RESUMEN
The signal regulatory protein α (SIRPα)/CD47 axis has emerged as an important innate immune checkpoint that enables cancer cell escape from macrophage phagocytosis. SIRPα expression is limited to macrophages, dendritic cells, and neutrophils-cells enriched in the tumor microenvironment. In this study, we present novel anti-SIRP Abs, SIRP-1 and SIRP-2, as an approach to targeting the SIRPα/CD47 axis. Both SIRP-1 and SIRP-2 bind human macrophage SIRPα variants 1 and 2, the most common variants in the human population. SIRP-1 and SIRP-2 are differentiated among reported anti-SIRP Abs in that they induce phagocytosis of solid and hematologic tumor cell lines by human monocyte-derived macrophages as single agents. We demonstrate that SIRP-1 and SIRP-2 disrupt SIRPα/CD47 interaction by two distinct mechanisms: SIRP-1 directly blocks SIRPα/CD47 and induces internalization of SIRPα/Ab complexes that reduce macrophage SIRPα surface levels and SIRP-2 acts via disruption of higher-order SIRPα structures on macrophages. Both SIRP-1 and SIRP-2 engage FcγRII, which is required for single-agent phagocytic activity. Although SIRP-1 and SIRP-2 bind SIRPγ with varying affinity, they show no adverse effects on T cell proliferation. Finally, both Abs also enhance phagocytosis when combined with tumor-opsonizing Abs, including a highly differentiated anti-CD47 Ab, AO-176, currently being evaluated in phase 1 clinical trials, NCT03834948 and NCT04445701 SIRP-1 and SIRP-2 are novel, differentiated SIRP Abs that induce in vitro single-agent and combination phagocytosis and show no adverse effects on T cell functionality. These data support their future development, both as single agents and in combination with other anticancer drugs.
Asunto(s)
Presentación de Antígeno , Antígenos de Diferenciación/inmunología , Antineoplásicos Inmunológicos/inmunología , Macrófagos/inmunología , Proteínas de Neoplasias/inmunología , Neoplasias/inmunología , Fagocitosis , Receptores Inmunológicos/inmunología , Linfocitos T/inmunología , Humanos , Células Jurkat , Células THP-1 , Células U937RESUMEN
Inhibitors of adaptive immune checkpoints have shown promise as cancer treatments. CD47 is an innate immune checkpoint receptor broadly expressed on normal tissues and overexpressed on many tumors. Binding of tumor CD47 to signal regulatory protein alpha (SIRPα) on macrophages and dendritic cells triggers a "don't eat me" signal that inhibits phagocytosis enabling escape of innate immune surveillance. Blocking CD47/SIRPα interaction promotes phagocytosis reducing tumor burden in numerous xenograft and syngeneic animal models. We have developed a next-generation humanized anti-CD47 antibody, AO-176, that not only blocks the CD47/SIRPα interaction to induce tumor cell phagocytosis, but also induces tumor cytotoxicity in hematologic and solid human tumor cell lines, but not normal noncancerous cells, by a cell autonomous mechanism (not ADCC). AO-176 also binds preferentially to tumor versus many normal cell types. In particular, AO-176 binds negligibly to RBCs in contrast to tumor cells, even at high concentrations up to 200 µg/mL and does not agglutinate RBCs up to 1 mg/mL in vitro These properties are expected not only to decrease the antigen sink, but also to minimize on-target clinical adverse effects observed following treatment with other reported RBC-binding anti-CD47 antibodies. When tested in cynomolgus monkeys, AO-176 was well tolerated with no adverse effects. Finally, we show that AO-176 demonstrates dose-dependent antitumor activity in tumor xenograft models. Taken together, the unique properties and antitumor activity of our next-generation anti-CD47 antibody, AO-176, distinguishes it from other CD47/SIRPα axis targeting agents in clinical development.
Asunto(s)
Anticuerpos Monoclonales Humanizados/farmacología , Antígeno CD47/antagonistas & inhibidores , Eritrocitos/metabolismo , Inmunidad Innata/inmunología , Neoplasias/tratamiento farmacológico , Fagocitosis , Receptores Inmunológicos/antagonistas & inhibidores , Animales , Anticuerpos Monoclonales Humanizados/química , Anticuerpos Monoclonales Humanizados/inmunología , Antígenos de Diferenciación/inmunología , Apoptosis , Antígeno CD47/inmunología , Proliferación Celular , Femenino , Humanos , Inmunidad Innata/efectos de los fármacos , Macaca fascicularis , Ratones , Ratones Endogámicos BALB C , Ratones Desnudos , Neoplasias/inmunología , Neoplasias/patología , Receptores Inmunológicos/inmunología , Linfocitos T/efectos de los fármacos , Linfocitos T/inmunología , Células Tumorales Cultivadas , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
CTL based vaccine strategies in the macaque model of AIDS have shown promise in slowing the progression to disease. However, rapid CTL escape viruses can emerge rendering such vaccination useless. We hypothesized that such escape is made more difficult if the immunizing CTL epitope falls within a region of the virus that has a high density of overlapping reading frames which encode several viral proteins. To test this hypothesis, we immunized macaques using a peptide-loaded dendritic cell approach employing epitopes in the second coding exon of SIV Tat which spans reading frames for both Env and Rev. We report here that autologous dendritic cells, loaded with SIV peptides from Tat, Rev, and Env, induced a distinct cellular immune response measurable ex vivo. However, conclusive in vivo control of a challenge inoculation of SIVmac239 was not observed suggesting that CTL epitopes within densely overlapping reading frames are also subject to escape mutations.
Asunto(s)
Células Dendríticas/inmunología , Productos del Gen env/genética , Productos del Gen rev/genética , Productos del Gen tat/genética , Sistemas de Lectura/genética , Virus de la Inmunodeficiencia de los Simios/inmunología , Linfocitos T Citotóxicos/inmunología , Vacunas de Subunidad , Carga Viral , Animales , Recuento de Linfocito CD4 , Cartilla de ADN , Ensayo de Inmunoadsorción Enzimática , Productos del Gen env/química , Productos del Gen env/inmunología , Productos del Gen rev/química , Productos del Gen rev/inmunología , Productos del Gen tat/química , Productos del Gen tat/inmunología , Macaca mulatta , Datos de Secuencia Molecular , Mutación , Fragmentos de Péptidos/inmunología , Reacción en Cadena de la Polimerasa , VacunaciónRESUMEN
GBV-C virus infection has been linked to improved clinical outcome in HIV-1 co-infected individuals. The epidemiology of GBV-C has, thus far, been limited to the gay male, HIV+ population. Here we describe the prevalence of antibodies against GBV-C envelope glycoprotein E2 and GBV-C viremia in an HIV+ inner city population. This study group is predominantly African-American; 41% of the participants are women. The major risk factor for HIV infection is intravenous drug use. Overall, 56% of the study population had evidence of current or past infection with GBV-C. GBV-C exposure was not associated with hepatitis C virus infection. The group of participants, who had GBV-C viremia and anti-E2 antibodies, had high percentage of patients with an undetectable HIV-1 viral load. These data provide increased insight into the prevalence of GBV-C co-infection in the HIV epidemic in this understudied population.