Pembrolizumab and Enzalutamide in Patients with Abiraterone Acetate-Pretreated Metastatic Castration-Resistant Prostate Cancer: Cohort C of the Phase 1b/2 KEYNOTE-365 Study.

BACKGROUND: Limited responses have been observed in patients treated with enzalutamide after disease progression on abiraterone for metastatic castration-resistant prostate cancer (mCRPC), but androgen receptor signaling impacts T-cell function. OBJECTIVE: To evaluate the efficacy and safety of pembrolizumab plus enzalutamide in mCRPC. DESIGN, SETTING, AND PARTICIPANTS: Patients in cohort C of the phase 1b/2 KEYNOTE-365 study, who received ≥4 wk of treatment with abiraterone acetate in the prechemotherapy mCRPC state and experienced treatment failure or became drug-intolerant, were included. INTERVENTION: Pembrolizumab 200 mg intravenously every 3 wk plus enzalutamide 160 mg orally once daily. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: The primary endpoints were safety, the confirmed prostate-specific antigen (PSA) response rate, and the objective response rate (ORR) according to Response Evaluation Criteria in Solid Tumors version 1.1 on blinded independent central review (BICR). Secondary endpoints included radiographic progression-free survival (rPFS) on BICR and overall survival (OS). RESULTS AND LIMITATIONS: A total of 102 patients received pembrolizumab plus enzalutamide. Median follow-up was 51 mo (interquartile range 37-56). The confirmed PSA response rate was 24% (95% confidence interval [CI] 16-33%). The confirmed ORR was 11% (95% CI 2.9-25%; 4/38 patients; two complete responses). Median rPFS was 6.0 mo (95% CI 4.1-6.3). Median OS was 20 mo (95% CI 17-24). Treatment-related adverse events (TRAEs) occurred in 94 patients (92%); grade 3-5 TRAEs occurred in 44 patients (43%). The incidence of treatment-related rash was higher with combination therapy than expected from the safety profile of each drug. One patient (1.0%) died of a TRAE (cause unknown). Study limitations include the single-arm design. CONCLUSIONS: Pembrolizumab plus enzalutamide had limited antitumor activity in patients who received prior abiraterone treatment without previous chemotherapy for mCRPC, with a safety profile consistent with the individual profiles of each agent. PATIENT SUMMARY: Pembrolizumab plus enzalutamide showed limited antitumor activity and manageable safety in patients with metastatic castration-resistant prostate cancer. The KEYNOTE-365 trial is registered on ClinicalTrials.gov as NCT02861573.

Pembrolizumab Plus Olaparib for Patients With Previously Treated and Biomarker-Unselected Metastatic Castration-Resistant Prostate Cancer: The Randomized, Open-Label, Phase III KEYLYNK-010 Trial.

PURPOSE: There is an unmet need for therapeutic options that prolong survival for patients with heavily pretreated, metastatic castration-resistant prostate cancer (mCRPC). The phase III, open-label KEYLYNK-010 study evaluated pembrolizumab plus olaparib versus a next-generation hormonal agent (NHA) for biomarker-unselected, previously treated mCRPC. METHODS: Eligible participants had mCRPC that progressed on or after abiraterone or enzalutamide (but not both) and docetaxel. Participants were randomly assigned (2:1) to pembrolizumab plus olaparib or NHA (abiraterone or enzalutamide). The dual primary end points were radiographic progression-free survival (rPFS) by blinded independent central review per Prostate Cancer Working Group-modified RECIST 1.1 and overall survival (OS). Time to first subsequent therapy (TFST) was a key secondary end point. Safety and objective response rate (ORR) were secondary end points. RESULTS: Between May 30, 2019, and July 16, 2021, 529 participants were randomly assigned to pembrolizumab plus olaparib and 264 to NHA. At final rPFS analysis, median rPFS was 4.4 months (95% CI, 4.2 to 6.0) with pembrolizumab plus olaparib and 4.2 months (95% CI, 4.0 to 6.1) with NHA (hazard ratio [HR], 1.02 [95% CI, 0.82 to 1.25]; P = .55). At final OS analysis, median OS was 15.8 months (95% CI, 14.6 to 17.0) and 14.6 months (95% CI, 12.6 to 17.3), respectively (HR, 0.94 [95% CI, 0.77 to 1.14]; P = .26). At final TFST analysis, median TFST was 7.2 months (95% CI, 6.7 to 8.1) versus 5.7 months (95% CI, 5.0 to 7.1), respectively (HR, 0.86 [95% CI, 0.71 to 1.03]). ORR was higher with pembrolizumab plus olaparib versus NHA (16.8% v 5.9%). Grade ≥3 treatment-related adverse events occurred in 34.6% and 9.0% of participants, respectively. CONCLUSION: Pembrolizumab plus olaparib did not significantly improve rPFS or OS versus NHA in participants with biomarker-unselected, heavily pretreated mCRPC. The study was stopped for futility. No new safety signals occurred.

