Coculture of Pediatric Acute Lymphoblastic Leukemia (ALL) Blasts with CD40 Ligand Transfected Cells Leads to Changes of Surface Antigens and RNA Expression.

Although multi-agent chemotherapy is remarkably successful in the treatment of pediatric acute lymphoblastic leukemia (ALL), about 25% of patients experience relapse. A possible way to increase the cure rate for leukemia could be to modulate the immune response against leukemic cells.

It is known that ALL blasts are poor stimulators of cellular immune responses. This is believed to be mainly the result of a reduced presentation of costimulatory molecules on the surface of the ALL blasts.

For B cells, CD40 is an essential molecule which can be targeted therapeutically through its ligand, CD40 ligand or CD152. Normal B cells can induce cytotoxic T cell responses following stimulation with a soluble trimeric CD40 ligand.

We therefore hypothesized that by coculture with CD40 ligand transfected HeLa cells for four days, pediatric ALL blasts could be induced to upregulate costimulatory molecules, apoptosis inducing ligands and cytokines. The expression of the surface antigens CD40, CD40 ligand, CD80, CD86, CD95/fas, HLA-ABC and HLA-DR was evaluated by flow cytometry and the RNA expression of CD40, CD80, CD86, Fas ligand (FasL), TRAIL, IL-4, IL-6, IL-10, TGF-β was assessed by semiquantitative RT-PCR.

We found that coculture with CD40 ligand transfected HeLa cells significantly increased the expression of CD40 ligand, CD80, CD86 and CD95/fas while the expression of HLA-ABC, HLA-DR and CD40 remained unchanged. We found a significantly increased RNA expression of IL-6, TGF-β and CD80, a small but not significant increase of CD86, but no change in expression for IL-4, IL-10, FasL, TRAIL and CD40 after coculture. Addition of IL-4 to the culture did not influence the results.

In summary CD40 ligand mediated stimulation lead to increased expression of costimulatory molecules CD80 and CD86 and the pro-apoptotic CD95/fas, while the anti-apoptotic cytokines IL-6 and TGF-β were also upregulated.

Our results show that stimulation through CD40 ligation upregulates costimulatory molecules on pediatric ALL blasts, while it has differential effects on apoptosis inducers. This might have functional consequences which could be therapeutically exploited to modulate the immune system in an attempt to increase cure rates in pediatric ALL.