SCIENTIFIC PROGRAMME
SESSION I
BIOLOGY OF B-CELL
PRECURSOR ALL
SESSION II
BIOLOGY OF T-CELL ALL
SESSION III
MINIMAL RESIDUAL
DISEASE MONITORING
SESSION IV
INDIVIDUALIZED
MANAGEMENT OF ALL
SESSION V
NEW ADVANCES IN ALL
SESSION VI
CAR T-CELLS &
ALLOGENEIC HSCT
SESSION VII
FRONTLINE
INCORPORATION OF
BITES AND ADCS
SESSION VIII
T-CELL ALL AND
LYMPHOBLASTIC
LYMPHOMA
SESSION IX
PH AND PH-LIKE ALL
SELECTED ABSTRACTS
FOR AN ORAL
PRESENTATION
SELECTED ABSTRACTS
AS E-POSTERS
DISCLOSURES
IMPACT OF TUMOR-ASSOCIATED MYELOID CELL DEPLETION ON T-CELL LEUKEMIA
DEVELOPMENT
Telma Costa1,2, Ivette Pacheco-Leyva1,2 and Nuno R. dos Santos1,2
(1) IPATIMUP - Institute of Molecular Pathology and Immunology, University of Porto, Porto, Portugal,
(2)i3S - Instituto de Investigação e Inovação em Saúde, Porto, Portugal
I
ntroduction
T-lymphoblastic leukemia/lymphoma (T-ALL/LBL) is an aggressive malignancy originating from
immature T-cell precursors, which depends not only on cell-intrinsic genetic alterations, but
also extrinsic stromal cell signals. Our group has previously shown that ETV6-JAK2 fusion
transgenic (also called TEL-JAK2; TJ2-Tg) mice exhibit an increased content of dendritic cells
(DCs) in the thymic lymphoma microenvironment, alongside with macrophages presence.
Although recent studies revealed that both DCs and macrophages promote proliferation or
survival of leukemic T cells in vitro, whether myeloid cells promote leukemogenesis in vivo
remains to be determined.
Material and Methods
Here, we aimed to deplete myeloid lineage cells before T-ALL/LBL development in TJ2-Tg mice,
and study the impact on disease development. For that we started by generating LysM-Cre/
R26iDTR mice, by crossing Lysozyme M (LysM)-Cre transgenic strain with ROSA26-loxP-STOP-
loxP-DTR (R26iDTR) strain. These mice express the simian Diphtheria Toxin (DT)
Receptor (DTR) in LysM+ myeloid cells after loss of the STOP sequence mediated by Cre
recombinase. Mice were injected intraperitoneally with optimized doses of DT to kill DTR-expressing
cells. Flow cytometry analysis of peripheral blood, hematopoietic organs (thymus,
spleen, bone marrow) and peritoneal exudate was performed to monitor myeloid cells
depletion post-DT injection. In addition, cell or tissue section immunofluorescence was
performed using anti-DTR together with myeloid (F4/80) or epithelial (Keratin) antibodies.
LysM-Cre─/R26iDTR mice were used as negative controls. TJ2-Tg/LysM-Cre/R26iDTR were
generated and treated with the optimized DT administration protocol.
Results
Immunofluorescence staining of primary macrophages isolated from the peritoneum revealed
co-expression of F4/80 and DTR proteins only in LysM-Cre+/R26iDTR mice, confirming Cre-mediated
loxP recombination in myeloid cells. Flow cytometry results indicate that treatment
of LysM-Cre+/R26iDTR mice with higher doses of DT initially, followed by lower doses for
maintenance seems to promote a long-term reduction in several myeloid cell populations
(DCs, macrophages, CD11b+ cells) in the organs analyzed. In turn, thymic and splenic
immunofluorescence analysis revealed no structural alterations in both LysM-Cre+/R26iDTR
and LysM-Cre─/R26iDTR mice post-treatment. TJ2-Tg/LysM-Cre+/R26iDTR mice treated
with DT showed a reduction in thymic CD8+ conventional DCs (cDCs) number compared to TJ2-
Tg/LysM-Cre─/R26iDTR mice, which was associated with a lower proportion of leukemic cells
in the thymus. On the other hand, the analysis of secondary lymphoid organs from DT-treated
TJ2-Tg/LysM-Cre+/R26iDTR mice revealed a higher proportion of TJ2+ cells, associated with
weaker myeloid cell depletion.
Discussion and Conclusion
Our preliminary data indicates that DT-mediated depletion of thymic CD8+ cDCs in TJ2-
Tg/LysM-Cre+/R26iDTR mice may favor leukemic cell egress from the thymus, and suggests
that these myeloid cells are fundamental for survival of TJ2+ cells in the thymic lymphoma
microenvironment. In the future, we intend to generate TJ2-Tg/LysM-Cre+/R26EYFP
POSTER 4