Pembrolizumab plus Olaparib in Patients with Metastatic Castration-resistant Prostate Cancer: Long-term Results from the Phase 1b/2 KEYNOTE-365 Cohort A Study.

BACKGROUND: Pembrolizumab and olaparib have shown single-agent activity in patients with previously treated metastatic castration-resistant prostate cancer (mCRPC). OBJECTIVE: To evaluate the efficacy and safety of pembrolizumab plus olaparib in mCRPC. DESIGN, SETTING, AND PARTICIPANTS: Cohort A of the phase 1b/2 KEYNOTE-365 study enrolled patients with molecularly unselected, docetaxel-pretreated mCRPC whose disease progressed within 6 mo of screening. INTERVENTION: Pembrolizumab 200 mg intravenously every 3 wk plus olaparib 400-mg capsule or 300-mg tablet orally twice daily. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: The primary endpoints were safety, confirmed prostate-specific antigen (PSA) response rate, and objective response rate (ORR) as per Response Evaluation Criteria in Solid Tumors (RECIST), version 1.1, by blinded independent central review. The secondary endpoints included radiographic progression-free survival (rPFS) and overall survival (OS). RESULTS AND LIMITATIONS: Of 104 enrolled patients, 102 were treated. The median age was 70 yr (interquartile range [IQR], 65-76), and 59 patients (58%) had measurable disease as per RECIST v1.1. The median time from the first dose to database cutoff was 24 mo (IQR, 22-47). The confirmed PSA response rate was 15%. The confirmed ORR was 8.5% (five partial responses) for patients with measurable disease. The median rPFS was 4.5 mo (95% confidence interval [CI], 4.0-6.5) and median OS was 14 mo (95% CI, 10.4-18.2). Clinical activity was consistent across the programmed death ligand 1 (PD-L1)-positive and homologous recombination repair mutation subgroups. Treatment-related adverse events (TRAEs) occurred in 93 patients (91%). Grade 3-5 TRAEs occurred in 49 patients (48%). Six deaths (5.9%) were due to adverse events; two (myocardial infarction and unknown cause) were attributed to treatment. Limitations of the study include the single-arm design. CONCLUSIONS: Pembrolizumab plus olaparib had a safety profile consistent with the profiles of the individual agents and demonstrated antitumor activity in previously treated patients with molecularly unselected, docetaxel-pretreated mCRPC. PATIENT SUMMARY: Pembrolizumab plus olaparib showed antitumor activity and expected safety in patients with metastatic castration-resistant prostate cancer.

Pembrolizumab Plus Docetaxel and Prednisone in Patients with Metastatic Castration-resistant Prostate Cancer: Long-term Results from the Phase 1b/2 KEYNOTE-365 Cohort B Study.

