MAIT Cells and Multiple Myeloma MAIT cells seem to be modified as quantities and functions in MM, although the data in the literature are sometimes discordant. protective or pathogenic activity in a range of neoplastic diseases. Nonetheless, experimental models and clinical studies have displayed that some unconventional T cells are potential therapeutic targets, as well as prognostic and diagnostic markers. In fact, cell-mediated immune response in tumors K 858 has become the focus in immunotherapy against neoplastic disease. This review concentrates on the present knowledge concerning the function of unconventional T cell units in the antitumor immune response in hematological malignancies, such as acute and chronic leukemia, multiple myeloma, and lymphoproliferative disorders. Moreover, we discuss the possibility that modulating the activity of unconventional T cells could be useful in the treatment of hematological neoplasms, in the prevention of specific conditions (such as graft versus host disease), and in the formulation of an effective anticancer vaccine therapy. The exact knowledge of the role of these cells could represent the prerequisite for the creation of a new form of immunotherapy for hematological neoplasms. Keywords: unconventional T cells, natural killer T cells, innate lymphoid cells, gamma delta T cells, MAIT cells, leukemia, K 858 lymphoma, multiple myeloma, vaccination, immunotherapy 1. Introduction 1.1. General Aspects on Unconventional T Cells In recent years, more attention has been paid to the unconventional T cell subsets and their role in anti-tumor immunity, especially in hematology malignancies, due to new findings on the topic. Unconventional T cells, namely, T cells, MAIT cells, and iNKT cells (invariant natural killer T) as a part of NKT cells, have features of both innate and adaptive immunity that can be summarized in three main points: rapid responses to innate immune cells due to antigen-independent activation thanks to cytokines and ligand acknowledgement; non-classical MHC to innate immune cells; the exhibition of limited T cell antigen receptor (TCR) repertoires, realizing unconventional peptide antigens as a distinctive feature. Depending on the expression of the delta chain variable region segment of their TCR, T cells are unique in subpopulations prevalently found in tissue or in blood. V1-positive cells are the most abundant populace in adult peripheral tissues, including the gut, skin, and liver. V2-positive cells are found mainly in blood, accounting for about 0.5C5% of total CD3+ cells and are usually paired with a V9 chain. Finally, as the non-V2 populace, you will find V3-positive cells accounting for only 0.2% of peripheral CD3+ cells, but their frequency can increase in lupus patients or in cytomegalovirus (CMV) and HIV-infected patients. Over the last few years, alongside V2+ T cells, the subpopulation of V9-unfavorable T cells clonally expands upon CMV contamination and shows effector function [1]. MAIT cells are abundant in humans representing up to 10% of circulating CD3+ T cells in the peripheral blood, but GRF2 they are preferentially localized in tissues and mucosa, representing up to 45% of liver T cells [2]. A minor populace representing only 0.1C1% of human T cells in the blood and liver are natural killer T (NKT) cells. They are divided into two subtypes: type I and type II NKT cells. Type I NKT cells are more commonly referred to as invariant NKT (iNKT) cells because their TCR is composed of an invariant -chain (V-24/J-18 in humans) bound to a limited array of -chains. To date, they represent the more analyzed subtype amongst NKT as the knowledge of type II NKT cells is currently limited given the inaccurate and imprecise methods used to detect them. Different from T cells and unconventional T cells, there are the innate lymphoid cells (ILCs) that develop from common lymphoid progenitor cells (CLPs) but have no rearranged antigen-specific receptors and, in contrast, are enriched on their surface of CD127 (IL-7R) [3]. Classically, they can be K 858 divided into three groups on the basis of the expression of transcriptional factors and cytokines responding differently to several stimulations [4]. So, we distinguish group 1 ILC (ILC1) with Th1-like properties which express transcriptional factor T-bet and respond to IL-12, IL-15, and IL-18 activation. Group 2 ILC (ILC2) can generate Th2-like cytokines under IL-25 and thymic stromal lymphopoietin (TSLP) induction and are characterized by transcriptional factors RoR and GATA3. Group 3 ILC (ILC3) is usually defined by the expression of RORt and AHR-producing IL-22 and/or IL-17 under the activation of IL-23 and/or IL-1. ILC3 can be divided into two subgroups based on their expression of the natural cytotoxicity receptor (NRC) NKp44; indeed, NKp44+ ILC3 is the main producer.