Our Research
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Novel approaches to block immune evasion mechanisms
See manuscript in Science (30 Mar 2018) MICA and MICB (MICA/B) are expressed by many human cancers due to cellular stress and tag cells for elimination by cytotoxic lymphocytes through NKG2D receptor activation. However, tumors evade this immune recognition pathway through proteolytic shedding of MICA and MICB proteins. We rationally designed antibodies targeting the MICA α3 domain, the site of proteolytic shedding, and found that these antibodies prevented loss of cell surface MICA/B by human cancer cells. These antibodies inhibited tumor growth in multiple fully immuno-competent mouse models and also reduced human melanoma metastases in a humanized mouse model. Anti-tumor immunity was mediated mainly by NK cells through activation of NKG2D and CD16 Fc receptors. This novel approach prevents the loss of important immunostimulatory ligands by human cancers and reactivates antitumor immunity. This project offers opportunities for studying the role of NK cells, innate T cells and CD8 T cells in tumor immunity, and we are advancing this approach to clinical application. de Andrade, L.F., Tay, R.E., Pan, D., Luoma, A.M., Ito, Y., Badrinath, S., Tsoucas, D., Franz, B., May, K.F., Harvey, C.J. and Kobold, S., 2018. Antibody-mediated inhibition of MICA and MICB shedding promotes NK cell–driven tumor immunity. Science, 359(6383), pp.1537-1542. |
MICA antibodies block proteolytic shedding and enable activation of NK cells through the NKG2D and CD16 receptors. This results in potent NK cell-mediated tumor immunity.
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In vivo Discovery of Targets for Cancer Immunotherapy
See manuscript in Nature (Feb 2014)
Recent work has shown that T cells play a central role in controlling tumor growth. Clinical trials have demonstrated that antibodies targeting two inhibitory receptors on the surface of T cells –CTLA-4 and PD-1 – can induce durable responses in a subset of cancer patients despite metastatic spread. We have recently developed a novel approach for in vivo discovery of genes that inhibit T cell function in the tumor microenvironment. In a normal immune response, T cells proliferate extensively following antigen recognition, but this physiological response is severely blunted by multiple immunosuppressive mechanisms in tumor micro-environments. We reasoned that shRNAs targeting critical negative regulators in T cells can restore their proliferative response to tumor antigen recognition.
We infect CD8 T cells with pool shRNA libraries and transfer these T cells into tumor-bearing mice. One week later, T cells are isolated to quantify the representation of shRNAs in tumors and control tissues by deep sequencing. We have discovered a large number of genes that inhibit T cell function in the tumor microenvironment. We now investigate the molecular mechanisms by which these genes constrain T cell function in tumors and use these insights to develop novel T cell-based therapeutic approaches.
See manuscript in Nature (Feb 2014)
Recent work has shown that T cells play a central role in controlling tumor growth. Clinical trials have demonstrated that antibodies targeting two inhibitory receptors on the surface of T cells –CTLA-4 and PD-1 – can induce durable responses in a subset of cancer patients despite metastatic spread. We have recently developed a novel approach for in vivo discovery of genes that inhibit T cell function in the tumor microenvironment. In a normal immune response, T cells proliferate extensively following antigen recognition, but this physiological response is severely blunted by multiple immunosuppressive mechanisms in tumor micro-environments. We reasoned that shRNAs targeting critical negative regulators in T cells can restore their proliferative response to tumor antigen recognition.
We infect CD8 T cells with pool shRNA libraries and transfer these T cells into tumor-bearing mice. One week later, T cells are isolated to quantify the representation of shRNAs in tumors and control tissues by deep sequencing. We have discovered a large number of genes that inhibit T cell function in the tumor microenvironment. We now investigate the molecular mechanisms by which these genes constrain T cell function in tumors and use these insights to develop novel T cell-based therapeutic approaches.
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In vivo shRNA screen for discovery of negative regulators of T cell function in tumors. A. T cells are infected with pooled shRNA libraries in a lentiviral vector and injected into mice bearing B16-Ovamelanomas. B. shRNAs that target key negative regulators enable substantial T cell expansion in tumors in response to tumor antigen recognition. C. Deep sequencing of the shRNA cassette from purified T cells provides a quantitative representation of all shRNAs in the pool across different tissues. shRNAs that enable T cell proliferation in tumors are substantially enriched because the lentiviral vector has integrated into the genome of the T cells.
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Zhou, P., Shaffer, D. R., Alvarez Arias, D. A., Nakazaki, Y., Pos, W., Torres, A. J., Cremasco, V., Dougan, S. K., Cowley, G. S., Elpek, K., Brogdon, J., Lamb, J., Turley, S. J., Ploegh, H. L., Root, D. E., Love, J. C., Dranoff, G., Hacohen, N., Cantor, H., and Wucherpfennig, K. W. (2014) In vivo discovery of immunotherapy targets in the tumour microenvironment, Nature 506, 52-57.
Mechanism of resistance to cancer immunotherapy
See manuscript in Science (Jan 2018)
A genome-scale gRNA library is introduced into a tumor cell line that expresses Cas9. Selection is then performed with tumor-specific T cells compared to control T cells. Depleted gRNAs represent resistance genes because inactivation of these genes results in more effective T cell-mediated cytotoxicity.
See manuscript in Science (Jan 2018)
A genome-scale gRNA library is introduced into a tumor cell line that expresses Cas9. Selection is then performed with tumor-specific T cells compared to control T cells. Depleted gRNAs represent resistance genes because inactivation of these genes results in more effective T cell-mediated cytotoxicity.
Many human cancers are resistant to immunotherapy for reasons that are poorly understood. We have discovered many novel resistance genes in a T cell-based genome-scale CRISPR/Cas9 screen. We discovered a major chromatin regulator that confers resistance, which is the PBAF subtype of the SWI/SNF complex. Inactivation of three genes encoding unique subunits of the PBAF complex (Pbrm1, Arid2 and Brd7) sensitized tumor cells to cytotoxic T cells. Loss of PBAF function increased tumor cell sensitivity to interferon-g, resulting in enhanced secretion of chemokines that recruit effector T cells into the tumor. In a back-to-back paper, clinical colleagues at Dana-Farber demonstrated that inactivating mutations of one of these genes (PBRM1) was significantly associated with better clinical responses to immunotherapy with PD-1/PD-L1 antibodies (Science 2018, 359: 801). In many human cancers, expression of PBRM1 and ARID2 inversely correlates with expression of T cell cytotoxicity genes, and Pbrm1-deficient murine melanomas are more strongly infiltrated by cytotoxic T cells. We are now characterizing other novel genes that we discovered as resistance mechanisms, with the goal of identifying novel therapeutic targets that expand the benefit of cancer immunotherapy.
Pan, D., Kobayashi, A., Jiang, P., de Andrade, L.F., Tay, R.E., Luoma, A., Tsoucas, D., Qiu, X., Lim, K., Rao, P. and Long, H.W., 2018. A major chromatin regulator determines resistance of tumor cells to T cell–mediated killing. Science, p.eaao1710.
Pan, D., Kobayashi, A., Jiang, P., de Andrade, L.F., Tay, R.E., Luoma, A., Tsoucas, D., Qiu, X., Lim, K., Rao, P. and Long, H.W., 2018. A major chromatin regulator determines resistance of tumor cells to T cell–mediated killing. Science, p.eaao1710.