Immunity in the absence of CD28 and CD137 (4-1BB) molecules

Role of peripheral immune response in microglia activation and regulation of brain chemokine and proinflammatory cytokine responses induced during VSV encephalitis

We report herein that neuroinvasion by vesicular stomatitis virus (VSV) activates microglia and induces a peripheral dendritic cell (DC)-dependent inflammatory response in the central nervous system (CNS). VSV neuroinvasion rapidly induces multiple brain chemokine and proinflammatory cytokine mRNAs that display bimodal kinetics. Peripheral DC ablation or T cell depletion suppresses the second wave of this response demonstrating that infiltrating T cells are primarily responsible for the bimodal characteristics of this response. The robust infiltrate associated with VSV encephalitis likely depends on sustained production of brain CCL19 and CCR7 expression on infiltrating inflammatory cells.

The promise of 4-1BB (CD137)-mediated immunomodulation and the immunotherapy of cancer

The continuing efforts in biomedical research to develop new therapies for cancer are entering an exciting new phase. Research over the past two to three decades has yielded a much more detailed understanding of the complexities of the cellular and molecular interactions involved in the generation and regulation of immune responses. We are also gaining insights into the mechanisms by which tumors evade or escape immune recognition and by which they become resistant to various existing chemotherapeutic and/or radiotherapeutic strategies. A clear conclusion that can be drawn from these studies is that effective treatments of cancer will become much more multifaceted and will include immunotherapeutic approaches. The identification and molecular cloning of genes encoding the receptors and ligands that play crucial roles in the generation and regulation of immune responses provides exciting new opportunities to induce and enhance effective endogenous immune responses to cancer. In this regard, the genes that comprise the tumor necrosis factor and tumor necrosis factor receptor superfamilies show particular promise. One receptor:ligand pair (4-1BB/CD137 and 4-1BBL/CD137L) is emerging as a target with important potential in its ability to enhance the generation of effective tumor-specific immune responses in situ. The results of the studies cited in this review highlight the potentials of 4-1BB-mediated immunotherapy.

Distinct approaches to investigate the importance of the murine 4-1BB-4-1BBL interaction in the antibody response to Streptococcus pneumoniae

Protection against infection with Streptococcus pneumoniae is based mainly on the generation of antibodies to the pneumococcal capsular polysaccharides (caps-PS). Although caps-PS are considered thymus-independent antigens, there is a growing body of evidence that T lymphocytes and costimulatory molecules are involved in the regulation of the antibody response to caps-PS. We investigated whether the interaction between 4-1BB and 4-1BB ligand (4-1BBL) is involved in the modulation of the antibody response to caps-PS after immunization with Pneumovax or with intact heat-killed S. pneumoniae. Treatment with agonistic anti-4-1BB mAb, which mimics engagement of 4-1BB by 4-1BBL, had no effect on the IgG and IgM immune response to caps-PS (Serotype 3) after immunization with Pneumovax or with S. pneumoniae Serotype 3. However, anti-4-1BB treatment strongly inhibited the IgG response to pneumococcal surface protein A (PspA). By contrast, the IgG anti-caps-PS (Serotype 3) antibody response was reduced strongly in 4-1BBL(-/-) mice immunized with S. pneumoniae Serotype 3. The IgG anti-PspA antibody response in the 4-1BB(-/-) mice was comparable with the immune response in the wild-type mice. We conclude that distinct pathways are involved in the humoral antibody response to pneumococcal antigens, depending on the nature of the antigen and the context in which the different antigens are presented. The 4-1BB-4-1BBL interaction is not involved in the antibody response to soluble caps-PS. The influence of the 4-1BB-4-1BBL interaction in the immune reaction to S. pneumoniae Serotype 3 depends on the experimental system used.

Blockade of the 4-1BB (CD137)/4-1BBL and/or CD28/CD80/CD86 costimulatory pathways promotes corneal allograft survival in mice

To explore the roles of 4-1BB (CD137) and CD28 in corneal transplantation, we examined the effect of 4-1BB/4-1BB ligand (4-1BBL) and/or CD28/CD80/CD86 blockade on corneal allograft survival in mice. Allogeneic corneal transplantation was performed between two strains of wild-type (WT) mice, BALB/c and C57BL/6 (B6), and between BALB/c and B6 WT donors and various gene knockout (KO) recipients. Some of the WT graft recipients were treated intraperitoneally with agonistic anti-4-1BB or blocking anti-4-1BBL monoclonal antibody (mAb) on days 0, 2, 4 and 6 after transplantation. Transplanted eyes were observed over a 13-week period. Allogeneic grafts in control WT B6 and BALB/c mice treated with rat immunoglobulin G showed median survival times (MST) of 12 and 14 days, respectively. Allogeneic grafts in B6 WT recipients treated with anti-4-1BB mAb showed accelerated rejection, with an MST of 8 days. In contrast, allogeneic grafts in BALB/c 4-1BB/CD28 KO and B6 CD80/CD86 KO recipients had significantly prolonged graft survival times (MST, 52.5 days and 36 days, respectively). Treatment of WT recipients with anti-4-1BB mAb resulted in enhanced cellular proliferation in the mixed lymphocyte reaction and increased the numbers of CD4(+) CD8(+) T cells, and macrophages in the grafts, which correlated with decreased graft survival time, whereas transplant recipients with costimulatory receptor deletion showed longer graft survival times. These results suggest that the absence of receptors for the 4-1BB/4-1BBL and/or CD28/CD80/CD86 costimulatory pathways promotes corneal allograft survival, whereas triggering 4-1BB with an agonistic mAb enhances the rejection of corneal allografts.