Engineered Plasma B Cells to Enhance Tumor Immunotherapy against Diffuse Intrinsic Pontine Glioma

The overarching goal of this study is to establish a novel combinatorial immunotherapy not limited to T cells, yet leveraging the early success achieved with CAR T cell therapy against DIPG. Here, we propose to utilize engineered GD2 antibody-producing B cells in combination with B7-H3-targeting CAR T cells. We will employ our B7-H3-targeting CAR T cells that in a completed phase 1 trial (BrainChild-03) demonstrated a median survival of 19.8 month, now leading to a phase 2 trial to further define the clinical benefit of these CAR T cells.

This success supporting further investigation of B7-H3-targeting CAR T cells as a combinatorial treatment regimen. Similarly, work at Stanford University showed GD2 CAR T cell therapy was effective for multiple DIPG patients, including one complete response, rendering GD2 another promising immunotherapy target. However, like with the B7-H3 CAR T cell experience, exceptional responses were observed but were unfortunately not universal. Limited persistence of CAR T cells potentially impairing duration of response was observed in both trials. While co-targeting of B7-H3 and GD2 may be effective, responses could potentially be improved by introducing a complimentary immunotherapeutic with greater persistence. Therefore, we propose to harness engineered GD2 antibody-producing B cells as a targeted cellular therapeutic as B cell longevity and continued antibody production can overcome the limitation of CAR T cell exhaustion and the need for repeated dosing.

Notably, these B cells can be injected intracranially, preventing adverse effects that may arise from systemic administration of GD2 antibodies alone. In partnership with Seattle Children’s James Lab, leaders in B cell engineering, we have designed a targeting strategy for expression of GD2-specific antibodies to engineer GD2 antibody-secreting B cells. To now investigate the efficacy of an engineered B and T cells combination treatment against DIPG, this work will include two central aims:

Firstly, we will characterize the efficacy of GD2 antibody-secreting B cells in DIPG models. We hypothesize that secreted GD2 antibodies will induce tumor-targeted antibody-dependent cellular cytotoxicity and phagocytosis. In vitro, we will perform effector:tumor cell co-culture assays (focusing on macrophages and NK cells) to evaluate GD2 antibody-mediated tumor cell killing. Further, we will assess GD2 antibody function on DIPG tumor cells alone to determine antibody binding, internalization and mechanistic effects. For in vivo studies, we will use our treatment-naïve, biopsy-derived DIPG cell culture models as well as immunocompetent syngeneic models of DIPG to assess B cell activity, immune cell response and tumor burden over time. We will collect whole brain tissue as well as blood plasma from time point and end point mice for following immunohistochemistry and GD2 antibody detection.

Secondly, we will determine the preclinical efficacy of GD2 antibody-secreting B cells in combination with B7- H3-targeting CAR T cells in DIPG. We hypothesize that GD2 antibody-mediated cytotoxicity together with B7- H3-targeting CAR T cell therapy combines two different immunotherapeutic approaches that substantially enhance targeted cellular immunotherapy against DIPG. In vitro, we will determine combinatorial efficacy and assess whether antibody therapy prior to CAR T cell therapy or vice versa provides a more efficacious tumor cell killing strategy. In vivo, we will focus on the immunocompetent syngeneic DIPG model to assess pre-clinical efficacy of our two different immune cell therapy modalities in combination. We will test both GD2 antibody- secreting B cell therapy prior to CAR T cell therapy and CAR T cell therapy followed by B cell injection. B cells and CAR T cells will be injected via the same ICV route into the brains of tumor-bearing mice. Whole brains and blood plasma will be collected at endpoint and survival outcomes measured to evaluate the therapeutic benefit of a combination treatment of B7-H3-targeting CAR T cells and engineered GD2-secreting plasma B cells against DIPG.