Quantification and clinical relevance of soluble HLA class I molecules in the plasma of head neck cancer patients

Abstract

HLA peptides, presented on the cell surface, have also been found in small levels in soluble forms in body fluids comprising plasma. Soluble HLA levels have been shown to be increased in many cancer entities. However, the role of soluble HLA for cancer immune surveillance has not been conclusively resolved, which is of tremendous relevance with regard to upcoming peptide-based immunotherapy approaches for cancer treatment. However, inconsistent results across studies based on small and heterogenic cohorts as well as unreliable assay systems hamper the interpretation and evaluation of sHLA in cancer. Thus, the first aim of this thesis was to, refining a method of quantifying of soluble HLA class I in plasma. In a next step we used this assay system to get first insight into the role of soluble HLA in head and neck cancer, an entity with little to no information on soluble HLA to date. To gain insight into the role of soluble HLA, a reliable, sensitive and stable method of quantification was needed. An initially available ELISA protocol yielded values that were too high and too unstable, necessitating establishment and refinement of the procedure. After refinement we could present a protocol yielding reliable, stable levels with high sensitivity similar to those reported in the literature. Using this assay, we quantified HLA class I levels in the plasma of patients with advanced stages of disease (cohort 1), who have been under treatment for a longer period of time, as well as patients with newly diagnosed tumors (cohort 2), who have not yet been treated. In comparison with a cohort of healthy volunteers, we could show an increased concentration of sHLA in the plasma of cohort 1, whereas no increased concentration was observed in cohort 2. In more detailed analysis, we observed that the amount of sHLA in cohort 1 correlates significantly with the tumor mass and the number of metastases in the individual patients as was already reported for other tumor entities. In summary, we here described a reliable method for determining the concentration of sHLA in plasma samples and could show that the concentration of sHLA in the plasma of patients with head and neck tumors was elevated compared to healthy volunteers and correlates with the number of metastases and tumor mass.