Tumors derived from antigen presenting cells.

Vaccine strategies aimed at enhancing the processing of tumor antigens by activated 'professional' antigen presenting cells (APCs) can sometimes result in the generation of systemic T-cell mediated anti-tumor immune responses capable of eradicating a micrometastatic tumor burden. This observation raises the interesting question of why certain tumors such as B-cell lymphomas or myeloid leukemias--malignancies in lineages normally characterized by potent APC capacity--fail to be eliminated by host T-cell responses. Potentially unique aspects of the immune response to such hematopoietic cancers are discussed in the context of the current understanding of factors regulating T-cell activation and tolerance. These considerations may have relevance for the application of cancer immunotherapy to this class of diseases.