Introduction: Mutations in EGFR correlate with impaired response to immune checkpoint inhibitors and the development of novel immunotherapeutic approaches for EGFR mutant NSCLC is of particular interest. Immunization against epidermal growth factor (EGF) has shown efficacy in a phase III trial including unselected NSCLC patients, but little was known about the mechanisms involved in the effects of the anti-EGF antibodies generated by vaccination (anti-EGF VacAbs) or their activity in tumor cells with EGFR mutations.
Methods: The EGFR-mutant, NSCLC cell lines H1975, and PC9, together with several gefitinib and osimertinib-resistant cells derived from PC9, were treated with anti-EGF VacAbs and/or EGFR tyrosine kinase inhibitors (TKIs). Cell viability was analyzed by proliferation assays, cell cycle by fluorescence-activated cell sorting analysis, and levels of RNA and proteins by quantitative retro-transcription polymerase chain reaction and Western blotting.
Results: Anti-EGF VacAbs generated in rabbits suppressed EGF-induced cell proliferation and cycle progression and inhibited downstream EGFR signaling in EGFR-mutant cells. Sera from patients immunized with an EGF vaccine were also able to block activation of EGFR effectors. In combination, the anti-EGF VacAbs significantly enhanced the antitumor activity of all TKIs tested, suppressed Erk1/2 phosphorylation, blocked the activation of signal transducer and activator of transcription 3 (STAT3) and downregulated the expression of AXL receptor tyrosine kinase (AXL). Finally, anti-EGF VacAbs significantly delayed the emergence in vitro of EGFR TKI resistant clones.
Conclusions: EGFR-mutant patients can derive benefit from immunization against EGF, particularly if combined with EGFR TKIs. A phase I trial of an EGF vaccine in combination with afatinib has been initiated.