Whether these chemokines also contribute more generally to the phenomenon of oncogene addiction remains to be seen. CD4+ T cells co-ordinate multiple components of both the innate and adaptive immune system [81]. Therefore, the contribution of other immune effectors to the mechanisms

of oncogene addiction is likely. These results are consistent with observations in other murine models of oncogene-induced hepatocellular carcinoma, pancreatic PCI-32765 chemical structure tumour and B cell lymphoma that have implicated innate immune members such as mast cells [66] and macrophages [42] as barriers to tumour growth and facilitators of tumour regression. Notably, the restoration of the p53 tumour suppressor had been shown previously to induce tumour senescence, elicit chemokine expression and induce the activation and recruitment of innate immune cells that contribute to tumour clearance [82]. Thus, the restoration of normal function of a single tumour suppressor or oncogene elicits oncogene addiction through changes in the tumour microenvironment dependent CHIR99021 upon various host immune effectors. The apparent requirement of an intact

host immune system in mediating oncogene addiction underscores the potential role of immune effectors in mediating the efficacy of targeted therapeutics. The kinetics of tumour cell elimination, the degree of tumour elimination, the elimination of minimal residual disease

(MRD) and the duration of a clinical response could all be dictated by the host immune status (Fig. 2). Oncogene inactivation appears to directly antagonize many of the hallmark features of tumorigenesis (Fig. 1b), while the immune system appears to play a fundamental role in contributing not only to how oncogene activation initiates these features, but equally importantly to the reversal of these features upon oncogene inactivation (Fig. 2). Specifically, the ability of the tumour to regulate self-renewal versus cellular senescence and the capacity of the host to regulate the angiogenic state may both be tightly coupled to the ability of CD4+ T cells to regulate other immune effectors and IMP dehydrogenase cytokines (Fig. 2). These mechanisms may also contribute to tumour dormancy [83], the notion that there can be a pause or latency in cancer progression. Future targeted therapeutic strategies could include targeting genes in the senescence pathway through the induction of p53 activity or modulating genes in the cell cycle machinery [84]. Targeted therapeutic strategies that modulate the expression of genes that control angiogenesis are used currently in the clinic with limited success [85], and more effective strategies need to be designed and implemented.