Human T-follicular helper and T-follicular regulatory cell maintenance is independent of germinal centers.

The monoclonal anti-CD20 antibody rituximab (RTX) depletes B cells in the treatment of lymphoma and autoimmune disease, and contributes to alloantibody reduction in transplantation across immunologic barriers. The effects of RTX on T cells are less well described. T-follicular helper (Tfh) cells provide growth and differentiation signals to germinal center (GC) B cells to support antibody production, and suppressive T-follicular regulatory (Tfr) cells regulate this response. In mice, both Tfh and Tfr are absolutely dependent on B cells for their formation and on the GC for their maintenance. In this study, we demonstrate that RTX treatment results in a lack of GC B cells in human lymph nodes without affecting the Tfh or Tfr cell populations. These data demonstrate that human Tfh and Tfr do not require an ongoing GC response for their maintenance. The persistence of Tfh and Tfr following RTX treatment may permit rapid reconstitution of the pathological GC response once the B-cell pool begins to recover. Strategies for maintaining remission after RTX therapy will need to take this persistence of Tfh into account.

The adjuvant GLA-SE promotes human Tfh cell expansion and emergence of public TCRß clonotypes.

The generation of protective humoral immunity after vaccination relies on the productive interaction between antigen-specific B cells and T follicular helper (Tfh) cells. Despite the central role of Tfh cells in vaccine responses, there is currently no validated way to enhance their differentiation in humans. From paired human lymph node and blood samples, we identify a population of circulating Tfh cells that are transcriptionally and clonally similar to germinal center Tfh cells. In a clinical trial of vaccine formulations, circulating Tfh cells were expanded in Tanzanian volunteers when an experimental malaria vaccine was adjuvanted in GLA-SE but not when formulated in Alum. The GLA-SE-formulated peptide was associated with an increase in the extrafollicular antibody response, long-lived antibody production, and the emergence of public TCRß clonotypes in circulating Tfh cells. We demonstrate that altering vaccine adjuvants is a rational approach for enhancing Tfh cells in humans, thereby supporting the long-lived humoral immunity that is required for effective vaccines.

T Follicular Regulatory Cells and Antibody Responses in Transplantation.

De novo donor-specific antibody (DSA) formation is a major problem in transplantation, and associated with long-term graft decline and loss as well as sensitization, limiting future transplant options. Forming high-affinity, long-lived antibody responses involves a process called the germinal center (GC) reaction, and requires interaction between several cell types, including GC B cells, T follicular helper (Tfh) and T follicular regulatory (Tfr) cells. T follicular regulatory cells are an essential component of the GC reaction, limiting its size and reducing nonspecific or self-reactive responses.An imbalance between helper function and regulatory function can lead to excessive antibody production. High proportions of Tfh cells have been associated with DSA formation in transplantation; therefore, Tfr cells are likely to play an important role in limiting DSA production. Understanding the signals that govern Tfr cell development and the balance between helper and regulatory function within the GC is key to understanding how these cells might be manipulated to reduce the risk of DSA development.This review discusses the development and function of Tfr cells and their relevance to transplantation. In particular how current and future immunosuppressive strategies might allow us to skew the ratio between Tfr and Tfh cells to increase or decrease the risk of de novo DSA formation.

The Calcineurin Inhibitor Tacrolimus Specifically Suppresses Human T Follicular Helper Cells.

Background: T follicular helper (Tfh) cells are key players in the production of antibody-producing B cells via the germinal center reaction. Therapeutic strategies targeting Tfh cells are important where antibody formation is implicated in disease, such as transplant rejection and autoimmune diseases. We investigated the impact of the immunosuppressive agent tacrolimus on human Tfh cell differentiation and function in transplant recipients. Methods: Paired blood and lymph node (LN) samples were obtained from 61 transplant recipients immediately prior to organ implantation. Living-donor recipients received a week of tacrolimus prior to kidney transplantation. Deceased-donor recipients served as controls, as tacrolimus was not administered until after the transplant operation. Flow cytometry was used to compare LN and circulating cell subsets. Results: The calcineurin inhibitor (CNIs) tacrolimus specifically suppresses both LN Tfh cells and circulating Tfh cells, but not their regulatory counterparts or other CD4 T cell subsets. Conclusion: Our findings suggest that CNIs may have a more important role in the prevention of antibody formation than previously understood and, therefore, have potential for antibody-associated conditions in which aberrant Tfh function has been implicated in disease.

Superficial temporal recipient vessels in microvascular orbit and scalp reconstruction of oncologic defects.

The superficial temporal artery and vein (STA/V) are often considered suboptimal recipient vessels due to anecdotal reports that they are unreliable and prone to spasm. This is unfortunate, as their position greatly facilitates reconstruction of the scalp and orbit. We present our experience with 28 patients who underwent microvascular craniofacial reconstruction of oncological defects using the STA/V as recipients over a 4-year period at a single institution. Rates of vessel thrombosis, total flap loss, and partial flap loss were not significantly different from 282 flaps anastomosed to neck vessels. With knowledge of the anatomy and proper technique, the STA/V are reliable and available in most patients and can facilitate microvascular orbit and scalp reconstruction. The proximity they offer allows more flexibility in flap pedicle length requirement and avoids the use of vein grafts. Caution should be exercised if there is a history of radiation therapy.