BACKGROUND: Patients with metastatic castration-resistant prostate cancer (mCRPC) frequently receive docetaxel after they develop resistance to abiraterone or enzalutamide and need more efficacious treatments. OBJECTIVE: To evaluate the efficacy and safety of pembrolizumab plus docetaxel and prednisone in patients with mCRPC. DESIGN, SETTING, AND PARTICIPANTS: The trial included patients with mCRPC in the phase 1b/2 KEYNOTE-365 cohort B study who were chemotherapy naïve and who experienced failure of or were intolerant to ≥4 wk of abiraterone or enzalutamide for mCRPC with progressive disease within 6 mo of screening. INTERVENTION: Pembrolizumab 200 mg intravenously (IV) every 3 wk (Q3W), docetaxel 75 mg/m2 IV Q3W, and prednisone 5 mg orally twice daily. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: The primary endpoints were safety, the prostate-specific antigen (PSA) response rate, and the objective response rate (ORR) according to Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1) by blinded independent central review (BICR). Secondary endpoints included time to PSA progression; the disease control rate (DCR) and duration of response (DOR) according to RECIST v1.1 by BICR; ORR, DCR, DOR, and radiographic progression-free survival (rPFS) according to Prostate Cancer Working Group 3-modified RECIST v1.1 by BICR; and overall survival (OS). RESULTS AND LIMITATIONS: Among 104 treated patients, 52 had measurable disease. The median time from allocation to data cutoff (July 9, 2020) was 32.4 mo, during which 101 patients discontinued treatment, 81 (78%) for disease progression. The confirmed PSA response rate was 34% and the confirmed ORR (RECIST v1.1) was 23%. Median rPFS and OS were 8.5 mo and 20.2 mo, respectively. Treatment-related adverse events (TRAEs) occurred in 100 patients (96%). Grade 3-5 TRAEs occurred in 46 patients (44%). Seven AE-related deaths (6.7%) occurred (2 due to treatment-related pneumonitis). Limitations of the study include the single-arm design and small sample size. CONCLUSIONS: Pembrolizumab plus docetaxel and prednisone demonstrated antitumor activity in chemotherapy-naïve patients with mCRPC treated with abiraterone or enzalutamide for mCRPC. Safety was consistent with profiles for the individual agents. Further investigation is warranted. PATIENT SUMMARY: We evaluated the efficacy and safety of the anti-PD-1 antibody pembrolizumab combined with the chemotherapy drug docetaxel and the steroid prednisone for patients with metastatic prostate cancer resistant to androgen deprivation therapy , and who never received chemotherapy. The combination showed antitumor activity and manageable safety in this patient population. This trial is registered on ClinicalTrials.gov as NCT02861573.

Measuring Tumor Mutational Burden (TMB) in Plasma from mCRPC Patients Using Two Commercial NGS Assays.

Tumor tissue mutational burden (TMB) has emerged as a promising predictive biomarker for immune checkpoint therapy. Measuring TMB from circulating tumor DNA (ctDNA) found in plasma is attractive in tissue-constrained indications. We compared the performance of two plasma-based commercial TMB assays including the effect of two different collection methods. Our findings suggest that the two plasma based TMB assays are highly correlated and they are also both correlated with a tissue-based TMB assay for relatively high TMB samples. The two collection methods are also found to be very comparable. Plasma-based TMB assays may be mature enough to be clinically useful in mCRPC and potentially other indications.

Pembrolizumab as Second-Line Therapy for Advanced Urothelial Carcinoma.

