Myeloid-derived suppressor cells (MDSC) play a key immunosuppressive role in various types

Integration of PDX models as a preclinical platform for assessment of drug efficacy may allow a higher success-rate in critical end points of clinical benefit.

Purpose Since TLR agonists have been well characterized as DC activators, we hypothesized that the admixture of TLR4 agonist into a cellular vector could improve the anti-tumor response in vivo. Experimental Design GM-CSF secreting whole cell tumor cell vector (GVAX) was formulated with LPS, a TLR4 agonist, and its intratumoral therapeutic efficacy was tested in three different murine models. We utilized immunohistochemistry, FACS, ELISPOT, and in vivo CTL analysis to assess both local innate immune responses within the tumor tissue as well as the downstream generation of anti-tumor T-cell responses. Results Intratumoral treatment of LPS absorbed GVAX showed efficacy in improving an antitumor response in vivo in comparison to GVAX alone. Improved anti-tumor efficacy of this novel admixture was not present in TLR4 signaling impaired mice. In the CT26 model, 40-60% of the mice showed regression of the transplanted tumor. When rechallenged with CT26 tumor cells, these mice proved to be immunized against the tumor. Tumors treated with TLR4 agonist absorbed GVAX showed increased infiltrating CD4 and CD8 T-cells as well as increased numbers of CD86+ cells in the tumor tissue. Draining lymph nodes from the treated mice had enhanced number of activated CD86+, MHCII+, and CD80+ dendritic cells in comparison to GVAX alone and mock treated groups. ELISPOT assay and in vivo CTL assay showed increased numbers of CTLs specific for the AH1 tumor antigen in mice treated with LPS absorbed GVAX. Conclusions TLR4 on APCs in the tumor microenvironment may be targeted using cell-based vectors for improved anti-tumor response in vivo.

The blockade of immune checkpoints is a promising therapeutic avenue for cancer therapy, with durable objective responses observed in patients with a variety of solid tumors. Despite these successes, current animal models do not reliably identify targets with the greatest clinical potential, due in part to differences between human and murine immune systems. Hence, robust preclinical tools to test these drugs directly against human cancers in the context of a human immune system are required. Champions Oncology has now developed the ImmunoGraft, whereby two innovative technologies, the patient-derived xenograft and humanized mice (immunodeficient mice reconstituted with a human immune system), are combined in a single platform. Immune-compromised NOG (PrkdcscidIl2rgtm1Sug) mice were reconstituted (humanized) with human CD34+ cells and twelve weeks after humanization, mature human CD45+ cells comprised close to 50% of the leukocytes detected in the circulation and secondary lymphoid tissues of the now humanized animals. Growth of NSCLC tumors implanted into humanized NOG animals was comparable to those in non-humanized counterparts, and when humanized animals harboring NSCLC tumor implants were treated with ipilimumab, tumor growth was slowed, exhibiting marked regression. Systemic immune activation was observed in humanized mice following treatment with ipilimumab, characterized by robust proliferation of huCD3+ T cells and activated huCD4+ Th1 cells, as well as an increase in tumor-infiltrating huCD8+ cytotoxic T lymphocytes (all relative to vehicle controls). We have developed an innovative new preclinical cancer model, the ImmunoGraft, which will enable novel immunotherapeutic agents to be accurately evaluated for efficacy against virtually any cancer indication that can be engrafted. As a proof-of-concept of the utility of the ImmunoGraft, we demonstrated how effectively ipilimumab restricted the growth of NSCLC implants engrafted in humanized animals. This translational platform is, therefore, more reflective of the human tumor microenvironment (both immune and non-immune cell-based) and is the most clinically-relevant model for screening immune system-targeting therapies, as single agents or in combination with standard-of-care drugs and other immuno-modulators. The ImmunoGraft has strong potential to revolutionize the application of immunotherapy to both personalized oncology and translational drug discovery. Citation Format: Gilson Baia, David Vasquez-Dunddel, Daniel Ciznadija, David Sidransky, Amanda Katz, Keren Paz. A humanized mouse model for translational assessment of targeted immune checkpoint blockade. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5031. doi:10.1158/1538-7445.AM2015-5031