Polymorphisms in FcγRII (CD32) mediate abnormal antibody half-life in NOD SCID mice and reduce antibody-mediated tumour cell deletion

NOD SCID (NS) mice are commonly used for the assessment of monoclonal antibody (mAb) therapeutics and form the genetic background of NSG mice widely used in human patient derived xenograft models. However, relatively little is known regarding how the NS background effects monoclonal antibody (mAb) pharmacokinetics and how this might influence therapeutic response. To address this we examined mAb half-life and clearance of hCD20 transgenic EμTCL-1 tumours in NS mice following administration of anti-hCD20 hIgG1 mAb and showed mAb half-life to be significantly shorter in NS versus SCID mice, correlating with reduced therapy. Reduced half-life was also seen with mIgG2a but not mIgG1 or hIgG2 isotypes. Additionally, NS mice lacking CD32 or the FcR γ-chain demonstrated this rapid loss was dependent on the expression of CD32 and not activatory FcγRs. Sequencing confirmed the NOD strains carry the rare ly17.1 variant of CD32. Recombinant ly17.1 displayed increased affinity for hIgG1 compared to the more common ly17.2 variant, providing a potential mechanism for its more rapid removal from serum. Importantly, the reduced half-life was dependent on the presence of both SCID and NOD mutations. SCID mice lack endogenous IgG and so we reasoned this might accentuate the effects of the NOD CD32 polymorphic variant. Accordingly, reconstitution of NS mice with physiological levels of mIgG restored normal half-life. These findings highlight the importance of examining mAb pharmacokinetics in complex mouse strains and demonstrate that therapeutic studies in mice on the NS background should be performed in the presence of exogenous IgG.