Memory T follicular helper cells drive donor-specific antibodies independent of memory B cells and primary germinal center and alloantibody formation.

Human leukocyte antigen antibodies are important immunologic mediators of renal allograft loss and are difficult to control. The inability to permanently eliminate donor-specific antibodies (DSA) is partly due to an incomplete understanding of the cellular mechanisms driving alloantibody formation, recurrence, and maintenance. Memory T follicular helper (mTfh) cells rapidly interact with memory B cells upon antigen re-exposure for anamnestic humoral responses, but little is known about Tfh memory in transplantation. We hypothesized that alloreactive mTfh cells form after transplantation and play a critical role in DSA formation following alloantigen re-encounter. To test this hypothesis, we utilized murine skin allograft models to identify and characterize Tfh memory and interrogate its ability to mediate alloantibody responses. We identified alloreactive Tfh memory as a mediator of accelerated humoral alloresponses independent of memory B cells and primary germinal center, or DSA, formation. Furthermore, we demonstrate that mTfh-driven alloantibody formation is susceptible to CD28 costimulation blockade. These findings provide novel insight into a pathologic role for memory Tfh in alloantibody responses and strongly support shifting therapeutic focus from the singular targeting of B cell lineage cells and alloantibodies themselves to multimodal strategies that include inhibition of mTfh cells to treat DSA.

The Potential Impact of Food Insecurity in an Urban Trauma Population.

BACKGROUND: Food insecurity (FI) has been defined as a lack of consistent access to enough food for a healthy active lifestyle. As of 12.7% of the United States are suffering from FI, which has been correlated with increased hospital costs and poorer health outcomes. Currently, limited data exists examining the relationship between trauma populations and FI despite both having similar root causes. We sought to determine this and validate a screening tool for FI in this population. METHODS: A cross-sectional survey study of trauma patients was conducted at a level 1 trauma center in Atlanta, Georgia. Survey questions included the first two items of the Core Food Security Module. Zip codes were used to determine FI, defined by the USDA Food Access Research and compared to individual participant survey responses. Binary classification test metrics were calculated to validate the two items as a screening tool in this population. RESULTS: The cohort included 136 patients, of which the majority were black (60.3%) and male (60.3%). Thirty-one respondents affirmed food security (22.8%) despite over half (51.5%) living in a food insecure community. The sensitivity and specificity for this screening to predict FI were 25 and 80%, respectively. CONCLUSION: Although the specificity is high, this screening tool has a low sensitivity, accuracy, NPV, and PPV to determine food insecurity in this population. Community-level statistics suggests that food insecurity is a significant public problem amongst trauma patients. Prevention efforts should, therefore, aim to address both issues simultaneously.

CXCL13 Is an Indicator of Germinal Center Activity and Alloantibody Formation Following Transplantation.

Donor-specific antibodies (DSA) are a recognized cause of allograft injury, yet biomarkers that indicate their development posttransplant or guide management are not available. CXCL13 (chemokine [C-X-C motif] ligand 1) is a chemoattractant produced within secondary lymphoid organs necessary for germinal center (GC) and alloantibody formation. Perturbations in serum CXCL13 levels have been associated with humoral immune activity. Therefore, CXCL13 may correlate with the formation of HLA antibodies following transplantation. METHODS: A murine skin graft model was utilized to define the production and kinetics of CXCL13 in response to alloantigen. Human Tfh:B-cell in vitro cocultures were performed to evaluate CXCL13 production by human lymphocytes, and serum from healthy controls and human transplant recipients with and without de novo DSA was tested for CXCL13. RESULTS: CXCL13 was detectable in the blood of allografted mice and correlated with Tfh and GC B-cell responses. Greater CXCL13 expression was observed in the draining lymph nodes of allografted mice as compared with naïve or syngeneic graft recipients, and serum levels preceded the detection of DSA posttransplant. Similarly, productive human Tfh:B-cell interactions that led to plasmablast differentiation and IgG formation also exhibited CXCL13 expression. CXCL13 levels in human transplant recipients with de novo DSA were greater than in healthy controls and stable transplant patients and also correlated with the development of alloantibodies in a small cohort of serially monitored recipients. CONCLUSIONS: CXCL13 indicates GC alloreactivity and alloantibody formation and correlated with DSA formation in kidney transplant recipients, thereby introducing CXCL13 as a potential biomarker for HLA antibodies.

Superior inhibition of alloantibody responses with selective CD28 blockade is CTLA-4 dependent and T follicular helper cell specific.

Anti-donor antibodies cause immunologic injury in transplantation. CD28 blockade with CTLA-4-Ig has the ability to reduce the incidence of these donor-specific antibodies (DSA), but its mechanism is suboptimal for the inhibition of alloimmunity in that CTLA-4-Ig blocks both CD28 costimulation and CTLA-4 coinhibition. Thus selective CD28 blockade that spares CTLA-4 has potential to result in improved inhibition of humoral alloimmunity. To test this possibility, we utilized a full allogeneic mismatch murine transplant model and T follicular helper (Tfh):B cell co-culture system. We observed that selective blockade with an anti-CD28 domain antibody (dAb) compared to CTLA-4-Ig led to superior inhibition of Tfh cell, germinal center, and DSA responses in vivo and better control of B cell responses in vitro. CTLA-4 blockade enhanced the humoral alloresponse and, in combination with anti-CD28 dAb, abrogated the effects of selective blockade. This CTLA-4-dependent inhibition was Tfh cell specific in that CTLA-4 expression by Tfh cells was necessary and sufficient for the improved humoral inhibition observed with selective CD28 blockade. As CD28 blockade attracts interest for control of alloantibodies in the clinic, these data support selective CD28 blockade as a superior strategy to address DSA via the sparing of CTLA-4 and more potent targeting of Tfh cells.