ROR1 CAR T-cell therapy for CLL

During the 2nd European CAR T Cell Meeting in Sitges, ES, Jennifer Specht, Fred Hutch, Seattle, US, provided a summary of ROR1 chimeric antigen receptor (CAR) T-cell therapy in chronic lymphocytic leukemia (CLL) and solid tumors. This article will focus on ROR1 CAR-T for CLL.

What is ROR1?

ROR1 is an orphan tyrosine kinase receptor expressed only at a a specific stage of immature B cells and, in low levels, in adipocytes, the pancreas, parathyroid, and some parts of the gastrointestinal tract. In cancer, ROR1 is expressed on the cell surface of CLL cells, mantle cell lymphoma (MCL) cells, a subset of acute lymphoblastic leukemia (ALL) cells, and some epithelial cancer cells, such as breast and ovarian, where high ROR1 expression is associated with a poor prognosis.

ROR1 CAR T-cell therapy

• R12 ROR1 CAR:
  • Rabbit single chain variable fragment (scFv)
  • Lentiviral vector R12/4-1BB-ζ also encodes a truncated epidermal growth factor receptor (EGFRt) so that ROR1 CAR T cells also express EGFRt
• In rhesus macaques, transfer of these CAR T cells were safe in lymphoreplete and lymphodeplete models

Phase I study, FHCRC 9330 (NCT02706392)

• Primary objective:
  • Evaluate safety of adoptive CAR T-cell therapy using ex vivo autologous CD8⁺ and CD4⁺ ROR1 CAR T cells
• Secondary objectives:
  • Determine in vivo persistence and phenotype of CAR T cells
  • Determine trafficking of ROR1 CAR T cells to tumor site and function in vivo
  • Evaluate preliminary anti-tumor activity
• Two cohorts of patients with ROR1⁺ tumors (defined as > 20% by immunohistochemistry or flow cytometry):
  • Cohort A: patients with CLL, MCL, and ALL
    • CLL: beyond first remission with progression on combination chemoimmunotherapy with anti-CD20 antibody or prior tyrosine kinase or PI3 kinase inhibitors, or who were not eligible for or who were declined this therapy
    • MCL: previously treated. Patients with prior autologous stem cell transplant were eligible
    • ALL: relapsed with ROR1 expression > 90% on leukemic blasts
  • Cohort B: epithelial solid tumors 
• Eligibility for both cohorts: a Karnofsky performance score ≥ 70%, adequate organ function, and negative pregnancy test
• Treatment consisted of:
  • Conditioning therapy
  • Day 0: infusion of ROR1 CAR T cells
    • There were four dose levels (1–4) starting at 3.3 × 10⁵ up to 1 × 10⁷
  • Day +21: tumor biopsy
  • Day 28–60: restaging
  • Day 180: restaging
  • Long-term follow-up for one year
  • A 2^nd dose of ROR1 CAR-T was considered after Day +28

At the time of this presentation, two patients had been treated in Cohort A; both patients had CLL and were aged 67 and 57 years. Both were male and had refractory CLL following eight and 13 prior treatments, respectively. Neither patient experienced a dose limiting toxicity at Dose Level 1 (3.3 x 10⁵). The maximum grade adverse event experienced by both patients was four; both experienced a Grade 4 decrease in lymphocytes and neutrophils. One patient experienced Grade 2 cytokine release syndrome (CRS).

The first patient had a decrease in the abnormal B-cell population in peripheral blood but had 54% CLL cells in bone marrow aspirate (BMA) and died 11 months following CAR T-cell therapy with refractory disease. The second patient had a decrease in abnormal B-cell population in BMA and no detectable abnormal B cells in peripheral blood at baseline after first or second infusion. The second patient received two infusions of the CAR-T product, one at Dose Level 2, and is due to return in January 2020 for evaluation, having not received interval therapy.

Conclusion

In Cohort A of this phase I study, two patients with CLL were treated with ROR1 CAR T cells. One patient had an anti-tumor response. One CRS event was observed, and one patient experienced prolonged neutropenia. In both patients, CAR T-cell persistence was observed.