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The immune system, which defends the body against a wide array of threats, is gaining a growing role in the fight against cancer. For an immunotherapy to be successful, it needs to overcome intrinsically weak tumour-specific immune responses. There are two broad approaches to achieving this goal: targeting the various arms of the immune system or targeting the cancer and its microenvironment. The experiments discussed in this thesis adopt the second approach. Tumours were transduced with a combination of costimulatory molecules: CD48, CD54, CD70 & CD86, the chemokine CX3CL1 and the cytokines: IFNγ, GM-CSF and IL-12. Transduction of costimulatory molecules enhances priming in-vitro and cause tumour rejection and delayed tumour growth in-vivo. This effect is demonstrated with single costimulatory molecules but is more pronounced when multiple costimulatory molecules are transduced. Addition of the cytokines and chemokine enhanced tumour rejection, and also resulted in partial rejection of contralateral parental tumours. Attempts to enhance anti-tumour memory by fusing IL-2 and IL-15 to their respective receptors are also discussed. Work in a human/mouse chimeric PD-1 mouse model shows that transduction of multiple costimulatory molecules is able to overcome intrinsic anti-PD-1 resistance. Radiation is known to result in upregulation of several costimulatory molecules within tumours or their infiltrating dendritic cells. The experiments presented here suggest that radiation therapy may be useful in overcoming anti-PD-1 therapy resistance. In human trials, approximately three quarters of cancers fail to respond to anti-PD-1 therapies. Understanding and potentially overcoming anti-PD-1 therapy resistance is therefore of great interest.

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The adaptive immune response forms an essential part of the cancer immuno-editing process, whereby nascent malignant cells are detected and destroyed prior to forming tumours. The process is tightly controlled to minimise collateral damage to healthy tissue. One of the mechanisms evolved for this purpose and frequently co-opted by malignant cells is the creation of a microenvironment scarce in essential amino-acids through the use of catabolic enzymes such as Indoleamine 2,3-dioxygenase (IDO) , responsible for the rate-limiting step in tryptophan catabolism. The evolutionary conserved GCN2 and mTORC1 pathways respond to amino-acid starvation by triggering emergency homeostatic response programmes that aim to conserve nutrients by shutting down biosynthetic pathways, slowing cell cycle progression and facilitating autophagy. This research project focuses on elucidating the interaction between IDO activity and these pathways and its implications for the immune-editing process. The role of the mTOR kinase as a regulator of T cell fate following exposure to cognate antigen has recently become apparent. Experiments described herein confirm that in murine and human models of T cell activation exposure to tryptophan starvation results in significant mTORC1 inhibition and a modified phenotype with reduced Tbet expression, altered cytokine secretion profile, greatly impaired proliferative capability and expanded CD4⁺ FoxP3⁺ CD25^high subpopulations. Additional results confirmed that the action of IDO is sufficient to deplete tryptophan from the microenvironment to levels sufficient to depress the mTORC1 axis and trigger GCN2 activity even in tumour cell lines. Lower extracellular tryptophan levels were necessary to perturb these pathways In IDO expressing cell lines, suggesting that compensatory mechanisms allow continued proliferation of malignant cells in the face of conditions that severely impede an anti-cancer immune response. In conclusion, manipulation of the mTORC1 axis via IDO-induced tryptophan depletion is an important tumour immune-escape mechanism that can be a target for cancer immunotherapies.

