The immune mechanism of pembrolizumab induced mycobacterium tuberculosis granuloma formation in metastatic nasopharyngeal carcinoma

Abstract

Undifferentiated nasopharyngeal carcinoma (NPC) (WHO Type III), an Epstein-Barr Virus (EBV)-induced malignancy, remains a health concern because of the low survival rate in relapsed patients. NPC displays a distinctive and complex tumour microenvironment of heavy immune cell infiltration. Immune checkpoint inhibitor (ICI) related clinical trials are now under way to explore new treatment options. Pembrolizumab is an ICI that targets the programmed death-1/programmed death-ligand 1(PD-1/PD-L1) pathway which reactivates the tumour surveillance ability. Intriguingly, various cases of pembrolizumab-induced mycobacterium tuberculosis (MTB) have been reported. Indeed, the primary targets of pembrolizumab, CD4 T helper cells and CD8 cytotoxic T cells, also play crucial roles in anti-MTB immunity by releasing interferon gamma (IFN) and tumour necrosis factor alpha (TNF). Although both CD4 and CD8 can be the source of proinflammatory cytokines, the role of CD4 is believed to be more predominant. Moreover, the dendritic cells and macrophages also play important roles in innate anti-MTB immunity. The polarisation of macrophages has strong effect on immune microenvironment since CD68+CD163- macrophage I (M1) is responsible for granuloma formation, distinctive MTB infection, and antimicrobial activity, but the anti-inflammatory CD163+ macrophage II (M2) is responsible for tissue repair. Meanwhile, the DEC205+ dendritic cells can present the foreign antigen to T cells through major histocompatibility class (MHC) I and II. Despite the numerous works to decipher the mechanisms for this phenomenon, a comprehensive investigation of the roles of innate and adaptive immune responses is still lacking. Two metastatic NPC patients who were treated at Queen Marry Hospital Clinical Oncology Department suffered from pembrolizumab-induced MTB infections, and their granuloma, malignant (tumour) and non-malignant (normal) tissues had been retrieved. This study focused on investigating the role the immune cells and EBV in pembrolizumab-induced MTB granuloma formation using multiplex immunohistochemistry staining. The modifications of EBV were both found between the malignant and non-malignant group, suggesting the role in granuloma formation was modest. Despite the noticeable trend of lowering PD-1 expression in granuloma samples, only PD-1+CD8+ cells displayed decrease under the influence of pembrolizumab. The IFNCD8+ T cells also increased in numbers in the granuloma samples, and the changes of IFNand PD-1 seemed to be closely associated. The increase of CD8 functionality was also supported by the increase in DEC205+MHC Class I+ dendritic cells, since CD8 priming could be performed through MHC Class I. CD68+CD163- M1 also displayed an increase in the granuloma tissue. The recruitment and activation of M1 could be dependent to IFN from T cells since IFNCD4+ displayed a granuloma-specific positive correlation with M1 cells, and IFNCD8+ also displayed a granuloma-specific negative correlation with suppressive PD-L1+ M1 cells. Pembrolizumab might strengthen the role of CD8 in anti-MTB immunity in terms of reducing PD-1 and increasing IFNexpression, and the changes were supported by the increase of DEC205+MHC Class I+. IFN induced M1 polarisation was also noticed, which might explain the reason of pembrolizumab-induced granuloma since M1 was responsible for initiating granuloma. Future studies should focus on verification and resolving the potential risk for ICI-treated patients