Immune response and its correlation with the disease activity in patients with advanced colorectal cancer (aCRC): Results from a prospective observational study

471 Background: Currently limited biomarkers are available to monitor disease status in cancer patients. Although host factors are critical in regulating cancer, the role of immune responses in aCRC is less clear. A predominant T helper 1 (Th1) response may be more effective to contain cancer than one with a substantial Th2 component. The Th1/Th2 phenotype can be inferred from relative prevalence of IgG isotypes among anti-cancer antibodies and may provide an innovative way to assess disease activity. The study aims to develop an ELISA assay to monitor IgG1:IgG2 and its utility in predicting disease status in aCRC. Methods: A validated ELISA assay (Bertech Pharma) utilizing CRC cell lines was developed to measure IgG1 (Th2) and IgG2 (Th1) levels. A sample size of 44 (24 CRC and 20 healthy control [HC]) was estimated to achieve 80% power and α error of 0.05 assuming that the assay correctly detect CRC specific antibody in > 80% cases. The IgG1:IgG2 was compared between/within groups with HC and aCRC. Results: Samples were collected from 62/66 individuals recruited at 2:1 over 1 yr. 43 CRC patients had median age of 65 yrs (39-86) and M:F 2.3:1. 25 had >1 metastatic site, 31 underwent primary tumor resection and 37 received chemotherapy. Using standard criteria, 14/43 (33%) CRC patients had elevated 1gG1 titer compared with 2/19 (10%) HCs (p = 0.06). Mean IgG1 of CRC group was 0.18±0.05 compared with 0.15±0.01 in HC (p = 0.01). Conversely, mean IgG2 level of CRC group was 0.26±0.11 compared with 0.38±0.15 in HC (p = 0.003). Mean IgG2:IgG1 of CRC group was 1.5±0.35 compared with 2.5±0.97 in HC (p < 0.001). Among 43 CRC patients, 7/12 (58%) with disease progression (DP) had elevated IgG1 compared 7/31 (23%) with stable disease (p = 0.03). Strikingly, 9/12 (75%) patients who died had elevated IgG1 compared with 5/31 (16%) who were alive during the follow up, p = 0.001. Logistic regression revealed positive association among elevated IgG1 and DP, HR:4.8 (95% CI:1.2-19.9) and mortality, HR:15 (95% CI:3.1-78.8). Conclusions: Our results revealed that patients with aCRC have abnormal IgG1:IgG2 compared with HC and elevated IgG1 (a predominant Th2 response) levels in aCRC correlate with DP and mortality.