High-Risk Acute Lymphoblastic Leukemia Cells with bcr-abl and Ink4a/Arf Mutations Retain Susceptibility to Alloreactive T Cells

INK4A/ARF mutations are acquired in bcr/abl+ lymphoid blast phase chronic myelogenous leukemia (CML) and bcr/abl+ acute lymphoblastic leukemia (ALL). Donor lymphocyte infusion and graft-versus-leukemia (GVL) are generally ineffective in such ALLs, whereas GVL is highly active against bcr/abl+ CML, which does not have a lesion in the INK4A/ARF locus. The mechanisms for the ineffectiveness of GVL are not fully known, and it is possible that intrinsic resistance of acute lymphoid leukemias to immune effectors associated with allogeneic GVL may contribute to ineffectiveness. This work tested the hypothesis that INK4A/ARF mutations that are associated with transformation of bcr/abl+ CML to an ALL phenotype, and that are associated with increased resistance to apoptosis render ALL cells insensitive to allogeneic immune responses to minor histocompatibility antigens (mHA). Murine acute pre-B ALLs were induced by transfer of the human p210 bcr/abl gene into bone marrow of INK4A/ARF null mice. These ALL lines were then studied in a murine model of MHC-matched, mHA-mismatched allogeneic BMT. In vivo growth of these ALLs was inhibited in allogeneic transplants characterized by active allogeneic immune responses compared to their behavior in syngeneic transplants. In vitro ALLs with INK4A/ARF, p210 bcr/abl, or p190 bcr/abl mutations remained sensitive to anti-mHA cytolytic T cells. In addition, the ALLs were capable of inducing primary immune responses to mHAs in vivo. Thus, ALLs with INK4A/ARF or bcr/abl mutations are not intrinsically resistant to allogeneic T cell responses, suggesting that active immunotherapies against mHA have the potential to control such acute lymphoblastic leukemias.