We have previously demonstrated that a CD8+ T lymphocyte-mediated immune response against tumours is limited in its capability to inhibit tumour development by unknown factors. Macrophages are often present in very high numbers as a consequence of CD8+ T cell infiltration in the tumour. Depleting these macrophages appears to enhance the effectiveness of the CD8+ T cell-mediated immune response against tumour. Therefore, we postulate that the CD8+ T cell response against tumour is self-limited because CD8+ T cells attract immunosuppressive macrophages to the tumour. We will determine whether CD8+ T cells actually cause macrophages to infiltrate tumour. Any macrophages in tumour will be better characterized and the effects of macrophages on CD8+ T cell mediated tumour killing will be evaluated. The work described will determine whether inhibition of macrophages enhances the likelihood of success of any tumour vaccination strategy.