Acute myeloid leukemia (AML) is the most common and aggressive acute leukemia found in adults. An estimated 13,000 people develop AML in the United States every year, and 8,800 die from it. Immunotherapy has led to important clinical advances in cancer therapy in recent years due to superior cure rates compared with standard therapy. Here, we propose targeting B7-H3 (CD276), a promising immune checkpoint protein that has been reported to inhibit immune cells function by binding its receptor on natural killer (NK) cells and T lymphocytes. It has been reproted that B7-H3 is overexpressed in several solid tumors and hematological malignancies. However, this protein has not been used as a target in immunotherapy so far, probably due to lack of tools that could inhibit its function. Our preliminary data suggest that B7-H3 is over expressed in paeripheral blood and bone marrow cells collected from AML patients (n=61) at MD Anderson cancer center compared to normal samples (n=10). Inhibition of B7-H3 expression in AML cells activated NK cells-mediated killing of AML cells. To therapeutically target B7-H3 in AML cells, we have generated four monoclonal antibodies that binds B7-H3 with unique specificity and possess immuno-modulatory function. Our preliminary data suggests that addtion of anti-B7-H3 mAbs to AML and NK cell co-cultures, blocked B7-H3 function and enhanced NK cell-mediated killing of AML cells.
In order to develop these antibodies for human trials, we need to generate human comaptible anti-B7-H3 antibodies. To this end, we identified the protein sequences of all four antibodies that binds to B7-H3 protein. We will use these sequences to generate mouse-human chimeric monoclonal antibdoies that could be tested in animal models. We will test these antibodies for their ability to block B7-H3 fucntion and activate NK cells to kill AML cells. We will use these novel anti–B7-H3 chimeric mAbs to inhibit AML growth in humanized NSG mouse models containing human NK cells. We will use AML patient-derived xenograft (PDX) models expressing B7-H3 developed in our laboratory which are ideal for the proposed experiments in animals. We will implant AML-PDX cells in humanized mice and treat them with anti–B7-H3 chimeric mAbs to determine the effect of anti–B7-H3 chimeric antibodies on NK cell–mediated AML cell killing. Next, to understand the mechanism of B7-H3 mediated immunomodulation, we aim to identify its receptor on NK cells. To this end, we have generated recombinant B7-H3 protein that is conjugated with a molecular tag. We will perform protein pull down assays to isolate B7-H3 binding proteins in natural killer cells followed by mass spectrometry to identify the B7-H3 receptor. The objective of this proposal is to develop therapeutic tools to functionally block B7-H3 and enhance immune cell–mediated AML cell killing. We anticipate that the selected recombinant chimeric antibody will be suitable for use in human trials.