Tessera Therapeutics Showcases New Preclinical Data Advancing In Vivo Program in Sickle Cell Disease and CAR-T Applications at the American Society of Gene and Cell Therapy 29th Annual Meeting

Presented improved editing data in non-human primates (NHP) for sickle cell disease (SCD), demonstrating a single dose of Gene Writer achieved an average of 85% of long-term hematopoietic stem cells (LT-HSCs) with at least one allele edited on single cell analysis, exceeding the anticipated curative threshold
Reported first demonstration of permanent chimeric antigen receptor (CAR) integration in NHP with a single dose of Gene Writer delivered as all-RNA in T cell-directed lipid nanoparticles (LNP), which expanded to ~60% of circulating T cells and resulted in meaningful B cell clearance in blood and lymph nodes

SOMERVILLE, Mass., May 14, 2026 (GLOBE NEWSWIRE) -- Tessera Therapeutics (“Tessera”), the biotechnology company pioneering a new approach in genetic medicine known as Gene Writing™, is presenting updates across its in vivo genetic medicine programs for SCD and T cell therapies, including its proprietary delivery platform that enables extra-hepatic LNP delivery to hematopoietic stem cells (HSCs) and T cells. These data were shared across four presentations at the American Society of Gene and Cell Therapy (ASGCT) Annual Meeting taking place in Boston, Massachusetts, May 11 – 15, 2026.

“Our latest data represent a significant advancement towards demonstrating the potential of an in vivo Gene Writing program as a transformative approach for genetic medicine. In non-human primates, a single dose of our Gene Writer achieved levels of editing in long-term hematopoietic stem cells that are well above the levels believed to be required for curative benefit in sickle cell disease. Notably, this was accomplished without stem cell mobilization, myeloablative conditioning, or transplantation,” said Michael Severino, M.D., CEO of Tessera Therapeutics. “In parallel, for the first time in multiple NHP species, we have shown that a single dose of Gene Writers formulated in T cell targeted LNPs successfully inserted a CAR permanently into the genome, which resulted in the generation of functional CAR-T cells directly in vivo with meaningful B cell depletion in blood and lymph nodes. Together, these results highlight the breadth and potential of our Gene Writing and delivery platforms.”

In Vivo SCD Data

SCD is the most common lethal monogenic disease worldwide, arising from a mutation in the hemoglobin beta-globin (HBB) gene that results in hemoglobin S, which can cause red blood cell sickling, chronic hemolytic anemia, recurrent vaso-occlusive events (VOEs) and progressive multi-organ damage.

In NHPs treated with an optimized Gene Writer formulated in LNP, single cell analysis of LT-HSCs demonstrated that an average of 85% of cells had at least one edited HBB gene after a single dose. This represents a meaningful improvement over earlier data presented at the American Society of Hematology 67 ^th Annual Meeting, where 40% of cells had mono or bi-allelic HBB editing after a single dose of Gene Writer administered.
This level of edited cells (85%) substantially exceeds the 20-30% edited HSC threshold associated with meaningful clinical benefit, including resolution of VOEs and improved anemia¹^-⁴, and is further supported by in-house preclinical transplant data in the Townes disease mouse model demonstrating comparable functional correction regardless of whether cells carried one or two corrected HBB gene copies. Notably, these levels are within the range of editing and transduction levels reported for approved ex vivo gene therapy products⁴^,5.
In NHPs, a single dose of various optimized LNP-delivered Gene Writers targeting HBB was well tolerated, without meaningful changes in clinical chemistry and hematology parameters, while achieving robust editing.
Longitudinal data in NHP demonstrated durable HBB editing in LT-HSCs for up to ~19 months, with consistent levels of editing observed across multiple hematopoietic lineages, indicating intact HSC function with continued follow-up.

Advances Towards In Vivo T-Cell Therapies

Tessera is applying its Gene Writing and proprietary LNP delivery platforms to develop in vivo cell therapies for potential oncology and autoimmune disease applications.

For the first time in multiple NHP species, including cynomolgus and Rhesus macaque, a single low dose of either 0.1 mg or 0.05 mg/kg Gene Writer with CD20 CAR cargo formulated in a proprietary targeted LNP successfully generated functional T cells in vivo.
In NHP, these CD20 targeted CAR-T cells underwent robust and rapid CAR-T cell expansion to approximately 60% of circulating T cells, and exhibited low transgene copy number per cell.
These in vivo generated CAR-T cells mediated B cell depletion in peripheral blood and lymph nodes, as confirmed by immunohistochemistry, for up to 35 days.

This research was funded, in part, by the Advanced Research Projects Agency for Health (ARPA-H). The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the U.S. Government.

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¹ Leonard A, et al., Blood Advances. 2024
² Magnani A, et al., Haematologica. 2020
³ Fitzhugh CD, et al., Blood. 2017
⁴ Kanter J, et al. Am J Hematol. 2023
⁵ Frangoul H, et al. NEJM. 2024

About Tessera Therapeutics

Tessera Therapeutics is a clinical-stage biotechnology company pioneering an innovative approach to genome engineering through the development of its Gene Writing™ and delivery platforms, with the goal of advancing in vivo genetic medicines. Our Gene Writing platform utilizes all-RNA constructs and is designed to write therapeutic messages into the genome by leveraging a process known as target-primed reverse transcription (TPRT) to efficiently change single or multiple DNA base pairs or add exon-length sequences or whole genes. Our proprietary lipid nanoparticle delivery platform is designed to enable the in vivo delivery of RNA to targeted cell types. We believe our Gene Writing and delivery platforms position us to advance differentiated in vivo genetic medicines designed to not only cure monogenic diseases but also create engineered cells to fight cancer and autoimmune disease and modify inherited risk factors to treat common diseases. Tessera Therapeutics was founded in 2018 by Flagship Pioneering, a life sciences innovation enterprise which invents and builds platform companies, each with the potential for multiple products that transform human health, sustainability, and beyond.

For more information about Tessera, please visit www.tesseratherapeutics.com.

Contact
Jonathan Pappas
LifeSci Communications, LLC
jpappas@lifescicomms.com

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