APC was synthesized as described previously (19 (link)). In brief, 1 mg of anti-mouse/human CD44 monoclonal antibody (6.7 nmol; clone IM7; Bio X Cell, West Lebanon, NH, USA) was incubated with five-fold molar excess of IR700 NHS ester (10 mM in DMSO; LI-COR Biosciences, Lincoln, NE, USA) in 100 mM Na2HPO4 solution (pH 8.5) for one hour at room temperature. The mixture was purified with PD-10 columns containing Sephadex G25 resin (GE Healthcare, Piscataway, NJ, USA). The resulting APC was abbreviated as CD44-IR700.