CD33‐directed immunotherapy with third‐generation chimeric antigen receptor T cells and gemtuzumab ozogamicin in intact and CD33‐edited acute myeloid leukemia and hematopoietic stem and progenitor cells.

Immunotherapies, such as chimeric antigen receptor (CAR) modified T cells and antibody‐drug conjugates (ADCs), have revolutionized the treatment of cancer, especially of lymphoid malignancies. The application of targeted immunotherapy to patients with acute myeloid leukemia (AML) has been limited in particular by the lack of a tumor‐specific target antigen. Gemtuzumab ozogamicin (GO), an ADC targeting CD33, is the only approved immunotherapeutic agent in AML. In our study, we introduce a CD33‐directed third‐generation CAR T‐cell product (3G.CAR33‐T) for the treatment of patients with AML. 3G.CAR33‐T cells could be expanded up to the end‐of‐culture, that is, 17 days after transduction, and displayed significant cytokine secretion and robust cytotoxic activity when incubated with CD33‐positive cells including cell lines, drug‐resistant cells, primary blasts as well as normal hematopoietic stem and progenitor cells (HSPCs). When compared to second‐generation CAR33‐T cells, 3G.CAR33‐T cells exhibited higher viability, increased proliferation and stronger cytotoxicity. Also, GO exerted strong antileukemia activity against CD33‐positive AML cells. Upon genomic deletion of CD33 in HSPCs, 3G.CAR33‐T cells and GO preferentially killed wildtype leukemia cells, while sparing CD33‐deficient HSPCs. Our data provide evidence for the applicability of CD33‐targeted immunotherapies in AML and its potential implementation in CD33 genome‐edited stem cell transplantation approaches. What's new? In the development of immunotherapy for acute myeloid leukemia (AML), a target of interest is CD33, which is expressed on blast cells in more than 90 percent of AML patients. CD33 is also expressed on healthy myeloid and progenitor cells, however, raising the risk for off‐target effects with CD33 therapies. Here, the authors introduce a CD33‐directed third‐generation chimeric antigen receptor (CAR) T‐cell product (3G.CAR33‐T). 3G.CAR33‐T cells were effective against CD33‐positive cells, including AML blasts, and successfully overcame AML drug resistance. Genomic deletion of CD33 in hematopoietic stem and progenitor cells resulted in preferential killing of leukemia cells by 3G.CAR33‐T cells. [ABSTRACT FROM AUTHOR]