4-1BB triggering ameliorates experimental autoimmune encephalomyelitis by modulating the balance between Th17 and regulatory T cells.

Agonistic anti-4-1BB Ab is known to ameliorate experimental autoimmune encephalomyelitis. 4-1BB triggering typically leads to the expansion of CD8(+) T cells, which produce abundant IFN-γ, and this in turn results in IDO-dependent suppression of autoimmune responses. However, because neutralization of IFN-γ or depletion of CD8(+) T cell only partially abrogates the effect of 4-1BB triggering, we sought to identify an additional mechanism of 4-1BB-triggered suppression of autoimmune responses using IFN-γ- or IFN-γR-deficient mice. 4-1BB triggering inhibited the generation of Th17 cells that is responsible for experimental autoimmune encephalomyelitis induction and progression, and increased Foxp3(+)CD4(+) regulatory T (Treg) cells, particularly among CD4(+) T cells. This was not due to a direct effect of 4-1BB signaling on CD4(+) T cell differentiation: 4-1BB signaling not only reduced Th17 cells and increased Treg cells in wild-type mice, which could be due to IFN-γ production by the CD8(+) T cells, but also did so in IFN-γ-deficient mice, in that case by downregulating IL-6 production. These results show that although secondary suppressive mechanisms evoked by 4-1BB triggering are usually masked by the strong effects of IFN-γ, 4-1BB signaling seems to modulate autoimmune responses by a number of mechanisms, and modulation of the Th17 versus Treg cell balance is one of those mechanisms.

Analysis of the Relationship Between Lower leg Muscle Mass and Preservation of Lower Extremity in Patients with Diabetic Foot Ulcer.

This study aimed to determine how the muscle mass of the lower leg affects the preservation of the lower extremities in patients with diabetic foot ulcer. This study analyzed patients with diabetic foot ulcer between January 2014 and June 2018 with a follow-up of at least 2 years. Of these 181 patients whose ulcer is located distal to the metatarsophalangeal joint, which was categorized as grade ≤2 by the Wagner classification were classified into 4 grades: grade 0 (treated without amputation), grade 1 (amputation distal to the metatarsophalangeal joint), grade 2 (Ray, transmetatarsal, Lisfranc, and Chopart amputation), and grade 3 (Syme, below-knee, and above-knee amputation) according to the final amputation degree. The muscles of the lower leg were classified into 4 compartments: anterior, lateral, deep posterior, and superficial posterior. The cross-sectional area and attenuation to estimate the muscle volume and density were measured at the axial image of computed tomography (CT) angiography. No significant differences were observed in the sex ratio and mean age among the grades (P = .966 and .962). The cross-sectional area of the anterior, lateral, and posterior compartments demonstrated no significant differences, but that of the superficial posterior compartment exhibited significant differences among the grades (P < .001). Moreover, the attenuation of the anterior, lateral, and deep posterior compartments showed no significant differences, but that of the posterior compartment showed significant differences among the grades (P = .003). The muscle mass of the superficial posterior compartment of the lower leg could be a good indicator of the preservation of the lower extremity in patients with diabetic foot ulcer. Therefore, a strengthening exercise for the triceps surae and plantaris muscles in the early stage could help preserve as much of the lower extremities as possible.

Peripheral 4-1BB signaling negatively regulates NK cell development through IFN-gamma.

Stimulation of 4-1BB (CD137) was shown to produce strong anticancer effects in vivo. In contrast, 4-1BB-deficient (4-1BB(-/-)) B6 mice are remarkably resistant to tumor growth. We set out to determine the mechanisms involved in these seemingly contradictory observations. We found that the therapeutic effects of 4-1BB triggering were mainly dependent on CD8(+) T cells and partially on NK cells, whereas CD8(+) T and NK cells were equally needed to suppress tumor growth in 4-1BB(-/-) mice. Cellular analysis showed that the frequency and number of NK cells in the spleen and bone marrow were decreased by 4-1BB triggering but were increased in the absence of 4-1BB signaling in tumor-challenged mice. The 4-1BB-mediated downregulation of NK cell development was primarily dependent on IFN-gamma, which was produced by peripheral CD8(+) T and NK cells. The suppression of NK cell development by 4-1BB-mediated IFN-gamma production occurred in the bone marrow. As 4-1BB signaling increased in the periphery, more CD8(+) T cells but fewer NK cells contributed to the antitumor immunity. As 4-1BB signaling decreased, more NK cells participated in the antitumor immunity. We conclude that 4-1BB signaling results in a shift of the dominant type of immune cell in antitumor immunity from the innate NK cell to the adaptive CD8(+) T cell and that the level of IFN-gamma is critical for this 4-1BB-mediated shift.

4-1BB functions as a survival factor in dendritic cells.

