Expression of CD62L on Donor CD4+ T Cells in Allografts: Correlation with Graft-Versus-Host Disease after Unmanipulated Allogeneic Blood and Marrow Transplantation

Graft-versus-Host Disease Modulation by Innate T Cells

Allogeneic cell therapies, defined by genetically mismatched transplantation, have the potential to become a cost-effective solution for cell-based cancer immunotherapy. However, this type of therapy is often accompanied by the development of graft-versus-host disease (GvHD), induced by the mismatched major histocompatibility complex (MHC) between healthy donors and recipients, leading to severe complications and death. To address this issue and increase the potential for allogeneic cell therapies in clinical practice, minimizing GvHD is a crucial challenge. Innate T cells, encompassing subsets of T lymphocytes including mucosal-associated invariant T (MAIT) cells, invariant natural killer T (iNKT) cells, and gamma delta T (γδ T) cells, offer a promising solution. These cells express MHC-independent T-cell receptors (TCRs), allowing them to avoid MHC recognition and thus GvHD. This review examines the biology of these three innate T-cell populations, evaluates research on their roles in GvHD modulation and allogeneic stem cell transplantation (allo HSCT), and explores the potential futures for these therapies.

Naive T Cells in Graft Versus Host Disease and Graft Versus Leukemia: Innocent or Guilty?

The outcome of allogeneic hematopoietic cell transplantation (allo-HCT) largely depends on the development and management of graft-versus-host disease (GvHD), infections, and the occurrence of relapse of malignancies. Recent studies showed a lower incidence of chronic GvHD and severe acute GvHD in patients receiving naive T cell depleted grafts compared to patients receiving complete T cell depleted grafts. On the other hand, the incidence of acute GvHD in patients receiving cord blood grafts containing only naive T cells is rather low, while potent graft-versus-leukemia (GvL) responses have been observed. These data suggest the significance of naive T cells as both drivers and regulators of allogeneic reactions. The naive T cell pool was previously thought to be a quiescent, homogenous pool of antigen-inexperienced cells. However, recent studies showed important differences in phenotype, differentiation status, location, and function within the naive T cell population. Therefore, the adequate recovery of these seemingly innocent T cells might be relevant in the imminent allogeneic reactions after allo-HCT. Here, an extensive review on naive T cells and their contribution to the development of GvHD and GvL responses after allo-HCT is provided. In addition, strategies specifically directed to stimulate adequate reconstitution of naive T cells while reducing the risk of GvHD are discussed. A better understanding of the relation between naive T cells and alloreactivity after allo-HCT could provide opportunities to improve GvHD prevention, while maintaining GvL effects to lower relapse risk.

Variable impact of graft CD3+ cell content on graft versus host disease in hematopoietic stem cell transplant recipients: Is the role of donor CD3+ cells overestimated?

Graft cellular composition is considered as a significant determinant of transplant outcome. Donor CD3⁺ cells were shown to have a significant association with the development of graft vs host disease (GvHD). The aim of this study was to investigate the impact of graft CD3⁺ cell content on transplant outcome, particularly in terms of GvHD and relapse. We retrospectively analysed the records of 515 allo-HCT recipients [median age: 37(15-71) years; male/female: 323/192]. The optimal threshold of infused CD3⁺ cell count for acute GvHD development was estimated to be 197.5 × 10⁶/kg (AUC: 0.572; 95 % CI: 0.513-0.631; p = 0.018) and 198.5 × 10⁶/kg (AUC: 0.6; 95 % CI: 0.520-0.679; p = 0.019) for the general population and reduced-intensity conditioning (RIC) subgroup, respectively. Acute GvHD was more frequent in low-CD3⁺ group in the whole study population, particularly in RIC transplants. The incidence of cytomegalovirus reactivation was higher in low-CD3⁺ group and neutrophil engraftment occured earlier in the same group of patients. Overall survival and non-relapse mortality were comparable between high and low-CD3⁺ groups. Age, ECOG performance status, hypogammaglobulinemia, chronic GvHD and post-transplant relapse were found to predict prognosis in multivariate analysis. By focusing mainly on donor T cells, the potential role of host immune cells in the early post-transplant milieu may have been underestimated. Drawing a more detailed profile of graft and host immune cells in the joint microenvironment may elucidate our way to a better understanding of GvHD pathogenesis. By this way a comprehensive pre-transplant risk assessment could be improved to generate more personalized approaches.

