CD40 Ligand Levels in Pediatric Cohorts Correlate with Baseline Platelet Count and Transplant-Associated Mortality but Not with Endothelial Injury

Abstract

Introduction CD40 ligand (CD40L), primarily expressed on activated CD4+ T lymphocytes, is also secreted in soluble form by T cells and platelets. CD40L modulates the immune response, largely via binding to CD40 on B lymphocytes. CD40L is also expressed on endothelial cells and with CD40 regulates endothelial cell integrity and vascular inflammation. Recently, it has been reported that single nucleotide polymorphisms (SNPs) in the CD40LG gene are associated with increased risk of endothelial complications following allogeneic stem cell transplantation (Rachakonda et al JCO 36(8)789-800). We hypothesized that incidence of thrombotic microangiopathy (TMA), a severe endothelial complication, would be associated with protein levels of CD40L early after transplant. Methods We analyzed serum collected prospectively from two cohorts of pediatric HSCT patients at their pre-transplant baseline. Serum was analyzed at day + 14 after transplant for cohort 1. CD40L levels were measured via R&D Quantikine ELISA. Genotyping of the previously reported SNPs (rs3092920 rs3092952 and rs3092936) was performed for cohort 1 using Applied Biosystems TaqMan technology. Results Initial analysis of cohort 1 revealed that patients with bone marrow failure syndromes had dramatically decreased CD40L levels as compared to other diagnoses, likely due to underlying cytopenias (Figure 1). These patients were excluded from further analysis due and a total of 125 patients were then analyzed across two cohorts. Associations between baseline CD40L levels and outcome are shown in Table 1. There is no significant correlation between CD40 level and TMA or GVHD. Cohort 1 also showed no correlation between CD40L level and GVHD or TMA at day +14. Interestingly, in both cohorts there is a significant association between post-transplant mortality and low baseline CD40L levels. This finding is independent of the indication for transplantation. CD40L is produced by platelets and platelet counts correlated with CD40L level at baseline. Mortality was increased in those with lower pre-transplant platelet counts. There was no association between genotype at the assessed SNPs and baseline CD40L levels or mortality (Table 2). No association was seen with genotype and day +14 CD40L levels. Conclusion CD40L levels prior to HSCT and at day +14 (when endothelial injury occurs) do not correlate with the risk of developing TMA. Levels of CD40L do not correlate with genotype at three SNPs either, including rs3092936 where the CC/CT genotype has been reported to increase risk of TMA and death. However, lower baseline levels of CD40L are associated with risk for post-transplant mortality, independent of diagnosis. Additionally, they correlate with baseline platelet count. We hypothesize that CD40L levels serve as a surrogate for platelet count and that baseline platelet count itself may predict risk for transplant related mortality.