CD45RA-CD25highCD127-CD4+ activated regulatory T cells are correlated with de novo donor-specific anti-HLA antibody formation after kidney transplantation in standard immunosuppression

Impaired SARS-CoV-2-specific responses via activated T follicular helper cells in immunocompromised kidney transplant recipients

Activated T follicular helper (aTfh) cells are likely important in host immune responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccination. We characterized the immune responses of aTfh cells to the second (D2) and third (booster; D3) doses of an mRNA vaccine in the peripheral blood of 40 kidney transplant recipients (KTRs) and 17 healthy control volunteers (HCs). A significant increase in SARS-CoV-2-specific IgG antibody was seen after D3 in the KTRs; nonetheless, the levels after D2 and D3 were significantly lower than in the HCs. After D2, dramatic increases in activated CD45RA-CXCR5+ICOS+PD1+ circulating Tfh (acTfh) cells were observed in the HCs, as well as the seropositive patients among the KTRs, when compared with the seronegative patients among the KTRs. Unlike the HCs, KTRs had less prominent immune responses, including the acTfh and T cells that produce interferon gamma, tumor necrosis factor alpha, and interleukin 21. In addition, the increase in acTfh cells was significantly associated with anti-IgG antibody levels after D3. These results indicate impaired SARS-CoV-2-specific responses via acTfh cells in KTRs, and they suggest that acTfh cells in peripheral blood may play an important role in antibody maintenance following SARS-CoV-2 mRNA vaccination.

Effect of Mammalian Target of Rapamycin Inhibition on Activated Regulatory T-Cell Expansion in Kidney Transplantation

BACKGROUND

The mammalian target of rapamycin (mTOR) plays a critical role in the host immune response in organ transplantation. This study evaluates the regulatory benefits of mTOR inhibitors in kidney transplant recipients (KTRs).

METHODS

The mTOR-dependent immune-regulating effects in KTRs were evaluated by examining T-cell subsets among peripheral blood mononuclear cells from 79 KTRs. Recipients included an early introduction of everolimus (EVR) and reduced-exposure tacrolimus group (n = 46) and a standard tacrolimus-based without EVR (non-EVR) group (n = 33).

RESULTS

Trough concentrations of tacrolimus at 3 months and 1 year were significantly lower in the EVR group than the non-EVR group (both P < .001). In addition, the respective proportions of patients without estimated glomerular filtration rate < 20% in the EVR and non-EVR groups were 100% and 93.3% at 1 year, 96.3% and 89.7% at 2 years, and 96.3% and 89.7% at 3 years after blood collection, respectively (P = .079). The frequencies of CD3⁺ T cells and CD4⁺ T cells among peripheral blood mononuclear cells were comparable between groups. Total CD25^highCD127^-CD4⁺ regulatory T (Treg) cells were similar in the EVR and non-EVR groups. In contrast, circulating CD45RA^-CD25^highCD127^-CD4⁺ activated Treg cells were significantly higher in the EVR group (P= .008).

CONCLUSION

These results suggest that the early introduction of mTOR benefits long-term kidney graft function and circulating activated Treg-cell expansion in KTRs.

CD4+CD25+ T regulatory cells in renal transplantation

The immune response to an allograft activates lymphocytes with the capacity to cause rejection. Activation of CD4+CD25+Foxp3+T regulatory cells (Treg) can down-regulate allograft rejection and can induce immune tolerance to the allograft. Treg represent <10% of peripheral CD4+T cells and do not markedly increase in tolerant hosts. CD4+CD25+Foxp3+T cells include both resting and activated Treg that can be distinguished by several markers, many of which are also expressed by effector T cells. More detailed characterization of Treg to identify increased activated antigen-specific Treg may allow reduction of non-specific immunosuppression. Natural thymus derived resting Treg (tTreg) are CD4+CD25+Foxp3+T cells and only partially inhibit alloantigen presenting cell activation of effector cells. Cytokines produced by activated effector cells activate these tTreg to more potent alloantigen-activated Treg that may promote a state of operational tolerance. Activated Treg can be distinguished by several molecules they are induced to express, or whose expression they have suppressed. These include CD45RA/RO, cytokine receptors, chemokine receptors that alter pathways of migration and transcription factors, cytokines and suppression mediating molecules. As the total Treg population does not increase in operational tolerance, it is the activated Treg which may be the most informative to monitor. Here we review the methods used to monitor peripheral Treg, the effect of immunosuppressive regimens on Treg, and correlations with clinical outcomes such as graft survival and rejection. Experimental therapies involving ex vivo Treg expansion and administration in renal transplantation are not reviewed.

Immunological imprint on peripheral blood in kidney transplant recipients after two doses of SARS-CoV-2 mRNA vaccination in Japan

The immunological imprint after two doses of severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2) mRNA vaccination for patients after kidney transplantation (KTx) remain unclear. This study included KTx recipients and volunteer healthy controls (HCs) who received two doses of SARS-CoV-2 mRNA vaccine (Pfizer BioNTech) from January 2021 to December 2021. We analyzed safety within 21 days after each vaccination dose and compared the immune response in peripheral blood mononuclear cells (PBMCs) between the two groups. No graft rejection was observed throughout this study. Adverse events were generally observed within 5 days. The KTx group exhibited a significantly lower degree of symptoms between doses 1 and 2 (P &lt; 0.001). Increases in activated subsets of T and B cells expressing human leukocyte antigen (HLA)-DR and/or CD38 were observed in the HC group after dose 2 (both P &lt; 0.001), with the greatest increases in HLA-DR+CD8+ T cells and CD38+CD19+ B cells (P = 0.042 and P = 0.031, respectively). In addition, PD1+CD8+ T cells—but not PD1+CD4+ T cells—increased significantly in the HC group (P = 0.027). In the KTx group, however, activated HLA-DR+, CD38+, and PD1+ cells remained at baseline levels. Immunoglobulin (Ig)G against SARS-CoV-2 was detected in only four KTx recipients (13.3%) after dose 2 (P &lt; 0.001). Multivariate logistic regression analyses revealed that ΔHLA-DR+CD8+ T cells and ΔCD38+CD19+ B cells were significantly associated with IgG formation (both P = 0.02). SARS-CoV-2 mRNA vaccine generates impaired cellular and humoral immunity for KTx recipients. Results indicate the need for modified vaccination strategies in immunocompromised KTx recipients.