Determining the best combination of TLR Agonist and Tumour Peptide for Cancer Vaccination

Abstract

Immunotherapy has revolutionised the treatment of cancer in recent years; significantly improving patient response and long-term survival. Though many immunotherapies focus on increasing the effector function of immune cells, the ability to generate and stimulate new tumour-specific immune cells has become an important topic for patients who do not respond to first line therapy. Previous work in our laboratory identified that intracellularly reversible conjugation of mode antigen ‘Ovalbumin’(OVA) to CpG B adjuvant improves the tumour specific response both in terms of immune cell activation, proliferation, and cytokine release, leading to complete tumour clearance in mice. This year I aimed to repeat this using the clinically significant melanoma antigen ‘gp100’ instead of OVA and to compare the use of CpG B adjuvant to CpG C adjuvant, which stimulates additional cytokine release, in the conjugate vaccine model. Using a combination of reversed phase high performance liquid chromatography (RP-HPLC) and cell culture, conjugates were produced and tested on their ability to activate Dendritic cells, induce their production of pro-inflammatory cytokines and induce T cell response in co-culture. Purification of gp100 conjugates was unsuccessful via RP-HPLC and testing reverted to the OVA model when comparing CpG conjugates. In antigen presenting cells, both conjugates induced similar levels of activation and antigen presentation but had unique cytokine profiles, with both conjugates trending towards higher levels of IL-1β and IL-12p70. Both CpG B-OVA and CpG C-OVA conjugates also induced a strong tumour-specific response with increased CD4+ and CD8+ T cell proliferation and significantly increased CD8+ T cell IFN-γ secretion. With these results in mind, both conjugates appear as strong candidates for therapeutic vaccination trials as either a monotherapy or a combined therapy with Checkpoint Blockade or Adoptive T Cell Therapy. In vivo testing using the CpG C construct is needed to assess its efficacy over CpG B.