Immunological Senescence and Thymic Function in Transplantation

T-cell receptor excision circle levels and safety of paediatric immunization: A population-based self-controlled case series analysis

T-cell receptor excision circle levels are a surrogate marker of T-cell production and immune system function. We sought to determine whether non-pathological levels of infant T-cell receptor excision circles were associated with adverse events following immunization. A self-controlled case series design was applied on a sample of 231,693 children who completed newborn screening for severe combined immunodeficiency in Ontario, Canada between August 2013 and December 2015. Exposures included routinely administered pediatric vaccines up to 15 months of age. Main outcomes were combined health services utilization for recognized adverse events following immunization. 1,406,981 vaccination events were included in the final dataset. 103,007 children received the Pneu-C-13 or Men-C-C vaccine and 97,998 received the MMR vaccine at 12 months of age. 67,725 children received the varicella immunization at 15 months. Our analysis identified no association between newborn T-cell receptor excision circle levels and subsequent health services utilization events following DTa-IPV-Hib, Pneu-C-13, and Men-C-C vaccinations at 2-month (RI 0.94[95%CI 0.87-1.02]), 4-month (RI 0.82[95%CI 0.75-0.9]), 6-month (RI 0.63[95%CI 0.57-0.7]) and 12-month (RI 0.49[95%CI 0.44-0.55]). We also found no trends in health services utilization following MMR (RI 1.43[95%1.34-1.52]) or varicella (RI 1.14[95%CI 1.05-1.23]) vaccination. Our findings provide further support for the safety of pediatric vaccinations.

Lymph node and circulating T cell characteristics are strongly correlated in end-stage renal disease patients, but highly differentiated T cells reside within the circulation

Ageing is associated with changes in the peripheral T cell immune system, which can be influenced significantly by latent cytomegalovirus (CMV) infection. To what extent changes in circulating T cell populations correlate with T cell composition of the lymph node (LN) is unclear, but is crucial for a comprehensive understanding of the T cell system. T cells from peripheral blood (PB) and LN of end-stage renal disease patients were analysed for frequency of recent thymic emigrants using CD31 expression and T cell receptor excision circle content, relative telomere length and expression of differentiation markers. Compared with PB, LN contained relatively more CD4⁺ than CD8⁺ T cells (P < 0·001). The percentage of naive and central memory CD4⁺ and CD8⁺ T cells and thymic output parameters showed a strong linear correlation between PB and LN. Highly differentiated CD28^null T cells, being CD27^- , CD57⁺ or programmed death 1 (PD-1⁺ ), were found almost exclusively in the circulation but not in LN. An age-related decline in naive CD4⁺ and CD8⁺ T cell frequency was observed (P = 0·035 and P = 0·002, respectively) within LN, concomitant with an increase in central memory CD8⁺ T cells (P = 0·033). Latent CMV infection increased dramatically the frequency of circulating terminally differentiated T cells, but did not alter T cell composition and ageing parameters of LN significantly. Overall T cell composition and measures of thymic function in PB and LN are correlated strongly. However, highly differentiated CD28^null T cells, which may comprise a large part of circulating T cells in CMV-seropositive individuals, are found almost exclusively within the circulation.

