Paper Details

ABSTRACT

Background: CD70 (CD27L) is a transmembrane costimulatory molecule that has been implicated in leukemogenesis through activation of Wnt signaling pathways. Although CD70-directed therapies are emerging, the prevalence of CD70 expression and its clinical significance across molecular subtypes of pediatric and adolescent/young adult (AYA) acute myeloid leukemia (AML) remain undefined. Methods: CD70 expression was analyzed in 2,200 pediatric/AYA AML patients (age <30 years) enrolled on COG phase III trials AAML0531 (N=1,070) and AAML1031 (N=1,097) through the TARGET initiative. Adult AML comparator cohorts included TCGA-LAML (N=173) and BeatAML and SWOG-0106 datasets. RNA sequencing quantified CD70 expression as transcripts per million (TPM). Based on expression in normal hematopoietic controls, CD70 positivity was defined as TPM≥2. Surface CD70 protein expression was evaluated by multi-dimensional flow cytometry (MDF) in diagnostic bone marrow samples from 655 pediatric AML patients.
Results: CD70 expression was nearly absent in normal hematopoietic tissues, with median expression of 0.25 TPM (range, 0.03-0.78) in normal bone marrow and 0.22 TPM (range, 0.05-0.65) in CD34+ peripheral blood stem cells. In contrast, 34.7% of patients in the TARGET AML cohort expressed CD70 above the positivity threshold.  CD70 expression was highly enriched in AML with either KMT2A or MLLT10 fusions, demonstrating highest median expression levels (3.58 TPM and 3.16 TPM, respectively). Among KMT2A-rearranged (KMT2A-r) AML, 61% of patients (n=466) were CD70-positive. KMT2A::MLLT3 AML exhibited the highest CD70 expression, with a median of 6.98 TPM. These observations were confirmed by CD70 protein expression where 61% of positives of CD70 cases expressed KMT2A-r  and 26% of all KMT2A-r samples were CD70 positive. In pediatric AML samples, MDF was used to measure CD70 expression and found a broad distribution across AML samples, with a subset of patients showing markedly high positivity. Out of 655  pediatric patients, 71 were positive by flow for CD70 expression and 43 (61%) of the CD70 positives expressed KMT2A-r. Out of 165 patients with KMT2A-r AML, 43 (26%) expressed CD70. 

We assessed clinical outcomes according to CD70 expression. Patients with CD70 expression above 90th percentile (n=135) had significantly inferior 5-yr EFS and OS compared with those below 90th percentile (n=1780) (EFS:36.7% vs. 46%, P=0.007; OS: 50.5% vs. 64.0%, P=0.0003). 

We also compared transcriptomes of CD70-positive and CD70-negative AML. Nearly 100 genes involved in Wnt signaling and downstream Wnt target programs were differentially expressed between the two groups, supporting an association between CD70 expression and activation of leukemogenic Wnt pathways.

To evaluate the therapeutic relevance of CD70 expression, we tested CD70-targeted CAR NK cells expressing IL-15 in disseminated AML xenograft models. In both MOLM-14 and THP-1 leukemia models, CD70 CAR/IL-15 NK-cell treatment resulted in marked suppression of leukemia progression compared with untreated controls, as demonstrated by serial bioluminescence imaging, and significantly prolonged overall survival. These findings demonstrate robust in vivo antileukemic activity and provide functional evidence that CD70 is not only associated with high-risk AML biology but also represents an effective therapeutic target for CAR NK-cell therapy.

To determine whether our findings were conserved across age groups, CD70 expression was evaluated in adult AML cohorts. Increased CD70 expression was observed across BeatAML, TCGA-LAML, and SWOG-0106 datasets, with individual samples exceeding 300 TPM in BeatAML and TCGA-LAML. Consistent with pediatric AML, adult KMT2A-r AML demonstrated significantly higher CD70 expression. CD70 expression patterns were comparable between pediatric/AYA TARGET AML and adult TCGA-LAML AML, supporting CD70 as a conserved biologic feature across AML age groups.

Conclusion: CD70 is frequently expressed in pediatric and AYA AML and is enriched in KMT2A-r disease, indentifying a subset of patients with inferior survival. The conservation of CD70 expression across pediatric and adult AML supports its broader therapeutic relevance. These data provide strong biologic justification for CD70-targeted immunotherapeutic strategies and directly support ongoing clinical investigation of a CD70-engineered IL-15 transduced cord blood derived NK-CAR platform for children and adults with AML at our institution.