BACKGROUND: Patients with advanced urothelial carcinoma that progresses after platinum-based chemotherapy have a poor prognosis and limited treatment options. METHODS: In this open-label, international, phase 3 trial, we randomly assigned 542 patients with advanced urothelial cancer that recurred or progressed after platinum-based chemotherapy to receive pembrolizumab (a highly selective, humanized monoclonal IgG4κ isotype antibody against programmed death 1 [PD-1]) at a dose of 200 mg every 3 weeks or the investigator's choice of chemotherapy with paclitaxel, docetaxel, or vinflunine. The coprimary end points were overall survival and progression-free survival, which were assessed among all patients and among patients who had a tumor PD-1 ligand (PD-L1) combined positive score (the percentage of PD-L1-expressing tumor and infiltrating immune cells relative to the total number of tumor cells) of 10% or more. RESULTS: The median overall survival in the total population was 10.3 months (95% confidence interval [CI], 8.0 to 11.8) in the pembrolizumab group, as compared with 7.4 months (95% CI, 6.1 to 8.3) in the chemotherapy group (hazard ratio for death, 0.73; 95% CI, 0.59 to 0.91; P=0.002). The median overall survival among patients who had a tumor PD-L1 combined positive score of 10% or more was 8.0 months (95% CI, 5.0 to 12.3) in the pembrolizumab group, as compared with 5.2 months (95% CI, 4.0 to 7.4) in the chemotherapy group (hazard ratio, 0.57; 95% CI, 0.37 to 0.88; P=0.005). There was no significant between-group difference in the duration of progression-free survival in the total population (hazard ratio for death or disease progression, 0.98; 95% CI, 0.81 to 1.19; P=0.42) or among patients who had a tumor PD-L1 combined positive score of 10% or more (hazard ratio, 0.89; 95% CI, 0.61 to 1.28; P=0.24). Fewer treatment-related adverse events of any grade were reported in the pembrolizumab group than in the chemotherapy group (60.9% vs. 90.2%); there were also fewer events of grade 3, 4, or 5 severity reported in the pembrolizumab group than in the chemotherapy group (15.0% vs. 49.4%). CONCLUSIONS: Pembrolizumab was associated with significantly longer overall survival (by approximately 3 months) and with a lower rate of treatment-related adverse events than chemotherapy as second-line therapy for platinum-refractory advanced urothelial carcinoma. (Funded by Merck; KEYNOTE-045 ClinicalTrials.gov number, NCT02256436 .).

Sipuleucel-T immune parameters correlate with survival: an analysis of the randomized phase 3 clinical trials in men with castration-resistant prostate cancer.

PURPOSE: Sipuleucel-T, the first FDA-approved autologous cellular immunotherapy for treatment of advanced prostate cancer, is manufactured by activating peripheral blood mononuclear cells, including antigen presenting cells (APCs), with a fusion protein containing prostatic acid phosphatase. Analysis of data from three phase 3 trials was performed to immunologically characterize this therapy during the course of the three doses, and to relate the immunological responses to overall survival (OS). METHODS: Sipuleucel-T product characteristics [APC numbers, APC activation (CD54 upregulation), and total nucleated cell (TNC) numbers] were assessed in three randomized, controlled phase 3 studies (N = 737). Antigen-specific cellular and humoral responses were assessed in a subset of subjects. The relationships between these parameters and OS were assessed. RESULTS: APC activation occurred in the first dose preparation [6.2-fold, (4.65, 7.70); median (25th, 75th percentile)] and increased in the second [10.6-fold (7.83, 13.65)] and third [10.5-fold (7.89, 13.65)] dose preparations. Cytokines and chemokines associated with activated APCs were produced during the manufacture of each dose; T-cell activation-associated cytokines were detected in the second and third dose preparations. Antigen-specific T cells were detectable after administration of the first sipuleucel-T dose. Cumulative APC activation, APC number, and TNC number correlated with OS (P < 0.05). Antigen-specific immune responses were observed in 78.8 % of monitored subjects and their presence correlated with OS (P = 0.003). CONCLUSION: Sipuleucel-T broadly engages the immune system by activating APCs ex vivo and inducing long-lived immune responses in vivo. These data indicate antigen-specific immune activation as a mechanism by which sipuleucel-T prolongs OS.

Active-specific immunotherapy for non-small cell lung cancer.

Non-small cell lung cancer constitutes about 85% of all newly diagnosed cases of lung cancer and continues to be the leading cause of cancer-related deaths worldwide. Standard treatment for this devastating disease, such as systemic chemotherapy, has reached a plateau in effectiveness and comes with considerable toxicities. For all stages of disease fewer than 20% of patients are alive 5 years after diagnosis; for metastatic disease the median survival is less than one year. Until now, the success of active-specific immunotherapy for all tumor types has been sporadic and unpredictable. However, the active-specific stimulation of the host's own immune system still holds great promise for achieving non-toxic and durable antitumor responses. Recently, sipuleucel-T (Provenge(®); Dendreon Corp., Seattle, WA) was the first therapeutic cancer vaccine to receive market approval, in this case for advanced prostate cancer. Other phase III clinical trials using time-dependent endpoints, e.g. in melanoma and follicular lymphoma, have recently turned out positive. More sophisticated specific vaccines have now also been developed for lung cancer, which, for long, was not considered an immune-sensitive malignancy. This may explain why advances in active-specific immunotherapy for lung cancer lag behind similar efforts in renal cell cancer, melanoma or prostate cancer. However, various vaccines are now being evaluated in controlled phase III clinical trials, raising hopes that active-specific immunotherapy may become an additional effective therapy for patients with lung cancer. This article reviews the most prominent active-specific immunotherapeutic approaches using protein/peptide, whole tumor cells, and dendritic cells as vaccines for lung cancer.

