4-1BBL enhances anti-tumor responses in the presence or absence of CD28 but CD28 is required for protective immunity against parental tumors

Adoptive T-cell therapy using autologous tumor-infiltrating lymphocytes for metastatic melanoma: current status and future outlook

Immunotherapy using autologous T cells has emerged to be a powerful treatment option for patients with metastatic melanoma. These include the adoptive transfer of autologous tumor-infiltrating lymphocytes (TILs), T cells transduced with high-affinity T cell receptors against major tumor antigens, and T cells transduced with chimeric antigen receptors composed of hybrid immunoglobulin light chains with endodomains of T-cell signaling molecules. Among these and other options for T-cell therapy, TILs together with high-dose interleukin 2 have had the longest clinical history with multiple clinical trials in centers across the world consistently demonstrating durable clinical response rates near 50% or more. A distinct advantage of TIL therapy making it still the T-cell therapy of choice is the broad nature of the T-cell recognition against both defined and undefined tumors antigens against all possible major histocompatibility complex, rather than the single specificity and limited major histocompatibility complex coverage of the newer T cell receptors and chimeric antigen receptor transduction technologies. In the past decade, significant inroads have been made in defining the phenotypes of T cells in TIL-mediating tumor regression. CD8+ T cells are emerging to be critical, although the exact subset of CD8+ T cells exhibiting the highest clinical activity in terms of memory and effector markers is still controversial. We present a model in which both effector-memory and more differentiated effector T cells ultimately may need to cooperate to mediate long-term tumor control in responding patients. Although TIL therapy has shown great potential to treat metastatic melanoma, a number of issues have emerged that need to be addressed to bring it more into the mainstream of melanoma care. First, we have a reached the point where a pivotal phase II or phase III trial is needed in an attempt to gain regulatory approval of TILs as standard of care. Second, improvements in how we expand TILs for therapy are needed that minimize the time the T cells are in culture and improve the memory and effector characteristics of the T cells for longer persistence and enhanced anti-tumor activity in vivo. Third, there is a critical need to identify surrogate and predictive biomarkers to better select suitable patients for TIL therapy to improve response rate and duration. Overall, the outlook for TIL therapy for melanoma is very bright. We predict that TILs will indeed emerge to become an approved treatment in the upcoming years through pivotal clinical trials. Moreover, new approaches combining TILs with targeted signaling pathway drugs, such as mutant B-RAF inhibitors, and synergistic immunomodulatory interventions enhancing T-cell costimulation and preventing negative regulation should further increase therapeutic efficacy and durable complete response rates.

Combination immunotherapy with 4-1BBL and CTLA-4 blockade for the treatment of prostate cancer

Immune regulation has been shown to be involved in the progressive growth of some murine tumours. Interruption of immune regulatory pathways via activation of 4-1BB or cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) blockade appears to be a promising strategy for cancer immunotherapy. In this study, we examined the effectiveness of 4-1BBL-expressing tumor cell vaccine in combination with CTLA-4 blockade on rejection of murine prostate cancer RM-1. We found that the combination of both a vaccine consisting of 4-1BBL-expressing RM-1 cells and CTLA-4 blockade resulted in regression of RM-1 tumors and a significant increase in survival of the tumour cell recipients, compared to that of either treatment alone. The combined vaccination resulted in higher CTL against RM-1 cells and increased secretion of IFN-γ, TNF-α, and IL-2 in the mix-cultured supernatant. These results suggest that combining activation of 4-1BB and blockade of CTLA-4 may offer a new strategy for prostate cancer immunotherapy.

