumour-associated antigens (TAA) is a potential therapeutic strategy in patients with leukaemia, since the endogenous T cell repertoire is often depleted of cells with anti-tumour activity. However, since some normal cells also express the same TAA, there is a potential risk of autoimmunity, and conversely, a concern that repetitive stimulation of the transferred cytotoxic T lymphocytes (CTL) may result in the induction of unresponsiveness or tolerance. Tolerance induction was clearly documented in murine models, and possibly also impairs adoptive T cell therapy in humans, as efficient CTL engraftment does not usually correlate with efficient tumour immunity. A better understanding of the mechanisms that impair T cell function in vivo will benefit the development of strategies to improve the efficacy of T cell therapy.
In this project I will use a murine adoptive T cell transfer model to determine the function CTL expressing TCRs specific for a TAA that is widely expressed in normal tissues. The MDM2 oncogene shows increased expression in leukaemia compared to normal cells, and the expression pattern in normal tissues is similar in mice and humans. Using the allo-restricted approach, the host laboratory has isolated high and low avidity murine CTL clones specific for murine MDM2. Recently, the TCRs of these CTL were isolated and their MDM2-specificity was confirmed. In this project I will produce retroviral vectors to generate MDM2-specific CTL that will be used in adoptive T cell transfer experiments. Initially, I will modify the retroviral vector, pMP71, to generate pMP71-TCR -IRES-TCR vectors that incorporate and TCR genes from both high and low avidity MDM2-specific clones. The retroviral vectors will be used to transduce murine T cells, followed by cell sorting to obtain purified CD4+ and CD8+ T cell populations. These T cell populations will be adoptively transferred into syngeneic hosts to monitor T cell expansion, effector differentiation and long-term survival. Specifically, I will test the following working hypothesis:
1. Transfer of MDM2-specific CD8+ T cells to syngeneic hosts expressing MDM2 in normal tissues will induce T cell tolerance
2. Induction of tolerance in transferred CD8+ T cells will be reduced by the provision of CD4+ T cell help and/or enhancement of antigen presentation via vaccination
This project will allow me to gain experience in retroviral gene transfer and T cell biology, which will help me to develop a career related to immunotherapy of haematological malignancies.