Signaling through OX40 enhances antitumor immunity.

The existence of tumor-specific T cells, as well as their ability to be primed in cancer patients, confirms that the immune response can be deployed to combat cancer. However, there are obstacles that must be overcome to convert the ineffective immune response commonly found in the tumor environment to one that leads to sustained destruction of tumor. Members of the tumor necrosis factor (TNF) superfamily direct diverse immune functions. OX40 and its ligand, OX40L, are key TNF members that augment T-cell expansion, cytokine production, and survival. OX40 signaling also controls regulatory T-cell differentiation and suppressive function. Studies over the past decade have demonstrated that OX40 agonists enhance antitumor immunity in preclinical models using immunogenic tumors; however, treatment of poorly immunogenic tumors has been less successful. Combining strategies that prime tumor-specific T cells together with OX40 signaling could generate and maintain a therapeutic antitumor immune response.

Depletion of tumor-induced Treg prior to reconstitution rescues enhanced priming of tumor-specific, therapeutic effector T cells in lymphopenic hosts.

We reported previously that vaccination of reconstituted, lymphopenic mice resulted in a higher frequency of tumor-specific effector T cells with therapeutic activity than vaccination of normal mice. Here, we show that lymphopenic mice reconstituted with spleen cells from tumor-bearing mice (TBM), a situation that resembles the clinical condition, failed to generate tumor-specific T cells with therapeutic efficacy. However, depletion of CD25(+) Treg from the spleen cells of TBM restored tumor-specific priming and therapeutic efficacy. Adding back TBM CD25(+) Treg to CD25(-) naïve and TBM donor T cells prior to reconstitution confirmed their suppressive role. CD25(+) Treg from TBM prevented priming of tumor-specific T cells since subsequent depletion of CD4(+) T cells did not restore therapeutic efficacy. This effect may not be antigen-specific as three histologically distinct tumors generated CD25(+) Treg that could suppress the T-cell immune response to a melanoma vaccine. Importantly, since ex vivo depletion of CD25(+) Treg from TBM spleen cells prior to reconstitution and vaccination fully restored the generation of therapeutic effector T cells, even in animals with established tumor burden, we have initiated a translational clinical trial of this strategy in patients with metastatic melanoma.

Disruption of TGF-beta signaling prevents the generation of tumor-sensitized regulatory T cells and facilitates therapeutic antitumor immunity.

Regulatory T (Treg) cells represent a major roadblock to the induction of antitumor immunity through vaccine approaches. TGF-beta is a cytokine implicated in the generation and maintenance of Treg cells, as well as in their suppressive function. These experiments examined whether the generation of tumor-sensitized Treg cells was TGF-beta dependent and evaluated whether TGF-beta produced by Treg cells blocked the priming of tumor-specific T cells in vaccinated reconstituted lymphopenic mice. We show that tumor-sensitized Treg cells (CD25(+)/FoxP3(+)) obtained from tumor-bearing mice block the generation of tumor-specific T cells in reconstituted lymphopenic mice. Strikingly, this suppression is absent if tumor-sensitized Treg cells are acquired from tumor-bearing mice expressing the dominant-negative TGFbetaRII in T cells. This loss of suppression was a result of the crucial role of TGF-beta in generating tumor-sensitized Treg cells, and not due to the insensitivity of naive or tumor-primed effector T cells to the direct suppressive influence of TGF-beta. We conclude that blocking TGF-beta in a tumor-bearing host can inhibit the induction of highly suppressive tumor-sensitized Treg cells. These data suggest that an integrative strategy combining "up-front" Treg cell ablation followed by vaccination and TGF-beta blockade may limit generation of new tumor-sensitized Treg cells and improve the generation of therapeutic immune responses in patients with cancer.

