Blood Podcast – February 12, 2026

Main Theme and Overview

This episode of the Blood Podcast, hosted by Dr. Laurie Sen for the American Society of Hematology, presents in-depth conversations with leading researchers about two major recent publications in Blood:

1. Mechanistic insights into hematopoietic stem cell (HSC) aging, focusing on Notch signaling and its regulation by the ligand Jagged2 (JAG2) (Interview with Dr. Carolina Florian)
2. Advances in immunotherapy for KMT2A (MLL) rearranged leukemia using off-the-shelf dual CAR invariant NKT (CAR-iNKT) cells (Interview with Dr. Anastasios (Tassos) Karadimitris)

The episode explores the biological underpinnings, translational potential, and future research directions of these pioneering studies.

I. Notch Transactivation to CIS Inhibition Switch in HSC Aging

Guest: Dr. Carolina Florian, Institut d’Investigació Biomèdica de Bellvitge (IDIBELL), Spain

1. Background and Study Motivation

• Traditional focus has been on Notch signaling during early HSC development, with its role in adult and aged HSCs unclear.
• The study investigates how aging alters Notch signaling and the bone marrow microenvironment to affect HSCs.

Quote [01:18]:
“Notch is one of the most important and developmentally conserved signaling pathways...the role of Notch signaling later in adult and aged mice was largely unknown. We thought that it was worth investigating.” – Dr. Carolina Florian

2. Methods and Key Findings

[03:00]

• Primary method: 3D histology and deep-learning image analysis to reconstruct HSC spatial distribution in bone marrow.
• Used Notch-GFP reporter mice and conditional JAG2 knockout models.
• Core findings:
  • Aging increases quiescent, Notch-inactive HSCs, identifiable by their shifted bone marrow position.
  • These HSCs expand in clonal myeloid-biased clusters—explaining age-associated myeloid skewing.
  • Deletion of JAG2 on bone marrow vasculature mimics aging phenotypes, showing JAG2’s key regulatory role.

Quote [03:00]:
“We could show that with aging, there is increase in the amount of stem cells that are inactive. And these cells are the ones that do expand with aging.” – Dr. Carolina Florian

3. Mechanistic Insights: Notch to CIS Inhibition Switch

[05:58]

• Novel maladaptive mechanism: aged HSCs begin to express JAG2 ligand themselves, leading to CIS inhibition—shutting off Notch signaling in an autocrine manner.
• This contributes to loss of regenerative potential.

Quote [05:58]:
“We indeed observe this switch where HSCs in aged mice start expressing themselves the JAG2 ligand…and this induces a CIS inhibition…leading to the functional impairment that we demonstrate with transplantation assays.” – Dr. Carolina Florian

4. Translational Implications and Future Directions

[07:41] & [08:48]

• Opportunity to rejuvenate aged hematopoietic systems by targeting the niche and preempting pathological clonal expansions.
• Next steps include translating findings to humans and exploring connections to clonal hematopoiesis and leukemia.

Quote [07:41]:
“…there are possibility of intervention by targeting the surrounding niche and prevent the clonal expansion before it happens. And this is actually what we aim to investigate in the future in the lab.” – Dr. Carolina Florian

II. Off-the-Shelf Dual CAR-iNKT Cell Immunotherapy for KMT2A Rearranged Leukemia

Guest: Dr. Anastasios (Tassos) Karadimitris, Imperial College London

1. Rationale for CAR-iNKT Use in High-Risk Leukemia

[11:20]

• Previous work showed iNKT cells outperforming T cells when engineered with similar CARs.
• High-risk KMT2A-rearranged ALL (acute lymphoblastic leukemia) often relapses and disproportionately affects infants.

Quote [11:30]:
“We demonstrated their higher performance when compared with T cells both engineered with the same CAR…So that was the motivation.” – Dr. Anastasios Karadimitris

2. Dual Target Engineering: CD19 and CD133

[12:37]

• CD19 is standard but relapses often show CD19-negative disease.
• Targeted a second antigen, CD133 (uniquely overexpressed in KMT2A-rearranged leukemia), informed by collaboration with Tom Milne at Oxford.

