New Allo-HCT Approach Boosts Immune Response, Survival

Michael Scordo, MD

While ex vivo CD34-selected allogeneic hematopoietic stem cell transplants (HCTs) are promising treatments for patients with hematologic and myeloid malignancies, they can be limited by delayed immune recovery and increased risk of death not caused by relapse.

A late-breaking abstract presented at the 2024 Transplantation and Cellular Therapy Tandem Meetings investigated a new approach to allogeneic HCT. Investigators of the phase 2 PRAISE-IR study (NCT04872595) explored using a model-based approach to determine the optimal dose of antithymocyte globulin (ATG), which is used to prevent graft-vs-host disease after transplant. Previous studies suggested high ATG exposure might contribute to nonrelapse mortality.

According to Michael Scordo, MD, the model successfully achieved a low posttransplant ATG exposure, and immune reconstitution by day 100 was achieved in 69% of patients, meeting the study’s primary end point. Further, the 2-year rates of nonrelapse mortality and relapse were 9% and 13%, respectively, and relapse-free survival and overall survival rates were high at 78% and 86%, respectively.

These findings suggest that using a model to determine the ATG dose for ex vivo CD34-selected allogeneic HCT can lead to improved immune reconstitution and excellent survival outcomes. This approach may help reduce nonrelapse mortality previously observed in other trials and improve the safety and effectiveness of this type of transplant.

In an interview with Targeted Oncology^TM, Scordo, bone marrow transplant specialist and cellular therapist at Memorial Sloan Kettering Cancer Center in New York, New York, discussed the findings from this study and their implications for the allogeneic HCT treatment landscape.

Targeted Oncology: What was the rationale or inspiration for the study you presented at the Tandem Meetings?

Scordo: Ex vivo CD34-selected [allogeneic] transplant is one of the many methods of reducing graft-vs-host disease. It uses a myeloablative conditioning platform and integrates ATG, antithymocyte globulin, into that platform to help reduce the risk of rejection. This has been well studied over the years, but 1 of the downsides of this approach is the delayed immune recovery, particularly the T-cell immune recovery that occurs after [allogeneic] transplant with this approach. What we did based on a recent publication that we have from last year was we used a different dosing of ATG to ensure that the T-cell immune recovery after [allogeneic] transplant using ex vivo CD34 selection would be improved.

What are some of the unmet needs in this space?

There are many methods to reduce graft-vs-host disease after transplant CD34 selection. Many of the other methods including posttransplant cyclophosphamide [PTCy], which has now become a standard of care, are out there and should be used in the appropriate setting. In matched donor transplants, ex vivo CD34 selection is one of the methods of being able to use an ablative or intensive conditioning regimen with very low rates of particularly chronic graft-vs-host disease. We saw this as an opportunity to improve on this platform significantly, using a novel approach but a simple approach.

What were the goals of this study?

The primary end point of the study was the ability to improve the CD34 T-cell immune recovery by day 100 after transplant. This was a sort of a validated predictor in other studies. We had key secondary end points that included nonrelapse mortality, relapse rates, progression-free, and overall survival. With the primary end point, we exceeded that end point. With our trial, about 70% of our 56 patients achieved this appropriate immune recovery by day 100, which was significantly higher than our historical numbers had shown.

What were some of the other findings?

Aside from achieving the primary end point, we saw very low rates of nonrelapse mortality at 2 years, estimated at 8%, which is much lower than some of the previously published data using this platform in the last couple of years. [We also saw] low relapse rates [of] about 12% at 2 years and very favorable progression-free and overall survival, which was 80% and 87%, respectively, at 2 years.

What are some of the takeaways?

I look at this as a simple but novel approach to improving on a platform. We have existing platforms that work well, but we can improve them doing well. To community oncologists, I would say that for patients with myeloid malignancies, there are many different types of transplants that can be done safely and effectively. The appropriate choice of a platform really depends on many factors. We can improve on all these platforms individually, including PTCy. [For] ex vivo CD34 selection, I look at this as a method of just improving on what we have already shown to be an effective platform, being able to use dose-intensive chemotherapy or total body radiation to achieve maximal disease control but making the platform safe and tolerable.

REFERENCE:

Scordo M, Perales M, Mauguen A, et al. Phase II study of pharmacokinetic model-based ATG dosing to improve survival through enhanced immune reconstitution in pediatric and adult patients undergoing ex vivo CD34-selected allogeneic HCT (PRAISE-IR). Presented at: 2024 Transplantation & Cellular Therapy Meetings; San Antonio, Texas; February 21-24, 2024. Abstract LBA1.