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Vaccines typically achieve immune protection by induction of humoral immunity. Recently, interest has increased in vaccines capable of eliciting both humoral and cellular immunity. Since the majority of vaccines are subunit or protein-based and CD8 T cells are typically primed by endogenous proteins expressed within the target cell, effective induction of CD8 T cell (CTL) responses by vaccines has been erratic. Exogenous antigen can be presented on MHC class I to CD8 T cells via an inefficient and poorly defined process termed cross-priming. We have used our in vitro MIMIC® technology to optimize CTL cross-priming immune responses to subunit vaccines. We have shown in vitro CTL responses to soluble influenza nucleoprotein (NP) by activating, or licensing, of dendritic cells (DC) by CD4 T cells. Further optimization has involved modification of various assay parameters: cell ratios/kinetics, antigen load, DC types used, addition of DC maturation/activation factors. Generation of the cross-priming response has been evaluated by the ability of CTL to make combinations of multiple cell factors (CD107a, IFN-γ, IL-2 and TNF-α) via intracellular cytokine staining and the ability of the CTL to eliminate targets in a fluorescent-based cytotoxic assay. The MIMIC® system can be used to evaluate CTL response to various protein/adjuvant combinations and identify corresponding vaccine candidates capable of efficiently inducing cellular immunity.