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Background Current cellular expansion platforms fall short in emulating the molecular activity of the immune synapse responsible for selective T cell activation and expansion. This leads to polyclonal, non-specific expansion, with inefficient use of materials, and the emergence of undesired phenotypes. To reproduce the capability of the immune system, a scalable, programmable system is required that can selectively expand therapeutically relevant T cell subsets (e.g. CD8 + cytotoxic T cells) while reducing time and cost in manufacturing cell and gene therapies (CAGTs). To address this, we developed a customizable and Programmable Cellular Interface (sbPCI) which emulates immune synapse architecture. This approach enables selective expansion of T cell subsets directly from peripheral blood mononuclear cells (PBMCs), eliminating the need for T cell isolation, with direct implications for cancer immunotherapy innovation.Methods Human red blood cells (RBCs) under 42 days old were engineered with sbPCI to display co-stimulatory antibodies. These sbPCI constructs were directly added to PBMCs isolated from sourced lymphocytes. A high-throughput screening (HTS) platform was used to evaluate hundreds of molecular configurations, including antibodies to CD3, CD28, CD137, over a 5-day culture period. T cell activation and phenotype were assessed via flow cytometry (CD45, CD3, CD4, CD8, CD69, CD25, IFNg, Perforin, Granzyme B) and CFSE-based proliferation assays.Results sbPCI enabled robust T cell activation from PBMCs across multiple configurations. Distinct proliferation kinetics between CD4 + and CD8+ T cells were revealed, with some conditions favoring CD8+ cytotoxic subsets. While specific phenotypic outcomes varied, the results demonstrate that sbPCI configuration influenced the balance between T cell subsets.Conclusions sbPCI offers a rapid, scalable method for selectively expanding T cells directly from PBMCs, eliminating the need for isolation steps. By leveraging high-throughput screening to optimize parameters of the immune synapse, this platform supports the development of customized T cell products. Next steps include expanding the application of the sbPCI platform beyond T cells.