Costimulatory molecule expression on human uveal melanoma cells: functional analysis of CD40 and B7-H1

Costimulatory molecules play important roles in regulating T cell function in tumor immunity. In this study, we investigated costimulatory molecule expression on human uveal melanoma cells (a primary culture, and OCM-1, OMM-1 and 92-1 cell lines) and assessed the functional roles of selected costimulatory molecules. Uveal melanoma cells were incubated in the presence or absence of IFN-γ and expression of costimulatory molecules on the cells was measured by flow cytometry. The costimulatory effect of B7-H1-expressing uveal melanoma cells on cytokine production by purified T cells was studied in uveal melanoma/T cell co-culture experiments using a blocking anti-B7-H1 monoclonal antibody (mAb). The functional role of CD40-mediated interactions in modifying immune responses to uveal melanoma cells was assessed in vitro using recombinant human CD40 ligand (rhCD40L). MHC class I and B7-H1 were consistently detected and further upregulated by IFN-γ stimulation in all human uveal melanoma cell cultures. CD40 was consistently detected and further upregulated by IFN-γ stimulation in primary culture, OCM-1, and OMM-1 but not 92-1. IL-2 production from purified CD3(+) T cells co-stimulated with IFN-γ-treated uveal melanoma cells was significantly enhanced by the addition of anti-B7-H1 mAb. Treatment of primary culture, OCM-1, or OMM-1 with rhCD40L induced or enhanced secretion of chemokines IL-8, MCP-1, IP-10 and RANTES. These results suggest that the expression of B7-H1 on IFN-γ-treated uveal melanoma cells contributes to suppression of T cells by decreasing IL-2 production. In contrast, CD40 expressed on uveal melanoma cells plays an important role in augmenting anti-tumor immunity by stimulating chemokine production. The dual effects of CD40 and B7-H1 may contribute to positive or negative regulation of anti-tumor immune responses to human uveal melanoma.

Chimeric antigen receptors combining 4-1BB and CD28 signaling domains augment PI3kinase/AKT/Bcl-XL activation and CD8+ T cell-mediated tumor eradication

To enhance the strength of activation afforded by tumor antigen-specific receptors, we investigated the effect of adding combined CD28 and 4-1BB costimulatory signaling domains to a chimeric antigen receptor (CAR) specific for prostate-specific membrane antigen (PSMA). Having transferred receptors encompassing the CD28, 4-1BB, and/or CD3zeta cytoplasmic domains in primary human CD8(+) T cells, we find that the P28BBz receptor, which includes all three signaling domains, is superior to receptors that only include one or two of these domains in promoting cytokine release, in vivo T-cell survival and tumor elimination following intravenous T-cell administration to tumor-bearing severe combined immunodeficient (SCID)/beige mice. Upon in vitro exposure to PSMA, the P28BBZ receptor-induced the strongest PI(3)Kinase/Akt activation and Bcl-X(L) expression, and the least apoptosis in transduced peripheral blood CD8(+) T cells. These findings further support the concept of integrating optimized costimulatory properties into recombinant antigen receptors to augment the survival and function of genetically targeted T cells within the tumor microenvironment.

In vivo anti-melanoma efficacy of allo-restricted CTLs specific for melanoma expanded by artificial antigen-presenting cells

Cytotoxic CD8(+) T cells are key effectors in the immunotherapy of malignant and viral diseases. However, autologous T cell responses to tumor antigens presented by self-MHC are usually weak and ineffective. Allo-restricted T cells represent a potent source of tumor-specific T cells for adoptive immunotherapy. This study reports in vivo anti-melanoma efficacy of the pTRP2-specific allo-restricted CTLs expanded from the BALB/c splenocytes by multiple stimulations with aAPCs made by coating H-2K(b)-Ig/pTRP2 dimeric complexes, anti-CD28 antibody, 4-1BBL molecules and CD83 molecules to cell-sized latex beads. The induced allo-restricted CTLs exhibited specific lysis against RMA-S cells pulsed with the peptide pTRP2 and H-2K(b+) melanoma cells expressing TRP2, while a murine Lewis lung carcinoma cell line 3LL could not be recognized by the CTLs. The peptide-specific activity was inhibited by anti-H-2K(b) monoclonal antibody Y3. Adoptive transfer of the allo-restricted CTLs specific for malignant melanoma expanded by the aAPCs can mediate effective anti-melanoma response in vivo. These results suggested that the specific allo-restricted CTLs expanded by aAPCs coated with an MHC-Ig/peptide complex, anti-CD28 antibody, 4-1BBL and CD83 could be a potential option of specific immunotherapy for patients with malignant melanoma.

