Major K. Lee

Promotion of Allograft Survival by CD4+CD25+ Regulatory T Cells: Evidence for In Vivo Inhibition of Effector Cell Proliferation

Regulatory T cells preserve tolerance to peripheral self-Ags and may control the response to allogeneic tissues to promote transplantation tolerance. Although prior studies have demonstrated prolonged allograft survival in the presence of regulatory T cells (T-reg), data documenting the capacity of these cells to promote tolerance in immunocompetent transplant models are lacking, and the mechanism of suppression in vivo remains unclear. We used a TCR transgenic model of allograft rejection to characterize the in vivo activity of CD4+CD25+ T-reg. We demonstrate that graft Ag-specific T-reg effectively intercede in the rejection response of naive T cells to established skin allografts. Furthermore, CFSE labeling demonstrates impaired proliferation of naive graft Ag-specific T cells in the draining lymph node in the presence of T-reg. These results confirm the efficacy of T-reg in promoting graft survival and suggest that their suppressive action is accomplished in part through inhibition of proliferation.

Cutting Edge: Transplant Tolerance Induced by Anti-CD45RB Requires B Lymphocytes

Selective interference with the CD45RB isoform by mAb (anti-CD45RB) reliably induces donor-specific tolerance. Although previous studies suggest participation of regulatory T cells, a mechanistic understanding of anti-CD45RB-induced tolerance is lacking. We report herein the unexpected finding that tolerance induced by this agent is not established in B cell-deficient mice but can be recovered by preemptive B lymphocyte transfer to B cell-deficient hosts. Using B cells from genetically modified donors to reconstitute B cell-deficient recipients, we evaluate the role of B lymphocyte-expressed CD45RB, T cell costimulatory molecules, and the production of Abs in this novel tolerance mechanism. Our data document an Ab-induced tolerance regimen that is uniquely B lymphocyte-dependent and suggest mechanistic contributions to tolerance development from the B cell compartment through interactions with T cells.

CD25+ Immunoregulatory CD4 T Cells Mediate Acquired Central Transplantation Tolerance

Transplantation tolerance is induced reliably in experimental animals following intrathymic inoculation with the relevant donor strain Ags; however, the immunological mechanisms responsible for the induction and maintenance of the tolerant state remain unknown. We investigated these mechanisms using TCR transgenic mice (TS1) that carry T cells specific for an immunodominant, MHC class II-restricted peptide (S1) of the influenza PR8 hemagglutinin (HA) molecule. We demonstrated that TS1 mice reject skin grafts that have transgene-encoded HA molecules (HA104) as their sole antigenic disparity and that intrathymic but not i.v. inoculation of TS1 mice with S1 peptide induces tolerance to HA-expressing skin grafts. Intrathymic peptide inoculation was associated with a dose-dependent reduction in T cells bearing high levels of TCR specific for HA. However, this reduction was both incomplete and transient, with a full recovery of S1-specific thymocytes by 4 wk. Peptide inoculation into the thymus also resulted in the generation of immunoregulatory T cells (CD4+CD25+) that migrated to the peripheral lymphoid organs. Adoptive transfer experiments using FACS sorted CD4+CD25− and CD4+CD25+ T cells from tolerant mice revealed that the former but not the latter maintain the capacity to induce rejection of HA bearing skin allografts in syngeneic hosts. Our results suggest that both clonal frequency reduction in the thymus and immunoregulatory T cells exported from the thymus are critical to transplantation tolerance induced by intrathymic Ag inoculation.