Quote [12:37]:
“CD19 is not enough…so we had to target the second leukemia associated antigen...CD133, which is almost exclusively expressed in high risk KMT2a rearranged leukemia.” – Dr. Anastasios Karadimitris

3. Novel Mechanism: NKG2D-Dependent Killing

[13:39]

• Unexpected discovery: CAR-iNKT cells upregulate NK activating receptor NKG2D significantly upon tumor engagement, more so than CAR-T cells.
• This allows CAR-iNKTs to kill target-negative leukemia cells in the vicinity via NKG2D, a critical bystander effect.

Quote [14:39]:
“When we co-culture CAR NKT with leukemia cells and we checked expression of NKG2D the next day, it went up from 40% average to 100%...if the leukemia cell next to it doesn't express one or both of the CAR targets, it can still be killed through the NKG2D dependent manner.” – Dr. Anastasios Karadimitris

4. Superior CNS Penetration

[16:10]

• CAR-iNKT cells were effective in clearing leptomeningeal (CNS) leukemia, where CAR-T cells fail.
• This ability involves high VLA-4 integrin expression on iNKT cells, which facilitates migration across the blood-brain barrier.

Quote [16:10]:
“CAR NKT could clear established secondary B cell lymphoma very efficiently in preclinical models…We identify VLA4 as an integrin which is preferential and higher expressed in INKT compared to T cells and that allows CAR NKT to adhere more firmly on endothelial cells, including endothelial cells of the blood brain barrier...” – Dr. Anastasios Karadimitris

5. Clinical Outlook and Limitations

[18:09]

• Acknowledgment that persistence and efficacy in humans remains to be proven; clinical trials are pending.
• Technology licensed in Australia, with phase I trials for B-cell lymphoma expected in 2026, paving the way for trials in KMT2A leukemia.

Quote [18:09]:
“It won’t be too long before at least our technology will be tested in the clinical setting...if things go well...developing also the type of immunotherapy we described in this article...” – Dr. Anastasios Karadimitris

Notable Quotes and Timestamps

• “Notch is one of the most important and developmentally conserved signaling pathways...the role of Notch signaling later in adult and aged mice was largely unknown. We thought that it was worth investigating.” – Dr. Carolina Florian [01:18]
• “We could show that with aging, there is increase in the amount of stem cells that are inactive. And these cells are the ones that do expand with aging.” – Dr. Carolina Florian [03:00]
• “We indeed observe this switch where HSCs in aged mice start expressing themselves the JAG2 ligand…and this induces a CIS inhibition…leading to the functional impairment...” – Dr. Carolina Florian [05:58]
• “If the leukemia cell next to it doesn't express one or both of the CAR targets, it can still be killed through the NKG2D-dependent manner. So that was really a very exciting finding.” – Dr. Anastasios Karadimitris [14:39]
• “CAR NKT could clear established secondary B cell lymphoma very, very efficiently in preclinical models, of course, whereas CAR T could not do that....we identify VLA4 as an integrin which is preferential and higher expressed in INKT...that allows CAR NKT to adhere more firmly on endothelial cells, including endothelial cells of the blood brain barrier...” – Dr. Anastasios Karadimitris [16:10]

Key Segments and Timestamps

• [00:40] Notch & HSC Aging: Introduction to Dr. Carolina Florian’s research
• [01:18] Background on Notch in hematopoiesis
• [03:00] 3D histology methodology and data on stem cell niche and positional aging
• [05:58] Maladaptive Notch-to-CIS inhibition switch in aging HSCs, significance
• [07:41] Rejuvenation potential and future directions in targeting aged HSC microenvironment
• [08:48] Translational vision—human applications and leukemia relevance
• [11:16] Introduction to CAR-iNKT immunotherapy in high-risk leukemia (Dr. Karadimitris)
• [12:37] Dual targeting rationale: CD19 and CD133 in CAR design
• [13:39] NKG2D-mediated bystander killing emerges as novel mechanism
• [16:10] CNS clearance advantage; integrin VLA-4 and blood-brain barrier traversal
• [18:09] Status and outlook for CAR-iNKT cell clinical translation

Conclusion

This episode delivers a focused, insight-rich dialogue with experts whose research is redefining our understanding of HSC aging and immunotherapy for high-risk leukemia. Their mechanistic discoveries—Notch pathway modulation in aging and NKG2D-driven bystander killing—signal tangible translational opportunities while highlighting the importance of niche biology, cellular engineering, and preclinical rigor.

For full articles and further details, visit www.bloodjournal.org.