Abstract C221: Glycoengineered anti-EGFR (GA201) elicits enhanced ADCC responses by NK cells from colorectal cancer patients despite tumor-associated impairments to natural cytotoxicity.

Abstract

Abstract Background: One component of the therapeutic efficacy of IgG1 monoclonal antibodies (mAb) is their ability to induce antibody dependent cellular cytotoxicity (ADCC) by NK cells and other immune effectors bearing the low-affinity Fc RIIIa (CD16) receptor. Clinical studies establish the relevance of ADCC finding widespread polymorphisms that encode a very low affinity CD16 (158F/F) predict limited clinical responses to Cetuximab or Rituximab. Now, mAbs with increased affinity for CD16 can be produced using GlycoMab technology. The altered glycosylation pattern in the Fc domain of these antibodies enhances CD16-binding and ADCC irrespective of genotype. Yet, the potential for enhanced ADCC in patients with advanced colorectal carcinoma (CRC) has not been demonstrated. Considering the potential for tumor-associated immune impairments and treatments-associated leukopenia, we enumerated and characterized NK cells from patients prior to chemotherapy, on active therapy, or following two-lines of standard treatment and compared responsiveness to standard and glycoengineered anti-EGFR mAbs. Methodology: PBMCs were isolated from blood of age-matched healthy donors and 100 patients: either at presentation with metastatic disease; during chemotherapy with FOLFOX, FOLFIRI, or Irinotecan; or at disease progression >4 weeks following second line failure. Laboratory tests included: immunophenotyping for CD3,CD8,CD45,CD4 and CD3,CD56/16,CD45,CD19 markers; measurements of CD16- and NKG2D-expressing NK cells; CD16 158 genotype; and assessment of K562-killing (natural cytotoxicity) and degranulation (CD107+) of NK cells among cryopreserved PBMC in response to K562 or EGFR+ A431 cells with 10 g/ml GlycoMAb anti-EGFR (GA201), wild-type GA201, Panitumumab or Cetuximab. Results: For each group of patients, the proportion of NK cells among lymphocytes remained similar to controls. However, NK cells counts were reduced about half in patients (affected primarily by disease and only slightly by treatment). Per NK cell killing capacity of K562 was substantially impaired in patients prior to therapy and most profoundly among the post-chemotherapy group. ADCC responses were similarly impaired but to lesser degrees. In all cohorts tested, GlycoMAb anti-EGFR was superior to cetuximab in activating more NK cells. The superior ADCC activation of NK cells by GlycoMAb was most pronounced in the patients with chemotherapy-resistant disease. Conclusion: Chemotherapy does not induce gross alterations in the immune phenotype of CRC patients. At all stages of treatment, patients retain CD16+ NK cells capable of ADCC. The impairments in the NK functional responses tested are likely due to host/tumor interaction and not a consequence of treatment. Despite impairments, the best activation of NK cells was always in response to GlycoMAb GA201 for all individuals tested. These findings support testing for enhanced ADCC by GA201 in clinical trials of CRC patients following two lines of chemotherapy or in combination with chemotherapy. Acknowledgements: Simon Hollingsworth, current affiliation Astra Zeneca UK Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C221.