CpG oligodeoxynucleotides enhance the capacity of adenovirus-mediated CD154 gene transfer to generate effective B-cell lymphoma vaccines.

Activation of CD40 by CD154 induces antigen-presenting cells (APC) to express immune costimulatory molecules, thereby enhancing their APC activity. Oligonucleotides (ODN), containing immunostimulatory DNA sequences (ISS) with nonmethylated CpG dinucleotides in a defined motif, also can induce similar changes in APC. In this study, we examined whether infection with recombinant adenovirus (Ad) encoding CD154 and/or treatment with ISS-ODN could enhance the capacity of A20 murine B lymphoma cells to function as APCs capable of inducing a syngeneic antilymphoma immune response. High-level expression of CD154 after infection with Ad-CD154 induced up-regulation of immune costimulatory molecules on A20 cells, as did incubation with ISS-ODN. Treatment of A20 cells with ISS-ODN also enhanced surface expression of alphav integrins, making them significantly more susceptible to Ad infection than nontreated A20 cells. In syngeneic mixed-lymphocyte reactions with BALB/c splenocytes, A20 cells activated with ISS-ODN and then transduced with Ad-CD154 were significantly more effective APCs than Ad-CD154 transduced cells, which, in turn, were significantly more effective than A20 cells treated with ISS-ODN alone. Also, injection of mice with ISS-activated, Ad-CD154-infected cells induced significantly better A20-specific immune responses against A20 cells, as assessed via enzyme-linked immunospot analysis in vitro and immune prophylaxis against subsequent challenge with A20 lymphoma cells in vivo. These data demonstrate that CpG-containing oligonucleotides can serve as an adjuvant for Ad-mediated gene therapy of B-cell malignancies.