Efficacy and toxicity evaluation of anti-human CD47 and SIRPa antibodies in genetically humanized B-hSIRPa/hCD47 mice
CD47 is a transmembrane protein expressed ubiquitously on the surface of human cells, including. SIRPa, one of the binding partners of CD47, is a member of the signal-regulatory-protein (SIRP) family which is expressed on many myeloid cells including phagocytic cells. Engagement of SIRPa by CD47 elicits the “do not eat me” signal to prevent phagocytosis of “self” cells by macrophages. Anti-CD47 and anti-SIRPa antibodies that interfere with the CD47-SIRPa interaction have demonstrated promise in clinical trials as new class of therapeutics. Despite such exciting potential, side effects associated with CD47/SIRPa blockade such as anemia may represent a significant toxicity concern. Therefore, evaluation of both efficacy and toxicity of human CD47/SIRPa antibody candidates emerges as one of most actively investigated areas in immuno-oncology in recent years. However, lack of animal models that enable expedient testing of anti-human CD47 or anti-human SIRPa antibodies in vivo has been a limiting factor for CD47/SIRPa antibody development.
To accelerate direct efficacy and toxicity testing of anti-human CD47 and SIRPa antibodies, Biocytogen has generated the double humanized mice, B-hSIRPa/hCD47, where the human extracellular domains of SIRPa and CD47 replace their respective murine counterparts. Homozygous B-hSIRPa/hCD47 mice express humanized but not the wild type mouse SIRPa and CD47. We present here that B-hSIRPa/hCD47 mice were successfully used for screening anti-human CD47 and anti-human SIRPa antibodies for efficacy and toxicity in tumor models of the engineered MC38-hCD47 cell line that expresses human CD47 in MC38 cells. Anti-human CD47 and anti-human SIRPa antibodies were efficacious in controlling MC38-hCD47 tumor growth in B-hSIRPa/hCD47 mice. Varied toxicity profiles were observed in terms of body weight loss, blood cell counts, and blood liver enzyme levels in anti-human CD47 antibody treatments. Further, we also created two triple humanized mouse strains, B-hPD1/hSIRPa/hCD47 and B-hPD-L1/hSIRPa/hCD47, where humanized PD1 and PD-L1 extracellular domains replace their mouse counterparts, respectively, in the B-hSIRPa/hCD47 background. Anti-human PD-1 and anti-human CD47 antibodies showed single agent and combination anti-tumor effect in B-hPD1/hSIRPa/hCD47 mice. So did anti-human PD-L1 and anti-human CD47 antibodies in B-hPD-L1/hSIRPa/hCD47 mice. Taken together, we have validated three double and triple humanized CD47/SIRPa mouse models and demonstrate that these humanized mice are useful tools in facilitating development of therapeutics targeting human CD47/SIRPa.