BACKGROUND: We have recently shown that standard treatments for prostate cancer, specifically hormone therapy (HT) and radiation therapy, induce antigen-specific immune responses in human patients. However, the contribution of these antigen-specific immune responses to clinical outcomes is not known. HYPOTHESIS: HT induces tumour-specific antibody and T cell responses that delay or prevent tumour recurrence. METHODS: We utilized the androgen-dependent Shionogi tumour cell line. Male DD/S mice bearing established Shionogi tumours (~64 mm2) were castrated to induce tumour regression, similar to HT in human prostate cancer patients. Control mice were not castrated. Mice were monitored for tumour recurrence. Tumour-specific antibody responses were measured by immunoblot, and T cell responses by ELISPOT and immunohistochemistry. Tumour-specific antigens were identified by serological screening of a cDNA expression library (SEREX). RESULTS: Following castration, 32/33 mice experienced complete tumour regression, while the remaining mouse experienced partial tumour regression. Of the 32 mice that underwent complete regression, 72% (23/32) experienced tumour recurrence 3-70 days post-castration, while the remaining 28% (9/32) remained tumour-free for the duration of the experiment until they were sacrificed for analysis (64-86 days post-castration). Shionogi tumours became heavily infiltrated by CD3+ T cells between 7-14 days post-castration, after which T cell infiltrates became progressively more sparse. Castration induced antibody responses to one or more tumour proteins in approximately one third of mice with an average latency of 21 days. The most common antibody response was against poly(A) binding protein, nuclear 1 (PABPN1). Interestingly, 71% (17/24) of mice with recurrent tumours had an antibody response against PABPN1, whereas only 11% (1/9) of mice that remained tumour-free had a PABPN1-specific antibody response. Put another way, the mean tumour-free interval for those mice that had a PABPN1 antibody response was approximately 25 days compared to approximately 63 days for those mice that did not have a PABPN1 antibody response. However, we found a moderate correlation between the timing of the PABPN1-specific antibody response and growth rate of the recurrent tumour, such that if a mouse had a PABPN1-specific antibody response that occurred shortly after castration, it was more likely to have a slower growing recurrent tumour. IFN-γ ELISPOT assays revealed that castration also induced a PABPN1-specific T cell response that persisted for the duration of the experiment (up to 92 days post-castration). Unexpectedly, this T cell response was exceedingly stronger in recurrent mice versus non-recurrent mice and was accompanied by splenomegaly in recurrent mice. Anti-CD3 staining of the recurrent tumours showed that the CD3+ T cells were confined to the periphery and stroma of the tumours. CONCLUSIONS: In the androgen-dependent murine Shionogi carcinoma model, HT induces robust antibody and T cell responses to PABPN1 that are associated with unfavourable outcomes. To determine why those mice that do not have PABPN1-specific antibody and T cell responses have better outcomes, we will further delineate the T cell response with respect to CD4+ versus CD8+ subpopulations. Additionally, we will investigate the use of immunomodulatory agents to amplify host CD8+ T cell responses and thereby improve the therapeutic effects of HT.

The incidence of colorectal cancer (CRC) is increasing and the prognosis for patients with advanced or metastatic disease is relatively poor. Immunotherapies hold great promise, but deploying them effectively in CRC patients will require further knowledge of the complex cellular and molecular interactions that occur between intestinal tumours and the host immune system. The objective of this study is to understand the mechanisms by which lack of immune cell regulation in the gut can drive the formation of colon adenocarcinomas. In addition, this work aims to identify new mechanisms involved in progression to metastatic disease. Using mouse model systems, we found that aberrant activity of Treg cells deficient in IL-10 can promote inflammation-driven CRC. IL-10 deficient Tregs have increased capacity to drive tumourigenesis compared to their CD4⁺ effector T cell counterparts. RNA sequencing revealed specific upregulation of several genes, including a newly-described cytokine, in tumour-promoting Tregs. We explored cytokine regulation and the tumour microenvironment, and show that the inflammatory cytokine IL-6 and TGFÎ2 are necessary for tumour formation in this model. Moreover, disease is associated with a marked stromal cell signature that is induced as a consequence of Treg deficiency in IL-10 production. Gp38⁺ stromal cells are dominant producers of IL-6, and potent ECM modellers. Furthermore, tumours driven by IL-10 deficient Tregs express high amounts of the pro-mesenchymal transcription factor Sox4. Using combined in vitro and in vivo analyses, we confirm that Sox4 is involved in tumour growth and characterise its expression in CRC patients. Collectively, our findings suggest that Tregs and stromal cells act together to foster a microenvironment that promotes disease progression, notably through the expression of Sox4 in tumour cells. These findings open an exciting avenue to explore the phenotype of tumour-promoting Tregs and to study Sox4 function in metastatic disease.

<p>The most important prognostic factor in breast cancer is the axillary lymph node status. The sentinel node biopsy (SNB) is reported to stage the axilla with an accuracy > 95 % in early breast cancer. Tumour-related perturbation of T-cell function has been observed in patients with malignancies, including breast cancer. The down-regulation of the important T-cell activation molecules CD3-ζ and CD28 may cause T-cell dysfunction, anergy, tolerance and deletion.</p><p>The expression of CD3-ζ and CD28 was evaluated in 25 sentinel node biopsies. The most pronounced down-regulation was seen in the paracortical area, where the best agreement between both parameters was observed. CD28 expression was significantly more suppressed in CD4+ than in CD8+ T-cells.</p><p>From the Swedish sentinel node database, 109 patients with breast cancer > 3 cm planned for both SNB and a subsequent axillary dissection were identified. The false negative rate (FNR) was 12.5%. Thirteen cases of tumour multifocality were detected on postoperative pathology. The FNR in this subgroup was higher (30.8%) than in patients with unifocal disease (7.8%; P = 0.012).</p><p>From the Swedish SNB multicentre cohort trial, 2246 sentinel node-negative patients who had not undergone further axillary surgery were selected for analysis. After a median follow-up time of 37 months (range 0-75), 13 isolated axillary recurrences (13/2246; 0.6%) were found. In another 14 cases, local or distant failure preceded or coincided with axillary relapse (27/2246; 1.2%). </p><p>In conclusion, the immunological analysis of the sentinel node might provide valuable prognostic information and aid selection of patients for immunotherapy. SNB is encouraged in breast cancer larger than 3 cm, if no multifocal growth pattern is present. The axillary recurrence rate after a negative SNB in Sweden is in accordance with international figures. However, a longer follow-up is mandatory before the true failure rate of the SNB can be determined.</p>