Induction of a VLA-2 (CD49b)-expressing effector T cell population by a cell-based neuroblastoma vaccine expressing CD137L

In malignancies where no universally expressed dominant Ag exists, the use of tumor cell-based vaccines has been proposed. We have modified a mouse neuroblastoma cell line to express either CD80 (B7.1), CD137L (4-1BBL), or both receptors on the tumor cell surface. Vaccines expressing both induce a strong T cell response that is unique in that among responding CD8 T cells, a T effector memory cell (T(EM)) response arises in which a large number of the T(EM) express the alpha-chain of VLA-2, CD49b. We demonstrate using both in vitro and in vivo assays that the CD49b(+) CD8 T cell population is a far more potent antitumor effector cell population than nonfractionated CD8 or CD49b(-) CD8 T cells and that CD49b on vaccine-induced CD8 T cells mediates invasion of a collagen matrix. In in vivo rechallenge studies, CD49b(+) T cells no longer expanded, indicating that CD49b T(EM) expansion is restricted to the initial response to vaccine. To demonstrate a mechanistic link between the expression of costimulatory molecules on the vaccine and CD49b on responding T cells, we stimulated naive T cells in vitro with artificial APC expressing different combinations of anti-CD3, anti-CD28, and CD137L. Although some mRNA encoding CD49b was induced by combining anti-CD3 with anti-CD28 or CD137L, the highest level was induced when all three signals were present. This indicates that CD49b expression results from additive costimulation and that the level of CD49b message serves as an indicator of the effectiveness of T cell activation by a cell-based vaccine.

Therapeutic antitumor efficacy of anti-CD137 agonistic monoclonal antibody in mouse models of myeloma

PURPOSE

Eradication of post-treatment residual myeloma cells is needed to prevent relapses, and immunostimulatory monoclonal antibodies (mAb) such as anti-CD137, CTLA-4, CD40, etc., which enhance the immune response against malignancies, represent a means of achieving this purpose. This study explores anti-CD137 mAbs for multiple myeloma treatment in preclinical models of the disease because they safely augment tumor immunity and are in clinical trials for other cancers.

EXPERIMENTAL DESIGN

The antitumor effect of anti-CD137 mAb on mouse plasmacytomas derived from HOPC and NS0 cell lines was studied and compared with that of anti-CTLA-4, anti-CD40, and anti-ICAM-2 mAbs. The antitumor effect of anti-CD137 mAb was also examined in a mouse syngeneic disseminated myeloma (5TGM1) model, which more closely resembles human multiple myeloma. Depletions of specific cell populations and gene-targeted mice were used to unravel the requirements for tumor rejection.

RESULTS

Agonistic mAb against CD137 and blocking anti-CTLA-4 mAb showed activity against i.p. HOPC tumors, resulting in extended survival of mice that also became immune to rechallenge. Anti-CD137 mAbs induced complete eradications of established s.c. NS0-derived tumors that were dependent on IFN-gamma, natural killer cells, and CD8(+) T lymphocytes. Natural killer cells accumulated in tumor draining lymph nodes and showed increased IFN-gamma production. Antitumor efficacy of anti-CD137 mAb was preserved in CD28-deficient mice despite the fact that CD28 signaling increases the expression of CD137 on CD8(+) T cells. Importantly, anti-CD137 mAb treatment significantly decreased systemic tumor burden in the disseminated 5TGM1 model.

CONCLUSIONS

The immune-mediated antitumor activity of anti-CD137 mAb in mouse models holds promise for myeloma treatment in humans.

