Abnormal expression of MHC class I molecules in malignant cells is a
frequent occurrence that ranges from total loss of all class I antigens
to partial loss of MHC specific haplotypes or alleles. Different
mechanisms are described to be responsible for these alterations,
requiring different therapeutic approaches. A complete characterization
of these molecular defects is important for improvement of the
strategies for the selection and follow-up of patients undergoing T-cell
based cancer immunotherapy. Precise identification of the mechanism
leading to MHC class I defects will help to develop new personalized
patient-tailored treatment protocols. There is significant new research
on the prevalence of various patterns of MHC class I defects and the
underlying molecular mechanisms in different types of cancer. In
contrast, few data is available on the changes in MHC class I expression
during the course of cancer immunotherapy, but the authors have recently
made discoveries that show the progression or regression of a tumor
lesion in cancer patients undergoing immunotherapy depends on the
molecular mechanism responsible for the MHC class I alteration and not
on the type of immunotherapy used. According to this notion, the nature
of the preexisting MHC class I lesion in the cancer cell has a crucial
impact on determining the final outcome of cancer immunotherapy. This
SpringerBrief will present how MHC class 1 is expressed, explain its
role in tumor progression, and its role in resistance to immunotherapy.