The trifunctional antibody catumaxomab amplifies and shapes tumor-specific immunity when applied to gastric cancer patients in the adjuvant setting.

Background: Patients with gastric cancer benefit from perioperative chemotherapy, however, treatment is toxic and many patients will relapse. The trifunctional antibody catumaxomab targets EpCAM on tumor cells, CD3 on T cells, and the Fcγ-receptor of antigen-presenting cells. While in Europe catumaxomab is approved for treating malignant ascites, it has not been investigated in the perioperative setting and its exact immunological mode of action is unclear.

Methods: In our study, gastric cancer patients received neoadjuvant platinum-based chemotherapy, one intraoperative application of catumaxomab, and 4 postoperative doses of intraperitoneal catumaxomab. Immunomonitoring was performed in 6 patients before surgery, after completion of catumaxomab treatment, and one month later.

Results: Intraperitoneal application of catumaxomab caused an increased expression of activation markers on the patients' T cells. This was accompanied by a transient decrease in numbers of CXCR3(+) effector T cells with a T-helper (Th)-1 phenotype in the peripheral blood. All patients evidenced pre-existing EpCAM-specific CD4(+) and/or CD8(+) T cells. While these cells transiently disappeared from the blood stream after intraperitoneal application of catumaxomab, we detected increased numbers of peripheral EpCAM-specific cells and a modified EpCAM-specific T-cell repertoire 4 weeks after completion of treatment. Finally, catumaxomab also amplified humoral immunity to tumor antigens other than EpCAM.

Conclusions: Our findings suggest that catumaxomab exerts its clinical effects by (1) activating peripheral T cells, (2) redistributing effector T cells from the blood into peripheral tissues, (3) expanding and shaping of the pre-existing EpCAM-specific T-cell repertoire, and (4) spreading of anti-tumor immunity to different tumor antigens.