Phase I–II clinical trial with CAR-NK cells against CD19-positive non-Hodgkin lymphoma or chronic lymphocytic leukemia

Therapy with chimeric antigen receptor (CAR) T cells has shown considerable efficacy against certain hematological malignancies. Currently, the U.S. Food & Drug Administration (FDA) and European Medicines Agency (EMA) have approved two anti-CD19 CAR T-cell products for the treatment of relapsed/refractory (R/R) large B-cell lymphoma. However, there are several drawbacks associated with these therapies, namely the complex and expensive production process and the unique toxicity profile, which can include cytokine release syndrome (CRS) and neurotoxicity (NT). Preclinical data on mice have indicated that these disadvantages might be avoided if CAR-natural killer (NK) cells are used instead. NK cells are part of the innate immune system and play a key role in immune surveillance. CAR-NK cells can be obtained from an allogeneic source, for example umbilical cord blood, and do not require full HLA matching between donor and patient.

Enli Liu, The University of Texas M.D. Anderson Cancer Center, Houston, US, and colleagues reported results on the first 11 patients from an ongoing phase I–II clinical trial (NCT03056339) assessing the safety and efficacy of escalating doses of CAR-NK cells for the treatment of R/R CD19-positive cancers. The results were published in The New England Journal of Medicine.¹

Study design

•  Patients: R/R CD19-positive cancers (non-Hodgkin lymphoma [NHL] or chronic lymphocytic leukemia [CLL])
• Lymphodepleting chemotherapy: 30 mg/m² fludarabine and 300 mg/m² cyclophosphamide, daily for three consecutive days
• Infusion: single infusion of CAR-NK cells at escalating doses of 1×10⁵ cells/kg, 1×10⁶ cells/kg, and 1×10⁷ cells/kg
• Post-remission therapy was permitted after the Day 30 assessment at the discretion of the treating physician
• NK cells were obtained from cord blood. The NK cells were transduced with a retroviral vector carrying a single chain variant fragment (scFv) against CD19, a CD28 transmembrane domain, and a CD28.CD3ζ signaling endodomain, in combination with the human interleukin-15 gene and inducible caspase-9 as a safety switch
• Data cut-off April 2019: 11 patients
  • The first nine patients received a CAR-NK product that was partially matched with the HLA genotype of the recipient
  • A subsequent protocol amendment permitted treatment with no consideration for HLA matching, which was the procedure used in the two other patients
• Response assessment:
  • 2018 criteria of the International Workshop on CLL²
  • 2014 Lugano classification for NHL³

Results

Patient characteristics

• Fifteen patients were enrolled from June 2017 to February 2019

• • Four patients withdrew prior to treatment initiation
  • Eleven patients received a single dose of CAR-NK cells
• Median age: 60 years (range, 47–70)
• Median prior lines of therapy: 4 (range, 3–11)
• Five patients had CLL (two patients with Richter’s transformation or accelerated CLL)
• Six patients had lymphoma:
  • Two patients with diffuse large B-cell lymphoma
  • Four patients with follicular lymphoma
  • 3/6 patients underwent transformation to high-grade lymphoma

Safety

• Adverse events that were reported in the 11 patients from the time of infusion of CAR-NK cells until Day 40, regardless of whether the investigators attributed the events to the treatment, can be seen in Table 1
• None of the patients exhibited symptoms of CRS or NT, and there were no increases in the levels of inflammatory cytokines
• No cases of graft-versus-host-disease (GvHD) were observed, despite the HLA mismatch between patients and CAR-NK product
• All patients experienced transient and reversible hematologic toxic events, which were mainly attributed to the lymphodepleting chemotherapy
• No patients experienced tumor lysis syndrome or Grade 3 or 4 non-hematologic toxicity
• The maximum tolerated dose of CAR-NK cells was not reached
• No patient was admitted to an intensive care unit for management of adverse events associated with CAR-NK cells

Efficacy

• Median follow-up: 13.8 months (range, 2.8–20.0)
• Eight patients (73%) had an objective response, including seven patients (three with CLL and four with lymphoma) with a complete response (CR)
  • Responses occurred within 1-month post-infusion
• An additional patient who had CLL with Richter’s transformation had remission of high-grade lymphoma but continued to have cytopenia, with bone marrow infiltration by CLL
  • The patient eventually had a CR whilst receiving post-remission therapy (venetoclax) and so the response was not attributed to the CAR-NK therapy
• Five of the patients with an objective response received post-remission therapy
• All eight patients who achieved an objective response were alive and in CR on the date of the last assessment, although three patients have positive measurable residual disease
• CAR-NK expansion was seen as early as 3 days after infusion, with cells persisting for at least 12 months

 Table 1. All adverse events observed in the 11 patients

Conclusion

Among 11 patients with heavily pre-treated, R/R CD19-positive NHL or CLL, the majority had an objective response to treatment with anti-CD19 CAR-NK cells without major toxic effects except high-grade transient myelotoxicity, which may be attributable to the prior lymphodepleting chemotherapy. None of the patients experienced GvHD, despite only partial HLA matches between donors and patients. Results suggest that anti-CD19 CAR-NK cells may be a less costly and less toxic treatment option than CAR T cells, which (unlike T cells) do not need to be autologous or fully HLA-matched.