Immune Reconstitution After Allogeneic Haematopoietic Cell Transplantation: From Observational Studies to Targeted Interventions

Immune reconstitution (IR) after allogeneic haematopoietic cell transplantation (HCT) represents a central determinant of the clinical post-transplant course, since the majority of transplant-related outcome parameters such as graft-vs.-host disease (GvHD), infectious complications, and relapse are related to the velocity, quantity and quality of immune cell recovery. Younger age at transplant has been identified as the most important positive prognostic factor for favourable IR post-transplant and, indeed, accelerated immune cell recovery in children is most likely the pivotal contributing factor to lower incidences of GvHD and infectious complications in paediatric allogeneic HCT. Although our knowledge about the mechanisms of IR has significantly increased over the recent years, strategies to influence IR are just evolving. In this review, we will discuss different patterns of IR during various time points post-transplant and their impact on outcome. Besides IR patterns and cellular phenotypes, recovery of antigen-specific immune cells, for example virus-specific T cells, has recently gained increasing interest, as certain threshold levels of antigen-specific T cells seem to confer protection against severe viral disease courses. In contrast, the association between IR and a possible graft-vs. leukaemia effect is less well-understood. Finally, we will present current concepts of how to improve IR and how this could change transplant procedures in the near future.

High proportions of CD3+ T cells in grafts delayed lymphocyte recovery and reduced overall survival in haploidentical peripheral blood stem cell transplantation

T cells in grafts serve an important role in the pathogenesis of graft versus host disease (GVHD) and immune recovery during HLA matched allogeneic stem cell transplantation. However, the role of T cells in the haploidentical peripheral blood stem cell transplantation (Haplo-PBSCT) is yet to be determined. In the present study, the role of CD3⁺ T cells in grafts and impact on hematopoietic and immune recovery, cytomegalovirus (CMV) reactivation, GVHD, relapse, progress free survival and overall survival (OS) were evaluated and analyzed. A total of 30 patients who underwent haplo-PBSCT were included in the present study. CD3⁺ T cells accounted for a median of 23.1% (range 8-47.4%) with a median dose of 299.7x10⁶/kg (range 104-623.4). Patients were divided into two groups according to the CD3⁺ T cell count: Above the median (high T cell group) and below the median CD3⁺ T cell (low T cell group). No significant difference was identified between neutrophil and platelet recovery time between two groups (P>0.05). The mean lymphocyte recovery time of high T cell group and low T cell group were 107.07 days (95% CI 79.88-134.25), and 50.4 days (95% CI 41.42-59.38), respectively. The lymphocyte recovery time of high T cell group was higher that of low T cell group (P<0.05). No significant difference between CMV reactivation, chronic GVHD and primary disease relapse rates was observed between two groups (P>0.05). The cumulative incidence of grade II or above acute GVHD was higher in the high T groups compared with low T groups (P<0.05). The overall survival and progress free survival rates were higher in the low T cell group compared with the high T cell group (P<0.05). In conclusion, high levels of CD3⁺ T cells in the grafts were associated with delayed lymphocyte recovery and an increased risk of acute GVHD and decreased overall survival.

Pre-transplant donor CD4- invariant NKT cell expansion capacity predicts the occurrence of acute graft-versus-host disease

Clinically useful pre-transplant predictive factors of acute graft-versus-host-disease (aGVHD) after allogeneic hematopoietic stem cell transplantation (allo-SCT) are lacking. We prospectively analyzed HSC graft content in CD34⁺, NK, conventional T, regulatory T and invariant natural killer T (iNKT) cells in 117 adult patients before allo-SCT. Results were correlated with occurrence of aGVHD and relapse. In univariate analysis, iNKT cells were the only graft cell populations associated with occurrence of aGVHD. In multivariate analysis, CD4^- iNKT/T cell frequency could predict grade II-IV aGVHD in bone marrow and peripheral blood stem cell (PBSC) grafts, while CD4^- iNKT expansion capacity was predictive in PBSC grafts. Receiver operating characteristic analyses determined the CD4^- iNKT expansion factor as the best predictive factor of aGVHD. Incidence of grade II-IV aGVHD was reduced in patients receiving a graft with an expansion factor above versus below 6.83 (9.7 vs 80%, P<0.0001), while relapse incidence at two years was similar (P=0.5).The test reached 94% sensitivity and 100% specificity in the subgroup of patients transplanted with human leukocyte antigen 10/10 PBSCs without active disease. Analysis of this CD4^- iNKT expansion capacity test may represent the first diagnostic tool allowing selection of the best donor to avoid severe aGVHD with preserved graft-versus-leukemia effect after peripheral blood allo-SCT.