Cancer immunotherapy: the role regulatory T cells play and what can be done to overcome their inhibitory effects.

Since multiple lines of experimental and clinical data clearly identified regulatory T cells as an integral part of the immune response, these cells have become a major focus of investigation in tumor immunology. Regulatory T cells are in place to dampen ongoing immune responses and to prevent autoimmunity, but they also have profound effects in blocking therapeutic anti-tumor activity. Therefore regulatory T cells are seen as a major hurdle that must be overcome in order for cancer immunotherapy to reach its therapeutic potential. Regulatory T cells are heterogeneous with sub-populations that exhibit distinct functional features. Here we will review the individual sub-populations in regards to their mode of action and their potential impact on blocking anti-tumor immunity. Approaches to measure function and frequency of regulatory T cells in model systems and clinical trails will be discussed. Finally, we will describe possible ways to interfere with regulatory T cell-mediated immune suppression with the focus on recent pre-clinical and clinical findings.

Increased susceptibility to immune destruction of B16BL6 tumor cells engineered to express a novel pro-Smac fusion protein.

Recent developments in immunology have provided new strategies to induce and augment the immune response to cancer. Nonetheless, objective clinical responses after vaccination are rare and even when high frequencies of tumor-specific T cells are achieved after adoptive immunotherapy, tumor cells continue to evade the immune response. We hypothesize that 1 mechanism of resistance of tumor cells to destruction by T cells is an elevated threshold for the induction of apoptosis. Inhibitor of apoptosis proteins (IAPs) are overexpressed in various tumors and have been associated with treatment failure and poor prognosis. As the mitochondrial peptide second mitochondria-derived activator of caspase (Smac) can antagonize IAPs, we designed a GFP-Smac fusion protein with a granzyme B (GrB) cleavage site. This fusion protein should be cleaved when tumor-specific cytolytic T cells recognize the tumor and, using the pore-forming protein perforin, insert GrB into the target. Here we report that transfer of a construct encoding a novel eGFP-Smac fusion protein (pro-Smac) containing a specific cleavage site for GrB, into the poorly immunogenic mouse melanoma cell line, B16BL6-D5 (D5), sensitizes tumor cells for killing by tumor-specific wild type, but not perforin-deficient (perforin-knockout), effector T cells in vitro and in vivo. These results describe the first example of a tumor-specific, T-cell-mediated approach to amplify the GrB-mediated cytotoxicity pathway with a pro-Smac fusion protein and provide an innovative approach to overcome IAPs and improve the efficacy of immunotherapy.

Therapeutic T cells induce tumor-directed chemotaxis of innate immune cells through tumor-specific secretion of chemokines and stimulation of B16BL6 melanoma to secrete chemokines.

BACKGROUND: The mechanisms by which tumor-specific T cells induce regression of established metastases are not fully characterized. In using the poorly immunogenic B16BL6-D5 (D5) melanoma model we reported that T cell-mediated tumor regression can occur independently of perforin, IFN-gamma or the combination of both. Characterization of regressing pulmonary metastases identified macrophages as a major component of the cells infiltrating the tumor after adoptive transfer of effector T cells. This led us to hypothesize that macrophages played a central role in tumor regression following T-cell transfer. Here, we sought to determine the factors responsible for the infiltration of macrophages at the tumor site. METHODS: These studies used the poorly immunogenic D5 melanoma model. Tumor-specific effector T cells, generated from tumor vaccine-draining lymph nodes (TVDLN), were used for adoptive immunotherapy and in vitro analysis of chemokine expression. Cellular infiltrates into pulmonary metastases were determined by immunohistochemistry. Chemokine expression by the D5 melanoma following co-culture with T cells, IFN-gamma or TNF-alpha was determined by RT-PCR and ELISA. Functional activity of chemokines was confirmed using a macrophage migration assay. T cell activation of macrophages to release nitric oxide (NO) was determined using GRIES reagent. RESULTS: We observed that tumor-specific T cells with a type 1 cytokine profile also expressed message for and secreted RANTES, MIP-1alpha and MIP-1beta following stimulation with specific tumor. Unexpectedly, D5 melanoma cells cultured with IFN-gamma or TNF-alpha, two type 1 cytokines expressed by therapeutic T cells, secreted Keratinocyte Chemoattractant (KC), MCP-1, IP-10 and RANTES and expressed mRNA for MIG. The chemokines released by T cells and cytokine-stimulated tumor cells were functional and induced migration of the DJ2PM macrophage cell line. Additionally, tumor-specific stimulation of wt or perforin-deficient (PKO) effector T cells induced macrophages to secrete nitric oxide (NO), providing an additional effector mechanism for T cell-mediated tumor regression. CONCLUSION: These data suggest two possible sources for chemokine secretion that stimulates macrophage recruitment to the site of tumor metastases. Both appear to be initiated by T cell recognition of specific antigen, but one is dependent on the tumor cells to produce the chemokines that recruit macrophages.