Reduced PARP1 as a Serum Biomarker for Graft Rejection in Kidney Transplantation

A serum proteomics platform enabling expression Profiling in transplantation-associated clinical subsets gives an opportunity to identify non-invasive biomarkers that can accurately predict transplant outcome. In this study, we attempted to identify candidate serum biomarkers that could predict kidney allograft rejection/injury, regardless of its etiological and therapeutic heterogeneity. Using serum samples collected from kidney transplantation patients and healthy controls, we first employed Clontech-500 Ab microarrays to Profile acute rejection (AR) and chronic graft injury (CGI) versus stable graft function (SF) and normal kidneys (NK). Using GenePattern analysis of duplicate arrays on pooled samples, we identified gender-independent biomarkers PARP1, MAPK1, SRP54, DP1, and p57 (FDR ≈ 25%), the concordant downregulation of which represented a detrimental Profile common for both rejection/ injury types (AR-CGI). The reverse phase arrays qualified a 2-fold upregulation of PARP1 with an ROC of 0.87 in individual samples from patients with SF vs. AR-CGI rendering serum PARP1 as a biomarker for early prognosis. Ingenuity Pathways Analysis (IPA) connected PARP1 to some other markers (MAPK1), elucidating their possible interactions and connections to the immune response and graft-versus-host disease signaling. The downregulation of serum PARP1 in the damaged graft tissues, represents a perspective non-invasive marker, predicting the failing kidney graft, regardless of rejection/injury causes or gender. Thus, the successful identification of PARP1 as a bio-marker in limited patient cohorts demonstrates that serum proteomics platform empowered by the GenePattern- and IPA-based Bioinformatics algorithm can guarantee a successful development of the clinically applicable prognostic biomarker panel.

Kinetics of homeostatic proliferation and thymopoiesis after rATG induction therapy in kidney transplant patients

BACKGROUND

Lymphocyte-depleting therapy is associated with long-lasting effects on repopulated T cells and subsequent increased rates of infections and malignancies. The mechanisms of T-cell repopulation and their posttransplantation kinetics are not fully understood.

METHODS

We studied thymopoiesis by CD31(+) naïve T cells (recent thymic emigrants) and homeostatic proliferation by Ki-67(+) T cells in rabbit antithymocyte globulin (rATG)-treated patients the first 6 months after transplantation. Patients receiving basiliximab or no induction therapy served as controls.

RESULTS

At 6 months after transplantation, T-cell numbers were lower than before transplantation in rATG-treated patients, whereas T-cell numbers remained stable in both control groups. In this time period, thymopoiesis was similar between the three treatment groups; CD8(+) T cells showed the highest percentage of recent thymic emigrants. At month 1, percentages of Ki-67(+) naïve and memory CD4(+) and CD8(+) T cells were the highest in rATG-treated patients, but these percentages declined in the months thereafter. When CD31 was used to distinguish between cytokine- and antigen-driven proliferation in naïve T cells, we found evidence for cytokine-dependent proliferation. Cytokine-dependent proliferation was also shown by in vivo increased percentages of phosphorylated STAT5 and high expression levels of the interleukin-7 receptor-α and interleukin-15 receptor-α by T cells.

CONCLUSION

These findings demonstrate that, in the first month after rATG therapy, cytokine-induced homeostatic proliferation is involved in T-cell repopulation of both naïve and memory T cells. At later time points, the contribution of homeostatic proliferation diminished, which explains the observed incomplete T-cell recovery.

Lymphodepletion and homeostatic proliferation: implications for transplantation

Control of the alloimmune response requires elimination and/or suppression of alloreactive immune cells. Lymphodepleting induction therapies are increasingly used to accomplish this goal, both as part of tolerance induction protocols or to reduce the requirements for maintenance immunosuppression in the peritransplant setting. However, it is well recognized that lymphopenia induces compensatory proliferation of immune cells, generally termed ``homeostatic proliferation,'' which favors the emergence of memory T cells. Paradoxically therefore, the result may be a situation that favors graft rejection and/or makes tolerance difficult to achieve or sustain. Yet all depletion is not alike, particularly with respect to the timing of reconstitution and the types of cells that repopulate the host. Thus, to design more effective induction strategies it is important to understand the homeostatic mechanisms, which exist to maintain a balanced repertoire of naïve and memory T and B cells in the periphery and how they respond to lymphodepletion. Here we will review the biology of homeostatic proliferation stimulated by lymphopenia, the effects of specific depleting agents on reconstitution of the T- and B-cell immune repertoire, drawing from both from animal models and human experience, and potential strategies to enhance allodepletion while minimizing the adverse effects of homeostatic proliferation.