Palliative? Tumour immunosuppression often correlates with tumour burden, making immunotherapy less effective in patients with advanced disease. a somatic mutation in the cancer and can be common recurrent mutations such as the BRAF CCT007093 V600E mutation or Kirsten rat sarcoma (KRAS) G12D [24]. However, the majority of these shared mutant antigens are poorly immunogenic [16] and with the advance of more widely available next-generation sequencing techniques, it is now clear that tumours express a varied number of neoantigens [25,26]. Higher neoantigen load is associated with increased T-cell infiltration MAP2K2 and improved outcomes [27,28,29]. Importantly, only a small fraction of putative mutated peptides are presented on MHC class I and/or MHC class II, and an even smaller subset of those are immunogenic [30,31]. The beauty of these neoantigens is that they are unique to the individual patient, and CCT007093 pave the way for personalized treatment strategies. Table 1 HER human epidermal growth factor receptor, TERT telomerase reverse transcriptase, PSA prostate specific antigen, MAGE melanoma-associated antigen, BAGE B-melanoma antigen, GAGE G antigen, NY-ESO-1 known as cancer testis antigen, CEA carcinoembryonic antigen, MUC mucin, TPBG trophoblast glycoprotein, HPV human papillomavirus, HBV hepatitis B virus, HHV human herpesvirus, KRAS Kirsten rat CCT007093 sarcoma 3. Antigen Presentation The concept that the body can differentiate between self and nonself tissue earned Macfarlane Burnett the Nobel Prize in 1960 [42] but a further half century of work was required to appreciate the complexity of how tumours coopt the immune system to ensure tolerance (Figure 1). Antigens released by dying cancer cells are ingested by dendritic cells and presented to CD8+ T-cells on MHC class I molecules. In order to induce a potent immune response, the antigen released must be accompanied by the emission of damage-associated molecular patterns (DAMPs) [43,44]. Surface-exposed DAMPs like heat-shock proteins (HSP 70/90), calreticulin (CRT) on cancer cells or secreted DAMPs such as adenosine triphopsphate (ATP), nucleic acids and high mobility group Table 1 protein (HMGB1) interact with respective receptors on DCs and lead to their maturation with upregulation of MHC class II expression [44,45]. Presentation of antigens by professional APC to na?ve T cells requires at least 3 signals: (i) signal 1 which results from the interaction of the MHC/Ag complex with the T cell receptor (TCR) and sends an activating signal to the T cells, (ii) signal 2 which results from the interaction of the B7 molecules (CD80 and CD86) with the CD28 stimulatory receptor expressed on T cells and (iii) signal 3 which results from secretion of cytokines like IL-12 and interferon (INF) / from APC. Il-12 receptors are expressed on natural killer cells (NKs), B and T lymphocytes [46]. Binding of IL-12 leads to activation of the JAK-STAT (Janus kinases and signal transducer and activator of transcription proteins) pathway and thus to transcription of genes for immune cell activation. Il-12 also increases INF- production from NKs and T cells which in turn leads to increased antigen presentation through upregulation of MHC molecules [47]. The combination of these 3 signals is hence essential for the activation of CD4 (through MHC class II) and CD8 (through MHC class I) T cells. Priming CD4+ T-helper cells is necessary to generate effective CTL-mediated anti-tumour responses as well as long-lasting memory CTLs [16,44,48,49,50]. Open in a separate window Figure 1 Key steps required for efficient priming of T cell responses within the cancer immunity cycle. Tumour antigen (yellow) is processed via the immune-proteasome (green) and other components of the antigen processing machinery leading to its expression on MHC class I molecule. Grey crosses indicate nodes at which tumour cells can lose antigen presentation rendering themselves invisible to the immune system. Aside from loss of antigen expression itself, other ways that cancer cells can reduce their ability to present tumour antigen include: (a) alterations/loss of b2-microglobulin resulting in absence of MHC class I impairing target recognition by CD8+ T cells; and (b) impairments of the antigen processing machinery. Loss or ineffective antigen.