Abstract A43: Comparative analysis of germline mutations of immune biomarkers pre- and post-HSCT in pediatric cancer patients
Authors: Pandya Pankita H. , Gao Hongyu , Chiang ChienWei , Ross Sydney , Rhodes Steven , Then Jenny , Haneline Laura , Murray Mary , Li Lang , Pollok Karen , Renbarger Jamie 
Published: May 2017

Background/Objectives: Hematopoietic stem cell transplantation (HSCT) is a high risk but curative treatment for many patients with malignant and non-malignant disorders; however, comes with significant and varying chemotherapy-induced toxicities. Here we probe variability in response of DNA collected pre-versus-post autologous-HSCT from pediatric patients. Germline DNA mutations in this population have not been assessed. The overall hypothesis is that new germline mutations are generated by exposure to high-dose chemotherapy in pediatric patients receiving autologous-HSCT and that these genetic changes may also be potential biomarkers of therapeutic response. It has been reported that activation of complement protein, C3, can decrease the risk of infections following HSCT by enabling stem cells to home to the bone marrow and stimulate their differentiation to various immune cells. This process then helps mediate the reconstitution of the immune system via regulatory mechanisms. In this study, chemotherapy-induced germline mutations among pre- and post-autologous HSCT pediatric patients, and the complement component, C3 were evaluated. Developing strategies to identify predictive biomarkers such as variability in chemotherapy-induced mutational burden of C3 among pediatric HSCT patients, could result in innovative approaches to treating these high-risk patients.

Design/Methods: Whole exome sequencing from an HSCT biorepository was exploited to assess genetic mutations and search for molecular signatures induced by anti-cancer therapy and autologous HSCT. Peripheral blood mononuclear cells (PBMCs) were isolated pre- and post-HSCT in six pediatric subjects undergoing autologous HSCT following myeloablative conditioning regimen involving carboplatin in combination with other standard of care agents. Whole exome sequencing was performed on germline DNA followed by canonical ingenuity pathway analysis® (IPA). Miliplex MAP Human Complement Panel 2 Multiplex Assay was performed on plasma from each patient pre- and post-HSCT to gain insight into status of the C3 complement protein levels following HSCT.

Results: Whole exome DNA sequencing indicated that approximately 10% of genes analyzed (959 genes) were commonly mutated in the germline DNA isolated from the post-HSCT versus the pre-HSCT, which included C3 complement component. Canonical IPA analysis using hypergeometric test indicated that the 10% commonly mutated genes are relevant in at least thirty-six statistically significant biological. Specifically, C3 was found to be associated with the PI3K signaling pathway in immune cells such as B lymphocytes (p=0.04). Preliminary multiplex complement panel data revealed a trend for increased complement protein concentrations for C3 in plasma at day 7 post-HSCT versus plasma collected pre-HSCT.

Conclusion: These preliminary experimental findings demonstrate that among the 959 commonly mutated genes, C3 consists of germline DNA mutations, as well as, having differences in expression at the protein level in patients pre- and post-HSCT. While investigation of the other commonly mutated genes and the thirty-five other relevant pathways elucidated in these studies is still ongoing, these studies highlight the importance for further investigation of the complement component C3 and its role in PI3K signaling in immune cells following chemotherapy-induced genetic mutations which may impact patient prognosis and care. Future studies using high-throughput exome sequencing may help elucidate predictive signatures and/or immune biomarkers such as differences in C3 gene and protein for developing personalized treatments for HSCT therapy, for properly managing HSCT-induced toxicities, and ameliorating clinical outcomes.

Citation Format: Pankita H. Pandya, Hongyu Gao, ChienWei Chiang, Sydney Ross, Steven Rhodes, Jenny Then, Laura Haneline, Mary Murray, Lang Li, Karen Pollok, Jamie Renbarger. Comparative analysis of germline mutations of immune biomarkers pre- and post-HSCT in pediatric cancer patients. [abstract]. In: Proceedings of the AACR Special Conference on Translational Control of Cancer: A New Frontier in Cancer Biology and Therapy; 2016 Oct 27-30; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2017;77(6 Suppl):Abstract nr A43.