4-1BB (CD137) is expressed on dendritic cells (DCs) and its biological function has remained largely unresolved. By comparing 4-1BB-intact (4-1BB(+/+)) and 4-1BB-deficient (4-1BB(-/-)) DCs, we found that 4-1BB was strongly induced on DCs during the maturation and that DC maturation was normal in the absence of 4-1BB. However, DC survival rate was low in the absence of 4-1BB, which was due to the decreased Bcl-2 and Bcl-x(L) in 4-1BB(-/-) DCs compared with 4-1BB(+/+) DCs after DC maturation. Consistent with these results, 4-1BB(-/-) DCs showed an increased turnover rate in steady state and more severely decreased in spleen by injecting LPS compared with 4-1BB(+/+) DCs. When OVA-pulsed DCs were adoptively transferred to recipient mice along with OVA-specific CD4(+) T cells, 4-1BB(-/-) DCs did not properly migrate to the T cell zone in lymph nodes and poorly induced proliferation of CD4(+) T cells, although both DCs comparably expressed functional CCR7. Eventually, 4-1BB(-/-) DCs generated a reduced number of OVA-specific memory CD4(+) T cells compared with 4-1BB(+/+) DCs. To further assess the role of 4-1BB on DC longevity in vivo, 4-1BB(+/+) and 4-1BB(-/-) C57BL/6 were administrated with Propionibacterium acnes that develop liver granuloma by recruiting DCs. Number and size of granuloma were reduced in the absence of 4-1BB, but the inflammatory cytokine level was comparable between the mice, which implied that the granuloma might be reduced due to the decreased longevity of DCs. These results demonstrate that 4-1BB on DCs controls the duration, DC-T interaction, and, therefore, immunogenicity.

4-1BB Signaling Enhances Primary and Secondary Population Expansion of CD8+ T Cells by Maximizing Autocrine IL-2/IL-2 Receptor Signaling.

4-1BB (CD137), a member of the tumor necrosis factor receptor superfamily (TNFRSF), is primarily expressed on activated T cells and is known to enhance proliferation of T cells, prevent activation-induced cell death, and promote memory formation of CD8+ T cells. In particular, it is well acknowledged that 4-1BB triggering preferentially enhances the expansion of CD8+ T cells rather than CD4+ T cells, but the underlying mechanism remains unclear. Here we found that 4-1BB triggering markedly increased IL-2Rα (CD25) and IL-2 expressions of CD8+ T cells but minimally for CD4+ T cells. Proliferation of CD8+ T cells was moderately enhanced by direct 4-1BB triggering in the absence of signaling through IL-2Rα/IL-2 interactions, but further promoted in the presence of IL-2Rα/IL-2 interactions. Among the TNFRSF members including OX40, GITR, CD30, and CD27, 4-1BB was superior in the ability to induce IL-2Rα expression on CD8+ T cells. When the primary and secondary expansions of CD8+ T cells in vivo were examined by adoptively transferring OVA-specific CD8+ T cells along with the treatment with agonistic anti-4-1BB and/or antagonistic anti-CD25 F(ab')2 mAb, 4-1BB triggering enhanced both primary and secondary expansion of CD8+ T cells in vivo, and the 4-1BB effects were moderately suppressed in primary expansion while completely abolished in secondary expansion of OVA-specific CD8+ T cells by blocking IL-2Rα. These results suggest that 4-1BB-mediated increases of IL-2Rα and IL-2 prolong the effects of transient TCR- and 4-1BB-mediated signaling in CD8+ T cells, and that 4-1BB triggering preferentially enhances the expansion of CD8+ T cells through the amplification of autocrine IL-2/IL-2R signaling loop.

4-1BB-based isolation and expansion of CD8+ T cells specific for self-tumor and non-self-tumor antigens for adoptive T-cell therapy.

Adoptive T-cell therapy is a promising approach to the immunotherapy of cancer, but for it to be a general cancer therapy a simple and standardized procedure for producing tumor-specific CD8 T cells is needed. On the basis of a unique property of 4-1BB (CD137), the selective expression on activated T cells, we have developed a simple and practical protocol to produce antigen-specific CD8 T cells from peripheral blood mononuclear cells. We have proved the feasibility of this procedure by isolating and expanding cytomegalovirus-specific CD8 T cells, and applied the procedure to produce Epstein-Barr virus (EBV)-specific CD8 T cells. By using this procedure, we could readily produce 10-10 antigen-specific CD8 T cells from 30 to 50 mL of blood in about 4 weeks. Moreover, our protocol allowed us to produce, from solid cancer patients, CD8 T cells that were specific for self/tumor antigens such as human telomerase reverse transcriptase (hTERT). It is interesting to note that, we were unable to amplify hTERT-specific CD8 T cells from healthy donors. Our protocol can be readily translated into cGMP-compliant production and is currently being used to produce EBV-specific CD8 T cells for phase I clinical trial. We believe that our method will provide a practical and effective option for adoptive T-cell therapy in the clinic.