Eradication of established renal cell carcinoma by a combination of 5-fluorouracil and anti-4-1BB monoclonal antibody in mice

Renal cell carcinoma (RCC), one of the most incurable malignancies, is highly resistant to chemotherapy and radiotherapy. Cytokine immunotherapy has been the standard approach, but the overall response rate is still very low. Administration of agonistic anti-4-1BB monoclonal antibody (mAb) has been shown to induce regression of several animal tumors but its effect on RCC is unknown. We show here that monotherapy with either anti-4-1BB mAb or the cytotoxic drug, 5-fluorouracil (5-FU), has little effect on established RCC, Renca tumors, but combination therapy with anti-4-1BB mAb and 5-FU eradicates the tumors in more than 70 % of mice. The regressing tumor tissues from mice receiving the combination therapy contained more apoptotic tumor cells and tumor infiltrating lymphocytes than tumor tissues from mice receiving 5-FU or anti-4-1BB mAb monotherapy. The number of lymphocytes in the spleens and tumor- draining lymph nodes (TDLNs) of the combination therapy mice was greatly increased compared to that of control or 5-FU monotherapy mice. Mice that had recovered due to the combination therapy rapidly rejected rechallenge with the tumor, pointing to the establishment of long-lasting tumor-specific memory. Our results indicate that targeting tumors with 5-FU, and immune cells with 4-1BB stimulation, could be a useful strategy for treating incurable RCC.

Adoptive transfer of pTRP2-specific CTLs expanding by bead-based artificial antigen-presenting cells mediates anti-melanoma response

Cytotoxic CD8(+) T cells are key effectors in the immunotherapy of malignant and viral diseases. However, the lack of efficient methods for their in vitro priming and expansion has become a bottleneck to the development of vaccines and adoptive transfer strategies. Synthetic artificial antigen-presenting cells (aAPCs) are now emerging as an attractive tool for eliciting and expanding CTL responses. This study reported a novel approach for targeting malignant melanoma with pTRP2-specific cytotoxic T lymphocytes (CTLs) expanded from the C57BL/6 splenocytes by multiple stimulations with aAPCs made by coating H-2K(b)-Ig/pTRP2 dimeric complexes, anti-CD28 antibody, 4-1BBL molecules and CD83 molecules to cell-sized latex beads. The induced CTLs exhibited specific lysis against RMA-S cells pulsed with the peptide pTRP2 and H-2K(b+) melanoma cells expressing TRP2, while a murine Lewis lung carcinoma cell line 3LL could not be recognized by the CTLs. The peptide-specific activity was inhibited by anti-H-2K(b) monoclonal antibody Y3. Adoptive Transfer of CTLs specific for malignant melanoma expanding by the aAPCs can mediate effective anti-melanoma response. These results suggested the bead-based aAPCs coated with an MHC-Ig/peptide complex, anti-CD28 antibody, 4-1BBL and CD83 could provide a useful tool for the reproducible expansion of specific CTLs for adoptive immunotherapy.

Multivalent 4-1BB binding aptamers costimulate CD8+ T cells and inhibit tumor growth in mice

4-1BB is a major costimulatory receptor that promotes the survival and expansion of activated T cells. Administration of agonistic anti-4-1BB Abs has been previously shown to enhance tumor immunity in mice. Abs are cell-based products posing significant cost, manufacturing, and regulatory challenges. Aptamers are oligonucleotide-based ligands that exhibit specificity and avidity comparable to, or exceeding, that of Abs. To date, various aptamers have been shown to inhibit the function of their cognate target. Here, we have described the development of an aptamer that binds 4-1BB expressed on the surface of activated mouse T cells and shown that multivalent configurations of the aptamer costimulated T cell activation in vitro and mediated tumor rejection in mice. Because aptamers can be chemically synthesized, manufacturing and the regulatory approval process should be substantially simpler and less costly than for Abs. Agonistic aptamers could therefore represent a superior alternative to Abs for the therapeutic manipulation of the immune system.

Leukemia-Specific T-Cell Reactivity Induced by Leukemic Dendritic Cells Is Augmented by 4-1BB Targeting

PURPOSE

Acute myelogenous leukemia (AML) blasts are able to differentiate into leukemia-derived dendritic cells (AML-DC), thereby enabling efficient presentation of known and unknown leukemic antigens. Advances in culture techniques and AML-DC characterization justify clinical application. However, additional measures are likely needed to potentiate vaccines and overcome the intrinsic tolerant state of the patients' immune system. Engagement of the costimulatory molecule 4-1BB can break immunologic tolerance and increase CTL responses. In this study, we examined the role of the 4-1BB ligand (4-1BBL) on T-cell responses induced by AML-DC.

