PLGA/PBAE aAPC (red) show higher levels of binding to cognate CD8+ T cells (green) compared to PLGA aAPC. DiD-labelled MHC DbIg-gp100 (cognate) or MHC KbIg-SIY (noncognate) aAPC were incubated with CFSE-labelled PMEL CD8+ T cells for 1 hour at 37 °C. Representative confocal images illustrate A) PLGA and B) PLGA/PBAE aAPC exhibit low levels of binding to non-cognate CD8+ T cells. C) PLGA aAPC show relatively low levels of binding to cognate CD8+ T cells. Blue arrows indicate binding events. D) PLGA/PBAE aAPC bind more frequently and in higher numbers to cognate-CD8+ T cells. Scale bars = 20 μm. E) After incubation of CD8+ T cells with particles, cells were washed and analyzed using flow cytometry. DiD fluorescence intensity was normalized to control samples with blank particles. PLGA/PBAE aAPC demonstrate enhanced binding to cognate CD8+ T cells, as evidenced by a more than 50-fold increase in DiD fluorescence intensity over CD8+ T cells incubated with PLGA aAPC. Error bars represent the SEM of 4 replicates, (* = p<0.05, ** = p<0.01, *** = p<0.001, **** = p<0.0001).