Abstract
Donor T-cells contribute to reconstitution of protective immunity after allogeneic hematopoietic stem cell transplantation (HSCT) but must acquire specific tolerance against recipient alloantigens to avoid life-threatening graft-versus-host disease (GvHD). Systemic immunosuppressive drugs may abrogate severe GvHD, but this also impedes memory responses to invading pathogens. Here, we tested whether ex vivo blockade of CD28 co-stimulation can enable selective T-cell tolerization to alloantigens by facilitating CD80/86-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) signaling. Treatment of human allogeneic dendritic cell/T-cell co-cultures with a human CD28 blocking antibody fragment (α-huCD28) significantly abrogated subsequent allospecific immune responses, seen by decreased T-cell proliferation and of type 1 cytokine (IFN-γ and IL-2) expression. Allo-tolerization persisted after discontinuation of CD28 blockade and secondary alloantigen stimulation, as confirmed by enhanced CTLA-4 and PD-1 immune checkpoint signaling. However, T-cells retained reactivity to pathogens, supported by clonotyping of neo-primed and cross-reactive T-cells specific for Candida albicans or third-party antigens using deep sequencing analysis. In an MHC-mismatched murine model, we tolerized C57BL/6 T-cells by ex vivo exposure to a murine single chain Fv specific for CD28 (α-muCD28). Infusion of these cells, after α-muCD28 washout, into bone marrow-transplanted BALB/c mice caused allo-tolerance and did not induce GvHD-associated hepatic pathology. We conclude that selective CD28 blockade ex vivo can allow the generation of stably allo-tolerized T-cells that in turn do not induce graft-versus-host reactions while maintaining pathogen reactivity. Hence, CD28 co-stimulation blockade of donor T-cells may be a useful therapeutic approach to support the immune system after HSCT.
Highlights
Very frequently, complications arise in hematopoietic stem cell transplantation (HSCT)
To test the effect of CD28 co-stimulatory blockade on human T-cell responses, we cultured CD3+, naive or memory T-cells with or without α-huCD28 (FR104) in a two-stage culture using allogeneic, LPS/IFN-γ-activated dendritic cells (DCs) (Figure 1, top). This provides a strong CD80/86 co-stimulatory signal, upon binding to CD28 to T-cells [33]. In this primary mixed leukocyte reactions (MLRs) of allogeneic DCs and bulk CD3+ T-cells, down modulation of allogeneic T-cell responses was evidenced by greatly reduced proliferation (Figure 2A, upper panel; Figure 2B, left panel), confirming a similar effect previously observed in MLRs using unseparated Peripheral blood mononuclear cells (PBMCs) [25]
Upon stimulation with fresh allogeneic DCs from the same donor, T-cell proliferation remained downregulated even though cultures were no longer supplemented with α-huCD28
Summary
Complications arise in hematopoietic stem cell transplantation (HSCT). Allogeneic T-cells, recognizing recipient cells as foreign, initiate cytotoxic immune responses known as graft-versus-host disease (GvHD) in up to 80% of patients [1, 2]. Examples of current therapies to reduce the risk for GvHD include pre-transplant serotherapy with thymoglobulin or anti-CD52 antibody and post-transplant immunosuppressive drugs [7]. These may prevent graft-versusleukemia (GvL) effects and increase the incidence of viral or invasive fungal infections up to 70% [8, 9]. Post-transplant cyclophosphamide treatment, leads to lysis of highly cytotoxic alloreactive haploidentical T-cells [10], but the incidence of acute GvHD still remains high, reaching up to 46% [11], and pathogenic infections still account for 10% mortality after haploidentical HSCT, underscoring the need for improved approaches for GvHD prophylaxis [12]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
