Heat-Shock Protein gp96 Enhances T Cell Responses and Protective Potential to Bacillus Calmette-Guérin Vaccine

gp96 Is Critical for both Human Herpesvirus 6A (HHV-6A) and HHV-6B Infections

Human herpesviruses 6A and 6B (HHV-6A and HHV-6B, respectively) are two virus species in the betaherpesvirus subfamily that exhibit T cell tropism. CD46 and CD134 are the cellular receptors for HHV-6A and HHV-6B, respectively. Interestingly, the efficiency of HHV-6A/6B entry is different among different types of target cells despite similar receptor expression levels on these cells. Here, we found that the cellular factor gp96 (also known as glucose-regulated protein 94 [GRP94]) is expressed on the cell surface and interacts with viral glycoprotein Q1 (gQ1) during virus entry. gp96 cell surface expression levels are associated with the efficiency of HHV-6A and HHV-6B entry into target cells. Both loss-of-function and gain-of-function experiments indicated that gp96 plays an important role in HHV-6 infection. Our findings provide new insight into the HHV-6 entry process and might suggest novel therapeutic targets for HHV-6 infection.IMPORTANCE Although new clinical importance has been revealed for human herpesviruses 6A (HHV-6A) and 6B, much is still unknown about the life cycles of these viruses in target cells. We identified a novel cellular factor, gp96, that is critical for both HHV-6A and -6B entry into host cells. As gp96 can function as an adjuvant in vaccine development for both infectious agents and cancers, it can be a potential therapeutic target for infection by these two viruses.

Toll-like receptor chaperone HSP90B1 and the immune response to Mycobacteria

Rationale

HSP90B1, also known as gp96, is a chaperone for multiple Toll-like receptors (TLRs) and is necessary for TLR-mediated inflammatory responses in murine myeloid cells. The molecule is also expressed in T-cells though its specific role is unknown. We hypothesized that human HSP90B1 regulates monocyte and T-cell responses to Mycobacterium tuberculosis (Mtb) and bacilli Calmette-Guerin (BCG) and that its variants are associated with susceptibility to TB disease.

Methods

We screened 17 haplotype-tagging SNPs in the HSP90B1 gene region for association with BCG-induced T-cell cytokine responses using both an ex-vivo whole blood assay (N = 295) and an intracellular cytokine staining assay (N = 180) on samples collected 10 weeks after birth. Using a case-control study design, we evaluated the same SNPs for association with TB disease in a South African pediatric cohort (N = 217 cases, 604 controls). A subset of these SNPs was evaluated for association with HSP90B1 expression in human monocytes, monocyte-derived dendritic cells, and T-cells using RT-PCR. Lastly, we used CRISPR/Cas9 gene editing to knock down HSP90B1 expression in a human monocyte cell line (U937). Knockdown and control cell lines were tested for TLR surface expression and control of Mtb replication.

Results

We identified three SNPs, rs10507172, rs10507173 and rs1920413, that were associated with BCG-induced IL-2 secretion (p = 0.017 for rs10507172 and p = 0.03 for rs10507173 and rs1920413, Mann-Whitney, dominant model). SNPs rs10507172 and rs10507173 were associated with TB disease in an unadjusted analysis (p = 0.036 and 0.025, respectively, dominant model) that strengthened with sensitivity analysis of the definite TB cases, which included only those patients with microbiologically confirmed Mtb (p = 0.007 and 0.012, respectively). Knockdowns of HSP90B1 in monocyte cell lines with CRISPR did not alter TLR2 surface expression nor influence Mtb replication relative to controls.

Conclusion

Among infants, an HSP90B1 gene-region variant is associated with BCG-induced IL-2 production and may be associated with protection from TB disease. HSP90B1 knockdown in human monocyte-like cell lines did not influence TLR2 surface localization nor Mtb replication. Together, these data suggest that HSP90B1 regulates T-cell, but not monocyte, responses to mycobacteria in humans.