The demand for bispecific antibody contructs (bispecifics) in the world of immunotherapy development is continuously increasing. The two commercially available bispecific antibody therapies had combined sales of just under $1 billion in 2018, and between June and September of 2019, two companies alone raised $136 million to further the development of their own bispecifics. Currently, there are about 271 bispecific antibody-based products in research and development and over 120 clinical trials at various stages involving bispecific antibody therapies, as shown in the above figure.
Bispecifics have two distinct binding specificities in their variable regions. By binding to both T cells and tumor cells, bispecifics can help endogenous T cells recognize and selectively kill cancer cells. CD19/CD3 bispecific T cell engager antibody constructs have been shown to induce high response rates and durable complete remission in patients with minimal residual disease in r/r B-ALL.1 In this case, the bispecific antibody engages CD3 positive T cells directly with CD19 positive malignant B-cells and attacks the tumor cells.5
Despite clinical success in treating hematologic malignancies and promising outcomes in solid tumors, it remains challenging to precisely characterize response differences in patients post introduction of bispecifics, and therefore it remains difficult to improve treatment efficacy and minimize side effects.2
Since this T cell engagement strategy shares many similarities with CAR-T therapies in terms of tumor targeting, polyclonal T cell activation, killing mechanisms through perforin and granzyme, and cytokine-based toxicities like cytokine release syndrome, better tools and markers to measure protein secretions in a more sensitive fashion are needed to reveal the underlying mechanisms of both types of therapies.3
IsoPlexis has previously revealed cytokine-based biomarkers by utilizing the Polyfunctional Strength Index (PSITM), which can objectively evaluate the quality of anti-tumor activity of CAR-T response in patients pre-therapy. IsoPlexis’ systems were able to correlate polyfunctional cytokine secreting CAR-T cells to patient outcome.4 Utilizing the PSI may help researchers better understand how T cells functionally respond to bispecifics engagement as well. PSI can also potentially reveal predictive biomarkers and mechanistic insights, which can significantly improve the procedure for choosing bispecifics for introduction into the clinic.
Applying Polyfunctional T Cell Responses to Pre-Clinical Bispecifics to Improve Potency and Solid Tumor Targeting
IsoPlexis’ system identifies the potent single cells that secrete multiple cytokines simultaneously, termed polyfunctional cells, and quantifies the functional cytokine secretions from each single cell. IsoPlexis’ single-cell Polyfunctional Strength Index (PSI™) aids researchers in understanding how T cells and other immune cells functionally respond to immunotherapies.
PSI has identified cytokine-based biomarkers and mechanistic insights to improve the decision-making process for finding lead candidates for various immunotherapies. “The ability to easily perform single-cell proteomics provides a way to understand the complexity of the cellular response to immunotherapy and then to design and test new therapies to enhance efficacy,” said Charles Sentman, PhD, Director, Center for Synthetic Immunity, Professor, Geisel School of Medicine, Dartmouth College.
PSI Quality of Immune Response and Target-Specific Potency of Bispecific Therapy
In a study featured in GEN, researchers at Dartmouth explored whether NKG2D ligands could be potential targets for cancer therapy and whether targeting those antigens would enhance the anti-tumor response of T cells in novel bispecific therapies. More than 90% of human tumors express these ligands, with much lower expression in normal tissues. Researchers engineered bispecific T cell engagers for two of these ligands to test whether targeting these antigens would improve anti-tumor T cell response.
IsoPlexis’ PSI was investigated across five functional cytokine groups (Figure 2). The results revealed a significant polyfunctional response versus the control, activated by both bispecifics in the CD4+ and CD8+ T cells. Between the two bispecifics, the more potent polyfunctional response was in the hNKG2D-OKT3 group over the B2-OKT3 group. NKG2D is known to be able to bind to multiple ligands, whereas B2 can only bind to one. These results suggest that bispecifics capable of binding to several antigens may hold better therapeutic effects.
Improving Understanding of Bispecifics with IsoPlexis’ Intuitive Visualizations
IsoPlexis’ software, IsoSpeak, automatically analyzes data from the IsoLight and offers several advanced visualizations for analysis of high dimensional functional single-cell data. The above figure reveals the functional immune potency of the bispecific T cell engagers via PSI. Other advanced visualizations include functional heatmap, polyfunctional activation topology principle component analysis (PAT PCA, shown below), t-SNE, and more. These representations help researchers to explore and characterize single-cell polyfunctional profiles and reveal cellular insight across samples.
The IsoPlexis platform enables advances in discovery and lead optimization, which means detecting potent functional immune cell subsets that accelerate pre-clinical decision making. For the first time, IsoPlexis has provided an opportunity for understanding the power of bispecifics by identifying correlative subsets of potent single immune cells and evaluating the functional quality of these bispecific constructs.
Check out our Application Highlight, “Employing PSI to Identify Optimal Bi-Specific Antibody Candidates” to learn more about how our technology can help advise lead choice in developing bispecific therapies.
- Baeuerle PA, et al. Bispecific T-cell engaging antibodies for cancer therapy. Cancer Res 69, 4941-4944 (2009).
- Thakur A, et al. Bispecific antibody based therapeutics: Strengths and challenges. Blood Rev 32, 339-347 (2018).
- Slaney CY, et al. CARs versus BiTEs: A Comparison between T Cell-Redirection Strategies for Cancer Treatment. Cancer Discov 8, 924-934 (2018).
- Rossi J, et al. Preinfusion polyfunctional anti-CD19 chimeric antigen receptor T cells are associated with clinical outcome in NHL. Blood 132, 804-814 (2018).
- Mackay S, et al. Single-cell proteomic analysis of T cells stimulated by Bi-Specific T-Cell Engagers shows robust and unique polyfunctional secretion profile. Journal for ImmunoTherapy of Cancer 6, Suppl 1, 114. (2018).