Abstract
Cancer Immunotherapy, particularly chimeric antigen receptor (CAR) therapy, has achieved unprecedented success in blood cancers of T/ B-cell origins. However, acute myeloid leukemia (AML) has largely evaded clinical benefit from immunotherapeutic approaches. Current AML CAR-T therapies targeting CD123 and CD33 have failed to exhibit clinical activity and are associated with serious cytopenia, as they share antigen expression with normal HSPCs. In contrast to other AML-associated antigens, CD70, that activates T, B, and NK cells via CD27, is aberrantly expressed in many AML cases compared to normal HSPCs, making it an attractive target. However, CD70-targeting antibody and CAR-T showed limited clinical activity due to antigen loss and heterogeneous expression, suggesting unmet need to identify combination strategies that overcome the limitations of existing immunotherapeutic approaches in AML.
To identify upstream regulators of CD70, we performed a genome-wide CRISPR knock out (KO) screen in myeloid leukemia cells using CD70 surface expression as a readout. TP53 emerged as top positive regulator of CD70 expression. We validated this finding in isogenic AML cell lines carrying WT, null and mutant TP53, where TP53 mutation or deletion significantly reduced CD70 expression. Consistently, p53 activation via Nutlin or conventional chemotherapy (cytarabine and daunorubicin) upregulated CD70 levels in TP53-wild-type (WT), but not in TP53-mutant or knockout cells. Analysis of bulk RNA-seq of primary AML samples (BeatAML database) and cell lines (DepMap database) also showed a significantly lower expression of CD70 in TP53-mutant/null cells across different cancer types. To further investigate mechanism of TP53-medited CD70 regulation, we performed chromatin immunoprecipitation sequencing. It revealed p53 binding downstream of the CD70 locus in TP53-WT cells but not null or R248Q mutant. Blocking this site with dCas9-KRAB suppressed CD70 expression, supporting direct transcriptional activation by p53 through enhancer binding.
To characterize underlying anti-tumor immune mechanism of CD70-directed therapy, we engineered CD70 overexpression (OE) in the Trp53-/- MLL-AF9 syngeneic AML mouse model. Strikingly, CD70 OE mice exhibited impaired leukemia engraftment and expansion in immunocompetent WT mice. Expansion of CD70 OE compared to EV tumors was also seen in Rag1-/- mice that lack T and B cells, but not in NSG mice, which lack T, B, and NK cells. Moreover, depletion of NK cells but not CD8+ T cells abolished the anti-immune effect of CD70 OE. These data together suggest that AML-associated CD70 activates NK cell-mediated anti-tumor immunity in vivo. Ex vivo assays further confirmed direct involvement of NK-cells in CD70-dependent immunity. Splenic NK cells preferentially killed CD70-OE AML cells, implicating CD70 promotes NK cell-mediated anti-leukemia immunity.
To finally explore therapeutic implications of our findings we generated our own CD70-directed CAR-T and TCR-T cells and evaluated CD70 CAR-T cell activity in the context of TP53 status. TP53-WT AML cells were sensitive to CD70 CAR-T-mediated killing, whereas TP53-mutant or KO cells were resistant. Chemical activation of p53 with Nutlin and chemotherapeutic drugs enhanced CD70 expression in cell lines and primary AML cells. A combination of p53 activating therapy, including Nutlin or chemotherapy, selectively synergized with CD70-targeting CAR-T and TCR-T in TP53-WT MV4-11 and MOLM13. Colony formation assay also remarkably showed that Nutlin + CD70 CAR-T combination effectively eliminated AML cells, while many colonies survived either monotherapy. Analysis of primary AML patient samples (n=47) revealed significantly higher CD70 expression in TP53 wild-type samples compared to TP53-mutant/deleted samples following ex vivo chemotherapy exposure. The clinical relevance is further supported by retrospective analysis of a cohort of AML patients, showing significantly better outcomes in patients with wild-type TP53 and high CD70 expression post-chemotherapy.
Collectively we show, TP53 status could serve as a predictive biomarker for CD70-targeted immunotherapy, and that combining p53 reactivation agents with CD70 CAR-T represents powerful therapeutic strategy. Our study for the first time identified TP53 as a key transcriptional regulator of CD70 in AML, linking p53 activity to NK cell-mediated immune surveillance and response to CD70-directed immunotherapy.
