Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:In this respect, we have recently shown that malignant transformation causes losses, gains, and imbalances in the expression of human MHC I and two antigen-processing gene products: the endoplasmic reticulum (ER) aminopeptidases ERAP1 and ERAP2 (13, 14).
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