Blood Podcast Summary

Episode: Novel Treatment Targets for Hemophilia A and AML
Date: December 25, 2025
Host: Dr. James Griffin (Dana Farber Cancer Institute)
Podcast: American Society of Hematology – Blood Podcast

Episode Overview

This episode explores recent advances in hematology published in Blood, focusing on two main topics:

1. A novel AAV gene therapy for Hemophilia A based on a compact, bispecific antibody instead of Factor VIII, presented by Dr. Vincent Wuchinski.
2. A phase 1 trial of CD371-targeted CAR T cells engineered to secrete IL-18 for refractory Acute Myeloid Leukemia (AML), presented by Dr. Mark Guyer and Dr. Susan DeWolf.

Both segments showcase innovative approaches overcoming longstanding limitations in treating these difficult hematologic conditions.

Segment 1: Alternative AAV Gene Therapy for Hemophilia A

Guest: Dr. Vincent Wuchinski
Start: [00:42]
Core Topic: Overcoming size constraints of AAV gene therapy for Hemophilia A using a novel, single-chain Factor VIII mimetic antibody ("Bi8").

Key Points & Insights

• Gene Therapy Limitations

  • Traditional AAV capsids have a DNA packaging limit (~4.7-5 kilobases), making it hard to fit the large Factor VIII gene required for Hemophilia A.
  • Smaller cassettes mean difficulty including regulatory elements or enhancing tissue specificity ([01:08]).

• Bispecific Antibody Approach

  • Existing treatment: Bispecific antibodies (e.g., emicizumab) effectively mimic Factor VIII function by bringing together Factors IX and X.
  • Research goal: Engineer a compact, single-chain bispecific antibody to fit within AAV constraints, but with full Factor VIII mimetic activity.

• Development of Bi8

  • Used single-chain variable fragments (scFv) targeting Factor IX and X, fused into a single 54 kDa molecule, "Bi8" ([02:04]).
  • Demonstrated identical function to the original larger antibody via in vitro and ex vivo assays ([03:07]).
  • Bi8’s coding sequence is only 1.5 kilobases, offering flexibility for regulatory elements and promoter choice in the AAV vector ([04:15]).

• Functionality and Animal Testing

  • Liver-targeted expression driven by a strong hepatic promoter (for tissue specificity).
  • Stable dose-dependent expression without formation of anti-drug antibodies in Hemophilia A mice for 8 weeks ([05:03]).
  • Functional assays (tail vein transection): Bi8 reduced or eliminated bleeding in a dose-responsive manner, matching results of wildtype and standard-treated mice ([06:22]).

• Advantages and Next Steps

  • Non-Factor VIII-based gene therapy could benefit patients with anti-Factor VIII inhibitors or those ineligible for classic gene therapy.
  • Bi8’s small size enables further cassette engineering.
  • Improving Pharmacokinetics: Current molecule has a short half-life (1-3 hours in humans), so plans are to fuse it with an albumin-binding peptide to prolong effect and further reduce vector dose, improving both safety and efficacy ([07:44]).

Listener Q&A

• Risk of Clotting with Bi8 (cf. Emicizumab)

  • Dr. Griffin [08:09]: "Emicizumab has been associated with some incidents of clotting. Would you expect the same potential issue from this approach and did you see any evidence of that in your mouse models?"
  • Dr. Wuchinski [08:27]: "In short, the answer is yes...the principle of mode of action remains the same. So it will be subjected or is likely to be subjected to the same kind of risk. We've not seen any...in our mouse model. But our mouse models are not thrombotic challenging models."

• Immunogenicity

  • Dr. Griffin [09:09]: "What can you tell us about the potential immunogenicity of this single chain antibody?"
  • Dr. Wuchinski [09:17]: "In our hands we haven't seen any immunogenicity... The risk seems to be relatively restricted. But this is something that will have to be demonstrated experimentally."

Notable Quotes

• “What was really striking is that despite the complete change of structure of that antibody, it was indeed retaining the absolutely equivalent function to the original emicizumab antibodies.” — Dr. Vincent Wuchinski [03:16]
• "It really works. It really gives us the possibility of developing a non-factor VIII based approach for the treatment of hemophilia A." — Dr. Vincent Wuchinski [06:44]

Segment 2: CD371-targeted CAR T Cells Secreting IL-18 in Refractory AML

Guests: Dr. Mark Guyer & Dr. Susan DeWolf
Start: [10:06]
Core Topic: A unique CAR T therapy targeting CD371 (CLEC12A) and engineered to secrete Interleukin-18, tested in a phase 1 study for refractory AML.

