Scott K. Pruitt

The effect of soluble complement receptor type 1 on hyperacute rejection of porcine xenografts

The use of xenografts (Xgs) from distantly related species to relieve the increasing shortage of organs for clinical transplantation is prevented by the occurrence of hyperacute rejection (HAR). This process, in which C activation plays a central role, cannot be inhibited with currently available immunosuppressants. In two clinically relevant xenotransplantation models, this study evaluated the effect of C inhibition using recombinant soluble complement receptor type 1 (sCR1) on HAR. In an ex vivo model in which porcine cardiac Xgs were perfused with human blood, cardiac function ceased within 34 min when the perfusate blood was untreated (n = 3). When the perfusate blood was treated with sCR1 (300 micrograms/ml), cardiac Xg function was maintained for up to 4 hr (n = 3). Immunohistologic examination of these Xgs demonstrated deposition of C3b/iC3b and C3d in Xgs perfused with untreated human blood but only C3d deposition in those Xgs perfused with sCR1-treated human blood. These findings are consistent with the cofactor activity of sCR1 for factor I-mediated degradation of deposited C3b/iC3b to C3d. Treatment with sCR1 also prevented the histopathologic changes of HAR observed when untreated blood was used as the perfusate. In an in vivo pig-to-primate heterotopic cardiac xenotransplantation model, in which porcine Xgs transplanted into untreated cynomolgus monkey recipients underwent HAR in 1 hr or less (n = 3), a single intravenous bolus of sCR1 (15 mg/kg) administered to the recipient immediately before Xg reperfusion markedly inhibited total and alternative pathway serum C activity and prolonged Xg survival to between 48 and 90 hr (n = 5). These studies confirm the important role of C activation in HAR of porcine cardiac Xgs by primates and indicate that sCR1 may be a useful agent for xenotransplantation.

Induction of Polyclonal Prostate Cancer-Specific CTL Using Dendritic Cells Transfected with Amplified Tumor RNA

Polyvalent cancer vaccines targeting the entire antigenic spectrum on tumor cells may represent a superior therapeutic strategy for cancer patients than vaccines solely directed against single Ags. In this study, we show that autologous dendritic cells (DC) transfected with RNA amplified from microdissected tumor cells are capable of stimulating CTL against a broad set of unidentified and critical prostate-specific Ags. Although the polyclonal CTL responses generated with amplified tumor RNA-transfected DC encompassed as a subcomponent a response against prostate-specific Ag (PSA) as well as against telomerase reverse transcriptase, the tumor-specific CTL were consistently more effective than PSA or telomerase reverse transcriptase CTL to lyse tumor targets, suggesting the superiority of the polyclonal response. Although tumor RNA-transfected DC stimulated CTL, which recognized not only tumor but also self-Ags expressed by benign prostate tissue, these cross-reactive CTL were exclusively specific for the PSA, indicating an immunodominant role of PSA in the prostate cancer-specific immune response. Our data suggest that tumor RNA-transfected DC may represent a broadly applicable, potentially clinically effective vaccine strategy for prostate cancer patients, which is not limited by tumor tissue availability for Ag preparation and may minimize the risk of clonal tumor escape.

The effect of soluble complement receptor type 1 on hyperacute xenograft rejection

In the guinea pig-to-rat model of hyperacute xenograft (Xg) rejection, the effect of complement inhibition using systemically administered soluble complement receptor type 1 (sCRl) on discordant cardiac Xg survival was investigated. In PBS-treated control Xg recipients (n=13), hyperacute rejection was rapid, with a mean Xg survival of 17±4 min. Therapy with sCRl prolonged survival of cardiac Xgs in a dose-dependent manner. A 3 mg/kg bolus of sCRl (n=4) prolonged Xg survival to 64±29 min (not significant). Increasing the sCRl dose to 5.9 mg/kg (n=4) significantly delayed Xg rejection to 71±17 min (P-0.026, log-rank test vs. control). In 10 recipients treated with 15 mg/kg sCRl, mean Xg survival was further prolonged to 189±36 min (P-0.0004) with no adverse effects. While 2 of 8 recipients receiving 60 mg/kg sCRl died with functioning Xgs at 30 and 300 min due to anastomotic bleeding, Xg survival averaged over 12 hr (747±100 min, P-0.0004) in the remaining 6 recipients. sCRl administration significantly inhibited serum complement activity in a parallel dose-dependent fashion, with the 60 mg/kg dose reducing complement activity by 95±1 and 96±1% five and 30 min following Xg reperfusion, respectively. Immunofluorescence microscopy revealed rat IgM bound to all cardiac Xgs in control as well as sCRl -treated recipients. In addition, serial histologic examination of cardiac Xgs harvested within 21 min of graft reperfusion revealed occlusive platelet aggregates within the coronary vessels as well as interstitial hemorrhage and myocardial necrosis in Xgs from control recipients, all of which were only minimally present in Xgs from recipients treated with sCRl. These studies show that complement inhibition with sCRl significantly delays hyperacute cardiac Xg rejection in this discordant model and may be an important component in a therapeutic protocol for xenotransplantation.

