T cell receptor gene therapy for mutant NPM1 to treat patients with relapsed or refractory acute myeloid leukemia.
Acute myeloid leukemia (AML) is caused by stepwise acquisition of genetic aberrations which ultimately lead to uncontrolled proliferation of myeloid progenitor cells in the bone marrow. Gene fusions and molecular aberrations often occur in the same genes, which govern the diagnosis and prognosis of patients and guide risk-adapted and targeted therapy.
Genetic aberrations occasionally create neoantigens that are presented on tumor cells by HLA and recognized by specific T cells. We investigated whether mutations in the nucleophosmin 1 (NPM1) driver gene, which occurs in 30-35% of AML, encode neoantigens that can be targeted by immunotherapy. The majority of mutations in NPM1 are 4 base pair frameshift insertions in exon 12 resulting in a novel C-terminal alternative reading frame of 11 amino acids.
HLA class I ligandome analysis of 12 primary AML was performed by tandem mass spectrometry. Peptide-HLA tetramers were used to search for specific T cells in patients and healthy individuals. Tetramer positive CD8 cells were isolated and analyzed for reactivity against AML. The T cell receptor (TCR) for mutant NPM1 was sequenced and cloned in a retroviral vector, and tested for reactivity against AML in vitro and in immunodeficient NOD/scid mice after gene transfer.
Various mutant NPM1 peptides were shown to be presented on primary AML by HLA-A*02:01, A*03:01 or A*11:01. For the HLA-A*02:01 binding peptide, various tetramer positive CD8 cells were isolated, and one T cell showed strong reactivity against AML. From this T cell, the TCR was cloned and shown to mediate recognition and lysis of HLA-A*02:01 positive AML with mutant NPM1 after retroviral gene transfer. Anti-tumor efficacy of TCR-transduced T cells was confirmed in immunodeficient mice engrafted with a human AML cell line expressing mutant NPM1.
The TCR for mutant NPM1 is able to react against AML in vitro and in immunodeficient mice, and is currently under clinical development for gene therapy. A fully humanized TCR for mutant NPM1 (dNPM1 TCR) has been cloned in a lentiviral vector and a GMP grade procedure has been developed for cell manufacturing on a closed system. The aim is to treat patients with relapsed or refractory AML with dNPM1 TCR-T cells in a clinical phase I/II study at the LUMC.