The word cancer stem cell (CSC) starts 25 years back with the data that CSC is a subpopulation of tumor cells that have renewal ability and can differentiate into several distinct linages. T cell genetic engineering and signaling, CAR T cells in targeting CSCs, and the barriers in using CAR T cells as immunotherapy to treat solid cancers. serum free media (Kang purchase BIBR 953 and Kang, 2007; He et al., 2012; Jiang et al., 2012; Tang et al., 2013; Wang P. et al., 2013). EpCAM is a transmembrane glycoprotein and is involved in cell adhesion as well as cells proliferation, differentiation, migration, signaling, and regeneration (Keller et al., 2019). Several studies have been using EpCAM plus CD44 as a marker for CSCs including CSC found E.coli monoclonal to V5 Tag.Posi Tag is a 45 kDa recombinant protein expressed in E.coli. It contains five different Tags as shown in the figure. It is bacterial lysate supplied in reducing SDS-PAGE loading buffer. It is intended for use as a positive control in western blot experiments in the liver, breast, prostate, colon, and pancreatic cancers (Yamashita et al., 2007; Gires et al., 2009). CD44 CD44 is another common marker to identify CSCs in various cancer types, similar to CD133 and EpCAM. It is transmembrane glycoprotein, however, it has several functions such as a receptor for hyaluronic acid, as well as the ability to be involve in the adhesion, migration, proliferation. and survival of cells (Codd et al., 2018). Unfortunately, as with the abovementioned markers, CD44 is also expressed on healthy cells, making it difficult to be used to specifically differentiate CSCs. However, the ability of CD44 encoding gene purchase BIBR 953 to express multiple isoforms including CD44v, CD44s, and other variants gave the opportunity to identify that CD44v is highly expressed on tumor-capable cells compared to CD44s, while other variants have been identified to be associated with the progression of several cancer types (Mashita et al., 2014; Todaro et al., 2014; Thapa and Wilson, 2016). Furthermore, in head and neck cancer, it was found that tumor cells expressing high levels of CD44 are less immunogenic than CD44lo cells. The latter was associated to the PD-L1 high expression by CD44hi cells (Lee et al., 2016). Targeting CD44 binding domain by IgG1 antibodies during clinical trials showed high level of safety but modest effect in patients. This might be due to the crucial purchase BIBR 953 role that CD44 plays in T cells, in particular T helper (Th) 1 cells, in the proliferation, survival, memory function, and proinflammatory cytokines production (Baaten et al., 2010; Schumann et al., 2015; Menke-van der Houven van Oordt et al., 2016). ALDH Aldehyde dehydrogenase (ALDH) is a superfamily of 19 human isozymes and highly expressed in healthy as well as cancer cells with stem-like characteristics, however, ALDH expression is not limited to stem cells but also can be expressed by mature cells (Fillmore and Kuperwasser, 2008; Xu et al., 2015; Vassalli, 2019). ALDH is an purchase BIBR 953 enzyme that has the ability to oxide varied range of aldehydes, endogenous and exogenous, to their carboxylic acids to provide protection against oxidative stress. Moreover, ALDH have the ability to regulate cellular homeostasis through its role in the biosynthesis of the responsible molecules including retinoic acid (Marchitti et al., 2008; Jackson et al., 2011; Vassalli, 2019). ALDH roles have made it an attractive molecule in studying CSCs; therefore, many reports have identified ALDH as a specific marker for CSCs in several cancers. Moreover, healthy stem cells and CSCs can be differentiated by measuring the catalytic activity of ALDH that can also be used to monitor the prognosis of certain cancer patients (Ginestier et al., 2007; Deng et al., 2010; van den Hoogen et al., 2010; Marcato et al., 2011; Silva et al., 2011; purchase BIBR 953 Singh et al., 2015). With regard to ALDH association with stem cells, most of the focus has been placed on ALDH members that play role in the biosynthesis of retinoic acid via their cytosolic enzyme activity such as ALDH1 (Vassalli, 2019). ALDH1A1 is highly expressed by malignant CSCs in several cancers (Xu et al., 2015). Moreover, CSC uses ALDH to.