In addition to the absence of the enzymes LDHA and LDHB (LDH−/−) (Figure 2a) [20], the LDH activity was significantly reduced in both LDH−/− tumor cell lines (Figure 2b), although the expression of the lactate transporter MCT1 remained unaffected by the CRISPR/Cas9-induced LDHA/B double knockout (Figure 2c). Here, LDHB is linked to neoplasm.