The most important prognostic factor in breast cancer is the axillary lymph node status. The sentinel node biopsy (SNB) is reported to stage the axilla with an accuracy &gt; 95 % in early breast cancer. Tumour-related perturbation of T-cell function has been observed in patients with malignancies, including breast cancer. The down-regulation of the important T-cell activation molecules CD3-ζ and CD28 may cause T-cell dysfunction, anergy, tolerance and deletion. The expression of CD3-ζ and CD28 was evaluated in 25 sentinel node biopsies. The most pronounced down-regulation was seen in the paracortical area, where the best agreement between both parameters was observed. CD28 expression was significantly more suppressed in CD4+ than in CD8+ T-cells. From the Swedish sentinel node database, 109 patients with breast cancer &gt; 3 cm planned for both SNB and a subsequent axillary dissection were identified. The false negative rate (FNR) was 12.5%. Thirteen cases of tumour multifocality were detected on postoperative pathology. The FNR in this subgroup was higher (30.8%) than in patients with unifocal disease (7.8%; P = 0.012). From the Swedish SNB multicentre cohort trial, 2246 sentinel node-negative patients who had not undergone further axillary surgery were selected for analysis. After a median follow-up time of 37 months (range 0-75), 13 isolated axillary recurrences (13/2246; 0.6%) were found. In another 14 cases, local or distant failure preceded or coincided with axillary relapse (27/2246; 1.2%). In conclusion, the immunological analysis of the sentinel node might provide valuable prognostic information and aid selection of patients for immunotherapy. SNB is encouraged in breast cancer larger than 3 cm, if no multifocal growth pattern is present. The axillary recurrence rate after a negative SNB in Sweden is in accordance with international figures. However, a longer follow-up is mandatory before the true failure rate of the SNB can be determined.

[Truncated abstract] A paradox exists in tumour immunology whereby progressive tumour growth exists in parallel with an anti-tumour T cell response. This defective T cell response is thought to result from the induction of T cell tolerance and/or tumour induced immunosuppression, which act to inhibit the activation, differentiation and function of tumour-specific CD8+ T cells. Dendritic cells (DCs) are professional antigen presenting cells (APCs) that are critical to the generation of effective CTL; however their function and phenotype is often defective or altered in tumour-bearing hosts, which may limit their capacity to mount an effective tumour specific T cell response. In this thesis, the role of DCs in the cross-presentation of tumour antigen was assessed in terms of their APC function, migration and location. In doing so the intention was to gain insight into the early processes that potentially contribute to the development of an ineffective anti-tumour immune response. This study examined cross-presentation of the nominal tumour antigen, influenza A hemagglutinin (HA) expressed by the murine malignant mesothelioma cell line, AB1-HA. Cross-presentation was predominantly restricted to the local draining lymph nodes throughout tumour growth and was mediated by CD8a+ and CD8a- DCs. This results in an ineffective CTL response due to the lack of DC activation and the presence of potentially immunosuppressive B7 molecules. However, the capacity of the CD8a- DC subset to cross-present antigen suggested a role for migratory tumour-resident DCs in this process. Analysis of tumour infiltrating DCs showed that they were paralysed in their capacity to cross-present tumour antigen and were immobilised at the tumour site. Conversely, cross-presentation of tumour antigen in the local draining lymph node was dependent on the continuous traffic of antigen from the tumour microenvironment. In this vein, small numbers of metastatic tumour cells were detected in the draining lymph nodes, however their isolation was dependent on the removal of DCs and T cells, suggesting immune control of metastatic spread. Thus, tumour cells may be the source of antigen for cross-presentation by DCs in the tumour draining lymph nodes. .... In conclusion, the results presented in this thesis support a role for DCs in the generation of tumour-specific T cell responses that fail to control tumour growth. In addition the results provide a basis for further investigation into the effects of chemotherapy on the source and form of tumour antigen for cross-presentation by specific DC subsets in the tumour bearing host. These findings may have important implications for the development of future anti-cancer immune therapies targeting DCs.