Drain Management after Pancreatoduodenectomy: Reappraisal of a Prospective Randomized Trial Using Risk Stratification

BACKGROUND A recent randomized trial used the Fistula Risk Score (FRS) to develop guidelines for selective drainage based on clinically relevant fistula (CR-POPF) risk. Additionally, postoperative day (POD) 1 drain and serum amylase have been identified as accurate postoperative predictors of CR-POPF. This study sought to identify patients who may benefit from selective drainage, as well as the optimal timing for drain removal after pancreatoduodenectomy. STUDY DESIGN One hundred six pancreatoduodenectomies from a previously reported RCT were assessed using risk-adjustment. The incidence of CR-POPF was compared between FRS risk cohorts. Drain and serum amylase values from POD 1 were evaluated using receiver operating characteristic (ROC) analysis to establish cut-offs predictive of CR-POPF occurrence. A regression analysis compared drain removal randomizations (POD 3 vs POD 5). RESULTS Three-quarters of patients had moderate/high CR-POPF risk. This group had a CR-POPF rate of 36.3% vs 7.7% among negligible/low risk patients (p = 0.005). The areas under the ROC curve for CR-POPF prediction using POD 1 drain and serum amylase values were 0.800 (p = 0.000001; 95% CI 0.70-0.90) and 0.655 (p = 0.012; 95% CI 0.55-0.77), respectively. No significant serum amylase cut-offs were identified. Moderate/high risk patients with POD 1 drain amylase ≤ 5,000 U/L had significantly lower rates of CR-POPF when randomized to POD 3 drain removal (4.2% vs 38.5%; p = 0.003); moreover, these patients experienced fewer complications and shorter hospital stays. CONCLUSIONS A clinical care protocol is proposed whereby drains are recommended for moderate/high FRS risk patients, but may be omitted in patients with negligible/low risk. Drain amylase values in moderate/high risk patients should then be evaluated on POD 1 to determine the optimal timing for drain removal. Moderate/high risk patients with POD 1 drain amylase ≤ 5,000 U/L have lower rates of CR-POPF with POD 3 (vs POD ≥ 5) drain removal; early drain removal is recommended for these patients.

Multicenter, Prospective Trial of Selective Drain Management for Pancreatoduodenectomy Using Risk Stratification.

Objective: This multicenter study sought to prospectively evaluate a drain management protocol for pancreatoduodenectomy (PD). Background: Recent evidence suggests value for both selective drain placement and early drain removal for PD. Both strategies have been associated with reduced rates of clinically relevant pancreatic fistula (CR-POPF)—the most common and morbid complication after PD. Methods: The protocol was applied to 260 consecutive PDs performed at two institutions over 17 months. Risk for ISGPF CR-POPF was determined intraoperatively using the Fistula Risk Score (FRS); drains were omitted in negligible/low risk patients and drain fluid amylase (DFA) was measured on postoperative day 1 (POD 1) for moderate/high risk patients. Drains were removed early (POD 3) in patients with POD 1 DFA ⩽5,000 U/L, whereas patients with POD 1 DFA >5,000 U/L were managed by clinical discretion. Outcomes were compared with a historical cohort (N = 557; 2011–2014). Results: Fistula risk did not differ between cohorts (median FRS: 4 vs 4; P = 0.933). No CR-POPFs developed in the 70 (26.9%) negligible/low risk patients. Overall CR-POPF rates were significantly lower after protocol implementation (11.2 vs 20.6%, P = 0.001). The protocol cohort also demonstrated lower rates of severe complication, any complication, reoperation, and percutaneous drainage (all P < 0.05). These patients also experienced reduced hospital stay (median: 8 days vs 9 days, P = 0.001). There were no differences between cohorts in the frequency of bile or chyle leaks. Conclusions: Drains can be safely omitted for one-quarter of PDs. Drain amylase analysis identifies which moderate/high risk patients benefit from early drain removal. This data-driven, risk-stratified approach significantly decreases the occurrence of clinically relevant pancreatic fistula.

Antibody-Induced Transplantation Tolerance That Is Dependent on Thymus-Derived Regulatory T Cells

Targeting of the CD45RB isoform by mAb (anti-CD45RB) effectively induces donor-specific tolerance to allografts. The immunological mechanisms underlying the tolerant state remain unclear although some studies have suggested the involvement of regulatory T cells (T-regs). Although their generative pathway remains undefined, tolerance promoting T-regs induced by systemic anti-CD45RB treatment have been assumed to originate in the peripheral immune system. We demonstrate herein that separable effects on the peripheral and central immune compartments mediate graft survival induced by anti-CD45RB administration. In the absence of the thymus, anti-CD45RB therapy is not tolerogenic though it retains peripheral immunosuppressive activity. The thymus is required for anti-CD45RB to produce indefinite graft survival and donor-specific tolerance, and this effect is accomplished through thymic production of donor-specific T-regs. These data reveal for the first time an Ab-based tolerance regimen that relies on the central tolerance pathway.

