CTLA4 and neoplasm: We impose no-flux boundary condition on all the remaining variables:NofluxforN,M,D,Tr,I2,I10,I12,PA,PD,A1,A4,EandSatr=R(t);(23)it is tacitly assumed here that the receptors PD-1 and CTLA-4, and ligands PD-L1 and B7 become active only after the T cells are already inside the tumor.