IgE-based cancer immunotherapy
Anti-tumour effect of monoclonal antibodies (mAbs) can be achieved through different mechanisms in which both target engagement with Fab arm and Fc-mediated recruitment of effector immune cells play an important role. As different antibody isotypes bind to different FcRs on immune cells and also differ in their potential to activate the complement system, they can skew the immune reaction towards different effector functions. Therefore, isotype selection can be of critical importance for treatment efficacy. For instance, the IgE isotype has shown superior tumour control to traditionally used IgG in several preclinical models and represents a promising alternative. This thesis offers a further evaluation of IgE therapy in cancer, by exploring different types of target antigens – surface, secreted, and intracellular. In addition, by conducting the experiments in wild-type mice with FcεRI expression limited to MCs and basophils, a particular focus was put on these cell types as less explored IgE effector cells in cancer settings. Firstly, a surface tumour antigen was targeted, and the efficacy of three different antibody isotypes (IgG2a, IgG1 and IgE) was directly compared in a syngeneic mouse tumour model. To this end, anti-Thy1.1 antibodies were used to target subcutaneously transplanted B16-OVA-Thy1.1 cells. The results show that the anti-Thy1.1 antibody with an IgG2a isotype was superior to the IgG1 and the IgE isotype antibodies in controlling tumour growth in this setup. IgE did not show any effect on tumour growth. Since MCs and basophils were mainly localised at tumour edges, we believe there was a poor interaction between them and tumour cells. Thus, targeting a surface tumour antigen does not seem optimal for unleashing IgE downstream effects. Next, the effects of IgE treatment targeting a secreted tumour antigen in combination with OT-1 adoptive cell transfer were studied in the B16-OVA model. Here, two different IgE antibodies targeting a secreted antigen (OVA) were used to achieve effector cell degranulation. My data shows that IgE-induced effects abolished the protective effect of OT-1 cells, suggesting that IgE induces unfavourable changes in the TME. Finally, I studied how the polyclonal immune response raised by immunising mice against an intracellular tumour antigen under type-2 immune skewing conditions affected the tumour development in B16-OVA syngeneic model and in the spontaneous prostate tumour model (TRAMP mice). Although the data are not completely conclusive, there are indications that type-2 immune skewing in combination with CD8+ T cell adoptive cell transfer has protective effects. This finding indicates that type-2 immune skewing made the TME less immune-suppressive, allowing the transferred CD8+ T cells to exert their cytotoxic effect more efficiently. In addition, three manuscripts that resulted from my PhD work are provided in the thesis appendix. First, we published a review article discussing the use of different antibody isotypes for tumour targeting antibodies, checkpoint inhibitors and agonistic antibodies in cancer settings. Second, the method for IgE purification with thiophilic interaction chromatography (TIC) was published. IgE purification is somewhat complicated, as standard methods used for IgG purification cannot be applied to IgE. Described TIC is relatively cheap, gentle in terms of pH and can be used to purify any IgE antibody, irrespective of its specificity or species of origin. Third, we published a manuscript describing the development of the first human IgE bispecific molecules. I developed human IgE bispecific antibodies as a novel format that would combine the increased selectivity of bispecific antibodies with the potent downstream effector function of the IgE isotype. Both knobs-into-holes strategy and leucine zipper mediated molecule pairing resulted in fully functional bispecific IgE molecules. Importantly, bispecific IgE was superior to its bispecific IgG1 homologue in ADCC-mediated in vitro killing of tumour cells. Taken together, the work described here contributes to our current understanding of IgE-mediated effects on tumour growth. Importantly, it focuses on greatly overlooked IgE effector populations in cancer – MCs and basophils, and gives insight on the different effects IgE can mediate through these cell types depending on the localisation of the targeted antigen and the type of exposure. This indicates that IgE based immunotherapy can lead to different outcomes depending on the context. In addition, my thesis offers important tools for further IgE research in terms of simplifying IgE purification and describing the human bispecific IgE formats for the first time.