Immunomodulatory Therapy of Solid Tumors : With a Focus on Monoclonal Antibodies

Abstract: Cancer, historically considered a genetic disease, is currently acknowledged to affect the whole body. Our immune system is one key player that can elicit a response against malignant cells but can also promote tumorigenesis. Tumors avoid immune recognition by creating a suppressive microenvironment and inducing tolerance. T-cells are regarded a major effector cell type in tumor immunotherapy. An important ”switch” needed for T-cell activation involves so-called costimulatory and coinhibitory receptors. In this thesis, experimental tumor models were used to investigate the potential of immunomodulatory antibodies to stimulate immune cells and subsequently eliminate tumors.First, systemic antibody blockade of two negative checkpoint regulators (CTLA-4 and PD-1) present on T-cells was evaluated in combination with local CpG therapy or standard BCG treatment. Indeed, this combinatorial therapy with CpG augmented anti-tumor effects with increased levels of tumor-directed T-cells and reduced tumor-infiltrating Tregs.Secondly, as these immunomodulatory antibodies elicit severe side effects in patients, a local low-dose delivery regimen was explored as an alternative to systemic bolus treatment. Our results demonstrated that an approximately seven times lower dose of aCTLA-4, compared to systemic delivery, could eradicate both primary and distant tumors.CD40-expressing APCs are another potential target in antibody-mediated cancer therapy. CD40-stimulated dendritic cells (DCs) have the capability to activate tumor-directed T-cells to kill tumor cells. We next sought to investigate agonistic CD40 antibody efficacy and in vivo biodistribution when delivered locally compared to the equivalent systemic dose. Anti-tumor effects were dependent on CD8+ T-cells, host CD40 expression and the presence of tumor antigen at the injection site. CD40 antibodies were cleared from the circulation and accumulated in lymphoid organs, where, upon repeated aCD40 dosing, target APC populations increased in numbers and upregulated their surface CD40 expression.Lastly, CD40 agonist antibodies were mixed with nanoparticles to enhance their stimulatory properties. B-cells demonstrated increased proliferative capacity and DCs became more activated when exposed to the cocktail. Further, this combination reduced serum levels of pro-inflammatory cytokines compared to plain antibodies.      The results herein advocate further exploratory studies of the delivery of monoclonal antibodies at the tumor site in order to improve anti-tumor effects and reduce toxicity.