Mechanisms for T cell tolerance induced with granulocyte colony-stimulating factor

Granulocyte colony-stimulating factor (G-CSF) has been widely accepted as a mediator of T cell tolerance. The immune modulatory effect of G-CSF on T cells is believed to be mediated exclusively through other effector cells, such as monocytes, tolerogenic dendritic cells (DC), and myeloid-derived suppressor cells. Recent advances confirmed the direct effects of G-CSF in inducing immune tolerance of T cells through the G-CSF-G-CSF receptor pathway and related molecular mechanisms. This review aims to summarize the findings associated with the direct and indirect mechanisms for T cell tolerance induced with G-CSF. The role of G-CSF in preventing graft-versus-host disease (GVHD) and in treating autoimmune diseases (ADs) is also discussed. It is conceivable that G-CSF and immune cell compositions, such as tolerogenic DC and CD4(+)CD25(+)Foxp3(+) T cells, modulated by G-CSF could become an integral part of the immunomodulatory therapies against GVHD and ADs in the future.

Induced pluripotent stem cells have similar immunogenic and more potent immunomodulatory properties compared with bone marrow-derived stromal cells in vitro

AIM

To evaluate the in vitro immunogenic and immunomodulatory properties of induced pluripotent stem cells (iPSCs) compared with bone marrow-derived mesenchymal stromal cells (MSCs).

MATERIALS & METHODS

Mouse embryonic fibroblasts (MEFs) were isolated from C3HeB/FeJ and C57BL/6J mice, and reprogrammed to generate iPSCs. Mixed leukocyte reactions were performed using MHC-matched and -mismatched responder leukocytes and stimulator leukocytes, iPSCs or MSCs. To assess immunogenic potential, iPSCs and MSCs were used as stimulator cells for responder leukocytes. To assess immunomodulatory properties, iPSCs and MSCs were cultured in the presence of stimulator and responder leukocytes. MEFs were used as a control.

RESULTS

iPSCs had similar immunogenic properties but more potent immunomodulatory effects than MSCs. Co-culture of MHC-mismatched leukocytes with MHC-matched iPSCs resulted in significantly less responder T-cell proliferation than observed for MHC-mismatched leukocytes alone and at more responder leukocyte concentrations than with MSCs. In addition, MHC-mismatched iPSCs significantly reduced responder T-cell proliferation when co-cultured with MHC-mismatched leukocytes, while MHC-mismatched MSCs did not.

CONCLUSION

These results provide important information when considering the use of iPSCs in place of MSCs in both regenerative and transplantation medicine.

Donor-derived CD4(+)/CCR7(+) T-cell partial selective depletion does not alter acquired anti-infective immunity

In previous studies, we observed that a high proportion of donor-derived CD4(+) T cells expressing the chemokine receptor 7 (CCR7) was a major determinant of acute GVHD, without interfering with the incidence of other post-transplant outcomes, especially relapse and nonrelapse mortality rates. Here, we investigated in vitro the impact of partially selective CD4(+)/CCR7(+) T lymphocytes on acquired anti-infective immune response in 10 donors who underwent G-CSF-primed PBSC collection. Similar quantitative and functional proliferative reactions were observed in lymphocyte cultures in the presence of adenovirus and pp65 Ags with unmanipulated and partially depleted donor samples. No responses were observed in the presence of human T-cell lymphotropic virus type 1 used as a negative control. These results complete the proof of concept needed to build a clinical trial investigating partially selective CD4(+)/CCR7(+) T cell-depleted allo-SCT.

Advancement of human leukocyte antigen-partially matched related hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is one of the most effective options for hematological malignancies, and human leukocyte antigen-partially matched related donors (PMRDs) are a valuable option for HSCT. Several protocols (with or without ex vivo T-cell depletion (TCD)) have been established worldwide. TCD including CD34(+) positive selection and CD3/CD19 depletion has successfully overcome the human leukocyte antigen disparity. However, TCD is associated with prolonged immune deficiencies, increased risks of infectious complications, and high transplantation-related mortality. PMRD HSCTwithout ex vivo TCD is well developed, and numerous patients have benefitted from it. Here, we review the literature on PMRD HSCT.

A direct comparison of expression profiles of adhesion molecules on naïve T cells between cord blood and steady-state bone marrow grafts of healthy donors

INTRODUCTION

We compared the profiles of adhesion molecule expression on naïve T cells between umbilical cord blood (UCB) and steady-state bone marrow (SS-BM) grafts.

METHODS

The expressions of 4 adhesion molecules, including very late antigen 4 (VLA-4), intercellular adhesion molecule-1 (ICAM-1), L-selectin, and lymophocyte function-associated antigen-1 (LFA-1) on naïve T cells in UCB (n = 25) and SS-BM (n = 10) were analyzed using flow cytometry.

