The interplay between anti-CD20 therapeutic antibodies and "memory" Natural Killer cells

Purpose: Our study focuses on the recently described long-lived and highly functional NK cell populations (dubbed memory NK cells), defined by the lack of expression of CD16-associatedFceRIg chain and the ability to produce high amounts of IFNg upon CD16 re-stimulation (1). Particularly relevant are our recent observations demonstrating that the sustained stimulation of NK cells with obinutuzumab (anti-CD20 mAb)-opsonised tumor cells leads to the selective down-regulation of FceRIg chain, along with the priming for enhanced IFNg production (2). Here we want to study the capability of anti-CD20 mAbs to support memory NK cell expansion. Methods: CD56+CD16+CD3-g- (memory) and CD56+CD16+CD3-g+(conventional) NK cells from healthy donors were quantified ex vivo and after 10 day co-culture with anti-CD20 mAb-opsonised CD20+ Raji cells in the presence of IL-2. Two different antiCD20 mAbs, currently employed in the treatment of B cell malignancies were chosen: first generation, reference molecule, rituximab, and next generation, Fc-engineered, obinutuzumab, which shows increased binding affinity to CD16. Results: Almost 55% of healthy donors exhibit a population of memory NK cells, accounting for 5%-70% of total peripheral blood NK cells. We observed that CD56+CD16+CD3- g- (memory) NK cells selectively undergo 2- to 12-fold expansion, upon co-culture with anti-CD20 opsonised targets, with no major differences between different anti-CD20 mAbs; on the opposite, CD56+CD16+CD3-g+ (conventional) NK cell proliferation is not affected by CD16 stimulation. The phenotypic and functional characterization of anti-CD20 mAb-expanded memory NK cells is under investigation. Conclusions: Our data highlight a new aspect of the interplay between therapeutic mAbs and NK cell plasticity, suggesting a potential tool for the clinical exploitment of NK cell effector functions.