T Cell Activation by t(9;22) Acute Lymphoblastic Leukemia-Derived Dendritic-Like Cells Is Associated with Increased Expression of Antigen Processing Machinery Components.

We have recently shown that dendritic-like cells derived from t(9;22) acute lymphoblastic leukemia (ALL) cells can activate T cells, while the original unmodified leukemic blasts cannot. To define the molecular basis of this functional difference, we have compared the level of antigen processing machinery components in unmodified blasts and ALL-derived dendritic-like cells, since they play a major role in antigen presentation. Six patient samples and one t(9;22) ALL cell line (Z119) were studied.

Dendritic-like cells were generated by in vitro culture with CD40 ligand, interleukin (IL)-1β, IL-3, IL-7, stem cell factor and tumor necrosis factor-α for six days. Maturation was verified by morphology and CD80/CD86 expression. Cells were studied for HLA class I and class II antigen expression. Furthermore, antigen processing machinery component expression was analyzed by intracellular staining with a unique panel of monoclonal antibodies which recognize the constitutive proteasome (Z, MB1, delta) and immunoproteasome (LMP2, LMP7, LMP10) subunits, the transporter subunits TAP 1 and 2 and the chaperones calnexin, ERp57, calreticulin and tapasin. HLA Class I antigen and HLA-DR/DQ/DP antigen expression was significantly up-regulated on the dendritic-like cells. LMP2, LMP7 and tapasin expression was significantly up-regulated in all t(9;22) ALL-derived dendritic-like cells, in comparison to the unmodified blasts. No significant difference was detected in the expression of the other antigen processing machinery components. These results suggest that T cell activation by t(9;22) ALL-derived dendritic-like cells is associated with increased expression of some, but not all, of the antigen processing machinery components. Whether t(9;22) ALL-derived dendritic-like cells can be used as a cellular vaccine for adoptive immunotherapy of ALL is being investigated.