Differentiation of a CD4+/CD8ab+ Double Positive T cell Population From the CD8 Pool is Sufficient To mediate Graft-vs-Host Disease but not Graft-vs-Leukemia Effects
Hess et al. (BioRxiv) DOI: 10.1101/2022.01.11.475845
Allogenic Hematopoietic Stem Cell transplant (allo-HSCT)
CD4+CD8ab+ Double Positive T cell
Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an effective treatment option to cure haematological malignancies, but one of the primary complications of this treatment is the development of Acute graft-vs-host disease (aGVHD). A better understanding of the cellular mechanism triggering aGVHD might provide new predictive markers and highlight directions for the development of targeted prophylactic treatment.
In this preprint, the authors report the differentiation of a mature CD4+CD8+ double positive T (DPT) cell population that correlates with the development of acute graft versus host disease in a model of xenogeneic transplantation as well as in the blood of patients with grade IV aGVHD. This DPT population raises following the transfer of either human peripheral blood mononuclear cells (PBMC), or enriched CD8+ T cells into immune-deficient NSG mice but not following the transfer of CD4+ T cells, suggesting that they originate from the mature CD8+ T cell pool. While profiling DPT cells by flow cytometry, they observed the expression of transcription factors and cytokines specific for both single positive CD4 and CD8 T cell population as well as an intermediate repertoire of co-stimulatory and inhibitory ligands. In addition, DPT cells display an increased ATP production from the glycolytic pathway and a high frequency of blasted cells reflecting a high activation status. The secondary transfer of sorted DPT cells into new recipients is sufficient to trigger aGVHD while the transfer of its single positive counterpart population doesn’t. Surprisingly, the authors couldn’t observe a second wave of DPT cells differentiation in this condition which could reflect a decrease of alloantigen specific T cells into the CD8+ pool. Overall, this study sheds light on a double positive population that could serve as an early marker and predictor for aGVHD development following allo-HSCT.
Lack of conclusive results for the origin of the DPT population. While the data suggest that DPT originate from CD8 T cells due to the results obtained by transplanting enriched CD8+ T cells, the lack of a second wave of differentiation following the transfer of sorted CD8+ T cells into a new recipient led to the interrogation of this statement. The authors should use sorted cells in their first set of experiments to validate that only human CD8+ T cells transplant lead to the generation of this DPT cell population. In addition, as the authors mentioned, the lack of a second wave of differentiation might highlight a modification in the CD8+ T cells TCR repertoire after the initial transplant due to a depletion of allo-Ag specific T cells. It could be investigated more conclusively by directly comparing the TCR repertoire of the DPT cells and SP T cells before and after transplant. Finally, would it be possible to transfer DPT cells coming from the first transplant into an immune deficient mouse with a different genetic background?
A direct comparison of single positive T cells and DPT cells at the transcriptomic level is missing. While in Figure 2, the authors generate a tSNE plot to check the proximity of the DPT cells to CD8 or CD4 single positive T cells using 8 markers (missing information regarding these markers), it would be more relevant and stronger to compare these three populations in a broader manner for example at the transcriptomic level. These could reveal which characteristics are shared between DPT and single positive CD4 or CD8 T cells and whether the DPT are closer to the CD8 T cells.
The authors claim that DPT cells are sufficient to trigger aGVHD but does not lead to GVL effect. This part of the study is completely misleading and not convincing. In the Figure 6, the authors compare the effect of either human PBMC directly transferred into their mouse model or DPT cells isolated from an initial transplanted mouse that they reinject in a second recipient. This comparison is misleading and indeed, when looking at proper comparison in figure S7, the effect is almost gone.
This study highlights in a xenogeneic model of allo-HSCT and in patient developing aGVHD, the presence of a mature and activated CD4+CD8+ T cell population that might be responsible for the disease.
The DPT cells detection could serve as a new screening strategy to detect at early timepoint the development of aGVHD in transplanted patient.
Reviewed by Anne Chauveau as part of the cross-institutional journal club of the Immunology Institute of the Icahn School of Medicine, Mount Sinai, the Kennedy Institute of Rheumatology and the Oxford Centre for Immuno-Oncology (OXCIO) (University of Oxford, GB) and Karolinska Institute’s Center for Infectious Medicine (CIM) & Center for Molecular Medicine (CMM).