M.Sc Thesis


M.Sc StudentAzoulay Tehila
SubjectThe Role of Natural Killer Cells in Diffuse Large B-cell
Lymphoma (DLBCL)
DepartmentDepartment of Medicine
Supervisors DR. Galit Sarig
DR. Shimrit Ringlshtein
Full Thesis textFull thesis text - English Version


Abstract

Human natural killer (NK) cells are part of the innate and adaptive immune responses, participating in the destruction of virally infected and malignant cells. They achieve this through the induction of direct cytotoxicity as well as secretion of cytokines and chemokines. NK cells can be divided into two subtypes, based on their relative expression of the CD56 surface antigen. While CD56bright NK cells mainly regulate the immune response via cytokine secretion, CD56dim NK cells actively identify and eliminate abnormal cells. The cytotoxicity of NK cells is tightly regulated by the balance between activating and inhibitory signals via a diverse repertoire of surface receptors.

Numerous studies over the last decade have demonstrated the essential role of NK cells in cancer immunosurveillance. Enhanced tumor progression, as well as increased cancer incidence have been observed in patients with inherited and acquired defects in NK cellular cytotoxicity. Based on reports suggesting NK aberrancy in several hematological malignancies, we aimed to characterize these cells in DLBCL patients, addressing their potential effect on disease pathogenesis.

In the first part of the study, the association between bone marrow (BM) NK cell percentage, phenotypic characteristics and clinical parameters were assessed in 148 DLBCL patients. High levels of BM NK cells (>15%) were associated with a favorable progression free survival and overall survival. Furthermore, 98% of the DLBCL cohort exhibited only the CD56dim NK subpopulation, with complete absence of the less mature CD56bright population.

In the second part of the study, peripheral blood (PB) NK-specific receptor distribution and cytotoxic activity were analysed in 26 DLBCL patients compared to 13 healthy controls (HC). Similar to what has been shown in the BM cohort; patient PB NK cells demonstrated lower frequency of the CD56bright subset compared to HC. In addition, phenotypic abnormalities, such as increased expression of the inhibitory receptor NKG2A, decreased expression of the activating receptors NKG2D and CD161, as well as altered expression of the inhibitory Killer-cell immunoglobulin-like receptors CD158a and CD158b were observed in patient NK cells.

NK cell cytotoxic activity was studied after stimulation by the MHC-deficient K562 cell line. Patient NK cells demonstrated a significantly reduced capacity for degranulation as assessed by CD107 staining, attenuated IFNγ and TNFα generations, and impaired direct lysis competence of the K562 target cell line.

We propose that the DLBCL environment, whether through direct contact or through the secretion of cytokines and chemokines, might be responsible for hampering NK cell maturation, resulting in an NK cell with a discordant and compromised receptor repertoire. This is accompanied by impaired effector function and cytotoxicity in PB. The lymphoma-specific mechanisms that could be responsible for affecting NK features in the marrow and secondary lymphoid tissues should be further studied.