Published: 01 October, 2019 | Volume 3 - Issue 1 | Pages: 023-027
Natural killer (NK) cells, the third population of lymphoid cells, comprise 5%-25% of peripheral blood (PB) lymphocytes and represent the first line of defense against infections and tumors [1-7]. They can be derived from: bone marrow, PB, cryopreserved umbilical cord blood (UCB), human embryonic stem cells (hESCs), induced pluripotent stem cells (iPSCs), and various cell lines such as NK-92 and KHYG-1 . NK cells; which have been divided into cytotoxic, tolerant, and regulatory subsets; are classified into: (1) naïve CD56 bright CD 16 dim CD 3 dim cells, (2) mature CD56 dim CD16 bright CD3 dim cells, and (3) lymphoid tissue-resident CD69+/CXCR6+ NK cells [1,2,8-11]. Although NK cells have been traditionally considered as part of the innate immune system, they have recently been shown to exhibit many of the features associated with adaptive immunity [8,12]. The functions of NK cells which are influenced by several cytokines include: elimination of infected cells, destruction of cancer cells, reducing the incidence of graft versus host disease (GVHD) following hematopoietic stem cell transplantation (HSCT), and regulation of pregnancy outcome [10,11,13].