A second generation of C3 humanized rats for preclinical evaluation of human C3 inhibitors.

Complement component 3 (C3) is an attractive therapeutic target for several inflammatory diseases; however, the strict primate specificity of emerging C3 inhibitors mandates the use of nonhuman primates (NHPs) for preclinical evaluation, creating significant ethical and economic barriers. Although we previously developed a human C3 complementary DNA knockin rat, the model was limited by low expression levels of human C3 and an inability to support gene-targeted therapies requiring genomic architecture. To overcome these limitations, we developed a second-generation humanized rat model by introducing the full-length human C3 gene onto a rat C3-deficient background. These rats exhibited significantly increased levels of human C3 in all tissues examined while maintaining normal renal function. We validated the utility of this new model using AMY-101, a clinical-stage, primate-specific C3 inhibitor, demonstrating its suppression of complement-mediated hemolysis both in vivo and in vitro. Notably, this inhibition primarily targeted the alternative pathway while sparing the classical pathway, consistent with the reported C3-bypass phenomenon. This second-generation C3 humanized rat model represents a robust, cost-effective preclinical platform for evaluating diverse human C3-targeted therapeutics, thereby reducing reliance on NHP models.