RESULTS

The expressions of ICAM-1 and L-selectin on CD4(+) T cells and CD8(+) T cells in UCB were significantly lower than those on SS-BM (P < .05 for all). The expressions of VLA-4 and LFA-1 on CD8(+) T cells in UCB were significantly lower than those of SS-BM (P = .002 and .047, respectively). Compared with SS-BM, we observed lower expression of ICAM-1 on naïve CD4(+) and CD8(+) T cells in UCB (P < .001 for all). The percentages of interferon (IFN)-γ positive cells among naïve CD4(+) and CD8(+) T-cell subsets were significantly lower in UCB, leading to ready polarization of naïve UCB T cells from a Th1 to Th2 phenotype versus those on SS-BM.

CONCLUSIONS

Our results among UCB suggested lower intensities of ICAM-1 expression on naïve T cells and their easier polarization from Th1 to Th2 elements.

High frequency of CD4+ CD25- CD69+ T cells is correlated with a low risk of acute graft-versus-host disease in allotransplants

Regulatory T cells (Tregs) maintain transplantation tolerance and suppress graft-versus-host disease (GvHD) in humans. We monitored 17 subjects with acute GvHD to determine whether Treg frequency correlates with acute GvHD. We found the percent of CD4(+) CD25(-) CD69(+) Tregs decreases when acute GvHD develops and increases after acute GvHD is controlled. We next sequentially studied 50 subjects receiving conventional allotransplants. We show a high frequency and increased numbers of CD4(+) CD25(-) CD69(+) Tregs are associated with a reduced risk of acute GvHD. We also show that CD4(+) CD25(-) CD69(+) Treg numbers increase substantially early after allografts and that a low percent of CD4(+) CD25(-) CD69(+) Tregs is associated with an increased risk of acute GvHD. Reconstitution of Tregs early post-transplant is associated with less acute GvHD. These data imply that CD4(+) CD25(-) CD69(+) Tregs are a novel subset of regulatory T cells that may protect against acute GvHD after allotransplants.

High frequencies of CD62L⁺ naive regulatory T cells in allografts are associated with a low risk of acute graft-versus-host disease following unmanipulated allogeneic haematopoietic stem cell transplantation

Regulatory T cells (T(regs) ) play a key role in the prevention of acute graft-versus-host disease (aGVHD). To investigate the association between T(reg) subsets and aGVHD, we prospectively analysed T cell subsets in the allografts of 35 patients undergoing myeloablative unmanipulated haematopoietic stem cell transplantation. Multivariate analysis found that patients infused with less than 0·29 × 10(6) /kg of CD4(+) CD25(high) CD45RA(+) CD62L(+) T cells during transplantation exhibited an increased incidence of II-IV aGVHD [hazard ratio (HR) = 0·000, 95% CI = 0·000-0·106, P = 0·013]. Next, we compared the reconstitution characteristics of T cell subsets between haploidentical haematopoietic stem cell transplantation (HSCT) and sibling HSCT by collecting peripheral blood samples at regular intervals (days 30, 60 and 90) after transplantation. No significant differences were observed in the reconstitution of conventional T cells between haploidentical HSCT and sibling identical HSCT. However, total counts of recovered naiveT(regs) and CD62L(+) naive T(regs) from haploidentical HSCT were significantly lower compared to sibling identical HSCT; P-values were 0·045 and 0·021, respectively. Although total counts of conventional T cells in aGVHD patients reached similar levels compared to non-aGVHD patients before day 60 post-HSCT, total counts of naive T(regs) and CD62L(+) naive T(regs) in aGVHD patients did not reach similar levels to non-aGVHD patients until 90 days post-HSCT. Taken together, our findings demonstrate that a large population of CD62L(+) naive T(regs) in allografts reduces the incidence of aGVHD. Further, development of aGVHD is related closely to the delayed reconstitution of the naive T(reg) population.

Unmanipulated HLA-mismatched/haploidentical blood and marrow hematopoietic stem cell transplantation

Extensive ex vivo T cell-depleted or unmanipulated haploidentical transplantation provides benefits of rapid and near universal donor availability for patients without HLA-identical sibling donors or those who urgently need transplant. However, CD34 selected haplotype mismatched transplantation was limited by delayed immune reconstitution (IR), although this protocol has now been an acceptable approach. Recently, Peking University researchers developed a novel approach to HLA-mismatched/haploidentical blood and marrow transplantation without in vitro T cell depletion (GIAC protocol). This review summarizes transplant outcomes, and factors correlating with transplant outcomes following the GIAC protocol. Moreover, future challenges in improving posttransplant IR and finding the best approach reducing the incidence and severity of GVHD, whereas preserving graft-versus-leukemia effect to prevent the recurrence of underlying malignancy, are also discussed.