Blockade of GITR–GITRL interaction maintains Treg function to prolong allograft survival

Involvement of Treg in transplant tolerance has been demonstrated in multiple models. During the active process of graft rejection, these regulatory cells are themselves regulated and inactivated, a process termed counter‐regulation. We hypothesize that ligation of the costimulatory molecule glucocorticoid‐induced TNF receptor‐related protein (GITR) on Treg inhibits their ability to promote graft survival, and by blocking GITR ligation graft survival can be prolonged. To this aim, we have designed a soluble GITR fusion protein (GITR‐Fc), which binds GITR ligand and inhibits activation of GITR. Here, we show that GITR‐Fc prolonged mouse skin graft survival, and this prolongation is dependent on Treg. In a full MHC‐mismatched skin graft setting, GITR‐Fc significantly improved graft survival when used in combination with MR1, anti‐CD40L, while GITR‐Fc alone did not demonstrate graft prolongation. These results demonstrate that disruption of binding of GITR with GITR ligand may be an important strategy in prolonging allograft survival.

GITR Blockade Facilitates Treg Mediated Allograft Survival

Background. Many models of transplant tolerance have been found to depend on the induction of regulatory T cells (Tregs). Innate immune signals are known to suppress Tregs thereby augmenting immunity by abrogating Treg function. Such signals may also provide a barrier to transplantation tolerance mediated by Tregs. A number of cell surface molecules expressed by Tregs have been found to inhibit Treg activity, the best characterized of which is the glucocorticoid-induced tumor necrosis factor receptor-related (GITR) protein. Methods. By using an adoptive transfer model of allograft rejection, we can study the effects of inflammation and antigen-specific Tregs on graft survival. Inflammation resulting from the transplant procedure counter-regulates the suppressor activity of Tregs. To assess whether Treg activity could be enhanced by blocking GITR signaling, we compared the capacity of Tregs to prolong the survival of grafts in the presence or absence of activation-inducible TNF receptor (AITRL)-Fc, a novel construct that binds GITR. Results. We report that interruption of GITR-GITR ligand (GITRL) binding by AITRL-Fc resulted in long-term Treg–dependent acceptance of skin grafts in the setting of innate immune signals that otherwise interfere with Treg activity. Conclusions. Inflammation and other innate immune signals may activate antigen presenting cells to upregulate GITRL. GITR-GITRL interaction is one pathway by which antigen presenting cells may enhance the adaptive response to foreign antigen by counter-regulating Tregs and by costimulating effector T cells. By blocking this interaction with AITRL-Fc, one can sustain the benefit conferred by graft-protective Tregs.

Regulatory T-cell counter-regulation by innate immunity is a barrier to transplantation tolerance.

Innate immune signals foster adaptive immunity through activation of antigen‐presenting cells. Recent in vitro evidence suggests that innate signaling may also contribute to immunity by countering the effects of regulatory T cells (T‐regs), counter‐regulation. We present in vivo evidence using a transgenic skin allograft model that the function of T‐regs is lost in the setting of acute skin transplantation but remains intact when grafts were transplanted 1 month prior to allow surgery‐induced inflammation to abate. Our findings identify T‐reg counter‐regulation as a naturally occurring process that accompanies transplantation and an important barrier to T‐reg–mediated tolerance. Our finding further highlights the central role of regulatory cell deactivation in the initiation of the immune response.

The efficacy of adjuvant therapy for pancreatic invasive intraductal papillary mucinous neoplasm (IPMN).

The literature investigating pancreatic invasive intraductal papillary mucinous neoplasm (IPMN) has largely come from small institutional studies, preventing adequately powered comparisons of adjuvant therapy versus surgery alone (SA) within specific patient subgroups.