Evaluation of NKG2D chimeric antigen receptor redirected CD45RA- T cells as treatment for pediatric acute leukemia

Abstract

Acute leukemia is the most frequent cancer in children and teens, and the second leading cause of cancer-related death in pediatric patients. Although treatment with CD19 chimeric antigen receptor expressed on T cells (CAR T) has achieved remarkable clinical success for B-cell malignancies, an effective and safe CAR T cell therapy both for relapsed/refractory (r/r) non-B cell leukemia and for those B-cell malignancies that relapse after CAR T cells targeting CD19 (CART19) treatment is yet to be found. Interactions between Natural Killer Group 2 Member D (NKG2D) receptor, expressed in cytotoxic immune cells, and NKG2D ligands (NKG2DL) that are upregulated in leukemic blasts, are important for anti-leukemia immunosurveillance. However, leukemic blasts may develop different immunoescape strategies like TGF-β release, downregulation of NKG2DL or NKG2DL shedding, which may downregulate NKG2D receptor, hindering anti-leukemia effects. In this study, we hypothesized that NKG2D-CAR T cells could overcome these limitations and become a novel therapeutic approach for pediatric acute leukemia. We found that NKG2D-CAR T cells in vitro, efficiently targeted pediatric acute leukemia cells, especially for acute myeloid leukemia (AML) and T cell acute lymphoblastic leukemia (T-ALL). Furthermore, when tested in vivo, NKG2D-CAR T cells decreased T-ALL progression and prolonged survival of the treated mice, but failed to completely eradicate the leukemia in our mice model. Additionally, it was observed that cytotoxicity of NKG2D-CAR T cells remained unaltered upon exposure soluble NKG2DL (sNKG2DL) and/or TGF-β. Interestingly, we found that after co-culture with NKG2D-CAR T cells, remaining leukemic blasts showed higher proliferation and stemness-related markers. This result could indicate that treatment with NKG2D-CAR T cells may only be effective against tumor cells with a more mature phenotype, while those with a rather stem phenotype and increased proliferation are able to circumvent the treatment. In conclusion, our results show NKG2D-CAR T cells exert anti-leukemia effects and are resistant to canonic resistance mechanisms, and therefore, could be a novel therapeutic agent for pediatric patients. The modest efficacy observed in vivo suggests that the use of NKG2D-CAR T cells as single agent may not be sufficient to cure the patients, and combination with other therapeutic approaches, e.g. as an induction agent and bridge to HSCT or as adoptive cell therapy after HSCT, may be more advantageous