Gammadelta T cells do not require fully functional cytotoxic pathways or the ability to recognize recipient alloantigens to prevent graft rejection

Deciphering the Contribution of γδ T Cells to Outcomes in Transplantation

γδ T cells are a subpopulation of lymphocytes expressing heterodimeric T-cell receptors composed of γ and δ chains. They are morphologically and functionally heterogeneous, innate yet also adaptive in behavior, and exhibit diverse activities spanning immunosurveillance, immunomodulation, and direct cytotoxicity. The specific responses of γδ T cells to allografts are yet to be fully elucidated with evidence of both detrimental and tolerogenic roles in different settings. Here we present an overview of γδ T-cell literature, consider ways in which their functional heterogeneity contributes to the outcomes after transplantation, and reflect on methods to harness their beneficial properties.

Translational Implications for Off-the-shelf Immune Cells Expressing Chimeric Antigen Receptors

Chimeric antigen receptor (CAR) endows specificity to T-cells independent of human leukocyte antigen (HLA). This enables one immunoreceptor to directly target the same surface antigen on different subsets of tumor cells from multiple HLA-disparate recipients. Most approaches manufacture individualized CAR(+)T-cells from the recipient or HLA-compatible donor, which are revealing promising clinical results. This is the impetus to broaden the number of patients eligible to benefit from adoptive immunotherapy such as to infuse third-party donor derived CAR(+)T-cells. This will overcome issues associated with (i) time to manufacture T-cells, (ii) cost to generate one product for one patient, (iii) inability to generate a product from lymphopenic patients or patient's immune cells fail to complete the manufacturing process, and (iv) heterogeneity of T-cell products produced for or from individual recipients. Establishing a biobank of allogeneic genetically modified immune cells from healthy third-party donors, which are cryopreserved and validated in advance of administration, will facilitate the centralizing manufacturing and widespread distribution of CAR(+)T-cells to multiple points-of-care in a timely manner. To achieve this, it is necessary to engineer an effective strategy to avoid deleterious allogeneic immune responses leading to toxicity and rejection. We review the strategies to establish "off-the-shelf" donor-derived biobanks for human application of CAR(+)T-cells as a drug.

Granulocyte colony-stimulating factor affects the distribution and clonality of TRGV and TRDV repertoire of T cells and graft-versus-host disease

Background

The immune modulatory effect of granulocyte colony-stimulating factor (G-CSF) on T cells resulted in an unexpected low incidence of graft-versus-host disease (GVHD) in allogeneic peripheral blood stem cell transplantation (allo-PBSCT). Recent data indicated that gamma delta⁺ T cells might participate in mediating graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) effect after allogeneic hematopoietic stem cell transplantation. However, whether G-CSF could influence the T cell receptors (TCR) of gamma delta⁺ T cells (TRGV and TRDV repertoire) remains unclear. To further characterize this feature, we compared the distribution and clonality of TRGV and TRDV repertoire of T cells before and after G-CSF mobilization and investigated the association between the changes of TCR repertoire and GVHD in patients undergoing G-CSF mobilized allo-PBSCT.

Methods

The complementarity-determining region 3 (CDR3) sizes of three TRGV and eight TRDV subfamily genes were analyzed in peripheral blood mononuclear cells (PBMCs) from 20 donors before and after G-CSF mobilization, using RT-PCR and genescan technique. To determine the expression levels of TRGV subfamily genes, we performed quantitative analysis of TRGVI~III subfamilies by real-time PCR.

Results

The expression levels of three TRGV subfamilies were significantly decreased after G-CSF mobilization (P = 0.015, 0.009 and 0.006, respectively). The pattern of TRGV subfamily expression levels was TRGVII >TRGV I >TRGV III before mobilization, and changed to TRGV I >TRGV II >TRGV III after G-CSF mobilization. The expression frequencies of TRGV and TRDV subfamilies changed at different levels after G-CSF mobilization. Most TRGV and TRDV subfamilies revealed polyclonality from pre-G-CSF-mobilized and G-CSF-mobilized samples. Oligoclonality was detected in TRGV and TRDV subfamilies in 3 donors before mobilization and in another 4 donors after G-CSF mobilization, distributed in TRGVII, TRDV1, TRDV3 and TRDV6, respectively. Significant positive association was observed between the invariable clonality of TRDV1 gene repertoire after G-CSF mobilization and low incidence of GVHD in recipients (P = 0.015, OR = 0.047).

Conclusions

G-CSF mobilization not only influences the distribution and expression levels of TRGV and TRDV repertoire, but also changes the clonality of gamma delta⁺ T cells. This alteration of TRGV and TRDV repertoire might play a role in mediating GVHD in G-CSF mobilized allo-PBSCT.

T10B9 monoclonal antibody: a short-acting nonstimulating monoclonal antibody that spares gammadelta T-cells and treats and prevents cellular rejection

T10B9.1A-31/MEDI-500 is a nonmitogenic immunoglobulin M kappa murine monoclonal antibody (mAb) directed against the alpha-beta (αβ) heterodimer of the T-lymphocyte receptor complex. The hybridoma was first produced by fusing spleen cells from BALB/C mice immunized with human peripheral blood T-lymphocytes with SP2/O-Ag14 mutant myeloma cells. The mAb is produced and purified using multistep ion exchange and molecular sieve chromatography protocols. T10B9 has been used successfully to treat acute cellular rejection in renal transplantation and as an immunosuppression induction agent in heart and simultaneous kidney-pancreas transplantation. Because T10B9 is nonmitogenic and causes minimal cytokine release, both treatment of rejection and induction of immunosuppression were accomplished with significantly fewer and milder untoward effects (cytokine release syndrome) than its comparator OKT3. Since T10B9 is directed against the αβ heterodimer of the CD3 epitope, it spares the gamma delta (γδ) region. These gamma delta (γδ) T cells have a unique role in the immune response controlling many serious human diseases and perhaps facilitating the development of immunologic tolerance. T10B9 has a relatively short duration of action, depleting T cells for only 10 to 14 days, unlike the protracted depletion seen with thymoglobulin and Campath-1H. There is no B-lymphocyte depletion with T10B9 as there is with both of the aforementioned reagents. The lack of prolonged lymphocyte depletion may account for less infection observed with T10B9 treatment.

Separating graft-versus-leukemia from graft-versus-host disease in allogeneic hematopoietic stem cell transplantation

Routine methods to maximize the graft-versus-leukemia (GvL) activity of allogeneic hematopoietic stem cell transplantation (HSCT) without the detrimental effects of graft-versus-host disease (GvHD) are lacking. Depletion or inhibition of alloreactive T cells is partially effective in preventing GvHD, but usually leads to decreased GvL activity. The current model for the pathophysiology of acute GvHD describes a series of immune pathways that lead to activation of donor T cells and inflammatory cytokines responsible for tissue damage in acute GvHD. This model does not account for how allotransplant can lead to GvL effects without GvHD, or how the initial activation of donor immune cells may lead to counter-regulatory effects that limit GvHD. In this review, we will summarize new findings that support a more complex model for the initiation of GvHD and GvL activities in allogeneic HSCT, and discuss the potential of novel strategies to enhance GvL activity of the transplant.