Effect of continuous complement inhibition using soluble complement receptor type 1 on survival of pig-to-primate cardiac xenografts

A single bolus of soluble complement (C) receptor type 1 (sCR1, TP-10) has been shown to delay hyperacute rejection (HAR) of porcine cardiac xenografts (Xgs) by primate recipients. In these recipients, C activity slowly returned and C deposition was noted in the Xgs at rejection. To evaluate the effect of sustained C inhibition using sCR1 on HAR, two additional cynomolgus monkeys received porcine cardiac Xgs and a continuous infusion of sCR1. In the first recipient, Xgs survival was 5 days (120+ hr), whereas in the second, Xg survival was 7 days (168+ hr). Serial biopsies of the Xgs were remarkable for an increasing cellular infiltrate composed predominantly of neutrophils and macrophages, and the development of edema, hemorrhage, and myocyte necrosis. These findings suggest that once C-mediated HAR has been inhibited, infiltration of the Xg by these cells may lead to accelerated acute rejection, which is an additional barrier to successful longer term Xg survival.

Current Trends in Regional Therapy for Melanoma: Lessons Learned from 225 Regional Chemotherapy Treatments between 1995 and 2010 at a Single Institution

BACKGROUND Hyperthermic isolated limb perfusion (HILP) and isolated limb infusion (ILI) are used to manage advanced extremity melanoma, but no consensus exists as to which treatment is preferable and how to monitor patients post-treatment. STUDY DESIGN Using a prospectively maintained database, we reviewed our experience with melphalan-based HILP (which included 62 first-time and 10 second-time) and ILI (which included 126 first-time and 18 second-time) procedures performed in 188 patients. PET/CT was obtained 3 months postregional treatment for 1 year and then every 6 months thereafter. RESULTS Overall response rate (complete response [CR] + partial response) of HILP was 81% (80% CI, 73-87%), and overall response rate from ILI was 43% (80% CI, 37-49%) for first-time procedures only. HILP had a CR rate of 55% with a median duration of 32 months, and ILI had a CR rate of 30% with median duration of 24 months. Patients who experienced a regional recurrence after initial regional treatment were more likely to achieve a CR after repeat HILP (50%, n = 10) compared with repeat ILI (28%, n = 18). Although the spectrum of toxicity was similar for ILI and HILP, the likelihood of rare catastrophic complication of limb loss was greater with HILP (2 of 62) than ILI (0 of 122). PET/CT was effective for surveillance after regional therapy to identify regional nodal and pulmonary disease that was not clinically evident, but often amenable to surgical resection (25 of 49; 51% of cases). In contrast, PET/CT was not effective at predicting complete response to treatment with an accuracy of only 50%. CONCLUSIONS In the largest single-institution regional therapy series reported to date, we found that although ILI is effective and well-tolerated, HILP is a more definitive way to control advanced disease.

Inhibition of complement, evoked antibody, and cellular response prevents rejection of pig-to-primate cardiac xenografts

Complement (C) inhibition alone using a recombinant soluble form of complement receptor type 1 (sCR1) prevents hyperacute rejection but not subsequent irreversible accelerated acute rejection of discordant pig-to-cynomolgus monkey cardiac xenografts, which occurs within 1 week. To inhibit accelerated acute rejection, which is associated with a rise in serum xenoreactive antibody (Ab) and a cellular infiltrate, triple therapy with standard immunosuppressive agents (cyclosporine, cyclophosphamide, and steroids [CCS]) was combined with continuous C inhibition using sCR1. Each of two monkeys that received sCR1 + CCS showed minimal evidence of rejection when killed on days 21 and 32 in comparison to a monkey that received sCR1 + subtherapeutic CCS (rejected at 11 days) and a control that received CCS alone (rejected at 38 min). Prolonged xenograft survival was associated with low Ab levels and a minimal cellular infiltrate, suggesting that combined inhibition of C, xenoreactive Ab responses, and cellular immunity may be a useful approach in overcoming the immune barriers to discordant xenotransplantation.

Sentinel Node Biopsy for Head and Neck Melanoma A Systematic Review

Objective. This systematic review was conducted to examine the test performance of sentinel node biopsy in head and neck melanoma, including the identification rate and false-negative rate. Data Sources. PubMed, EMBASE, ASCO, and SSO database searches were conducted to identify studies fulfilling the following inclusion criteria: sentinel node biopsy was performed, lesions were located on the head and neck, and recurrence data for both metastatic and nonmetastatic patients were reported. Review Methods. Dual-blind data extraction was conducted. Primary outcomes included identification rate and test performance based on completion neck dissection or nodal recurrence. Results. A total of 3442 patients from 32 studies published between 1990 and 2009 were reviewed. Seventy-eight percent of studies were retrospective and 22% were prospective. Trials varied from 9 to 755 patients (median 55). Mean Breslow depth was 2.53 mm. Median sentinel node biopsy identification rate was 95.2%. More than 1 basin was reported in 33.1% of patients. A median of 2.56 sentinel nodes per patient were excised. Sentinel node biopsy was positive in 15% of patients. Subsequent completion neck dissection was performed in almost all of these patients and revealed additional positive nodes in 13.67%. Median follow-up was 31 months. Across all studies, predictive value positive for nodal recurrence was 13.1% and posttest probability negative was 5%. Median false-negative rate for nodal recurrence was 20.4%. Conclusion. Sentinel node biopsy of head and neck melanoma is associated with an increased false-negative rate compared with studies of non–head and neck lesions. Positive sentinel node status is highly predictive of recurrence.

