# CAR T-Cell Therapy Targeting the Membrane-Proximal C2-Set Domain of CD33 for Treatment of Acute Myeloid Leukemia and Other CD33-Expressing Hematopoietic Neoplasms

> **NIH NIH R21** · FRED HUTCHINSON CANCER RESEARCH CENTER · 2021 · $157,326

## Abstract

ABSTRACT
Antigen-specific immunotherapies have long been pursued to improve outcomes in acute myeloid leukemia
(AML). So far most exploited for this purpose are antibodies targeting CD33, a glycoprotein displayed on the cell
surface of leukemic blasts in almost all cases and possibly leukemia stem cells in some. Improved survival of
some patients treated with the CD33 antibody-drug conjugate gemtuzumab ozogamicin (GO) validates this
approach, but many patients with CD33+ AML do not benefit from GO. This has prompted interest in developing
improved CD33-directed therapeutics, with several investigational drugs recently advancing to clinical testing.
Similar to GO, all these molecules recognize immune-dominant epitope(s) within the membrane-distal V-set
domain of CD33. In our preliminary studies with CD33V-set/CD3 bispecific antibodies, however, we have observed
enhanced immune-effector cell function and higher cytolytic efficacy with membrane-proximal binding of CD33.
We therefore hypothesize antibodies against the membrane-proximal C2-set domain will provide a superior
approach to CD33-targeted immunotherapy than existing therapeutics. Moreover, since the V-set but not C2-set
domain is missing in some CD33 splice variants, C2-set domain-directed antibodies can recognize all naturally-
occurring variants of CD33 (i.e. are “CD33PAN antibodies”). As a first step toward our long-term goal of developing
this new form of CD33 immunotherapy, we have recently generated murine and – with use of humanized
(“Trianni”) mice – fully human antibodies against the C2-set domain of human CD33. Proof of concept studies
with a murine CD33PAN/CD3 bispecific molecule demonstrated potent anti-leukemia activity and effective T-cell
engagement. We now propose to develop a new therapy that is based on T-cells expressing chimeric antigen
receptors (CARs) with human CD33PAN antibody binding sequences for patient use. We plan to rigorously test
the anti-leukemia properties of these CAR T-cells in vitro and in vivo, while at the same time studying how CD33
gene-edited normal hematopoietic stem and progenitor cells (HSPCs) can mitigate toxicity of our adoptive cell
therapy to normal blood cells. To accomplish these goals, we have assembled a multidisciplinary team of
investigators with complementary expertise in CD33-directed immunotherapies, CAR T-cell technology, and
transplantation of gene-modified HSPCs. Expected results will guide the further development of CD33PAN CAR
T-cells. Alone or together with engineered hematopoietic cells to widen their therapeutic window, these cells may
offer a new treatment option for AML and other CD33+ neoplasms for which outcomes continue to be
unsatisfactory.

## Key facts

- **NIH application ID:** 10069330
- **Project number:** 5R21CA245594-02
- **Recipient organization:** FRED HUTCHINSON CANCER RESEARCH CENTER
- **Principal Investigator:** Roland Bruno Walter
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $157,326
- **Award type:** 5
- **Project period:** 2019-12-10 → 2022-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10069330

## Citation

> US National Institutes of Health, RePORTER application 10069330, CAR T-Cell Therapy Targeting the Membrane-Proximal C2-Set Domain of CD33 for Treatment of Acute Myeloid Leukemia and Other CD33-Expressing Hematopoietic Neoplasms (5R21CA245594-02). Retrieved via AI Analytics 2026-06-11 from https://api.ai-analytics.org/grant/nih/10069330. Licensed CC0.

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