UC Davis

HIV-1 infection leads to the acquired immunodeficiency syndrome (AIDS). Antibody-dependent cellular phagocytosis (ADCP) by macrophages was found to contribute to HIV-1 clearance. CD47 is a cell-surface marker regulating macrophage phagocytic activity in both cancer and HIV models, providing “don’t eat me” signals preventing phagocytosis. Therefore, it seems reasonable that CD47 blockade (i.e. Hu5F9 anti-CD47 antibody) will enhance macrophage phagocytosis of HIV-1 infected cells. This study investigated whether anti-CD47 antibody treatment of SIV-infected target cells led to their increased phagocytosis by monocyte-derived macrophage (MDM) as compared to SIV-negative cells, suggesting that SIV-infection causes up- regulation of CD47 for immune evasion. We applied Leica confocal microscopy, flow cytometry, as well as EVOS microscopy and imaging system to detect and evaluate the fraction of macrophages containing ingested cells (“phagocytic ratio”) under different treatment conditions. We found that SIVmac251-infected T cells treated with Hu5F9 IgG1 anti-CD47 antibody are efficiently cleared by MDMs via ADCP in vitro. Also, Hu5F9 and related antibodies (e.g., of different subclasses) were useful in supporting phagocytosis of both the latently infected and reactivated J-Lat cells. In addition, Hu5F9 IgG1 could effectively synergize with 10-1074 broadly neutralizing antibody (bNAb) to encourage engulfment of SHIV-AD8-EO infected CD4+ T cells. Similar to previous cancer studies, another cell surface marker called Calreticulin (CRT) was found to interact with CD47 in the setting of HIV infection to provide balance between pro-phagocytosis and anti-phagocytosis. CRT-related mechanisms may be a topic of future investigation, and especially how such mechanisms might be exploited when combined with anti-CD47 treatment in HIV-1 infection. In conclusion, Hu5F9 IgG1 anti-CD47 antibody promotes monocyte-derived macrophage phagocytosis of HIV/SIV infected cells at several infection stages.