L-selectin expression defines a subpopulation of In vitro generated AML-reactive T-cells with superior anti-leukemic efficacy for adoptive immunotherapy

To determine the mechanisms by which adopive immunotherapy with leukemia–reactive cytotoxic T-cells (CTLs) could reduce AML lethality, a novel technique was developed to track, both leukemic blasts and adoptively transferred CTLs independently and simultaneously in vivo. Starting with splenocytes from eGFP (enhanced green fluorescent protein) transgeneic mice AML-reactive CTLs were genarated in vitro. Stable transfectants of the murine AML cell-line C1498 expressing the red fluorescent protein DSRed2 were obtained and injected into syngeneic mice. Three factors related to CTLs correlated with disease free survival (DFS): 1) CTL dose: 5×10⁶ CTLs/mouse versus 40×10⁶ CTLs/mouse (p=0.04) with the higher dose resulting in up to 50% DFS. 2) Duration of ex vivo expansion (9 days versus 16 days, p=0.01) with the shorter expansion period resulting in superior DFS. 3) L-selectin expression (L-selectin positive fraction versus L-selectin negative fraction, p=0.05) with the L-selctin high fraction resulting in 70% DFS. Although promising, such studies have provided insight as to the limitations of adoptive CTL transfer and should lead to new strategies to overcome tumor recurrence.