THERAPEUTIC ANTITUMOR RESPONSE AFTER IMMUNIZATION WITH A RECOMBINANT ADENOVIRUS ENCODING A MODEL TUMOR-ASSOCIATED ANTIGEN

Recombinant adenovirus (rAd), deleted of critical genes that enable vi ral replication and replaced with genes encoding heterologous proteins , has been shown to be a safe and effective vector in gene therapy stu dies. To evaluate a potential role for rAd as an immunogen, we used tw o different replication-defective type 2 rAds encoding the model Ag, b eta-galactosidase (beta-gal). To determine whether rAd elicited the ki nd of immune responses therapeutic in an anti-tumor setting, the beta- gal-expressing adenocarcinoma, CT26.CL25, was used, Splenocytes from B ALB/c mice immunized with 1 x 10(7) infectious units (iu) of rAd demon strated anti-beta-gal activity after in vitro culture with the relevan t L(d) beta-gal peptide. Adoptive transfer of these same splenocytes p roduced dramatic regression of established pulmonary metastases. Howev er, when tumor-bearing mice were treated with 1 x 10(7) iu of rAd, no reduction in established disease was observed even when rAd was given with exogenous IL-2. To increase the viral dose delivered to each anim al, we used an E1/E4-deleted rAd that could be grown to much higher ti ters. Significant reduction occurred when 10-fold more rAd (1 x 10(8) iu) was administered. Exogenous IL-2 administration with 1 x 10(8) iu of rAd resulted in augmentation of this anti-tumor effect. These findi ngs demonstrate that when using a nonreplicating virus, the viral dose is directly related to the immune response generated. These data cons titute the first reported use of rAd in the treatment of an establishe d experimental cancer and may have implications for the treatment of h uman cancer.