gms | German Medical Science

Objective: Frequently novel therapies such as immunotherapy are developed based on knowledge obtained from primary glioblastoma (pGBM), but are then also applied to treat recurrent tumors (rGBM). However, knowledge about expression changes, immunological changes and adaptations of the tumor microenvironment during GBM progression is still limited.

Methods: Therefore we performed a comprehensive analysis of pGBM and corresponding rGBM tissues of 60 patients regarding changes in the transcriptome, their immunogenicity and intratumoral immune cell infiltration.

Results: Multi-color-immunofluorescent stainings and subsequent software-based evaluation showed a significant accumulation of immunosuppressive M2-polarized microglia cells in recurrent tumors. These changes have been accompanied by a concomitant decrease of immune-relevant chemokines and cytokines as determined by Luminex analyses. On the other side, an age-dependent increase of CD8+ effector T cells was observed during tumor progression in association with a better survival. Subsequent microarray analyses revealed marked changes on the transcriptome level occurring from pGBM to rGBM suggesting unbeneficial tumor cell selection processes. To finally identify immunogenic antigens as well as changes in the immunogenic repertoire between pGBM and rGBM, a combination of protein fractionation (PF2D) and T cell activation assays (IFN‐γ ELISpot Assay) was employed. In most of the patients, severe changes regarding the spontaneous recognition of distinct protein fractions were observed. However, out of 1500 proteins identified by mass spectrometry to be present in immunogenic protein fractions of pGBM and rGBM, we recognized four immunogenic proteins showing frequent, spontaneous T cell responses in glioblastoma patients but not in healthy donors. Overexpression of these proteins and an inverse relation to survival strengthen their suitability as vaccine antigens for future immunotherapies not only in pGBM but also in rGBM.

Conclusion: Altogether our analysis might help to select patients, who are suited for immunotherapy even at the time of recurrence and to select for promising vaccine antigens in this setting.