Complex humoral immune response against a benign tumor: frequent antibody response against specific antigens as diagnostic targets

Abstract

There are numerous studies on the immune response against malignant human tumors. This study was aimed to address the complexity and specificity of humoral immune response against a benign human tumor. We assembled a panel of 62 meningioma-expressed antigens that show reactivity with serum antibodies of meningioma patients, including 41 previously uncharacterized antigens by screening of a fetal brain expression library. We tested the panel for reactivity with 48 sera, including sera of patients with common-type, atypical, and anaplastic meningioma, respectively. Meningioma sera detected an average of 14.6 antigens per serum and normal sera an average of 7.8 antigens per serum (P = 0.0001). We found a decline of seroreactivity with malignancy with a statistical significant difference between common-type and anaplastic meningioma (P < 0.05). We detected 17 antigens exclusively with patient sera, including 12 sera that were reactive against KIAA1344, 9 against natural killer tumor recognition (NKTR), and 7 against SRY (sex determining region Y)-box2 (SOX2). More than 80% of meningioma patients had antibodies against at least one of the antigens KIAA1344, SC65, SOX2, and C6orf153. Our results show a highly complex but specific humoral immune response against a benign tumor with a distinct serum reactivity pattern and a decline of complexity with malignancy. The frequent antibody response against specific antigens offers new diagnostic and therapeutic targets for meningioma. We developed a statistical learning method to differentiate sera of meningioma patients from sera of healthy donors.

Fig. 1.

Representative result of a spot assay. Each clone is spotted in duplicate. Tumor serum H92 detects three clones indicated by green frames. The library that serves as control and is indicated by gray frames is spotted three times on the membrane.

Fig. 2.

Serum reactivity against antigens previously identified by meningioma sera. Mean reactivity and standard deviation of sera derived from meningioma patients (n = 24) and healthy controls (n = 24) against 62 antigens are 7.75 ± 3.01 and 14.58 ± 4.79. Mean reactivity of sera derived from patients with common type meningioma (WHOI), atypical meningioma (WHOII), and anaplastic meningioma (WHOIII). Reactivity was tested against the complete set of antigens, meningioma-specific antigens, antigens that were found twice as frequent with sera of meningioma patients as with sera of healthy donors, and the remaining antigens. The difference between common-type and anaplastic meningioma was statistically significant for the combined sets of antigens that were specific for meningioma and were found twice as frequent in meningioma as in normal controls (P < 0.05). The difference between common-type and anaplastic meningioma was statistically not significant for the set of the remaining antigens.

Fig. 3.

Number of antigens that reacted with serum antibodies of meningioma patients and healthy individuals. (A) Overall percentage of antigens that react with meningioma sera only, with sera of healthy individuals only, and both with sera of meningioma and healthy individuals. (B) Frequency of antigens that show reactivity against meningioma sera and/or sera of normal individuals. The size of the circle reflects the number of antigens reactive against a given number of sera. Meningioma specific antigens are indicated in red. As an example, we found five antigens that reacted with four meningioma sera but not with any normal sera.

Fig. 4.

Separation of meningioma sera and sera of healthy donors by the “Bayesian approach.” (A) In a first test, we considered all meningioma sera, normal sera, and the complete set of antigens. Each serum is described by an index 1 to 48 (x axis). For each serum and its antigen pattern A (described by the set of indices of the antigens 1–62), we computed P(A) (y axis). Our approach classifies a serum as meningioma serum if P(A) is larger than a chosen threshold t. A threshold t = 45 results in a misclassification rate of 10%, a sensitivity of 1, and a specificity of 0.8. (B) In a second test, we considered sera from WHOI and WHOII meningioma, normal sera, and the complete set of antigens. A threshold t = 90 results in a misclassification rate of 10%, a sensitivity of 1, and a specificity of 0.8. A threshold at t = 150 results in a misclassification rate of 8%, a sensitivity of 0.92, and a specificity of 0.92. (C) In a third test, we considered sera from WHOI and WHOII meningioma, normal sera and meningioma-specific antigens only.