EXPERIMENTAL DESIGN

In allogeneic and autologous cocultures of T cells and AML-DC, the effect of the addition of 4-1BBL on T-cell proliferation, T-cell subpopulations, and T-cell function was determined.

RESULTS

Addition of 4-1BBL to cocultures of AML-DC and T cells induced a preferential increase in the proliferation of CD8(+) T cells. Increased differentiation into effector and central memory populations was observed in both CD4(+) and CD8(+) T cells in the presence of 4-1BBL. AML-DC induce a T helper 1 response, characterized by high IFN-gamma production, which is significantly increased by targeting 4-1BB. T cells primed in the presence of 4-1BBL show specificity for the leukemia-associated antigen Wilms' tumor 1, whereas cytotoxicity assays with leukemic blast targets showed the cytolytic potential of T cells primed in the presence of 4-1BBL.

CONCLUSION

We conclude that 4-1BBL is an effective adjuvant to enhance T-cell responses elicited by AML-DC.

4-1BB ligand enhances tumor-specific immunity of poxvirus vaccines

PURPOSE

Recombinant poxvirus vaccines have been explored as tumor vaccines. The immunogenicity of these vaccines can be enhanced by co-expressing costimulatory molecules and tumor-associated antigens. While the B7-CD28 interaction has been most comprehensively investigated, other costimulatory molecules utilize different signaling pathways and might provide further cooperation in T cell priming and survival. 4-1BB (CD137) is a TNF family member and is critical for activation and long-term maintenance of primed T cells. This study was conducted to determine if a poxvirus expressing the ligand for 4-1BB (4-1BBL) could further improve the immune and therapeutic responses of a previously reported poxvirus vaccine expressing a triad of costimulatory molecules (B7.1, ICAM-1, and LFA-3).

EXPERIMENTAL DESIGN

A recombinant vaccinia virus expressing 4-1BBL was generated and characterized in an in vitro infection system. This vaccine was then used alone or in combination with a vaccinia virus expressing CEA, B7.1, ICAM-1, and LFA-3 in CEA-transgenic mice bearing established MC38 tumors. Tumor growth and immune responses against CEA and other tumor-associated antigens were determined. The level of anti-apoptotic proteins in responding T cells was determined by flow cytometry on tetramer selected T cells.

RESULTS

The combination of 4-1BBL with B7.1-based poxvirus vaccination resulted in significantly enhanced therapeutic effects against CEA-expressing tumors in a CEA-transgenic mouse model. This was associated with an increased level of CEA-specific CD4(+) and CD8(+) T cell responses, induction of antigen spreading to p53 and gp70, increased accumulation of CEA-specific T cells in the tumor microenvironment, and increased expression of bcl-X(L) and bcl-2 in CD4(+) and CD8(+) T cells in vaccinated mice.

CONCLUSION

4-1BBL cooperates with B7 in enhancing anti-tumor and immunologic responses in a recombinant poxvirus vaccine model. The inclusion of costimulatory molecules targeting distinct T cell signaling pathways provides a mechanism for enhancing the therapeutic effectiveness of tumor vaccines.

CD28-mediated costimulation impacts on the differentiation of DC vaccination-induced T cell responses

Costimulatory signals such as the ones elicited by CD28/B7 receptor ligation are essential for efficient T cell activation but their role in anti-tumour immune responses remains controversial. In the present study we compared the efficacy of DC vaccination-induced melanoma specific T cell responses to control the development of subcutaneous tumours and pulmonary metastases in CD28-deficient mice. Lack of CD28-mediated costimulatory signals accelerated tumour development in both model systems and also the load of pulmonary metastases was strongly increased by the end of the observation period. To scrutinize whether lack of CD28 signalling influences priming, homing or effector function of Trp-2(180-188)/K(b)-reactive T cells we investigated the characteristics of circulating and tumour infiltrating T cells. No difference in the frequency of Trp-2(180-188)/K(b)-reactive CD8+ T cells could be demonstrated among the cellular infiltrate of subcutaneous tumours after DC vaccination between both genotypes. However, the number of IFN-gamma-producing Trp-2-reactive cells was substantially lower in CD28-deficient mice and also their cytotoxicity was reduced. This suggests that CD28-mediated costimulatory signals are essential for differentiation of functional tumour-specific CD8+ T-effector cells despite having no impact on the homing of primed CD8+ T cells.

