Abstract 5186: Human stem cell humanized mouse model for in vivo evaluation of bispecific antibody efficacy and drug-induced cytokine release

Bispecific antibodies have shown several promising advantages over monoclonal antibodies and are emerging as one of the growing cancer immunotherapies. Preclinical in vivo models to assess efficacy and cytokine release associated with immune cell engagement are needed. We have developed a human stem cell (HSC) humanized mouse model for testing efficacy and for quantifying cytokine release in response to bispecific antibody treatment. Here we evaluated an EGFR bispecific T cell engager (BiTE), using EGFR-positive MDA-MB-231 orthotopic breast cancer model in CD34+ HSC humanized NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG™) mice. BiTE treatment for 2 weeks resulted in complete tumor regression when dosing was initiated at an average tumor volume of around 100 mm3. In addition, BiTE treatment for 4 weeks effectively inhibited the tumor growth when dosing mice bearing larger tumors of around 400mm3 in volume. Sixteen hours after the first two doses as compared to PBS control, human cytokines IFN-γ, IL-6, and IL-10 were elevated. Cytokine levels then returned to the baselines following continuous dosing. We observed a similar time course and levels of cytokine release between these two BiTE-treated groups with different tumor sizes. T cell activation in the peripheral blood after the last dose was assessed by flow cytometry analysis. In the BiTE-treated group, T cell percentage decreased, as compared to the PBS control. Both CD4+ and CD8+ T cell subsets showed an increased frequency of CD69+ cells after BiTE treatment. Evaluation of drug efficacy and cytokine release in response to BiTE treatment using PBMC-humanized NSG™ mice with and without MDA-MB-231 tumors are underway and results will be discussed.

Citation Format: Li-Chin Yao, Danying Cai, Roberta Aliperta, Allison Colthart, Werner Meier, Mingshan Cheng, James G. Keck. Human stem cell humanized mouse model for in vivo evaluation of bispecific antibody efficacy and drug-induced cytokine release [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5186.

Preclinical evaluation of efficacy and cytokine release of bispecific T cell engagers in humanized NSG mice

Bispecific T cell engagers (BiTEs) are a growing class of cancer therapy that redirects effector T cells against target-expressing tumors. Mouse models to assess efficacy and cytokine release associated with T cell engagement are needed. JAX humanized NOD scid gamma (Hu-NSG™) mice are engrafted with cord blood-derived CD34+ HSC and have shown robust T cell reconstitution. In this report we evaluated two novel BiTEs, EGFR-CD3 and BCMA-CD3, in Hu-NSG™ mice implanted with MDA-MB-231 human breast cancer cells and NCI-H929 multiple myeloma, respectively. Following the initial dosing, we measured human cytokines and analyzed T cell activation by flow cytometry. Clinical observations and body weight change were also monitored. Treatment with EGFR-CD3 for 2 weeks resulted in complete tumor regression when the dosing was initiated around 100 mm3. 50% of the treated-tumors remained nonpalpable for 10 weeks after dosing ceased. EGFR-CD3 also inhibited tumor growth in mice bearing tumors of ~400 mm3 average in volume. In both cases human IFN-γ, IL-6, and IL-10 levels were elevated from the first dose before returning to the baseline and the frequency of CD69+ cells in T cell subsets increased after the treatment. BCMA-CD3 treatment also induced T cell activation and elevated levels of human IFN-γ, TNF-a, IL-6, and IL-10. NCI-H929 tumor growth inhibition by BCMA-CD3 showed donor to donor variability. We observed that significant growth inhibition in one donor while the other donor did not respond. Together, our Hu-NSG™ platform enables preclinical evaluation of drug efficacy and cytokine release induced by BiTEs and has the potential to be applied to other immunotherapies.

Retargeting of T lymphocytes to PSCA- or PSMA positive prostate cancer cells using the novel modular chimeric antigen receptor platform technology "UniCAR"

New treatment options especially of solid tumors including for metastasized prostate cancer (PCa) are urgently needed. Recent treatments of leukemias with chimeric antigen receptors (CARs) underline their impressive therapeutic potential. However CARs currently applied in the clinics cannot be repeatedly turned on and off potentially leading to severe life threatening side effects. To overcome these problems, we recently described a modular CAR technology termed UniCAR: UniCAR T cells are inert but can be turned on by application of one or multiple target modules (TMs). Here we present preclinical data summarizing the retargeting of UniCAR T cells to PCa cells using TMs directed to prostate stem cell- (PSCA) or/and prostate specific membrane antigen (PSMA). In the presence of the respective TM(s), we see a highly efficient target-specific and target-dependent activation of UniCAR T cells, secretion of pro-inflammatory cytokines, and PCa cell lysis both in vitro and experimental mice.

Retargeting of UniCAR T cells with an in vivo synthesized target module directed against CD19 positive tumor cells

Recent treatments of leukemias with T cells expressing chimeric antigen receptors (CARs) underline their impressive therapeutic potential but also their risk of severe side effects including cytokine release storms and tumor lysis syndrome. In case of cross-reactivities, CAR T cells may also attack healthy tissues. To overcome these limitations, we previously established a switchable CAR platform technology termed UniCAR. UniCARs are not directed against typical tumor-associated antigens (TAAs) but instead against a unique peptide epitope: Fusion of this peptide epitope to a recombinant antibody domain results in a target module (TM). TMs can cross-link UniCAR T cells with tumor cells and thereby lead to their destruction. So far, we constructed TMs with a short half-life. The fast turnover of such a TM allows to rapidly interrupt the treatment in case severe side effects occur. After elimination of most of the tumor cells, however, longer lasting TMs which have not to be applied via continous infusion would be more convenient for the patient. Here we describe and characterize a TM for retargeting UniCAR T cells to CD19 positive tumor cells. Moreover, we show that the TM can efficiently be produced in vivo from producer cells housed in a sponge-like biomimetic cryogel and, thereby, serving as an in vivo TM factory for an extended retargeting of UniCAR T cells to CD19 positive leukemic cells.

Bispecific antibody releasing-mesenchymal stromal cell machinery for retargeting T cells towards acute myeloid leukemia blasts

Bispecific antibodies (bsAbs) engaging T cells are emerging as a promising immunotherapeutic tool for the treatment of hematologic malignancies. Because their low molecular mass, bsAbs have short half-lives. To achieve clinical responses, they have to be infused into patients continously, for a long period of time. As a valid alternative we examined the use of mesenchymal stromal cells (MSCs) as autonomous cellular machines for the constant production of a recently described, fully humanized anti-CD33-anti-CD3 bsAb, which is capable of redirecting human T cells against CD33-expressing leukemic cells. The immortalized human MSC line SCP-1 was genetically modified into expressing bsAb at sufficient amounts to redirect T cells efficiently against CD33 presenting target cells, both in vitro and in an immunodeficient mouse model. Moreover, T cells of patients suffering from acute myeloid leukemia (AML) in blast crisis eliminated autologous leukemic cells in the presence of the bsAb secreting MSCs over time. The immune response against AML cells could be enhanced further by providing T cells an additional co-stimulus via the CD137-CD137 ligand axis through CD137L expression on MSCs. This study demonstrates that MSCs have the potential to be used as cellular production machines for bsAb-based tumor immunotherapy in the future.