C4A and neoplasm: In a comparative study of Atezolizumab and a newly developed C4 anti-PD-L1 antibody, Moroz et al. found that C4 distinguishes PD-L1 positive tumors while maintaining lower background in healthy organs than Atezolizumab in immunocompetent mice (tumor: 13.83 ± 0.5 C4 vs. 13.92 ± 1 Atezolizumab; liver: 7.33 ± 1.1 C4 vs. 6.79 ± 1.6 Atezolizumab; spleen: 6.05 ± 0.2 C4 vs. 19.95 ± 1.5 Atezolizumab; kidney: 2.76 ± 0.8 C4 vs. 6.71 ± 0.3%ID/g Atezolizumab, Table 1) (11, 18).