Development of a whole cell vaccine for acute myeloid leukaemia

We describe the modification of tumour cells to enhance their capacity to act as antigen presenting cells with particular focus on the use of costimulatory molecules to do so. We have been involved in the genetic modification of tumour cells to prepare a whole cell vaccine for nearly a decade and we have a particular interest in acute myeloid leukaemia (AML). AML is an aggressive and difficult to treat disease, especially, for patients for whom haematopoietic stem cell (HSC) transplant is not an option. AML patients who have a suitable donor and meet HSC transplant fitness requirements, have a 5-year survival of 50%; however, for patients with no suitable donor or for who age is a factor, the prognosis is much worse. It is particularly poor prognosis patients, who are not eligible for HSC transplant, who are likely to benefit most from immunotherapy. It would be hoped that immunotherapy would be used to clear residual tumour cells in these patients in the first remission following standard chemotherapy treatments and this will extend the remission and reduce the risk of a second relapse associated with disease progression and poor mortality rates. In this symposia report, we will focus on whole cell vaccines as an immunotherapeutic option with particular reference to their use in the treatment of AML. We will aim to provide a brief overview of the latest data from our group and considerations for the use of this treatment modality in clinical trials for AML.

TNF/TNFR family members in costimulation of T cell responses

Several members of the tumor necrosis factor receptor (TNFR) family function after initial T cell activation to sustain T cell responses. This review focuses on CD27, 4-1BB (CD137), OX40 (CD134), HVEM, CD30, and GITR, all of which can have costimulatory effects on T cells. The effects of these costimulatory TNFR family members can often be functionally, temporally, or spatially segregated from those of CD28 and from each other. The sequential and transient regulation of T cell activation/survival signals by different costimulators may function to allow longevity of the response while maintaining tight control of T cell survival. Depending on the disease condition, stimulation via costimulatory TNF family members can exacerbate or ameliorate disease. Despite these complexities, stimulation or blockade of TNFR family costimulators shows promise for several therapeutic applications, including cancer, infectious disease, transplantation, and autoimmunity.

Role of 4-1BB:4-1BB ligand in cancer immunotherapy

The activation of T cells plays a central role in antitumor immunity. In order to activate naïve T cells, two key signals are required. Signal one is provided through the T-cell receptor (TCR) while signal two is that of costimulation. The CD28:B7 molecules are one of the best-studied costimulatory pathways, thought to be the main mechanism through which primary T-cell stimulation occurs. However, a number of molecules have been identified which serve to amplify and diversify the T-cell response, following initial T-cell activation. These include the more recently described 4-1BB:4-1BB ligand (4-1BBL) molecules. 4-1BB:4-1BBL are a member of the TNFR:TNF ligand family, which are expressed on T cells and antigen-presenting cells (APCs), respectively. Therapies utilizing the 4-1BB:4-1BBL signaling pathway have been shown to have antitumor effects in a number of model systems. In this paper, we focus on the 4-1BB:4-1BBL costimulatory molecules. In particular, we will describe the structure and function of the 4-1BB molecule, its receptor and how 4-1BB:4-1BBL costimulation has and may be used for the immunotherapy of cancer.

