Abstract
Simple SummaryIn this study, we apply the ERBB2-chimeric antigen receptor (CAR)-modified natural killer (NK) cell line NK-92 (NK-92/5.28.z), a well-defined, good manufacturing practice (GMP)-compliant, third-party, off-the-shelf immune effector cell product as a novel immunotherapeutic approach for the treatment of high-risk rhabdomyosarcomas. Our preclinical in vitro data show enormous potential to improve immunotherapy of ERBB2-positive high-risk rhabdomyosarcoma a still incurable, rapidly lethal disease, assigning to NK-92/5.28.z cells rather than to unmodified parental NK-92 cells a multifarious role as ERBB2-specific CAR-targeted killers and modulators of endogenous adaptive immunity of the host, justifying the further evaluation of this approach in in vivo mouse xenograft models as a prerequisite for a possible future phase I/II clinical trial in defined subsets of high-risk rhabdomyosarcoma patients.The dismal prognosis of pediatric and young adult patients with high-risk rhabdomyosarcoma (RMS) underscores the need for novel treatment options for this patient group. In previous studies, the tumor-associated surface antigen ERBB2 (HER2/neu) was identified as targetable in high-risk RMS. As a proof of concept, in this study, a novel treatment approach against RMS tumors using a genetically modified natural killer (NK)-92 cell line (NK-92/5.28.z) as an off-the-shelf ERBB2-chimeric antigen receptor (CAR)-engineered cell product was preclinically explored. In cytotoxicity assays, NK-92/5.28.z cells specifically recognized and efficiently eliminated RMS cell suspensions, tumor cell monolayers, and 3D tumor spheroids via the ERBB2-CAR even at effector-to-target ratios as low as 1:1. In contrast to unmodified parental NK-92 cells, which failed to lyse RMS cells, NK-92/5.28.z cells proliferated and became further activated through contact with ERBB2-positive tumor cells. Furthermore, high amounts of effector molecules, such as proinflammatory and antitumoral cytokines, were found in cocultures of NK-92/5.28.z cells with tumor cells. Taken together, our data suggest the enormous potential of this approach for improving the immunotherapy of treatment-resistant tumors, revealing the dual role of NK-92/5.28.z cells as CAR-targeted killers and modulators of endogenous adaptive immunity even in the inhibitory tumor microenvironment of high-risk RMS.
Highlights
Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in children and accounts for 5% of all pediatric cancers [1,2]
Primary RMS cells from a bone marrow (BM) aspirate of, up to that point, an untreated, newly diagnosed adolescent patient with alveolar histopathologic subtype RMS positive for the PAX3-FOXO1 fusion gene were analyzed for surface expression of ERBB2 (Figure 2A)
The ERBB2-negative MDA-MB-468 breast cancer cell line was used as a negative control (MDA-MB-468, median fluorescence intensity (MFI) 1.2 ± 0.2, n = 3), while the MDA-MB-453 breast cancer cell line served as a positive control (MDA-MB-453, MFI 138.1 ± 26.3, n = 3)
Summary
Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in children and accounts for 5% of all pediatric cancers [1,2]. The five-year overall survival (OS) rates vary from 78% in low-risk patients to a dismal 8% in high-risk patients [3]. Most of the affected children (56%) have more than one risk factor and a dismal prognosis [3,4]: patients at an age greater than 10 years and patients with primary tumors in the extremities, trunk, retroperitoneum, or parameningeal region appear to have a poor outcome [3,5]. In addition to older age and unfavorable primary tumor site, alveolar histopathology has a negative influence on patient outcome, as alveolar RMS (aRMS) has a higher risk of metastatic disease than other types of RMS, with 68% of patients already carrying metastases when they are first diagnosed with aRMS [3,6,7]. Previous attempts to extend survival by intensifying and broadening chemotherapy or by offering haploidentical stem cell transplantation and new agents such as cixutumumab, a monoclonal antibody (mAb) directed against the human insulin-like growth factor-1 receptor (IGF-1R), or temozolomide have not improved outcomes, and some of these attempts have merely added to the known toxicities [4,9,17,18,19]
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