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Donor-derived anti-CD33 CAR T-cell therapy showed 20% overall response in 15 adults with relapsed AML/MDSDonor-Derived Cells Show Promise Against Leukemia Relapse

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Key Takeaway
Consider donor-derived anti-CD33 CAR T-cell therapy for relapsed AML/MDS post-transplant, noting high CRS risk and preliminary efficacy.

This Phase 1/2 clinical study evaluated donor-derived anti-CD33 CAR T-cell therapy (VCAR33) in 15 adults with relapsed or measurable residual disease (MRD)-positive CD33+ AML/MDS following allogeneic hematopoietic cell transplantation. The study setting and specific follow-up duration were not reported. The primary outcome was not reported, but secondary outcomes included response rates and safety events.

Regarding efficacy, the overall response rate was 20%, observed in 3 of 15 patients. No p-values or confidence intervals were reported for these results. Transient VCAR33 expansion was noted in 93.3% of patients (14 of 15).

Safety and tolerability findings included cytokine release syndrome in 93.3% of patients (14 of 15), all of which were less than grade 3. Immune cell-associated neurotoxicity syndrome occurred in 26.7% of patients (4 of 15), with one case being grade 3. Grade 3 acute graft-versus-host disease was observed in 6.7% of patients (1 of 15). One patient experienced grade 3 immune cell-associated neurotoxicity syndrome, and another experienced grade 3 acute graft-versus-host disease. Discontinuations were not reported, and overall tolerability was described as acceptable.

Key limitations include that the study ended for nonsafety reasons before escalation to DL3, and the maximum tolerated dose was not determined. The certainty of findings is preliminary, reflecting early antileukemic activity and acceptable safety in this small cohort.

  • New cell therapy targets leukemia cells after transplant.
  • Helps adults with high-risk leukemia returning after surgery.
  • Still in early testing, not available for patients yet.

A new treatment using donor immune cells shows early signs of fighting leukemia after transplant.

Imagine finishing a difficult cancer treatment, only to worry about the disease coming back. Many patients face this fear after a bone marrow transplant for leukemia. Now, scientists are testing a new way to keep that fear away.

Acute myeloid leukemia is a tough disease to beat. Even after a successful transplant, the cancer can return. Current options are limited when the disease comes back. Patients often run out of strong treatments to try.

Doctors usually rely on chemotherapy to fight returning cancer. But chemo can be hard on the body and might not work well enough. This new study tests a different approach using the patient's own donor cells.

Standard care often fails when the disease comes back quickly. The body may not accept new drugs well after a transplant. This creates a dangerous gap in treatment options for many.

The surprising shift

Think of the immune system as a security team. This therapy trains that team to spot cancer cells specifically. It uses a special marker called CD33 to find the bad cells. Once found, the cells attack and destroy them.

Scientists call these cells CAR T-cells because they are engineered. They are like soldiers with a map to find the enemy. The goal is to stop the cancer before it grows again.

How the cells fight back

Researchers tested this on fifteen adults with high-risk leukemia. The patients had already had a transplant but showed signs of cancer returning. They received the therapy at different doses to see what was safe.

Some patients had more cancer cells in their blood. Others had very few cells left but still needed help. The team split them into groups to test safety carefully.

The treatment worked for some patients, but not all. About one in five patients saw their cancer disappear or go into remission. Most people did not have severe side effects from the therapy.

Some patients had mild fever or confusion after the treatment. These are common signs that the immune system is active. Doctors watched closely to make sure no one got too sick.

This doesn’t mean this treatment is available yet.

Experts say this is a promising first step in research. It shows that using donor cells is safer than using the patient's own cells in some cases. It opens a door for future improvements in care.

Using cells from a donor might reduce the risk of rejection. It also helps the body fight the cancer longer. This is a key difference from older cell therapies.

What experts are saying

You cannot get this treatment at a hospital today. It is still being tested in a clinical trial. If you are a patient, talk to your doctor about standard options.

Ask your doctor if you qualify for similar studies. Being part of a trial helps future patients find better care. It is a brave choice that helps science move forward.

The study was small with only fifteen people involved. It did not test the highest possible dose because of safety concerns. We need more data to know if it works long-term.

Stopping the dose escalation means safety was the priority. Scientists want to ensure the treatment does not cause harm. They will learn from this before trying higher amounts.

More trials are needed to prove this therapy works better than current options. Scientists will look for ways to make the cells stronger and safer. Approval will take time before it reaches patients.

Clinical trials take years to complete and review. The process ensures that new medicines are safe for everyone. Patience is key while researchers continue their important work.

More trials are needed to prove this therapy works better than current options. Scientists will look for ways to make the cells stronger and safer. Approval will take time before it reaches patients.

Clinical trials take years to complete and review. The process ensures that new medicines are safe for everyone. Patience is key while researchers continue their important work.

Study Details

Study typePhase1
Sample sizen = 5
EvidenceLevel 4
PublishedApr 2026
View Original Abstract ↓
VCAR33, a donor-derived CD33-directed chimeric antigen receptor T-cell (CAR T) product, was developed to decrease relapse of high-risk acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) after allogeneic hematopoietic cell transplantation (alloHCT). We describe preclinical characterization of the VCAR33 construct, which was optimized for long-term antitumor surveillance based on killing and persistence assays. Prior to its use in post-alloHCT maintenance, we evaluated safety and efficacy of VCAR33 in a phase 1/2 clinical study for adults with relapsed or measurable residual disease (MRD)-positive CD33+ AML/MDS after alloHCT. Fifteen patients received VCAR33 across 2 arms stratified by disease burden: 7 patients in arm A (bone marrow blasts ≥5%) at dose level 1 (DL1; 1 × 106 CAR+ Ts per kg) and 8 patients in arm B (bone marrow blasts <5%) at DL1 (n = 5) and DL2 (3 × 106 CAR+ Ts per kg; n = 3). The study ended for nonsafety reasons before escalation to DL3 (1 × 107 CAR+ Ts per kg) and maximum tolerated dose was not determined. The most common treatment-related adverse event was cytokine release syndrome (93.3%; all <grade 3). Four patients (26.7%) experienced immune cell-associated neurotoxicity syndrome (1 ≥grade 3) and 1 patient (6.7%) had grade 3 acute graft-versus-host disease within 28 days of VCAR33 infusion. Fourteen patients (93.3%) had transient VCAR33 expansion. Overall response rate was 20%: 2 patients had complete remission with incomplete count recovery in arm A and 1 arm B patient achieved MRD clearance. This allogeneic CAR T product demonstrated acceptable safety and preliminary antileukemic activity. This trial was registered at www.clinicaltrials.gov as #NCT05984199.
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