Tumor-specific T cells signal tumor destruction via the lymphotoxin beta receptor.

BACKGROUND: Previously, we reported that adoptively transferred perforin k/o (PKO), and IFN-gamma k/o (GKO), or perforin/IFN-gamma double k/o (PKO/GKO) effector T cells mediated regression of B16BL6-D5 (D5) pulmonary metastases and showed that TNF receptor signaling played a critical role in mediating tumor regression. In this report we investigated the role of lymphotoxin-alpha (LT-alpha) as a potential effector molecules of tumor-specific effector T cells. METHODS: Effector T cells were generated from tumor vaccine-draining lymph node (TVDLN) of wt, GKO, LT-alpha deficient (LKO), or PKO/GKO mice and tested for their ability to mediate regression of D5 pulmonary metastases in the presence or absence of LT-betaR-Fc fusion protein or anti-IFN-gamma antibody. Chemokine production by D5 tumor cells was determined by ELISA, RT-PCR and Chemotaxis assays. RESULTS: Stimulated effector T cells from wt, GKO, or PKO/GKO mice expressed ligands for LT-beta receptor (LT-betaR). D5 tumor cells were found to constitutively express the LT-betaR. Administration of LT-betaR-Fc fusion protein completely abrogated the therapeutic efficacy of GKO or PKO/GKO but not wt effector T cells (p < 0.05). Consistent with this observation, therapeutic efficacy of effector T cells deficient in LT-alpha, was greatly reduced when IFN-gamma production was neutralized. While recombinant LT-alpha1beta2 did not induce apoptosis of D5 tumor cells in vitro, it induced secretion of chemokines by D5 that promoted migration of macrophages. CONCLUSION: The contribution of LT-alpha expression by effector T cells to anti-tumor activity in vivo was not discernable when wt effector T cells were studied. However, the contribution of LT-beta R signaling was identified for GKO or PKO/GKO effector T cells. Since LT-alpha does not directly induce killing of D5 tumor cells in vitro, but does stimulate D5 tumor cells to secrete chemokines, these data suggest a model where LT-alpha expression by tumor-specific effector T cells interacts via cross-linking of the LT-betaR on tumor cells to induce secretion of chemokines that are chemotactic for macrophages. While the contribution of macrophages to tumor elimination in our system requires additional study, this model provides a possible explanation for the infiltration of inate effector cells that is seen coincident with tumor regression.

Immunotherapy for melanoma: the good, the bad, and the future.

The past 20 years have seen remarkable advances in our understanding of the molecular and cellular processes controlling the development of an anticancer immune response. These advances have spawned a renaissance in the field of cancer immunotherapy, the original targeted therapy, during which investigators have pushed the envelope and translated promising strategies into investigational therapeutics in patients with cancer. An approach that combined nonmyeloablative lymphodepleting chemotherapy with adoptive transfer of tumor-specific CD4 and CD8 T cells exhibited an initial objective response rate of 51% for patients with stage IV melanoma. Although this strategy is extremely challenging, one can expect technological advances that may simplify this approach and further improve outcome.

Tumour-induced polarization of tumour vaccine-draining lymph node T cells to a type 1 cytokine profile predicts inherent strong immunogenicity of the tumour and correlates with therapeutic efficacy in adoptive transfer studies.

