Genetic deficiency of CTLA-4 leads to CD28-mediated severe autoimmunity in mice and humans, suggesting its function as a fundamental brake that restrains the expansion and activation of self-reactive T cells.
In contrast, co-inhibitory signaling by the CD28-B7 family is important to regulate immune homeostasis and host defense, as these signals limit the strength and duration of immune responses to prevent autoimmunity.
In addition, the development of multifarious autoimmune diseases as immune-related adverse events of anti-CTLA-4 and anti-PD-1/PD-L1 therapies and the successful clinical application of the CD28 blocking therapy using CTLA-4-Ig to the treatment of arthritis assure their crucial roles in the regulation of autoimmunity in human.
These data expand upon the mechanism of action of abatacept reported in other autoimmune diseases and identify new transcriptional targets of CD28-mediated costimulatory signaling in human regulatory T and Tfh cells, further informing on its potential use in diseases associated with dysregulated Tfh activity.
Memory T cells pose a significant problem to successful therapeutic control of unwanted immune responses during autoimmunity and transplantation, as they are differentially controlled by cosignaling receptors such as CD28 and CTLA-4.
The CD28/B7 interaction is critical for both effector T cell activation and forkhead box P3 (FOXP3)<sup>+</sup> regulatory T cell (Treg) generation and homeostasis, which complicates the therapeutic use of cytotoxic T lymphocyte-associated antigen 4 (CTLA-4)-immunoglobulin fusion protein (CTLA-4Ig) in autoimmunity.
T cells are central to the detrimental alloresponses that develop in autoimmunity and transplantation, with CD28 costimulatory signals being key to T cell activation and proliferation.
Moreover, after specific restimulation, PV1 blockade selectively blocked IFN-γ production by CD4+ lymphocytes Taken together, our data suggest that mPEG PV1-Fab' acts mainly on IFN-γ-producing CD4+ T cells and emphasize that this specific CD28 blockade strategy is a potential specific and alternative tool for the treatment of autoimmune disorders in the eye.
The detailed insight into these interactions reported here may inform the development of compounds that specifically inhibit the association of CD28 with these adaptor proteins to suppress excessive T cell responses, such as in allergies and autoimmune diseases.
Thus, autoimmunity occurring in mice with CD28-deficient Tregs appears to be driven primarily by loss of T<sub>FR</sub> cell differentiation and function with resulting B cell-driven inflammation.
CD4(+)CD28(-) T cells arise through repeated antigenic stimulation and are present in diseased tissues of patients with various autoimmune disorders, including multiple sclerosis (MS).
To replicate a single nucleotide polymorphism (SNP) of known genes for lupus (IRF5 rs10488631, PTPN22 rs2476601, BLK rs2736340 and TNFAIP3 rs5029939) and other autoimmune diseases (CD28rs1980422, IL2RA rs2104286 and KIF5A rs1678542) on a newly studied Egyptian cohort to investigate the genetic disparity with different studied ethnic groups in relation to lupus susceptibility.
Cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) and CD28 have been reported to be important candidate genes for conferring susceptibility to autoimmunity.
The data showed 4E5 function and suggested that blockade of CD80/CD28 co-stimulatory signal pathway with 4E5 is a promising strategy to decelerate the progression of lupus-like disease and other autoimmune diseases.
CD28 is one of the main activator receptors involved in systemic lupus erythematosus (SLE) pathogenesis, and its expression and serum levels are significantly higher in patients with SLE and other autoimmune diseases than in healthy controls (HC).
These findings identify CD28 and CD80/CD86 as important molecular components of the interaction between myeloma cells and the bone marrow microenvironment, point to similar interaction for normal plasma cells, and suggest novel therapeutic strategies to target malignant and pathogenic (e.g., in allergy and autoimmunity) plasma cells.
In this study we have examined the effect of single-gene deletions for interferon (IFN)-gamma, interleukin (IL)-4, IL-6 or CD28 in B10.S (H-2(s)) mice on heavy metal-induced autoimmunity.
These data support the hypothesis that CD28-B7 interactions play a critical role in the etiology of lethal autoimmune disease in scurfy mice by stimulating the differentiation of antigen-activated naive T cells into effector T cells.
SNPs in the 2q33 region within the genes of CD28 (+17T/C; intron 3) and CTLA4 (-318C/T; promoter and +49A/G; exon 1) are likely to affect T-cell proliferation and antigen presentation signaling, which may lead to altered sensitivity of allograft or self-tissue recognition and affect the incidence of autoimmune diseases.
Absence of CTLA-4 expression in CD40L-/- mice suggests that signaling via both CD28 and CD40L is important for T cell activation and subsequent autoimmunity in mHgIA.