Aberrant Repertoire and Deficient Proliferation of TCR γδ T Cells in Myelodysplastic Syndromes (MDS).
Authors: Kiladjian Jean-Jacques , Visentin Géraldine , Viey Emilie , Ayari Sameh , Bourhis Jean-Henri , Chouaib Salem , Fenaux Pierre , Caignard Anne 
Published: October 2019

Background: We recently showed that MDS natural killer cells display altered cytolytic function and proliferation in response to IL-2 (Leukemia, 2006;20:463–70). TCR γδ T cells are other important components of innate immunity, recently shown to be involved in the immune response against various tumors. Furthermore, a TCR γδ agonist synthetic phosphoantigen, the BrHPP molecule, is able to expand and activate in vitro Vδ2 cells (the peripheral blood circulating subset of γδ T cells). We studied γδ T cell population in MDS patients.

Methods: PBMCs from 31 MDS patients (WHO: 3 pure RA, 2 pure RAS, 1 RCMD-RS, 6 RCMD, 2 del5q, 8 RAEB1, 4 RAEB2, 5 MDS-U; IPSS: 9 low, 12 Int-1, 6 Int-2, 4 High) and 15 controls were stimulated with BrHPP and IL-2 during 8 to 15 days. Immunophenotyping of αβ and γδ T cells was determined by multi-color flow cytometry. Cytolytic capacity of activated Vδ2 T cells was assessed using 51Cr release and CD107a degranulation assays. IFNγ was measured by ELISA after TCR γδ triggering of expanded γδ T cells.

Results: % and absolute numbers of γδ T cells from MDS were comparable to those of controls, but MDS Vδ2 T cell repertoire was significantly skewed: 10/19 MDS Vδ2 T cells were characterized by a “naive” predominant population, 5/19 had a majority of “effectors” cells, and only 4 of 19 had a predominant “central memory population”, which was always the main Vδ2 compartment in healthy donors. Stimulation with BrHPP induced a significant increase of MDS Vδ2 T cells subset, indicating their specific activation. However, MDS Vδ2 T cells poorly proliferated in 2 week cultures in response to IL-2, in contrast with the high proliferation index of controls derived cells. On day 8 of culture, only 6 of the 29 MDS samples studied clearly responded to BrHPP+IL-2 (i.e. >60% of Vδ2 cells in culture) compared to 13/15 in controls, while 12/29 were intermediate responders (20 to 60% of Vδ2), and 11/29 non-responders. We found no correlation between response to BrHPP and WHO, cytogenetics or IPSS category. However, coexistence of immunologic abnormalities (rheumatoid arthritis in 5 patients, temporal arteritis in 1, antiphospholipid syndrome in 1, Raynaud’s phenomenon in 2, and thyroiditis in 2) was more frequent in non-responders. The 3 IL-2 receptor (IL-2-R) chains were normally expressed in MDS Vδ2 T cells and IL-2-Rα expression was normally induced in response to IL-2. We are currently investigating downstream signaling molecules of the IL-2-R pathway. Functional activity of MDS γδ T cells (cytotoxicity, degranulation, and IFNg secretion) was similar to that of healthy donor cells. In particular, those cells were cytotoxic against the MDS-derived P39 cell line.

Conclusion: in MDS, γδ T cell repertoire is profoundly skewed, and those cells do not proliferate in response to potent agonists, although their numbers and function seem normal. Those alterations did not correlate with MDS characteristics, but were more frequent in patients with associated immunological abnormalities. Our results further support the existence of important alterations of innate immunity effectors in MDS that could play a role in disease pathophysiology or progression.