Graduation Year

2012

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Biology (Cell Biology, Microbiology, Molecular Biology)

Major Professor

Sheng Wei

Keywords

cytokine therapy, IMiDs, Innate Immunity, NK receptor repertoire, STAT5

Abstract

Natural Killer cells (NK) are critical components of the innate immune system. Often referred to by their morphology, these large granular lymphocytes (LGLs) are bone marrow-derived lymphocytes and can be found throughout the body. NK cells reside in the liver, lymph nodes, spleen, thymus, and mucosal-associated lymphoid tissues (MALT). Importantly, NK cells also circulate throughout the blood where they function as surveyors of the body and are armed to eliminate malignant, infected, damaged, or foreign cells.

NK cells function by a dual receptor system. That is, NK receptors are broadly categorized as inhibitory or activating. It is a fine balance, or lack thereof, that dictates the function of an NK cell. Unlike their T and B cell adaptive counterparts, NK cell receptors (NKR) are germline encoded and do not undergo gene rearrangement. NKRs are expressed in a variegated but overlapping fashion such that different cell subsets in the NK compartment elaborate different combinations of activating and inhibitory NKR. Varying the array of NKRs used by each subset increases the potential specificities of the NK compartment, while retaining tolerance to self. Thus, a diverse and balanced NK cell receptor repertoire (NKRR) is extremely important in order for this lineage to respond to various immunologic challenges and to do so in a normal, effective manner.

As we have previously shown, aberrations in the expression of NKRs or downstream signaling can lead to severe immune deficiency, as observed in SHIP-deficient mice. We also showed that in the absence of SHIP-1, 2B4 becomes highly upregulated, functioning as a dominant inhibitory receptor and rendering the SHIP-1-deficient NK cell unresponsive to complex tumor targets. Traditionally MHC-I inhibitory ligands are largely responsible for the regulation of NK function. However, we show here that 2B4, which mediates MHC-I-independent inhibition, is required for formation of a normal NKRR, NK homeostasis, and effector functions. Moreover, in the absence of 2B4 and SHIP-1, NK cells have improper licensing, or education. In addition to SHIP-1 and 2B4 we show that the nature of the MHC-I ligands also play a significant role in repertoire formation, NK effector functions, and NK cell education.

As described above, NK cells are critical components of the immune system. Understanding how NK cell biology and function are regulated, or affected in the context of pathology is of high significance. NK function is often severely impaired in a diseased state, and more importantly, NK cells are frequently adversely affected by the treatments themselves. Here we sought out to determine the effects of an immunomodulating drug, lenalidomide, on the biology and function of healthy NK cells. Lenalidomide is a unique drug that displays immune enhancing functions yet can be cytotoxic to tumor cells. However, lenalidomide treatment can result in immune suppression and severe cytopenia, and has the ability to impair NK viability. We show here that if used in combination with cytokine treatment (e.g. IL-2 or IL-15), many of these negative affects can be overcome. Furthermore, we show that lenalidomide treatment results in what appears to be an NK activating phenotype with a down-modulation of inhibitory KIRs and upregulation of CD16. Lenalidomide also leads to a sustained and robust activation of STAT5 and consequential increase in perforin and granzyme B. Finally, we find that treatment with lenalidomide in combination with IL-2 or IL-15 enhances the expression of IL-Rβ and IL-2Rγ chains, a presumed mechanism of action, which may provide a positive feedback loop. These findings have important clinical application. We propose that using lenalidomide in combination with IL-15 can augment its immune activating effects, while minimizing unwanted cytopenias.

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