Kaufmann, Scott

Abstract Introduction Checkpoint blockade revolutionized cancer therapy. However, only a small proportion of cancers respond to checkpoint blockade. B7-H3 is a member of the B7 superfamily, which includes both co-inhibitory and co-stimulatory receptors. B7-H3 is upregulated by many tumors which is generally associated with a worse prognosis. However, the exact mechanism by which B7-H3 suppresses the immune response remains elusive. Methods We transfected human HEK293T cells and assessed the binding to recombinant Siglecs via flow cytometry. We generated monoclonal antibody F7 against human B7-H3 and tested its blocking function using B7-H3 transfected HEK293T cells. We examined the extent of degranulation and NK cell-mediated killing on B7-H3 expressing HEK293T cells in vitro, as well as the CART19 cells mediated killing in relapse model of B7-H3 expressing CD19+ leukemia Nalm6 cells NSG mice. Results We demonstrated that sialylated B7-H3 binds to the inhibitory receptor Siglec-9 on immune cells but not to the related protein Siglec-7. A high affinity monoclonal antibody (mAb) F7 against B7-H3 blocks Siglec-9 binding. Functionally, F7 enhances NK cell killing of B7-H3 expressing target cells in vitro. F7 also dramatically enhances CART19 mediated killing of B7-H3 expressing Nalm6 cells in a relapse model in NSG mice in vivo. Conclusion We have now shown for the first time that B7-H3 binds to the inhibitory receptor Siglec-9 and generated a novel monoclonal antibody F7 that target a unique sequence in B7-H3 as compared to other monoclonal antibodies being examined for clinical efficacy. F7 can promote NK cell killing of B7-H3 expressing target cells in vitro and synergize with CART19 to enhance killing of B7-H3 expressing tumor cells in vivo. As B7-H3 is overexpressed in many human cancers, this work is critical toward understanding how B7-H3 mediates immune evasion through Siglec-9 for enhancing anti-tumor immunity. Funding Source R01CA243545-01A1 Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)

ABSTRACTDecay of the HIV reservoir is slowed over time in part by expansion of the pool of HIV-infected cells. This expansion reflects homeostatic proliferation of infected cells by interleukin-7 (IL-7) or antigenic stimulation, as well as new rounds of infection of susceptible target cells. As novel therapies are being developed to accelerate the decay of the latent HIV reservoir, it will be important to identify interventions that prevent expansion and/or repopulation of the latent HIV reservoir. Our previous studies showed that HIV protease cleaves the host protein procaspase 8 to generate Casp8p41, which can bind and activate Bak to induce apoptosis of infected cells. In circumstances where expression of the anti-apoptotic protein BCL2 is high, Casp8p41 instead binds BCL2, and cell death does not occur. This effect can be overcome by treating cells with the clinically approved BCL2 antagonist venetoclax, which prevents Casp8p41 from binding BCL2, thereby allowing Casp8p41 to bind Bak and kill the infected cell. Here we assess whether the events that maintain the HIV reservoir are also antagonized by venetoclax. Using the J-Lat 10.6 model of persistent infection, we demonstrate that proliferation and HIV expression are countered by the use of venetoclax, which causes preferential killing of the HIV-expressing cells. Similarly, during new rounds of infection of primary CD4 T cells, venetoclax causes selective killing of HIV-infected cells, resulting in decreased numbers of HIV DNA-containing cells.IMPORTANCECure of HIV infection requires an intervention that reduces the HIV reservoir size. A variety of approaches are being tested for their ability to impact HIV reservoir size. Even if successful, however, these approaches will need to be combined with additional complementary approaches that prevent replenishment or repopulation of the HIV reservoir. Our previous studies have shown that the FDA-approved BCL2 antagonist venetoclax has a beneficial effect on the HIV reservoir size following HIV reactivation. Here we demonstrate that venetoclax also has a beneficial effect on HIV reservoir size in a model of homeostatic proliferation of HIV as well as in acute spreading infection of HIV in primary CD4 T cells. These results suggest that venetoclax, either alone or in combination with other approaches to reducing HIV reservoir size, is a compound worthy of further study for its effects on HIV reservoir size.