Increased TNF/NGF Receptor Expression on BCP-ALL Blasts Carrying the Prognostically Favorable TEL-AML Rearrangement.

TEL-AML the most common genetic alteration in childhood precursor B (BCP)-ALL is associated with a favorable prognosis yet the underlying mechanism remains largely unknown. Among the tumor necrosis factor (TNF) receptors CD40 is a key regulator of B cell maturation while nerve growth factor receptor (NGFR), CD27 and CD95 have been implicated in cell cycle arrest and blast apoptosis. Here we prospectively assessed baseline surface expression of the different TNF receptors and the costimulatory molecules CD70, CD80 and CD86 on primary BCP-ALL blasts in a pediatric cohort of TEL-AML positive (n=29) and negative patients (pts) (n=89) treated according to the CoALL06-97 protocol. In the TEL-AML positive subgroup, the percentage of blasts positive for CD40 (median; interquartile range: 100%, 100–100% vs. 82%, 56–97%; p<0.001), NGFR (36%, 11–77% vs. 8%, 1–49%; p=0.008) and CD27 (80%, 61–86% vs. 5%, 2–25%; p<0.001) was significantly higher than in the group negative for genetic aberrations such as TEL-AML, BCR-ABL and MLL-AF4. With low to negligible baseline expression for the remaining surface markers, no difference was detected for CD95 (p=0.24), CD70 (p=0.54), CD80 (p=0.87) and CD86 (p=0.06). As signaling via CD40 is known to modulate expression of costimulatory molecules of the TNF receptor/ligand family (CD27 and CD70) and of the IgG superfamily (CD80 and CD86), we compared upregulation of these molecules in TEL-AML positive and negative patients after CD40 crosslinking. To this end blast samples (n=31) were cultured for three days on genetically modified feeder cells expressing CD40 ligand. Although CD80 and CD86 expression was 5- and 3-fold (± 1 and 0.8 SEM) enhanced in CD40-activated blasts (p<0.001), there was no difference in TEL-AML positive and negative patients (CD80: p=0.13; CD86: p=0.17). In contrast there was a significant difference in CD70 upregulation with a 50-fold (± 42 SEM) increase of CD70 positive blasts in the TEL-AML group compared to only a 4.5-fold (± 0.7 SEM) upregulation in TEL-AML negative blasts (p=0.015). Of note as a costimulatory molecule, CD70 is critical not only for activation but particularly for expansion of cytotoxic T cells. CD40-induced upregulation of CD70 was accompanied by 2-fold (± 0.3 SEM) downregulation of initially high baseline expression of CD27 in the TEL-AML positive group only, a phenomenon that is also seen in maturation of normal CD27 positive B cells. In summary our findings provide first evidence for a differential phenotype of TEL-AML positive BCP-ALL blasts with regard to molecules of the TNF receptor/ligand family. Thus TEL-AML positive blasts exhibit a more mature immunophenotype with a significantly higher percentage of CD40, CD27 and NGFR positive blasts at diagnosis potentially contributing to superior survival by enhancing sensitivity towards pro-apoptotic signals via CD27 and NGFR and improving the T cell stimulatory capacity of BCP-ALL blasts by pronounced CD40-dependent upregulation of the costimulatory molecule CD70 critical for sustaining anti-leukemic immune responses.