Previously we have shown that vaccination with the poorly immunogenic B16BL6-D5 melanoma (D5) elicits a dominant type 2 (T2) cytokine response that fails to protect the host from a subsequent tumour challenge. Here we investigated whether the inherent immunogenicity of a tumour can be correlated with its ability to bias the anti-tumour cytokine response towards either a type 1 (T1) or a T2 profile. The immune response to six tumours of different inherent immunogenicity was assayed. By isolating l-selectinlow T cells from tumour vaccine draining lymph nodes (TVDLN), it was possible to detect tumour-specific cytokine responses from both immunogenic, poorly immunogenic and non-immunogenic tumours. Immunogenic tumours (MCA-304, MCA-309, MPR-4) induced a predominant tumour-specific T1 cytokine response. In contrast, weakly (MCA-310, MPR-3) and poorly/non-immunogenic tumours (MPR-5, D5) sensitized T cells with a predominant tumour-specific T2 cytokine response. A significant correlation (P < 0.025) between immunogenicity and the ratio of tumour-specific interferon-gamma : interleukin-4 (IL-4) secretion by TVDLN T cells was identified. We then documented that non-therapeutic T cells primed by the poorly immunogenic D5, recognized "tumour-rejection" antigens and that reprogramming their cytokine response, by in vitro culture with IL-12 and anti-IL-4, to a T1 profile uncovered therapeutic efficacy. In contrast, TVDLN T cells primed by a therapeutic vaccine lose therapeutic efficacy when cultured with IL-4. These results provide insights into the development of a protective anti-tumour immune response and strengthen the hypothesis that a T1 cytokine response is critical for T-cell-mediated tumour regression.

TNF plays an essential role in tumor regression after adoptive transfer of perforin/IFN-gamma double knockout effector T cells.

We have recently shown that effector T cells (T(E)) lacking either perforin or IFN-gamma are highly effective mediators of tumor regression. To rule out compensation by either mechanism, T(E) deficient in both perforin and IFN-gamma (perforin knockout (PKO)/IFN-gamma knockout (GKO)) were generated. The adoptive transfer of PKO/GKO T(E) mediated complete tumor regression and cured wild-type animals with established pulmonary metastases of the B16BL6-D5 (D5) melanoma cell line. PKO/GKO T(E) also mediated tumor regression in D5 tumor-bearing PKO, GKO, or PKO/GKO recipients, although in PKO/GKO recipients efficacy was reduced. PKO/GKO T(E) exhibited tumor-specific TNF-alpha production and cytotoxicity in a 24-h assay, which was blocked by the soluble TNFRII-human IgG fusion protein (TNFRII:Fc). Blocking TNF in vivo by administering soluble TNFR II fusion protein (TNFRII:Fc) significantly reduced the therapeutic efficacy of PKO/GKO, but not wild-type T(E). This study identifies perforin, IFN-gamma, and TNF as a critical triad of effector molecules that characterize therapeutic antitumor T cells. These insights could be used to monitor and potentially tune the immune response to cancer vaccines.

Development of antitumor immune responses in reconstituted lymphopenic hosts.

When naïve T cells reconstitute lymphopenic hosts, they transiently proliferate and differentiate into memory-like T cells. Here we report that tumor-specific T cells preferentially expand in tumor vaccine-draining lymph nodes after a melanoma vaccine given to RAG1 mice reconstituted with naïve T cells from normal mice. The percentage of tumor-specific Tc1 T cells detected by intracellular cytokine staining was increased approximately 4-fold in reconstituted lymphopenic hosts compared with normal hosts. Concomitantly, vaccination-induced Th1 T cells were also dramatically increased in vaccinated, reconstituted RAG1 hosts. T cells derived from reconstituted RAG1 hosts exhibited a higher level of melanoma-specific cytotoxicity in vitro. These cells were significantly more potent at mediating tumor regression in vivo after adoptive transfer into mice bearing established pulmonary metastases. Vaccination is best performed concomitantly with reconstitution; delayed vaccination resulted in T cells with less therapeutic activity.