Immunologic detection of acoustic neuroma: preliminary report

The inflammatory microenvironment in vestibular schwannoma

Vestibular schwannomas are tumors arising from the vestibulocochlear nerve at the cerebellopontine angle. Their proximity to eloquent brainstem structures means that the pathology itself and the treatment thereof can be associated with significant morbidity. The vast majority of these tumors are sporadic, with the remainder arising as a result of the genetic syndrome Neurofibromatosis Type 2 or, more rarely, LZTR1-related schwannomatosis. The natural history of these tumors is extremely variable, with some tumors not displaying any evidence of growth, others demonstrating early, persistent growth and a small number growing following an extended period of indolence. Emerging evidence now suggests that far from representing Schwann cell proliferation only, the tumor microenvironment is complex, with inflammation proposed to play a key role in their growth. In this review, we provide an overview of this new evidence, including the role played by immune cell infiltration, the underlying molecular pathways involved, and biomarkers for detecting this inflammation in vivo. Given the limitations of current treatments, there is a pressing need for novel therapies to aid in the management of this condition, and we conclude by proposing areas for future research that could lead to the development of therapies targeted toward inflammation in vestibular schwannoma.

B7-H1 expression in vestibular schwannomas

HYPOTHESIS

B7-H1 is expressed in vestibular schwannomas.

BACKGROUND

Little is known about how benign human vestibular schwannomas interact with antibody-mediated or cell-mediated immunity. We report on the aberrant expression of a novel T-cell coregulatory molecule, B7 homolog 1 (B7-H1), in vestibular schwannomas and discuss the implications of B7-H1 expression and tumor aggressiveness and a potential regulator of B7-H1 expression.

METHODS

Immunohistochemical staining for B7-H1, CD8+, CD3+, and CD4+ lymphocytes were performed on 48 fresh-frozen vestibular schwannoma tissue specimens. A clinical review of patient presenting symptoms and tumor characteristics was performed. Real-time polymerase chain reaction was used to determine if there was differential expression of B7-H1 messenger RNA and microRNA-513, a known regulator of B7-H1, in several strongly positive and negative B7-H1 vestibular schwannomas.

RESULTS

Nine (19%) of 48 tumors were negative, 23 (48%) tumors were 1+ mildly positive (<20% section area), and 16 (33%) stained 2+ strongly positive (>or=20% section area) for B7-H1. The average number of CD8 cells per high-power field was 2.1 for positive-staining tumors and 1.0 for negative tumors (p = 0.16). Failure of tumor control with stereotactic radiation (p = 0.029) was significantly greater in the strongly positive B7-H1 tumors. Real-time polymerase chain reaction did not show significant differential expression of microRNA-513 (p = 0.62) or B7-H1 messenger RNA (p = 0.35) between the tumors showing strong and negative immunohistochemical staining for B7-H1 protein.

CONCLUSION

Vestibular schwannoma tumors express B7-H1, which has been associated with immune tolerance and adverse disease characteristics in several malignancies. Growing tumors that were surgically removed after failed stereotactic radiation therapy were significantly more likely to strongly express B7-H1 protein, which lends some credibility to the hypothesis that immuno-evasion may play some role in their continued growth. Although clinical trends were seen, greater statistical power is required to evaluate whether B7-H1 expression correlates with more aggressive tumor growth or poorer hearing class. B7-H1 seems to be expressed in equal amounts at the RNA level in all vestibular schwannoma tumors that suggests that differential protein expression is occurring at the posttranscriptional level. However, microRNA-513 does not regulate B7-H1 protein expression in these tumors.

Specific cellular immunity in acoustic neuroma patients

An indirect leukocyte migration agarose technique to detect cell-mediated immunity was modified to obtain a specific assay for release of human leukocyte migration inhibitory factor. Acoustic neuroma patients exhibited a significant cellular immune response against acoustic neuroma extract (P less than .01) as well as perilymph from acoustic neuroma patients (P less than .01) when compared to healthy control persons. All 19 patients tested reacted to acoustic neuroma extract. Seven of 21 perilymph samples did not elicit migration inhibition. Crossover determination of antigenicity of two negative and four positive perilymph samples against three patients revealed highly reproducible results, uncorrelated to perilymph concentration of potassium and protein. Flow cytofluorometry did not reveal malignant DNA patterns in 10 acoustic neuromas examined. Immunofluorescence studies did not reveal autoantibodies against acoustic neuromas in sera from 11 patients. The responsible antigen(s), the mechanism of immunization, and the diagnostic implications remain to be determined.