Generation of Autologous Pre-B Acute Lymphocytic Leukemia (ALL) Reactive T Cell Lines Using ALL Blasts as Antigen Presenting Cells.

Abstract 2035

Poster Board II-12

Although hematologic remissions can be achieved in the majority of patients with adult acute lymphocytic leukemia (ALL) by chemotherapy, long term survival is only 30–40%. The inability of the immune system to recognize and eliminate residual malignant leukemia cells may be an important mechanism contributing to relapse. In this study, we investigated the possibility of using pre-B-ALL cells as antigen presenting cells in an in vitro culture to induce autologous ALL reactive T cells. After 7 day culture of Pre-B-ALL peripheral blood mononuclear cells (CD19⁺ 93±4%) in 96 well culture plates in culture medium supplemented with a cytokine combination of IL-2/IL-3/IL-4/IL-7/GM-CSF, CD80, CD86, CD83, CD54, HLA-Dr and CD40 expression was analyzed. Significant enhancement of CD80, CD86, CD83 and CD40 on ALL cells was observed (n=8, P≦0.001-0.02). Addition of lipopolysaccharide (LPS) to the cytokine combination further increased CD80, CD86 or CD40 expression by 3 of 8 ALL samples above the baseline enhancement by cytokines (Figure), while CD40 ligand (CD40L) enhanced expression of the co-stimulatory molecules in 4 of 8 cases. Autologous T cells remaining in the culture after day 7 were then expanded with high dose IL-2 and autologous ALL reactive T cell lines were identified by IFN-g release by T cells in response to autologous ALL cells. Autologous ALL reactive T cells were generated from 5 of 8 pre-B ALL samples studied. The data from 3 experiments demonstrated that although the cytokine combination plus LPS or CD40L could effectively induce ALL cell expression of co-stimulatory molecules, the presence of CD40L and LPS in the culture induced significantly greater activation of autologous ALL-reactive T cells than did the cytokine combination plus LPS alone, as assessed by average IFN-g release of 24-48 culture wells (P≦0.004). ALL-reactive T cell lines selected by high IFN-g release response showed effective elimination of autologous ALL cells in a 2 day co-culture assay with an E:T ratio of 1:1 by flow cytometry analysis. Average residual CD19⁺ cells was 2.0±1.4% for highly reactive T cell lines (n=17) vs 16.5±25.9% for the less reactive control T cell lines (n=9) (P<0.02). Conclusion: Autologous ALL-reactive T cells can be induced from most ALL patients in an in vitro culture with a cytokine combination. Adoptive transfer of these anti-ALL CTL to patients is a possible therapeutic approach for further study.

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