SIRPα (Signal-regulatory protein alpha) is a transmembrane protein widely expressed in myeloid cells, stem cells and neurons. Its extracellular part includes 3 Immunoglobulin like domains. SIRPα binds to its ligand CD47 through the variable IgV-like domains. CD47 is also widely expressed in multiple tissue cells. CD47+ cells activate SIRPα on macrophage surface, and such interaction can prevent phagocytosis. Previous studies reveal that the interruption of SIRPα-CD47 interaction substantially inhibits a variety of tumors. SIRPα/CD47 antibodies are considered as the next star immunotherapy following PD1/PD-L1 antibodies.
mRNA Expression Analysis
RT-PCR Analysis of SIRPα mRNA expression. The hSIRPα mRNA, but not mSIRPα mRNA was detectable in splenocytes of the homozygous B-hSIRPα Mice.
Protein Expression Analysis
Abdominal cells from both wild type (WT) C57BL/6 and homozygous B-hSIRPα mice were analyzed by flow cytometry. Mouse SIRPα + cells were detectable in non-T and non-B cells from both WT C57BL/6 and the homozygous B-hSIRPα mice, while human SIRPα+ cells were only detectable in non-T and non-B cells from the homozygous B-hSIRPα mice. This might be resulted from the cross recognition of hSIRPα by anti-mSIRPα antibody.
Human SIRPα mAb Efficacy Evaluation (MC38-hCD47 Cells)
Murine colon cancer MC38-hCD47 cells (without mCD47 cells) were subcutaneously implanted into homozygous B-hSIRPα mice. Mice were grouped when the tumor size was approximately 150±50 mm3 (n=5). Three human SIRPα antibodies differently inhibited tumor growth, confirming that the B-hSIRPα mouse model is a powerful tool for in vivo SIRPα antibody pharmacological efficacy study. (A) Tumor average volume ± SEM, (B) Mice average weight ± SEM.
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