Enhanced DNA Repair and Genomic Stability in HIV(+) Diffuse Large B Cell Lymphoma of Germinal Center Origin

Introduction:

HIV infected individuals are 17x more likely to receive a diagnoses of Diffuse Large B cell Lymphoma (DLBCL) compared to their uninfected counterparts. Moreover, DLBCL is more aggressive in HIV infected individuals, with up to 70% of patients being primary refractory to chemotherapeutic regimens. However, the molecular pathology driving the aggressive nature of HIV related DLBCL is poorly understood. Here, we have assessed the genomic and transcriptional differences between HIV(+) and HIV(-) DLBCL in order to identify the mechanisms driving the enhanced aggressive and refractory nature of HIV related DLBCL.

Methods:

A total of 66 cases, including 27 HIV(+) from the AIDS Cancer Specimen Resource Network (https://acsr.ucsf.edu/) and 39 HIV(-) institutional cases were included in this study. Fresh H&Es were reviewed by a hematopathologist to validate diagnosis and determine tumor content. Samples with <60% tumor content were macro-dissected. A total of 4x 5µm FFPE sections per sample were used for DNA and RNA extraction. DNA damage at the gross aberration level was assessed using array comparative genomic hybridization (aCGH). NanoString digital gene expression profiling (GEP) was used to perform the Lymph2Cx DLBCL Cell of Origin molecular subtyping assay (Germinal Center B-cell/ GCB, Activated B-Cell/ ABC, Unclassifiable/UNC) and to assess the differential expression of genes with known roles in cancer using the PanCancer Pathways panel.

Results:

Both the HIV(+) and HIV(-) cohorts were found to be GCB enriched with GCB-ABC-UNC distributions of 70%(19/27)-11%(3/27)-19%(5/27) and 54%(21/39)-33%(13/39)-13%(5/39) respectively. For both statistical and biological reasons, analysis was restricted to the GCB-DLBCL subtype only. Array CGH revealed the HIV(+) tumors have less DNA aberrations than their HIV(-) counterparts, indicative of enhanced genomic stability. GEP GSEA analysis revealed significant differences in the HIV(+) cohort compared to the HIV(-) cohort; including increases in DNA replication (MCM2, MCM4, MCM7) and Cell Cycle progression (CDC25A, CCNA2, CCNB1, E2F1) related genes as well as decreases in cell cycle negative regulators (CDKN1A, CDKN1B, CDKN2B, RB1), pro-apoptotic BCL2 genes (BAX, BIM, BMF, PUMA, BNIP3) and pro-survival BCL2 genes (BCL2, BCLW). Analyses also revealed significant increases in DNA repair related genes, particularly those with roles in the Fanconi Anemia-Homologous Recombination-Translesion Synthesis axis (FANCA, FANCD1/BRCA2, FANCE, FANCG, FANCR/RAD51, FANCS/BRCA1, FANCT, FANCV/MAD2L2).

Conclusions:

Our results show, for the first time, that GCB DLBCL arising in HIV infected individuals possesses a distinct molecular pathology to that which arises in uninfected individuals. These results indicate that the aggressive nature of HIV(+) GCB DLBCL is mediated by increased proliferation in conjunction with reduced cell cycle inhibitory capabilities and potentiated by heightened DNA repair that promotes genomic stability. Moreover, it is probable that the bolstered DNA repair capabilities confer an innate ability to repair DNA damage resulting from the administration of genotoxic chemotherapeutic agents and may be the mechanism underlying the high primary refractory rate to chemotherapeutics in HIV related DLBCL.