Programmed cell-death 1 ligand 1 (PD-L1) is a member of the B7/CD28 family of proteins that control T-cell activation. Many tumors can upregulate expression of PD-L1, inhibiting antitumor T-cell responses and avoiding immune surveillance and elimination. We have identified and characterized MEDI4736, a human IgG1 monoclonal antibody that binds with high affinity and specificity to PD-L1 and is uniquely engineered to prevent antibody-dependent cell-mediated cytotoxicity. In vitro assays demonstrate that MEDI4736 is a potent antagonist of PD-L1 function, blocking interaction with PD-1 and CD80 to overcome inhibition of primary human T-cell activation. In vivo MEDI4736 significantly inhibits the growth of human tumors in a novel xenograft model containing coimplanted human T cells. This activity is entirely dependent on the presence of transplanted T cells, supporting the immunological mechanism of action for MEDI4736. To further determine the utility of PD-L1 blockade, an anti-mouse PD-L1 antibody was investigated in immunocompetent mice. Here, anti-mouse PD-L1 significantly improved survival of mice implanted with CT26 colorectal cancer cells. The antitumor activity of anti-PD-L1 was enhanced by combination with oxaliplatin, which resulted in increased release of HMGB1 within CT26 tumors. Taken together, our results demonstrate that inhibition of PD-L1 function can have potent antitumor activity when used as monotherapy or in combination in preclinical models, and suggest it may be a promising therapeutic approach for the treatment of cancer. MEDI4736 is currently in several clinical trials both alone and in combination with other agents, including anti-CTLA-4, anti-PD-1, and inhibitors of IDO, MEK, BRAF, and EGFR.

MEDI9447 is a human monoclonal antibody that is specific for the ectoenzyme CD73 and currently undergoing Phase I clinical trials. Here we show that MEDI9447 is a potent inhibitor of CD73 ectonucleotidase activity, with wide ranging immune regulatory consequences. MEDI9447 results in relief from adenosine monophosphate (AMP)-mediated lymphocyte suppression in vitro and inhibition of mouse syngeneic tumor growth in vivo. In contrast with other cancer immunotherapy agents such as checkpoint inhibitors or T-cell agonists, MEDI9447 drives changes in both myeloid and lymphoid infiltrating leukocyte populations within the tumor microenvironment of mouse models. Changes include significant alterations in a number of tumor micro-environmental subpopulations including increases in CD8+ effector cells and activated macrophages. Furthermore, these changes correlate directly with responder and non-responder subpopulations within animal studies using syngeneic tumors. Combination data showing additive activity between MEDI9447 and anti-PD-1 antibodies using human cells in vitro and mouse tumor models further demonstrate the potential value of relieving adenosine-mediated immunosuppression. Based on these data, a Phase I study to test the safety, tolerability, and clinical activity of MEDI9447 in cancer patients was initiated (NCT02503774).

Adenoviral vectors used in gene therapy are predominantly derived from adenovirus serotype 5 (Ad5), which infects a broad range of cells. Ad5 cell entry involves interactions with the coxsackie-adenovirus receptor (CAR) and integrins. To assess these receptors in vivo, we mutated amino acid residues in fiber and penton that are involved in receptor interaction and showed that CAR and integrins play a minor role in hepatic transduction but that integrins can influence gene delivery to other tissues. These data suggest that an alternative entry pathway exists for hepatocyte transduction in vivo that is more important than CAR or integrins. In vitro data suggest a role for heparan sulfate glycosaminoglycans (HSG) in adenovirus transduction. The role of the fiber shaft in liver uptake was examined by introducing specific amino acid changes into a putative HSG-binding motif contained within the shaft or by preparing fiber shaft chimeras between Ad5 and Ad35 fibers. Results were obtained that demonstrate that the Ad5 fiber shaft can influence gene transfer both in vitro and to the liver in vivo. These observations indicate that the currently accepted two-step entry pathway, which involves CAR and integrins, described for adenoviral infection in vitro, is not used for hepatic gene transfer in vivo. In contrast, alpha(v) integrins influence gene delivery to the lung, spleen, heart, and kidney. The detargeted vector constructs described here may provide a foundation for the development of targeted adenoviral vectors.

The humanized monoclonal antibody Abegrin TM , currently in phase II trials for treatment of solid tumors, specifically recognizes the integrin A v B 3 . Due to its high expression on mature osteoclasts, angiogenic endothelial cells, and tumor cells, integrin A v B 3 functions in several pathologic processes important to tumor growth and metastasis. Targeting of this integrin with Abegrin TM results in antitumor, antiangiogenic, and antiosteolytic activities. Here, we exploit the species specificity of Abegrin TM to evaluate the effects of direct targeting of tumor cells (independent of targeting of endothelia or osteoclasts). Flow cytometry analysis of human tumor cell lines shows high levels of A v B 3 on many solid tumors, including cancers of the prostate, skin, ovary, kidney, lung, and breast. We also show that tumor growth of A v B 3 -expressing tumor cells is inhibited by Abegrin TM in a dose-dependent manner. We present a novel finding that high-dose administration can actively impair the antitumor activity of Abegrin TM . We also provide evidence that antibody-dependent cellular cytotoxicity contributes to in vitro and in vivo antitumor activity. Finally, it was observed that peak biological activity of Abegrin TM arises at serum levels that are consistent with those achieved in clinical trials. These results support a concept that Abegrin TM can be used to achieve selective targeting of the many tumor cells that express A v B 3 integrin. In combination with the well-established concept that A v B 3 plays a key role in cancer-associated angiogenesis and osteolytic activities, this triad of activity could provide new opportunities for therapeutic targeting of cancer.