Class I MHC-restricted T cell responses to tumors can be demonstrated in patients with various types of tumors,yet most of these tumors do not express costimulatory molecules.Which mechanism most likely explains how naive CD8⁺ T cells specific for antigens expressed by these tumors are stimulated to differentiate into cytolytic T lymphocytes?

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Quizplus · Accepted Answer

Tumor cells,or the protein antigens they produce,may be taken up by professional antigen-presenting cells (APCs),especially dendritic cells,and the antigens may then be delivered into the cytoplasm to gain access to the class I MHC pathway of antigen presentation.In this way,naive T cells specific for the tumor antigens can be activated by the APCs;i.e. ,through cross-presentation.Once differentiated into cytolytic T lymphocytes (CTLs),the T cells can then be activated by and kill the tumor cells,which present the same antigen,even in the absence of costimulation.There is no reason why malignant transformation of the T cells should occur.There is no evidence for cross reactivity between microbes and tumor antigens,nor of tumors secreting T cell-activating cytokines.Antigenic modulation is a mechanism by which tumors evade T cells,not activate them.

Class I MHC-Restricted T Cell Responses to Tumors Can Be