Map Leukemia-immune Cell Communication with Nanoplasmon Ruler in CAR T-Cell Immunotherapy Genetically engineered T-cells modified with chimeric antigen receptors (CAR) targeting CD19 provide an innovative method for treating cancer, especially for B-cell acute lymphoblastic leukemia (B-ALL). Unfortunately, practical application of this immunotherapy is greatly hindered by the unsatisfactory CAR T-cell function, long- lasting B cell aplasia and accompanied cytokine release syndrome (CRS). Improved therapeutic and preventive treatments require comprehensive understanding of the complex and dynamic cytokine secretion behavior of CAR T-cells and their communication with cancer cells and other immune cells in the tumor microenvironment. More importantly, real-time and traceable monitoring of both the location and timing of cytokine secretion would enable mechanistic understanding of CAR T-cell physiopathology in initiation, activation, communication and subsequent functional responses in leukemic bone marrow immunity. Such spatiotemporal monitoring technique is critically lacking within existing clinical practices, which are primarily based on measurements under “static” conditions. Thus, there is an emerging need for platforms that allow direct visualization and mapping of cytokine production, diffusion, transportation for better understanding the highly heterogeneous functional diversity of polyfunctional CAR T-cells and immune cell communications. To address this need, the central objectives of this proposal are to develop novel integrated `nanoplamson ruler'-based nanosensing technology to resolve the temporal dynamics of cytokine secretion from individual CD19 CAR T-cells and the crosstalk with B-ALL cells and bone marrow immune suppressor cells. The success of this technology will allow, for the first time, the direct visualization of multiplex cytokine secretion from individual CAR T-cell in a high-sensitivity, multiplex, label-free, in situ and real-time traceable manner. The proposed platform would provide a detailed and time-dependent mechanisms of how CAR T-cell response to stimulation and evolve in a suppressive niche for preclinical screening of optimal, effective and safe CAR T-cell therapy.