Induction of Human Dendritic Cell Maturation Using Transfection with RNA Encoding a Dominant Positive Toll-Like Receptor 4

Maturation of dendritic cells (DC) is critical for the induction of Ag-specific immunity. Ag-loaded DC matured with LPS, which mediates its effects by binding to Toll-like receptor 4 (TLR4), induce Ag-specific CTL in vitro and in vivo in animal models. However, clinical use of LPS is limited due to potential toxicity. Therefore, we sought to mimic the maturation-inducing effects of LPS on DC by stimulating TLR4-mediated signaling in the absence of exogenous LPS. We developed a constitutively active TLR4 (caTLR4) and demonstrated that transfection of human DC with RNA encoding caTLR4 led to IL-12 and TNF-α secretion. Transfection with caTLR4 RNA also induced a mature DC phenotype. Functionally, transfection of DC with caTLR4 RNA enhanced allostimulation of CD4+ T cells. DC transfected with RNA encoding the MART (Melan-A/MART-1) melanoma Ag were then used to stimulate T cells in vitro. Cotransfection of these DC with caTLR4 RNA enhanced the generation of MART-specific CTL. This CTL activity was superior to that seen when DC maturation was induced using either LPS or a standard mixture of cytokines (TNF-α, IL-6, IL-1β, and PGE2). We conclude that transfection of DC with RNA encoding a functional signaling protein, such as caTLR4, may provide a new tool for studying TLR signaling in DC and may be a promising approach for the induction of DC maturation for tumor immunotherapy.

The effect of soluble complement receptor type 1 on hyperacute allograft rejection

A major obstacle to successful organ transplantation in sensitized recipients is antibody-mediated hyperacute rejection. We hypothesized that human recombinant soluble complement receptor type 1 (sCR1), which inhibits activation of the complement cascade at multiple stages, would delay this process. Using a well-established model of hyperacute rejection, 21 Lewis rats each received three successive ACI rat skin grafts which resulted in high serum titers of ACI-specific antibodies. These hypersensitized Lewis rats then received heterotopic ACI cardiac allografts. Immediately prior to allograft reperfusion, sCR1 at 3 mg/kg (n = 11) or an equivalent volume of phosphate-buffered saline (PBS) (n = 10) was administered intravenously. Five minutes following allograft reperfusion, hemolytic complement activity was reduced by 63 +/- 2% (SEM) in the sCR1 group vs 25 +/- 3% in the PBS group (P less than 0.0001, Wilcoxon rank sum test (WRST)). Graft survival in the sCR1 group was prolonged to 32.0 +/- 4.47 hr vs 3.25 +/- 0.81 hr in the PBS group (P less than 0.0001, WRST). Serial histologic examination of allografts showed that sCR1 therapy prevented the early development of luminal platelet thrombi in the allograft coronary vessels. This study demonstrates that a single 3 mg/kg dose of sCR1 significantly prolongs ACI cardiac allograft survival in the hypersensitized Lewis rat recipient. Complement inactivation, mediated by sCR1, may prove useful for transplantation in sensitized recipients.

Enhancement of anti‐tumor immunity through local modulation of CTLA‐4 and GITR by dendritic cells

Cancer vaccines have now demonstrated clinical efficacy, but immune modulatory mechanisms that prevent autoimmunity limit their effectiveness. Systemic administration of mAbs targeting the immune modulatory receptors CTLA‐4 and glucocorticoid‐induced TNFR‐related protein (GITR) on Treg and effector T cells augments anti‐tumor immunity both experimentally and clinically, but can induce life‐threatening autoimmunity. We hypothesized that local delivery of anti‐CTLA‐4 and anti‐GITR mAbs to the sites where T cells and tumor antigen‐loaded DC vaccines interact would enhance the induction of anti‐tumor immunity while avoiding autoimmunity. To achieve this goal, DCs transfected with mRNA encoding the H and L chains of anti‐mouse CTLA‐4 and GITR mAbs were co‐administered with tumor antigen mRNA‐transfected DCs. We observed enhanced induction of anti‐tumor immunity and significantly improved survival in melanoma‐bearing mice, without signs of autoimmunity. Using in vitro assays with human DCs, we demonstrated that DCs transfected with mRNA encoding a humanized anti‐CTLA‐4 mAb and mRNA encoding a soluble human GITR‐L fusion protein enhance the induction of anti‐tumor CTLs in response to DCs transfected with mRNAs encoding either melanoma or breast cancer antigens. Based on these results, this approach of using local delivery of immune modulators to enhance vaccine‐induced immunity is currently being evaluated in a phase I clinical cancer immunotherapy trial.