Anti-leukemia activity of CD33-specific chimeric cytotoxic T lymphocytes in vitro and in vivo is impaired by addition of the CD28 costimulatory endodomain

Abstract

3052 Background: EBV-specific cytotoxic T cells (EBV-CTLs) expand and have long-term activity in vivo due to the sustained costimulation provided by the EBV-infected cells produced by this persistent virus. We exploited this phenomenon and redirected EBV-CTLs against CD33, a surface protein expressed on the malignant blasts of acute myeloid leukemia (AML) cells. Methods: EBV-CTLs generated from six EBV-seropositive donors were transduced using a retroviral vector encoding CD33 specific chimeric receptor (cR). We evaluated whether the high and sustained activity shown against native EBV+ target cells can be extended to the CD33+ EBV- targets of the chimeric receptor and whether the addition of CD28 signaling domain improved the receptor activity. Results: cRCD33-EBV-CTL maintained killed EBV-LCL and CD33+ targets (specific lysis respectively of 30% and 35% at E:T ratio 25:1). They produced Th-1, Th-2 and Tc cytokines on exposure to CD33+ targets. Addition of the CD28 intracellular domain did not increase cytotoxicity to CD33+ targets. Preincubation of CD33+ cells with the CD33-blocking MoAb resulted in up to 40% inhibition of lysis and up to 60% inhibition of cytokine release by cRCD33-EBV-CTLs confirming the specificity of the TCR interactions with CD33. NOD-SCID mice bearing a human CD33+ AML were injected with EBV-CTLs ×4 weekly starting 5 days after tumor inoculation. Significant tumor reduction was only observed in mice treated with the cRCD33-EBV-CTLs (p<0.05). Immunohistologic analysis showed the presence of a majority of CD8+ human T cells in the tumors of treated mice. Incorporation of the CD28 endodomain resulted in less tumor-infiltrating T cells in mice treated with cRCD33CD28-EBV-CTLs. There was no significant difference in the chemokines receptor expression on cRCD33CD28-EBV-CTLs but their rate of apoptosis was 16 % higher (p<0.05) than the one of cRCD33-EBV-CTLs. Conclusions: EBV- CTL expressing the CD33 chimeric receptor are functional in vitro and in vivo in mice. CD28 signaling may have a deleterious role for the activity of chimeric receptors in vivo. No significant financial relationships to disclose.