Immunodominance deters the response to other tumor antigens thereby favoring escape: prevention by vaccination with tumor variants selected with cloned cytolytic T cells in vitro.

Variant cancer cells which arise from the parent tumor during tumor progression can escape immunity but retain antigens. We have mixed highly immunogenic (A+B+) murine parental cancer cells with less immunogenic (A-B+) variant cancer cells to construct a model of a cancer containing escape variants. When such mixtures of cancer cells were injected into normal mice, the variant cells grew out because immune responsiveness to the B antigen on the variant was hindered by dominance of the A antigen on the surrounding parental tumor cells. However, A-B+ variant cells inoculated alone at a separate site induced B specific cytolytic T cells and were rejected. Moreover, mice immunized with A-B+ cells rejected a challenge which contained a mixture of variant and parental cancer cells, while immunization with A+B+ cells was ineffective. Thus, variant tumor cells selected from parental tumor cells by cytolytic T cells in vitro can be used to induce protective immunity against variants expected to escape tumor immunity in vivo. The immunodominance of the A antigen may be related to its ability to induce a much more rapid CTL response than the B antigen, since we show in another model that the pre-existence of a CTL response to one antigen prevented the subsequent induction of CTL to another antigen injected at the same site, even if both antigens were equally efficient at inducing CTL. These results indicate that immunodominance can affect strong as well as weak antigens. Vaccination with individual antigens at separate sites rather than with multiple antigens at one site may, therefore, be needed to prevent tumor escape and tumor recurrence or to counteract infectious diseases.