Germline Variation in Complement Genes and Event-Free Survival in Follicular Lymphoma.

Complement plays a central role in innate immunity, and also functions as a regulator of the overall immune response, including T-cell responses. We recently reported that germline genetic variation in C2, C5, C7 and C9 was associated with risk of developing non-Hodgkin lymphoma (Br J Haematol 2009;145:614). Here we evaluate whether complement genes are associated with event-free survival (EFS) in follicular lymphoma.

We genotyped 166 single nucleotide polymorphisms (SNPs) from 32 complement pathway genes in a prospective cohort study of 115 newly diagnosed follicular lymphoma patients enrolled at the Mayo Clinic from 2002-2005 as part of the Lymphoma SPORE. All patients were systematically followed through 2008 for EFS (defined as disease progression, retreatment, or death due to any cause). Tagging and nsSNPs were selected from HapMap for the genes encoding complement proteins and their key regulators (C1QB, C1QG, C1QR1, C1QTNF7, C1RL, C1S, C2, C3, C3AR1, C4BPA, C4BPB, C5, C5R1, C6, C7, C8B, C9, BF, CFH, CFHL5, CFHR1, CGHR4, CLU, CR1 (CD35), CR2 (CD21), DF, MASP2, MBL2, MCP (CD46), DAF (CD55), CD59 and SERPING1). Cox regression was used to estimate Hazard Ratios (HRs) for individual SNPs with EFS. The most prevalent homozygous genotype was used as the reference group, and each polymorphism was modeled individually as having a log-additive effect in the regression model. For gene-level analyses, we used a principal components based gene-level test. All models were adjusted for sex, FLIPI, follicular grade III, and initial treatment.

The median age at diagnosis was 61 years (range, 25-85). 57 (50%) of the patients had an event, at a median follow-up of 59 months (range, 33-73) for living patients. In gene-level analyses, CFH (p=0.004), CD55 (p=0.02), CFHR5 (p=0.02) and CFHR1 (p=0.02) were significant at p<0.05, and these genes had noteworthy q-values after consideration of multiple testing (q=0.04 for CFH and q=0.08 for CD55, CFHR5, and CFHR1). For CFH, 2 of the 11 tagSNPs (rs1329423, HR=0.46, p=0.001; and rs3766404, HR=2.0, p=0.003) were significantly associated with EFS, as was the nsSNP rs1065489 (amino acid change E936D: HR=0.39, p=0.004). For CD55, both tagSNPs (rs4844591, HR=0.58, p=0.03; and rs2564978, HR=0.58, p=0.03) were associated with EFS, as were 3 of 5 tagSNPs from CFHR5 (rs3748557, HR=0.52, p=0.03; rs12092294, HR=1.9, p=0.03; and rs6694672, HR=1.9, p=0.03) and the only tagSNP for CFHR1 (rs436719, HR=0.54, p=0.03).

Genetic variation in CFH, CD55, CFHR5, and CFHR1 was associated with EFS in follicular lymphoma after adjustment for clinical variables. These genes are part of a gene cluster at 1q32-q32.1 involved in the regulation of C3. CD55 encodes a membrane complement regulatory protein which can allow tumor cells to evade complement attack. These results are being validated in a second set of SPORE patients. Support: P50 CA97274, R01 CA92153.

No relevant conflicts of interest to declare.