In addition to glucose and fatty acids, cells also utilize glutamine and leucine amino acids, which play a vital role in Teff's differentiation. CD4+ T cells deprived of glutamine differentiate into Tregs in- vitro condition [67]; however, iTregs show less dependency on amino acids for their energy requirements [68]. Glutamine metabolism involves the influx of glutamine in the TCA-cycle in the form of α-ketoglutarate. This intermediate encourages Th1 cell differentiation by enhancing the expression of the inflammatory transcription factor T-bet [28, 68]. The deletion of neutral-amino-acid transporter genes (Slc7a5 and Slc1a5 (also known as ASCT2) reduce glutamine uptake, glucose metabolism, and overall Teffs differentiation, however, it does not affect the generation of iTregs [69, 70]. These metabolic variances show that Tregs have less dependency on amino acid metabolism for producing energy compared to Teffs.