Systems serology profiling of anti-tumor antibodies in high-grade serous ovarian cancer

Introduction::
In high-grade serous ovarian cancer (HGSOC) patients, malignant epithelial cells arise from the fallopian tube and ovarian surface epitheliums. Endogenous antibodies (anti- tumor antibodies; ATAbs) target these cells and should promote recognition by the immune system. Patient-derived tumors have been found to be frequently coated in IgG, and ATAbs are present both in the tumor mass and in the fluid that builds up in the peritoneum surrounding the tumor microenvironment. They are derived from B cells that have undergone somatic hypermutation, indicating an active immune response. However, despite their widespread abundance in HGSOC, ATAbs fail to eliminate the tumor cells. We hypothesized that ATAbs are unable to eliminate tumors due to the dysregulation of their Fc region. Therefore, we applied a quantitative, multiplexed assay for profiling the Fc properties and immune receptor interactions of ATAbs. Understanding the mechanisms of humoral immunity evasion will help with the prediction of therapeutic responses in cancer patients and uncovering how immunotherapies might reactivate effective humoral immunity.




Materials and Methods::
We profiled ATAb type, subclass, and interactions with Fc receptors across several viral and tumor antigens in HGSOC patient samples. Through autologous tumor cell binding, we selectively pulled out and isolated ATAbs. Our assay utilizes magnetic beads to capture ATAbs by class or by binding to tumor-associated antigens. The Fc properties of ATAbs are then quantified through the use of a panel of tagged detection reagents, including various Fc receptors.




Results, Conclusions, and Discussions:: Our collected data demonstrated that tumor responses were IgG4-biased (Fig. 1B), had a distinct lack of FcγRIIIa interaction despite maintaining FcγRIIa binding (Fig. 1C), and were enriched in Siglec-7 interaction as compared to viral and vaccination responses (Fig. 1D). These results are significant as they indicate that anti-tumor effector responses are blocked. The absence of FcγRIIIa interaction suggests that antibody-dependent cell killing (ADCC) is blocked, likely by glycan changes – antibody fucosylation disrupts FcγRIIIa interaction. Additionally, higher levels of Fc sialylation inhibit several effector cell responses through interaction with glycan receptors like Siglecs. IgG4 also indicates poor ability to drive effector cell responses as the subclass interacts poorly with Fc receptors. Thus, our results indicate several specific mechanisms by which humoral immunity against HGSOC is disrupted by poor effector responses.

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