Key Points & Insights

• Background: The AML CAR T Challenge

  • CAR T less successful in AML than B-cell cancers due to lack of leukemia-specific antigens and hostile tumor microenvironment ([10:32]).
  • CD371/CLEC12A is expressed on AML cells but sparing normal hematopoietic progenitors, making it a promising but not perfect target.

• Engineering a Better CAR T Product

  • Fully human scFv targeting CD371.
  • Advanced co-stimulatory domain to protect cells from exhaustion.
  • T cells engineered to secrete IL-18, promoting interferon-γ production and boosting cytotoxicity ([11:36]).

• Phase 1 Clinical Experience & Outcomes

  • Five relapsed/refractory AML patients, including post-allo transplant, low lymphocyte counts, heavily pretreated.
  • Reliable CAR T production even with low lymphocyte counts; 10- to 100-fold lower doses used compared to other CAR T studies ([12:13]).
  • Robust in vivo expansion and IL-18 secretion; peak at days 7–14 ([12:45]).
  • In 3/5 (all post-allo) patients: morphologic leukemia-free state by day 14 without minimal residual disease; enabled further therapy (stem cell boost or second transplant) ([13:20]).
  • Main toxicity: Prolonged cytopenias, dose-limiting at higher doses; manageable cytokine release syndrome (CRS); one case of ICANS ([13:56]).

• Challenges and Next Steps

  • Cytopenias likely multifactorial—CD371 expression, IL-18/interferon effect, poor marrow reserve.
  • Ongoing adaptation of the protocol: Inclusion of stem cell boost/transplantation soon after CAR T infusion to offset cytopenias ([15:56]).
  • Study being restarted with a new cohort at lower dose ([14:58]).

Translational Science & Immune Profiling

Dr. Susan DeWolf [16:40]:

• Deep, longitudinal profiling (flow cytometry, scRNAseq, TCRseq, cytokines) of patient samples across therapy timeline.

• Findings:

  • In vivo CAR T cells more cytotoxic than pre-infusion product.
  • Interferon pathways dominant, consistent with IL-18 function ([17:51]).
  • CAR T expansion in post-allo patients came exclusively from donor-derived T cells, with no observed graft-versus-host disease ([18:17]).
  • NK cell activation: NK cells also became highly activated and cytotoxic, suggesting broader immune remodeling ([19:28]).

• “We also saw a change in the NK cells. NK cells...were highly cytotoxic, very activated cells. Again suggesting that perhaps some of what is going on is remodeling of the immune environment in the context of this therapy.” — Dr. Susan DeWolf [19:28]

Listener Q&A

• CD371 as an AML Target: Expression and Safety
  • Dr. Griffin [20:37]: "There's only a handful of antigens... The second part of that question is given the neutropenia and thrombocytopenia that occurred, are we sure that there isn't much expression or any expression on hematopoietic STEM cells. What's CD371?"
  • Dr. DeWolf [21:07]: "CD371...is an antigen that we see on many mature myeloid cells, but is actually known to have some expression on, you know, stem and progenitor compartments. So...may be part of what we're seeing here in terms of toxicity."
  • Dr. Guyer [21:49]: "Even partial CD371 expression is sufficient to generate expansion... And you have some off target effects...just with the IL18 secretion probably improving the endogenous immune responses against those cancer cells."

Notable Quotes

• “We haven't yet seen those same results [of CAR T] in patients with acute myeloid leukemia, despite...a tremendous unmet need… This work here... arose from preclinical work… a novel CAR T cell product that has three significant features.” — Dr. Mark Guyer [10:32]
• “In three of the five patients... we were able to see a morphologic leukemia free state at just 14 days into treatment without evidence of minimal residual disease, which is quite remarkable in these extremely treatment refractory patients.” — Dr. Mark Guyer [13:20]
• “None of the patients developed graft versus host disease. So in spite of the fact that these were donor T cells, we did not see any clear secondary organ toxicity in the context of their proliferation.” — Dr. Susan DeWolf [18:26]

Timestamps for Major Segments

• Intro and Episode Overview: [00:02] – [00:42]
• Hemophilia A – Bi8 AAV Therapy: [00:42] – [10:06]
• AML – CD371 CAR T-IL18: [10:06] – [23:18]
• Closing and Credits: [23:26]

Overall Takeaways

• Bi8 Gene Therapy may open AAV-mediated, antibody-based options for Hemophilia A, particularly patients ineligible for classical gene therapy due to inhibitors.
• CD371-IL18 CAR T Cells show promise in refractory AML, inducing remissions—even enabling subsequent stem cell therapies—while illuminating opportunities and challenges in engineering both target specificity and the immune milieu.
• Both studies highlight how translational science, leveraging novel molecular formats and deep patient sample analysis, is driving a new era of individualized hematologic therapy.