Rituximab anti-CD20 mAb represents the front-line therapy for several B cell malignancies, and next-generation anti-CD20 mAbs, such as obinutuzumab, are approaching the clinical use. A poorly characterized aspect is the capability of mAb-based therapy to prime long-lasting anti-tumor T cell responses, the so-called "vaccinal effect", that may be highly relevant in mantaining long-term protection. Natural Killer (NK) cell-mediated Antibody Dependent Cellular Cytotoxicity (ADCC), based on the recognition of IgG-opsonized targets by the low affinity receptor for IgG, FcgRIIIA/CD16, represents one of the main mechanism by which therapeutic mAbs mediate their anti-tumor effects. Beside ADCC, CD16 ligation also results in cytokine production. In particular, NK-derived IFN-g is endowed with a well recognized role in the shaping of adaptive immune responses, and may represent a relevant factor in the vaccinal effect promoted by anti-tumor mAbs. Intriguingly, long-lived and highly functional populations of NK cells (dubbed "memory" NK cells) have been recently identified. Notably, such NK subset can be expanded in vitro by antibody-mediated recognition of virus-infected cells.
Our project will characterize the in vivo and in vitro dynamics of "memory" NK cells in response to therapeutic anti-CD20 mAb, and explore the potential of "memory" NK cells to drive anti-tumor adaptive responses.
Objectives:
1. To characterize the in vivo dynamics of "memory" NK cells in patients affected by B-cell chronic lymphocytic leukemia (CLL) and diffuse large B-cell lymphoma (DLBCL), before and after anti-CD20 mAb-based regimens.
2. To characterize the phenotypic and functional profile of in vitro-expanded memory NK cells upon stimulation with rituximab or obinutuzumab anti-CD20 mAb.
3. To analyze the ability of "memory" NK cells to enhance DC maturation and antigen-presenting functions, to support their role in the "vaccinal effect" of therapeutic mAbs.
The in-depth ex vivo and in vitro characterization of the phenotypic and functional profile of memory NK cells in therapeutic mAb-treated patients has several major implications: 1. to elucidate a novel mechanism of NK cell memory generation driven by CD16 (FcgammaRIIIa) in a therapeutic setting; 2. to provide a mechanistic explanation of the ability of NK cells to support the generation of an anti-tumor vaccinal effect in response to mAb treatment; 3. to provide an experimental framework for the rational design of combination therapy protocols aimed at optimising the efficacy of therapeutic mAb, and enhancing the anti-tumor activity of NK cells.
Our project focuses on the two most frequent lymphoproliferative disorders in the western countries, i.e. CLL (the most prevalent adult leukemia) and DLBCL (that accounts for approximately 30% of non Hodgkin Lymphoma cases). Despite the unprecedented success of rituximab anti-CD20 mAb, a proportion of patients still fails to respond to, or more commonly relapses, after receiving rituximab- containing chemoimmunotherapy. Indeed, the promotion of an endogenous long-lasting anti-tumor immune response in mAb-treated patients is becoming a major goal for improving the efficacy of mAb-based therapies. Our results will elucidate the capability of anti-CD20 mAb to generate memory NK cells, and will assess the ability of this cell subset to affect DC maturation and functions. These information will be instrumental for the design of anti-tumor mAb-based therapies able to promote the development of long-term adaptive responses, thus framing therapeutic antibodies in a more global immunotherapeutic approach aimed at strengthening the adaptive anti-tumor immune response developed in cancer patients.
Moreover, our results could lead to a better understanding of the impact of NK cells in the vaccine field in general, by revealing that memory function of NK cells can be exploited in clinical settings to improve the effectiveness of DC-based cancer vaccines.
Further, taking into account that poor in vivo survival and lack of specificity of NK cells have limited their use in adoptive therapy strategies, the definition of the phenotypic and functional profile of a long-lived NK cell population with powerful anti-cancer skills will be instrumental for the better exploitment of NK cells for the ultimate benefit of treating cancer patients.
In conclusion, we strongly believe that the results of this research project will uncover previously unrecognized mechanisms of NK cell plasticity, and provide information with a strong translational potential.