Therapeutic vaccination with tumor cells that engage CD137

Therapeutic cancer vaccination is based on the finding that tumors in both humans and experimental animals, such as mice, express potential immunological targets, some of which have high selectivity for cancer cells. In contrast to the successful vaccination against some infectious diseases, where most vaccines induce neutralizing antibodies that act prophylactically, the aim of therapeutic cancer vaccines is to treat established tumors (primarily micrometastases). Since most tumor-destructive immune responses are cell-mediated, therapeutic cancer vaccination needs to induce and expand such responses and also to overcome "escape" mechanisms that allow tumors to evade immunological destruction. Tumor antigens (as with other antigens) are presented by "professional" antigen-presenting cells, most notably dendritic cells (DC). Therefore DC that have been transfected or "pulsed" to present antigen provide a logical source of tumor vaccines, and some encouraging results have been obtained clinically as well as in preclinical models. An alternative and more physiological approach is to develop vaccines that deliver tumor antigen for in vivo uptake and presentation by the DC. Vaccines of the latter type include tumor cells that have been modified to produce certain lymphokines or express costimulatory molecules, as well as cDNAs, recombinant viruses, proteins, peptides and glycolipids which are often given together with an adjuvant. Several studies over the past 5 years have demonstrated dramatic therapeutic responses against established mouse tumors as a result of repeated injections of agonistic monoclonal antibodies (MAbs) to the costimulatory molecule CD137 (4-1BB). However, the clinical use of such MAbs may be problematic since they depress antibody formation, for example, to infectious agents. The alternative approach to transfect tumor cells to express the CD137 ligand (CD137L) increases their immunogenicity, but vaccination with tumor cells expressing CD137L is ineffective in several systems where injection of anti-CD137 MAb produces tumor regression. Recent findings indicate that a more effective way to engage CD137 towards tumor destruction is to transfect tumor cells to express a cell-bound form of anti-CD137 single-chain Fv fragments (scFv). Notably, tumors from melanoma K1735, growing either subcutaneously or in the lung, could be eradicated following vaccination with K1735 cells that expressed anti-CD137 scFv. This was in spite of the fact that K1735, as with many human neoplasms, expresses very low levels of MHC class I and has low immunogenicity. Similar results were subsequently obtained with other tumors of low immunogenicity, including sarcoma Ag104. We hypothesize that the concomitant expression of tumor antigen and anti-CD137 scFv effectively engages NK cells, monocytes and dendritic cells, as well as activated CD4(+) and CD8(+) T cells (all of which express CD137) so as to induce and expand a tumor-destructive Th1 response. While vaccines in the form of transfected tumor cells can be effective, at least in mouse models, the logical next step is to construct vaccines that combine genes that encode molecularly defined tumor antigens with a gene that encodes anti-CD137 scFv. Before planning any clinical trials, vaccines that engage CD137 via scFv need to be compared in demanding mouse models for efficacy and side effects with vaccines that are already being tested clinically, including transfected DC and tumor cells producing granulocyte-macrophage colony-stimulating factor.

Induction of 4-1BB (CD137) expression by DNA damaging agents in human T lymphocytes

4-1BB(CD137) is a member of the tumour necrosis factor receptor superfamily and is expressed on activated T cells, monocytes and natural killer (NK) cells. The interaction of 4-1BB and 4-1BB ligand provides a costimulatory signal leading to T-cell activation. The expression of 4-1BB has been known to be activation dependent. Interestingly, we found that expression of 4-1BB increased in human peripheral blood mononuclear cells after exposure to mitomycin C. Thus, we tested whether the treatment with other DNA-damaging agents, such as doxorubicin, bleomycin, and gamma-irradiation, could induce 4-1BB expression. The data indicated that 4-1BB expression increased dose-dependently by these agents reaching maximum at 2-3 days after the exposure. We found that the major 4-1BB-expressing population was CD3+ T cells, although a moderate number of CD14+ cells and a few NKB1+ cells also expressed 4-1BB. The levels of 4-1BB expression induced by anticancer drugs, were relatively lower than that induced by CD3 ligation. Interestingly, at subcytotoxic concentrations, doxorubicin and bleomycin considerably enhanced 4-1BB expression induced by CD3 ligation in CEM cells. The ligation of the damage-induced 4-1BB by monoclonal antibody enhanced the viability and proliferating capacity of the cells. In conclusion, the expression of 4-1BB might be one of the cellular responses of the immune cells against various genotoxic stresses.